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174-673: Agent Orange is a chemical herbicide and defoliant , one of the tactical use Rainbow Herbicides . It was used by the U.S. military as part of its herbicidal warfare program, Operation Ranch Hand , during the Vietnam War from 1961 to 1971. The U.S. was strongly influenced by the British who used Agent Orange during the Malayan Emergency . It is a mixture of equal parts of two herbicides, 2,4,5-T and 2,4-D . In addition to its damaging environmental effects, traces of dioxin (mainly TCDD ,

348-552: A 1995 panel of 13 scientists reviewing studies on the carcinogenicity of 2,4-D had divided opinions on the likelihood 2,4-D causes cancer in humans. As of 1992 , studies on phenoxy herbicides were too few to accurately assess the risk of many types of cancer from these herbicides, even although evidence was stronger that exposure to these herbicides is associated with increased risk of soft tissue sarcoma and non-Hodgkin lymphoma . Herbicides have widely variable toxicity in addition to acute toxicity arising from ingestion of

522-913: A November 2004 Zogby International poll of 987 people, 79% of respondents thought the U.S. chemical companies which produced Agent Orange defoliant should compensate U.S. soldiers who were affected by the toxic chemical used during the war in Vietnam and 51% said they supported compensation for Vietnamese Agent Orange victims. Several official investigations in Australia failed to prove otherwise even though extant American investigations had already established that defoliants were sprayed at U.S. airbases including Bien Hoa Air Base where Australian and New Zealand forces first served before being given their own Tactical area of responsibility (TAOR.) Even then, Australian and New Zealand non-military and military contributions saw personnel from both countries spread over Vietnam such as

696-543: A common mechanism of action via the aryl hydrocarbon receptor (AHR), but their potencies are very different. This means that similar effects are caused by all of them, but much larger doses of some of them are needed than of TCDD. Binding to the AHR as well as persistence in the environment and in the organism depends on the presence of so-called "lateral chlorines", in case of dioxins and furans, chlorine substitutes in positions 2,3,7, and 8. Each additional non-lateral chlorine decreases

870-700: A critical analysis of these studies and 35 others consistently found that there was no significant increase in prostate cancer incidence or mortality in those exposed to Agent Orange or 2,3,7,8-tetracholorodibenzo- p -dioxin. During the Vietnam War, the United States fought the North Vietnamese , and their allies, in Laos and Cambodia , including heavy bombing campaigns. They also sprayed large quantities of Agent Orange in each of those countries. According to one estimate,

1044-415: A few weeks) after being applied to soils of above-neutral pH . Under alkaline soil conditions, atrazine may be carried into the soil profile as far as the water table by soil water following rainfall causing the aforementioned contamination. Atrazine is thus said to have "carryover", a generally undesirable property for herbicides. Glyphosate had been first prepared in the 1950s but its herbicidal activity

1218-505: A field. Herbicides provided excellent control, reducing soil disruption because of less need to plough. Within little more than a decade, ryegrass and other weeds began to develop resistance. In response Australian farmers changed methods. By 1983, patches of ryegrass had become immune to Hoegrass ( diclofop-methyl ), a family of herbicides that inhibit an enzyme called acetyl coenzyme A carboxylase . Dioxins and dioxin-like compounds Dioxins and dioxin-like compounds ( DLCs ) are

1392-429: A fifty-fifty mixture of 2,4-D and dioxin-contaminated 2,4,5-T. Nine chemical companies produced it: Dow Chemical Company , Monsanto Company , Diamond Shamrock Corporation , Hercules Inc. , Thompson Hayward Chemical Co., United States Rubber Company (Uniroyal), Thompson Chemical Co., Hoffman-Taff Chemicals, Inc. , and Agriselect. The government of Vietnam says that up to four million people in Vietnam were exposed to

1566-429: A group of chemical compounds that are persistent organic pollutants (POPs) in the environment . They are mostly by-products of burning or various industrial processes or, in the case of dioxin-like PCBs and PBBs , unwanted minor components of intentionally produced mixtures. Some of them are highly toxic, but the toxicity among them varies 30,000-fold. They are grouped together because their mechanism of action

1740-549: A lack of consensus on the issue. Despite this, statistical analysis of the studies they examined resulted in data that the increase in birth defects/ relative risk (RR) from exposure to agent orange/dioxin "appears" to be on the order of 3 in Vietnamese-funded studies, but 1.29 in the rest of the world. There is data near the threshold of statistical significance suggesting Agent Orange contributes to still-births, cleft palate, and neural tube defects , with spina bifida being

1914-568: A likely relationship to increased risk of breast cancer , although a causal relationship remains unclear. Herbicide manufacturers have at times made false or misleading claims about the safety of their products. Chemical manufacturer Monsanto Company agreed to change its advertising after pressure from New York attorney general Dennis Vacco ; Vacco complained about misleading claims that its spray-on glyphosate-based herbicides, including Roundup, were safer than table salt and "practically non-toxic" to mammals, birds, and fish (though proof that this

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2088-469: A member of the basic helix-loop-helix / Per-Arnt-Sim (bHLH/PAS) family of transcription factors , and it acts to modify transcription of a number of genes (see figure). AH receptor activity is necessary for normal development and many physiological functions. Mice lacking the AH receptor (knockouts) are sick with cardiac hypertrophy, liver fibrosis, reproductive problems, and impaired immunology. The AH receptor

2262-604: A molecular mode of action for which there is no resistance. Because most herbicides could not kill all weeds, farmers rotate crops and herbicides to stop the development of resistant weeds. A 2008–2009 survey of 144 populations of waterhemp in 41 Missouri counties revealed glyphosate resistance in 69%. Weeds from some 500 sites throughout Iowa in 2011 and 2012 revealed glyphosate resistance in approximately 64% of waterhemp samples. As of 2023, 58 weed species have developed glyphosate resistance. Weeds resistant to multiple herbicides with completely different biological action modes are on

2436-678: A relatively high solubility in lipids . Therefore, they tend to associate with organic matter such as plankton, plant leaves, and animal fat. In addition, they tend to be adsorbed to inorganic particles, such as ash and soil. Dioxins are extremely stable and consequently tend to accumulate in the food chain . They are eliminated very slowly in animals, e.g. TCDD has a half-life of 7 to 9 years in humans. Incidents of contamination with PCBs are often reported as dioxin contamination incidents since these are of most public and regulatory concern. There are 75 possible congeners of polychlorinated dibenzo -p- dioxins, but only 7 of them have affinity for

2610-623: A result of exposure to Agent Orange there. One noteworthy exception, according to the U.S. Department of Labor, is a claim filed with the CIA by an employee of "a self-insured contractor to the CIA that was no longer in business." The CIA advised the Department of Labor that it "had no objections" to paying the claim and Labor accepted the claim for payment: Civilian Exposure to Agent Orange in Vietnam: GAO-05-371 April 2005.Figure 3: Overview of

2784-479: A result of these concerns, incineration processes have been improved with increased combustion temperatures (over 1,000 °C (1,830 °F)), better furnace control, and sufficient residence time allotted to ensure complete oxidation of organic compounds. Incineration or "coprocessing" of municipal and solid industrial wastes in cement kilns is another proven source of PCDD/F compounds despite extreme high temperatures 1,400–1,500 °C (2,550–2,730 °F), posing

2958-423: A result. The wood preservative pentachlorophenol often contained dioxins and dibenzofurans as impurities. The Stockholm Convention banned the production and use of dioxins in 2001. PCDD/F-compounds were never synthesized for any purpose, except for small quantities for scientific research. Small amounts of PCDD/Fs are formed whenever organics, oxygen and chlorine are available at suitable temperatures. This

3132-402: A risk in countries where coprocessing is increasingly employed as a primary waste management strategy if appropriate environmental monitoring and controls are not put in place. Ideally, an incineration process oxidizes all carbon to CO 2 and converts all chlorine to HCl or inorganic chlorides prior to the gases passing through the temperature window of 400-700 °C where PCDD/F formation

3306-483: A short period after application. Herbicides can be classified/grouped in various ways; for example, according to their activity, the timing of application, method of application, mechanism of their action, and their chemical structures. Chemical structure of the herbicide is of primary affecting efficacy. 2,4-D, mecoprop , and dicamba control many broadleaf weeds but remain ineffective against turf grasses. Chemical additives influence selectivity. Surfactants alter

3480-442: A significant quantity rapidly, and chronic toxicity arising from environmental and occupational exposure over long periods. Much public suspicion of herbicides revolves around a confusion between valid statements of acute toxicity as opposed to equally valid statements of lack of chronic toxicity at the recommended levels of usage. For instance, while glyphosate formulations with tallowamine adjuvants are acutely toxic, their use

3654-713: A single dose, high concentrations are found in the liver, but in a few days, adipose tissue will predominate. In rat liver, however, high doses cause induction of CYP1A2 enzyme, and this binds dioxins. Thus, depending on the dose, the ratio of fat and liver tissue concentrations may vary considerably in rodents. Dioxins have no common uses. They are manufactured on a small scale for chemical and toxicological research, but mostly exist as by-products of industrial processes such as chlorine bleaching of paper pulp , pesticide manufacture, and combustion processes such as incineration . The defoliant Agent Orange contained trace amounts of dioxin impurities and caused severe health issues as

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3828-399: A single plant. In 2015, Monsanto released crop seed varieties resistant to both dicamba and glyphosate, allowing for use of a greater variety of herbicides on fields without harming the crops. By 2020, five years after the release of dicamba-resistant seed, the first example of dicamba-resistant Palmer amaranth was found in one location. When mutations occur in the genes responsible for

4002-414: A study by Dr. Nguyen Viet Nhan, children in the areas where Agent Orange was used have been affected and have multiple health problems, including cleft palate, mental disabilities, hernias, and extra fingers and toes . In the 1970s, high levels of dioxin were found in the breast milk of South Vietnamese women, and in the blood of U.S. military personnel who had served in Vietnam. The most affected zones are

4176-665: A thorough benefit/risk analysis is needed before setting limits, in order to avoid increased other risks or lost benefits. The uncertainty and variability in the dose–response relationship of dioxins in terms of their toxicity, as well as the ability of dioxins to bioaccumulate , have led WHO experts to recommending very low tolerable daily intake (TDI) of dioxin, 1-4 pg/kg body weight per day, i.e. 7x10 to 2.8x10 g per 70-kg person per day, to allow for this uncertainty and ensure public safety in all instances. Authorities have then set weekly or monthly intake levels that equal to TDIs around 2 pg/kg. Because dioxins are eliminated very slowly,

4350-451: A variety of cancers in the lungs, larynx, and prostate. While in Vietnam, U.S. and Free World Military Assistance Forces soldiers were told not to worry about Agent Orange and were persuaded the chemical was harmless. After returning home, Vietnam veterans from all countries that served began to suspect their ill health or the instances of their wives having miscarriages or children born with birth defects might be related to Agent Orange and

4524-456: A weapon, by definition, is any device used to injure, defeat, or destroy living beings, structures, or systems, and Agent Orange did not qualify under that definition. It also argued that if the U.S. were to be charged for using Agent Orange, then the United Kingdom and its Commonwealth nations should be charged since they also used it widely during the Malayan Emergency in the 1950s. In 1969,

4698-420: A wick wetted with herbicide is suspended from a boom and dragged or rolled across the tops of the taller weed plants. This allows treatment of taller grassland weeds by direct contact without affecting related but desirable shorter plants in the grassland sward beneath. The method has the benefit of avoiding spray drift. In Wales , a scheme offering free weed-wiper hire was launched in 2015 in an effort to reduce

4872-414: Is augmented by metal catalysts such as copper. The optimal temperature range is 400 °C (752 °F) to 700 °C (1,292 °F). This means that formation is highest when organic material is burned in less-than-optimal conditions such as open fires, building fires, domestic fireplaces, and poorly operated and/or designed solid waste incinerators. Historically, municipal and medical waste incineration

5046-432: Is based on inappropriate activation of a physiologically important receptor, and therefore dose-response must be carefully considered. Inappropriate stimulation of many receptors leads to toxic outcomes, e.g. overdose of vitamin A leads to inappropriate activation of retinoid receptors resulting in e.g. malformations, and overdoses of corticosteroids or sex hormones lead to a multitude of adverse effects. Therefore, it

5220-479: Is called allelopathy . The applicability of these agents is unclear. Herbicide resistance became a critical problem in Australian agriculture after many Australian sheep farmers began to exclusively grow wheat in their pastures in the 1970s. Introduced varieties of ryegrass , while good for grazing sheep, compete intensely with wheat. Ryegrasses produce so many seeds that, if left unchecked, they can completely choke

5394-520: Is cancer promotion. A mixture of PCBs such as Aroclor may contain PCB compounds which are known estrogen agonists but are not classified as dioxin-like in terms of toxicity. Mutagenic effects have been established for some lower chlorinated chemicals such as 3-chlorodibenzofuran, which is neither persistent nor an AH receptor agonist. High doses . The symptoms reported to be associated with dioxin toxicity in animal studies are incredibly wide-ranging, both in

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5568-464: Is concentration in breast milk measured over decades. In many countries the concentrations have decreased to about one tenth of those in the 1970s, and the total TEQ concentrations are now of the order of 5-30 pg/g fat (please note the units, pg/g is the same as ng/kg, or the non-standard expression ppt used sometimes in the United States). The decrease is due to strict emission controls and also to

5742-418: Is described as having low residual activity if it is neutralized within a short time of application (within a few weeks or months) – typically this is due to rainfall, or reactions in the soil. A herbicide described as having high residual activity will remain potent for the long term in the soil. For some compounds, the residual activity can leave the ground almost permanently barren. Herbicides interfere with

5916-464: Is evidence on human carcinogenicity. Increases in cancer have been modest, in fact reaching statistical significance has been difficult even after high accidental or occupational exposures like in Yusho and Yucheng poisonings, Seveso accident, and combined occupational cohorts. Therefore, controversies on cancer risk at low population levels of dioxins are understandable. The problem with IARC evaluations

6090-503: Is extremely slow. This results in biological half-lives of several years for all dioxins. That of TCDD is estimated to be 7 to 8 years, and for other PCDD/Fs from 1.4 to 13 years, PCDFs on average slightly shorter than PCDDs. In mammals, dioxins are found mostly in fat. Concentrations in fat seem to be relatively similar, be it serum fat, adipose tissue fat, or milk fat. This permits measuring dioxin burden by analysing breast milk. Initially, however, at least in laboratory animals, after

6264-715: Is hoped to increase the reliability of risk assessment. Recently also developmental effects have been reassessed by the Contamination Panel of the European Food Safety Agency (EFSA). They propose decreasing the tolerable weekly intake (TWI) from 14 pg/kg to 2 pg/kg. This is likely to cause another controversy before being accepted by European countries. Dioxin intake and levels in breast milk in 1970s and 1980s were 5 to 10 times higher than presently, and very few effects have been found, possibly mild developmental effects on teeth. All dioxin-like compounds share

6438-618: Is important to separate the effects of low doses causing activation of the receptor around the physiological range from the effects of high toxic doses. This is all the more important because of large differences in exposures even among human beings. Western populations today are exposed to dioxins at doses leading to concentrations of 5 to 100 picograms/g (as TEQ in body fat), and the highest concentrations in accidental or deliberate poisonings have been 10,000 to 144,000 pg/g leading to dramatic but not lethal outcomes. The most relevant toxic outcomes of dioxins both in humans and animals are cancer and

6612-449: Is likely that the TDI for other population groups could be higher. One important cause for differences in different assessments has been carcinogenicity. If the dose-response of TCDD in causing cancer is linear, it might be a true risk. If the dose-response is of a threshold-type or J-shape, there is little or no risk at the present concentrations. Understanding the mechanisms of toxicity better

6786-529: Is meant to provide end-users with guidance on managing pesticide resistance. An example of a fully executed label compliant with the USEPA resistance management labeling guidance can be seen on the specimen label for the herbicide, cloransulam-methyl, updated in 2022. Optimising herbicide input to the economic threshold level should avoid the unnecessary use of herbicides and reduce selection pressure. Herbicides should be used to their greatest potential by ensuring that

6960-597: Is no longer harmful. Several herbicides were developed as part of efforts by the United States and the United Kingdom to create herbicidal weapons for use during World War II . These included 2,4-D, 2,4,5-T, MCPA (2-methyl-4-chlorophenoxyacetic acid, 1414B and 1414A, recoded LN-8 and LN-32), and isopropyl phenylcarbamate (1313, recoded LN-33). In 1943, the United States Department of the Army contracted botanist (and later bioethicist) Arthur Galston , who discovered

7134-575: Is often attributed to overuse as well as the strong evolutionary pressure on the affected weeds. Three agricultural practices account for the evolutionary pressure upon weeds to evolve resistance: monoculture , neglecting non-herbicide weed control practices, and reliance on one herbicide for weed control. To minimize resistance, rotational programs of herbicide application, where herbicides with multiple modes of action are used, have been widely promoted. In particular, glyphosate resistance evolved rapidly in part because when glyphosate use first began, it

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7308-461: Is possible. These substances cannot easily form organic compounds, and HCl is easily and safely neutralized in the scrubber while CO 2 is vented to the atmosphere. Inorganic chlorides are incorporated into the ash. Scrubber and particulate removal systems manage to capture some of the PCDD/F which forms even in sophisticated incineration plants. These PCDD/Fs are generally not destroyed but moved into

7482-478: Is relevant in toxicology for two very different reasons. First, it induces several enzymes important in the metabolism of foreign substances, so called xenobiotics . These include both oxidative phase I enzymes and conjugative phase II enzymes, e.g. CYP 1A2, CYP1B1, CYP2S1, CYP2A5, ALDH3, GSTA1, UGT1A1, UGT1A6, UGT1A7 and NQO1. This is in essence a protective function preventing toxic or carcinogenic effects of xenobiotics, but in some conditions it may also result in

7656-617: Is sharply reduced in contrast with unsprayed areas. The environmental destruction caused by this defoliation has been described by Swedish Prime Minister Olof Palme , lawyers, historians and other academics as an ecocide . The use of Agent Orange in Vietnam resulted in numerous legal actions. The United Nations ratified United Nations General Assembly Resolution 31/72 and the Environmental Modification Convention . Lawsuits filed on behalf of both U.S. and Vietnamese veterans sought compensation for damages. Agent Orange

7830-567: Is that they only assess hazard, i.e. carcinogenicity at any dose. It is likely that there is a practical safe threshold for the non-genotoxic dioxins, and the present population levels do not possess any risk of cancer. There is thus some agreement on that cancer risk is taken care of as well, if daily intake limits are set to protect from developmental effects. Among fishermen with high dioxin concentrations in their bodies, cancer deaths were decreased rather than increased. All this means that in case of important beneficial food items and breast feeding

8004-643: Is the cause of the other. The main problem is that similar associations can be found with many quite different POPs, which have only long half-lives and tendency to accumulate in lipids in common. This suggests that they may all be related to diet and obesity which are by far the most common causes of type 2 diabetes. Over the years there have been speculations on various effects of dioxins on endometriosis , sexual development, liver function , thyroid hormone levels, white blood cell levels, immune functions, and even learning and intelligence. While some of these effects might be possible after heavy exposures (like in

8178-488: Is the most toxic dioxin TCDD which per definition has a TEF of one. In essence, multiplying the amount of a particular congener with its TEF produces the amount toxicologically equivalent to TCDD, and after this conversion all dioxin-like congeners can be summed up, and the resulting toxicity equivalent quantity (TEQ) gives an approximation of toxicity of the mixture measured as TCDD. Dioxins are virtually insoluble in water but have

8352-598: Is the same. They activate the aryl hydrocarbon receptor (AH receptor), albeit with very different binding affinities, leading to high differences in toxicity and other effects. They include: Dioxins have different toxicity depending on the number and position of the chlorine atoms. Because dioxins refer to such a broad class of compounds that vary widely in toxicity, the concept of toxic equivalency factor (TEF) has been developed to facilitate risk assessment and regulatory control. TEFs exist for seven congeners of dioxins, ten furans and twelve PCBs. The reference congener

8526-1087: The Americal Division in the summer of 1970 continued to use Agent Orange for crop destruction in violation of the suspension. An investigation led to disciplinary action against the brigade and division commanders because they had falsified reports to hide its use. Defoliation and crop destruction were completely stopped by June 30, 1971. There are various types of cancer associated with Agent Orange, including chronic B-cell leukemia, Hodgkin's lymphoma, multiple myeloma, non-Hodgkin's lymphoma, prostate cancer, respiratory cancer, lung cancer, and soft tissue sarcomas. The government of Vietnam states that 4 million of its citizens were exposed to Agent Orange, and as many as 3 million have suffered illnesses because of it; these figures include their children who were exposed. The Red Cross of Vietnam estimates that up to 1 million people are disabled or have health problems due to Agent Orange contamination. The United States government has challenged these figures as being unreliable. According to

8700-545: The Centers for Disease Control and Prevention showed that there was an increase in the rate of birth defects of the children of military personnel as a result of Agent Orange. Agent Orange has also caused enormous environmental damage in Vietnam. Over 3,100,000 ha (7,700,000 acres) or 31,000 km (12,000 sq mi) of forest were defoliated. Defoliants eroded tree cover and seedling forest stock, making reforestation difficult in numerous areas. Animal species diversity

8874-491: The European Food Safety Agency (EFSA) recommended decreasing tolerable weekly intake (TWI) levels based on the Russian children study. This recommendation can be challenged, because it does not properly consider competing risks following from lost benefits of important and healthy food items such as certain fish. TWI levels are not applied for breast feeding, because benefits of breast milk are judged to be far more important than

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9048-547: The Rothamsted Experimental Station made the same discovery. Quastel was tasked by the Agricultural Research Council (ARC) to discover methods for improving crop yield. By analyzing soil as a dynamic system, rather than an inert substance, he was able to apply techniques such as perfusion . Quastel was able to quantify the influence of various plant hormones , inhibitors, and other chemicals on

9222-514: The Second World War as the result of research conducted independently in the United Kingdom and the United States into the potential use of herbicides in war . The compound 2,4-D was first synthesized by W. G. Templeman at Imperial Chemical Industries . In 1940, his work with indoleacetic acid and naphthaleneacetic acid indicated that "growth substances applied appropriately would kill certain broad-leaved weeds in cereals without harming

9396-710: The U.S. Congress were told, "crop destruction is understood to be the more important purpose ... but the emphasis is usually given to the jungle defoliation in public mention of the program." The first official acknowledgment of the programs came from the State Department in March 1966. When crops were destroyed, the Viet Cong would compensate for the loss of food by confiscating more food from local villages. Some military personnel reported being told they were destroying crops used to feed guerrillas, only to later discover, most of

9570-498: The Viet Nam Red Cross Society estimates that up to one million people were disabled or have health problems as a result of exposure to Agent Orange. The United States government has described these figures as unreliable. In general, many questions exist about the health and environmental effects of many herbicides because of the large number of herbicides and the myriad potential targets, mostly unintended. For example,

9744-553: The Vietnam War has left tangible, long-term impacts upon the Vietnamese people and U.S soldiers that handled the chemicals. More than 20% of South Vietnam's forests and 3.2% of its cultivated land were sprayed at least once between during the war. The government of Vietnam says that up to four million people in Vietnam were exposed to the defoliant, and as many as three million people have suffered illness because of Agent Orange, while

9918-631: The White House and the State and Defense Departments . Many U.S. officials supported herbicide operations, pointing out that the British had already used herbicides and defoliants in Malaya during the 1950s. In November 1961, Kennedy authorized the start of Operation Ranch Hand , the codename for the United States Air Force 's herbicide program in Vietnam. The herbicide operations were formally directed by

10092-434: The aryl hydrocarbon receptor (AH receptor) and are toxic via this mechanism. The crucial structures are so called lateral chlorines in positions 2,3,7, and 8. These 4 chlorines also make the congeners persistent, because they prevent microbial degradation. Additional chlorines make the compounds less potent, but basically the effects remain the same although at higher doses. There are 135 possible dibenzofurans, and 10 in which

10266-411: The body burden accumulated during the whole lifetime is high compared with daily doses, and occasional modest exceedances of limit values do not change it much. Therefore, long-term intake is much more important than daily intake. Specifically, the TDI has been assessed to guarantee the safety of children born to mothers exposed to such a daily intake of dioxins all their lifetime prior to pregnancy. It

10440-449: The dioxin 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD). TCDD was a trace (typically 2–3 ppm , ranging from 50 ppb to 50 ppm) - but significant - contaminant of Agent Orange. TCDD is the most toxic of the dioxins and is classified as a human carcinogen by the U.S. Environmental Protection Agency (EPA). The fat-soluble nature of TCDD causes it to enter the body readily through physical contact or ingestion. Dioxins accumulate easily in

10614-485: The fly ash . Catalytic systems have been designed which destroy vapor-phase PCDD/Fs at relatively low temperatures. This technology is often combined with the baghouse or SCR system at the tail end of an incineration plant. The European Union limit for concentration of dioxin-like compounds in the discharged flue gas is 0.1 ng/Nm³ TEQ. Both in Europe and in U.S.A., the emissions have decreased dramatically since

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10788-938: The liver , thymus , and other organs. Some effects such as thymic atrophy are common in many species, but e.g. liver toxicity is typical in rabbits. Low doses . Very few signs of toxicity are seen in adult animals after low doses, but developmental effects may occur at low dioxin levels, including foetal , neonatal , and possibly pubescent stages. Well established developmental effects are cleft palate , hydronephrosis , disturbances in tooth development and sexual development , and endocrine effects. Surprisingly, enzyme induction, several developmental effects and aversion to novel foods occur at similar dose levels in animals that respond differently to acute high-dose toxicity. Therefore, it has been suggested that dioxin effects be divided to type I effects (enzyme induction etc.) and type II effects (lethality, liver damage, anorexia, and tumour promotion). The reason may be different requirements of

10962-436: The 1980s, by even 90% (see Figure). This has also led to decreases in human body burdens, which is neatly demonstrated by the decrease of dioxin concentrations in breast milk . With the substantial decrease of emissions from municipal waste incinerators, other potentially large sources of dioxin-like compounds, for example from forest and wild fires, have increased relative to industrial sources. They are however not included in

11136-401: The AHR. Some toxic effects (especially of PCBs) may be independent of the AHR, and those are not taken into account by using TEQs. TEFs are also approximations with certain amount of scientific judgement rather than scientific facts. Therefore, they may be re-evaluated from time to time. There have been several TEF versions since the 1980s. The most recent re-assessment was by an expert group of

11310-506: The Arctic. Only a minor portion of PCBs in mixtures are dioxin-like. Other sources of PCDD/F include: Improvements and changes have been made to nearly all industrial sources to reduce PCDD/F production. In waste incineration, large amounts of publicity and concern surrounded dioxin-like compounds during the 1980s-1990s continues to pervade the public consciousness, especially when new incineration and waste-to-energy facilities are proposed. As

11484-604: The Bionetic Research Laboratories between 1965 and 1968 found malformations in test animals caused by 2,4,5-T, a component of Agent Orange. The study was later brought to the attention of the White House in October 1969. Other studies reported similar results and the Department of Defense began to reduce the herbicide operation. On April 15, 1970, it was announced that the use of Agent Orange was suspended. Two brigades of

11658-419: The British did in Malaya, the goal of the U.S. was to defoliate rural/forested land, depriving guerrillas of food and concealment and clearing sensitive areas such as around base perimeters and possible ambush sites along roads and canals. Samuel P. Huntington argued that the program was also a part of a policy of forced draft urbanization , which aimed to destroy the ability of peasants to support themselves in

11832-449: The British had established a precedent for warfare with herbicides in Malaya. In mid-1961, President Ngo Dinh Diem of South Vietnam asked the United States to help defoliate the lush jungle that was providing cover to his Communist enemies. In August of that year, the Republic of Vietnam Air Force conducted herbicide operations with American help. Diem's request launched a policy debate in

12006-552: The CIA--acting in the role of the employer and the insurance carrier--stated that it "had no objections" to paying the claim. Labor reviewed the claim and accepted it for payment." About 17.8% or 3,100,000 hectares (31,000 km; 12,000 sq mi) of the total forested area of Vietnam was sprayed during the war, which disrupted the ecological equilibrium. The persistent nature of dioxins, erosion caused by loss of tree cover, and loss of seedling forest stock meant that reforestation

12180-583: The Institute of Medicine (IOM), now known as the National Academy of Medicine , to issue reports every 2 years on the health effects of Agent Orange and similar herbicides. First published in 1994 and titled Veterans and Agent Orange , the IOM reports assess the risk of both cancer and non-cancer health effects. Each health effect is categorized by evidence of association based on available research data. The last update

12354-467: The New Zealand government finally admitted that New Zealanders had in fact been exposed to Agent Orange while serving in Vietnam and the experience was responsible for detrimental health conditions in veterans and their children. Amendments to the memorandum made in 2021 meant that more veterans were eligible for an ex gratia payment of NZ$ 40,000. Starting in the early 1990s, the federal government directed

12528-583: The Seveso disaster), these claims are only based on potential exposures of population, not supported by actual measurements of dioxin concentrations. E.g. absorption from bleached tampons claimed to be associated with endometriosis is insignificant compared with daily dioxin intake from food. Dioxins are well established carcinogens in animal studies, although the precise mechanism is not clear. Dioxins are not mutagenic or genotoxic . The United States Environmental Protection Agency has categorised dioxin, and

12702-657: The U.S. dropped 475,500 U.S. gal (1,800,000 L; 395,900 imp gal) in Laos and 40,900 U.S. gal (155,000 L; 34,100 imp gal) in Cambodia. Because Laos and Cambodia were both officially neutral during the Vietnam War, the U.S. attempted to keep secret its military operations in those countries, from the American population and has largely avoided compensating American veterans and CIA personnel stationed in Cambodia and Laos who suffered permanent injuries as

12876-460: The U.S. was violating the 1925 Geneva Protocol , which regulated the use of chemical and biological weapons in international conflicts. The U.S. defeated most of the resolutions, arguing that Agent Orange was not a chemical or a biological weapon as it was considered a herbicide and a defoliant and it was used in effort to destroy plant crops and to deprive the enemy of concealment and not meant to target human beings. The U.S. delegation argued that

13050-480: The UK has been linked to a decline in seed-eating bird species which rely on the weeds killed by the herbicides. Heavy use of herbicides in neotropical agricultural areas has been one of many factors implicated in limiting the usefulness of such agricultural land for wintering migratory birds. One major complication to the use of herbicides for weed control is the ability of plants to evolve herbicide resistance , rendering

13224-446: The United Kingdom commented on the draft Resolution 2603 (XXIV): The evidence seems to us to be notably inadequate for the assertion that the use in war of chemical substances specifically toxic to plants is prohibited by international law . The environmental destruction caused by this defoliation has been described by Swedish Prime Minister Olof Palme , lawyers, historians and other academics as an ecocide . A study carried out by

13398-517: The United States in 2012, about 91% of all herbicide usage, determined by weight applied, was in agriculture. In 2012, world pesticide expenditures totaled nearly $ 24.7 billion; herbicides were about 44% of those sales and constituted the biggest portion, followed by insecticides , fungicides , and fumigants . Herbicide is also used in forestry, where certain formulations have been found to suppress hardwood varieties in favor of conifers after clearcutting , as well as pasture systems. Prior to

13572-1354: The Weed Science Society of America (WSSA) and herbicide Resistance and World Grains (HRAC) systems, herbicides are classified by mode of action. Eventually the Herbicide Resistance Action Committee (HRAC) and the Weed Science Society of America (WSSA) developed a classification system. Groups in the WSSA and the HRAC systems are designated by numbers and letters, inform users awareness of herbicide mode of action and provide more accurate recommendations for resistance management. Most herbicides are applied as water-based sprays using ground equipment. Ground equipment varies in design, but large areas can be sprayed using self-propelled sprayers equipped with long booms, of 60 to 120 feet (18 to 37 m) with spray nozzles spaced every 20–30 inches (510–760 mm) apart. Towed, handheld, and even horse-drawn sprayers are also used. On large areas, herbicides may also at times be applied aerially using helicopters or airplanes, or through irrigation systems (known as chemigation ). Weed-wiping may also be used, where

13746-454: The Workers' Compensation Claims Process for Contract Employees: " ... Of the 20 claims filed by contract employees [of the united States government], 9 were initially denied by the insurance carriers and 1 was approved for payment. ... The claim that was approved by Labor for payment involved a self-insured contractor to the CIA that was no longer in business. Absent an employer or insurance carrier,

13920-505: The World Health organization in 2005. Greenpeace and some other environmental groups have called for the chlorine industry to be phased out. However, chlorine industry supporters say that "banning chlorine would mean that millions of people in the third world would die from want of disinfected water". Sharon Beder and others have argued that the dioxin controversy has been very political and that large companies have tried to play down

14094-412: The absolute and relative significance of dairy products and meat have decreased due to strict emission controls, and brought about the decrease of total intake. E.g. in the United Kingdom the total intake of PCDD/F in 1982 was 239 pg/day and in 2001 only 21 pg/day (WHO-TEQ). Since the half-lives are very long (for e.g. TCDD 7–8 years), the body burden will increase almost over the whole lifetime. Therefore,

14268-545: The active ingredient, picloram , in studies on rats. Herbicide use generally has negative impacts on many aspects of the environment. Insects, non-targeted plants, animals, and aquatic systems subject to serious damage from herbicides. Impacts are highly variable. Atrazine has often been blamed for affecting reproductive behavior of aquatic life, but the data do not support this assertion. Bird populations are one of many indicators of herbicide damage.Most observed effects are due not to toxicity, but to habitat changes and

14442-673: The activity of microorganisms in the soil and assess their direct impact on plant growth . While the full work of the unit remained secret, certain discoveries were developed for commercial use after the war, including the 2,4-D compound. When 2,4-D was commercially released in 1946, it became the first successful selective herbicide, triggering a worldwide revolution in agricultural output. It allowed for greatly enhanced weed control in wheat , maize (corn), rice , and similar cereal grass crops, because it kills dicots (broadleaf plants), but not most monocots (grasses). The low cost of 2,4-D has led to continued usage today, and it remains one of

14616-507: The actual amount or concentration of a congener by its TEF, the product is the virtual amount or concentration of TCDD having effects of the same magnitude as the compound in question. This multiplication is done for all compounds in a mixture, and these "equivalents of TCDD" can then simply be added, resulting in TEQ, the amount or concentration of TCDD toxicologically equivalent to the mixture. The TEQ conversion makes it possible to use all studies on

14790-409: The background levels of dioxins. They do not reach concentrations causing typical dioxin-like toxicity, however. The aryl hydrocarbon receptor (AH receptor) is an ancient receptor, and its many functions have been revealed only recently. It is an over 600-million-year-old protein occurring in all vertebrates, and its homologs have been discovered in invertebrates and insects. It is classified as

14964-456: The badly infested areas of fields, is another means of reducing total herbicide use. When resistance is first suspected or confirmed, the efficacy of alternatives is likely to be the first consideration. If there is resistance to a single group of herbicides, then the use of herbicides from other groups may provide a simple and effective solution, at least in the short term. For example, many triazine-resistant weeds have been readily controlled by

15138-572: The best proven effect is chloracne. The suspected effects in adults are liver damage, and alterations in heme metabolism, serum lipid levels, thyroid functions, as well as diabetes and immunological effects . Low exposures. Effects after low exposures such as from food have been difficult to prove. Levels of dioxins in contemporary population are 5 to 20 pg/g (TEQ in fat) and 50 to 100 pg in older people or at least 1000 times lower than those in poisonings (see above). Tooth deformities have been considered plausible after long breast-feeding, when

15312-408: The best studied TCDD to assess the toxicity of a mixture. This is most useful in regulatory work, but it can also be used in scientific studies. This resembles the common measure of all alcoholic drinks: beer, wine and whiskey can be added together as absolute alcohol, and this sum gives the toxicologically meaningful measure of the total impact. The TEQ only applies to dioxin-like effects mediated by

15486-409: The biochemical machinery that supports plant growth. Herbicides often mimic natural plant hormones , enzyme substrates, and cofactors . They interfere with the metabolism in the target plants. Herbicides are often classified according to their site of action because as a general rule, herbicides within the same site of action class produce similar symptoms on susceptible plants. Classification based on

15660-470: The biological mechanisms that herbicides interfere with, these mutations may cause the herbicide mode of action to work less effectively. This is called target-site resistance. Specific mutations that have the most helpful effect for the plant have been shown to occur in separate instances and dominate throughout resistant weed populations. This is an example of convergent evolution . Some mutations conferring herbicide resistance may have fitness costs, reducing

15834-499: The chemicals in the presence of personnel that the Australian government was forced to change their stance. Only in 1994 did the Australian government finally admit that it was true that defoliants had been used in areas of Vietnam where Australian forces operated and the effects of these may have been detrimental to some Vietnam veterans and their children. It was only in 2015 that the official Australian War Memorial accepted rewriting

16008-543: The city. The highest TCDD levels were found in children, up to 56,000 pg/g fat. Acute effects were limited to chloracne, although many animals such as rabbits died after eating contaminated grass. Dental aberrations were found after 25 years in persons exposed as children, and a slightly increased cancer risk was confirmed 35 years later. In line with animal studies, developmental effects may be much more important than effects in adults. These include disturbances of tooth development, and of sexual development. An example of

16182-476: The concentrations may increase five to tenfold from age 20 to age 60. For the same reason, short term higher intake such as after food contamination incidents, is not crucial unless it is extremely high or lasts for several months or years. The highest body burdens were found in Western Europe in the 1970s and early 1980s, and the trends have been similar in the U.S. The most useful measure of time trends

16356-408: The control of concentrations in food. In the U.S. young adult female population (age group 20–39), the concentration was 9.7 pg/g lipid in 2001-2002 (geometric mean). Certain professions such as subsistence fishermen in some areas are exposed to exceptionally high amounts of dioxins and related substances. This along with high industrial exposures may be the most valuable source of information on

16530-588: The countryside, forcing them to flee to the U.S.-dominated cities, depriving the guerrillas of their rural support base. Agent Orange was usually sprayed from helicopters or from low-flying C-123 Provider aircraft, fitted with sprayers and "MC-1 Hourglass" pump systems and 1,000 U.S. gal (3,800 L; 830 imp gal) chemical tanks. Spray runs were also conducted from trucks, boats, and backpack sprayers. Altogether, over 80,000,000 L (18,000,000 imp gal; 21,000,000 US gal) of Agent Orange were applied. The first batch of herbicides

16704-480: The crops," though these substances were too expensive and too short-lived in soil due to degradation by microorganisms to be of practical agricultural use; by 1941, his team succeeded in synthesizing a wide range of chemicals to achieve the same effect at lower cost and better efficacy, including 2,4-D. In the same year, R. Pokorny in the US achieved this as well. Independently, a team under Juda Hirsch Quastel , working at

16878-402: The decreases in abundance of species on which birds rely for food or shelter. Herbicide use in silviculture , used to favor certain types of growth following clearcutting , can cause significant drops in bird populations. Even when herbicides which have low toxicity to birds are used, they decrease the abundance of many types of vegetation on which the birds rely. Herbicide use in agriculture in

17052-540: The defoliant, and as many as three million people have suffered illness because of Agent Orange, while the Vietnamese Red Cross estimates that up to one million people were disabled or have health problems as a result of exposure to Agent Orange. The United States government has described these figures as unreliable, while documenting cases of leukemia , Hodgkin's lymphoma , and various kinds of cancer in exposed U.S. military veterans. An epidemiological study done by

17226-571: The defoliants later used in Agent Orange, and his employer University of Illinois Urbana-Champaign to study the effects of 2,4-D and 2,4,5-T on cereal grains (including rice) and broadleaf crops. While a graduate and post-graduate student at the University of Illinois, Galston's research and dissertation focused on finding a chemical means to make soybeans flower and fruit earlier. He discovered both that 2,3,5- triiodobenzoic acid (TIBA) would speed up

17400-593: The destroyed food was actually produced to support the local civilian population. For example, according to Wil Verwey, 85% of the crop lands in Quang Ngai province were scheduled to be destroyed in 1970 alone. He estimated this would have caused famine and left hundreds of thousands of people without food or malnourished in the province. According to a report by the American Association for the Advancement of Science,

17574-416: The developmental effects on offspring. Both have been documented at high doses, most accurately in animal experiments. As to developmental effects there is an agreement that the present dioxin levels in many populations are not very far from those causing some effects, but there is not yet consensus on the safe level. As to cancer, there is a disagreement on how to extrapolate the risk from high toxic doses to

17748-473: The dioxin concentrations were high in 1970s and 1980s. When the concentrations decreased during 1990s and 2000s, the effects were no longer seen. According to a study in Russia, sperm counts in 18-19 year old young men were lower when dioxin levels were higher at the age of 8 to 9 years. This was in industrial environments causing relatively high exposures to boys as well as their mothers. The contamination panel of

17922-586: The effectiveness of combining herbicides is also questioned, particularly in light of the rise of non-target site resistance. Plants developed resistance to atrazine and to ALS-inhibitors relatively early, but more recently, glyphosate resistance has dramatically risen. Marestail is one weed that has developed glyphosate resistance. Glyphosate-resistant weeds are present in the vast majority of soybean, cotton and corn farms in some U.S. states. Weeds that can resist multiple other herbicides are spreading. Few new herbicides are near commercialization, and none with

18096-421: The exception of liver cancer, these are the same conditions the U.S. Veterans Administration has determined may be associated with exposure to Agent Orange/dioxin and are on the list of conditions eligible for compensation and treatment. Military personnel who were involved in storage, mixture and transportation (including aircraft mechanics), and actual use of the chemicals were probably among those who received

18270-472: The first application. If these are resistant, then the second herbicide in the sequence may increase selection for resistant individuals by killing the susceptible plants which were damaged but not killed by the first application, but allowing the larger, less affected, resistant plants to survive. This has been cited as one reason why ALS-resistant Stellaria media has evolved in Scotland recently (2000), despite

18444-609: The flowering of soybeans and that in higher concentrations it would defoliate the soybeans. From these studies arose the concept of using aerial applications of herbicides to destroy enemy crops to disrupt their food supply. In early 1945, the U.S. Army ran tests of various 2,4-D and 2,4,5-T mixtures at the Bushnell Army Airfield in Florida. As a result, the U.S. began a full-scale production of 2,4-D and 2,4,5-T and would have used it against Japan in 1946 during Operation Downfall if

18618-677: The following biochemical mechanisms: The following terms are also used to describe cases where plants are resistant to multiple herbicides at once: Due to herbicide resistance – a major concern in agriculture – a number of products combine herbicides with different means of action. Integrated pest management may use herbicides alongside other pest control methods. Integrated weed management (IWM) approach utilizes several tactics to combat weeds and forestall resistance. This approach relies less on herbicides and so selection pressure should be reduced. By relying on diverse weed control methods, including non-herbicide methods of weed control,

18792-456: The following commercial products cycloxydim , clethodim , tralkoxydim , butroxydim , sethoxydim , profoxydim , and mesotrione . Knowing about herbicide chemical family grouping serves as a short-term strategy for managing resistance to site of action. The phenoxyacetic acid mimic the natural auxin indoleacetic acid (IAA). This family includes MCPA , 2,4-D , and 2,4,5-T , picloram , dicamba , clopyralid , and triclopyr . Using

18966-465: The food chain. Dioxin enters the body by attaching to a protein called the aryl hydrocarbon receptor (AhR), a transcription factor . When TCDD binds to AhR, the protein moves to the cell nucleus , where it influences gene expression. According to U.S. government reports, if not bound chemically to a biological surface such as soil, leaves or grass, Agent Orange dries quickly after spraying and breaks down within hours to days when exposed to sunlight and

19140-405: The formation of tumours caused by other factors, and adversely affect the normal mechanisms for inhibiting tumour growth. Some researchers have also proposed that dioxin induces cancer progression through a very different mitochondrial pathway. As with many toxic endpoints of dioxin, a clear dose–response relationship is difficult to establish. After accidental or high occupational exposures there

19314-496: The former U.S. airbases in Da Nang , Phù Cát District and Biên Hòa . Some of the soil and sediment on the bases have extremely high levels of dioxin requiring remediation. The Da Nang Air Base has dioxin contamination up to 350 times higher than international recommendations for action. The contaminated soil and sediment continue to affect the citizens of Vietnam, poisoning their food chain and causing illnesses, serious skin diseases and

19488-531: The government of South Vietnam. During the Vietnam War, between 1962 and 1971, the United States military sprayed nearly 20,000,000 U.S. gal (76,000,000 L; 17,000,000 imp gal) of various chemicals – the " rainbow herbicides " and defoliants – in Vietnam, eastern Laos, and parts of Cambodia as part of Operation Ranch Hand, reaching its peak from 1967 to 1969. For comparison purposes, an olympic size pool holds approximately 660,000 U.S. gal (2,500,000 L; 550,000 imp gal). As

19662-629: The health risks of dioxins. Dioxins are absorbed well from the digestive tract if they are dissolved in fats or oils (e.g. in fish or meat). On the other hand, dioxins tend to adsorb tightly to soil particles, and absorption may be quite low: 13.8% of the given dose of TEQs in contaminated soil was absorbed. The same features causing persistence of dioxins in the environment also cause very slow elimination in humans and animals. Because of low water solubility, kidneys cannot excrete them in urine as such. They must first be metabolised to more-water-soluble metabolites, but that metabolism, especially in humans,

19836-400: The heaviest exposures. Military members who served on Okinawa also claim to have been exposed to the chemical, but there is no verifiable evidence to corroborate these claims. Some studies have suggested that veterans exposed to Agent Orange may be more at risk of developing prostate cancer and potentially more than twice as likely to develop higher-grade, more lethal prostate cancers. However,

20010-485: The herbicide campaign had disrupted the food supply of more than 600,000 people by 1970. Many experts at the time, including plant physiologist and bioethicist Arthur Galston , opposed herbicidal warfare because of concerns about the side effects to humans and the environment by indiscriminately spraying the chemical over a wide area. As early as 1966, resolutions were introduced to the United Nations charging that

20184-497: The herbicide coming into direct contact with people or wildlife, inhalation of aerial sprays, or food consumption prior to the labelled preharvest interval. Under some conditions, certain herbicides can be transported via leaching or surface runoff to contaminate groundwater or distant surface water sources. Generally, the conditions that promote herbicide transport include intense storm events (particularly shortly after application) and soils with limited capacity to adsorb or retain

20358-460: The herbicides ineffective against target plants. Out of 31 known herbicide modes of action, weeds have evolved resistance to 21. 268 plant species are known to have evolved herbicide resistance at least once. Herbicide resistance was first observed in 1957, and since has evolved repeatedly in weed species from 30 families across the globe. Weed resistance to herbicides has become a major concern in crop production worldwide. Resistance to herbicides

20532-428: The herbicides. Herbicide properties that increase likelihood of transport include persistence (resistance to degradation) and high water solubility. Cases have been reported where Phenoxy herbicides are contaminated with dioxins such as TCDD ; research has suggested such contamination results in a small rise in cancer risk after occupational exposure to these herbicides. Triazine exposure has been implicated in

20706-479: The hospitals at Bong Son and Qui Nhon , on secondments at various bases, and as flight crew and ground crew for flights into and out of Da Nang Air Base - all areas that were well-documented as having been sprayed. It wasn't until a group of Australian veterans produced official military records, maps, and mission data as proof that the TAOR controlled by Australian and New Zealand forces in Vietnam had been sprayed with

20880-457: The jungle. Deployment of herbicides and defoliants served the dual purpose of thinning jungle trails to prevent ambushes and destroying crop fields in regions where the MNLA was active to deprive them of potential sources of food. As part of this process, herbicides and defoliants were also sprayed from Royal Air Force aircraft. The use of herbicides as a chemical weapon by the U.S. military during

21054-482: The lateral chlorines are dioxin-like. There are 209 PCB compounds. Analogously to PCDDs at least two lateral chlorines in each ring in positions 3,4, and/or 5 are needed for dioxin-like activity. Because the AH receptor requires a planar (flat) structure, only PCB congeners that can rotate freely along the C—C axis between the rings can attach the receptor. Substituents in ortho-positions 2 and 6 prevent rotation and thus hinder

21228-823: The leaf more readily at high humidity by lengthening the drying time of the spray droplet and increasing cuticle hydration. Light of high intensity may break down some herbicides and cause the leaf cuticle to thicken, which can interfere with absorption. Precipitation may wash away or remove some foliage-applied herbicides, but it will increase root absorption of soil-applied herbicides. Drought-stressed plants are less likely to translocate herbicides. As temperature increases, herbicides' performance may decrease. Absorption and translocation may be reduced in very cold weather. Non-selective herbicides, generally known as defoliants , are used to clear industrial sites, waste grounds, railways, and railway embankments. Paraquat , glufosinate , and glyphosate are non-selective herbicides. An herbicide

21402-560: The levels of MCPA in water courses. There is little difference in forestry in the early growth stages, when the height similarities between growing trees and growing annual crops yields a similar problem with weed competition. Unlike with annuals however, application is mostly unnecessary thereafter and is thus mostly used to decrease the delay between productive economic cycles of lumber crops. Herbicide volatilisation or spray drift may result in herbicide affecting neighboring fields or plants, particularly in windy conditions. Sometimes,

21576-410: The longer term. One practical advantage of sequences of two herbicides compared with mixtures is that a better appraisal of the efficacy of each herbicide component is possible, provided that sufficient time elapses between each application. A disadvantage with sequences is that two separate applications have to be made and it is possible that the later application will be less effective on weeds surviving

21750-424: The mixture of substances associated with sources of dioxin toxicity as a "likely human carcinogen". The International Agency for Research on Cancer has classified TCDD as a human carcinogen (class 1) on the basis of clear animal carcinogenicity and limited human data, and subsequently also 2,3,4,7,8-PCDF and PCB 126 as class 1 carcinogens. The mechanism is thought to be mainly promotion, i.e. dioxins can accelerate

21924-566: The molecule from assuming a planar position. Mono-ortho congeners (one Cl in 2, 2', 6, or 6') have minimal activity. No significant dioxin-like activities have been noticed, if there are two or more o-chlorines. Brominated dioxins and biphenyls have similar properties, but they have been studied much less. Many natural compounds have very high affinity to AH receptors. These include indoles, flavones, benzoflavones, imidazoles and pyridines. These compounds are metabolized rapidly, but continuous intake from food may cause similar receptor activation as

22098-456: The most commonly used herbicides in the world. Like other acid herbicides, current formulations use either an amine salt (often trimethylamine ) or one of many esters of the parent compound. The triazine family of herbicides, which includes atrazine , was introduced in the 1950s; they have the current distinction of being the herbicide family of greatest concern regarding groundwater contamination . Atrazine does not break down readily (within

22272-616: The most prominent symptom was chloracne after initial stomach pain indicating hepatitis and pancreatitis . These episodes show that a human being is not as sensitive as the most sensitive animals, since the doses must have been up to 25 μg/kg. Two serious food contamination accidents were caused by PCB oils used in heat exchangers. The PCB oil leaked to rice bran oil consumed by thousands of people in Japan ( Yusho disease 1968) and Taiwan ( Yu-cheng disease 1979). The toxic effects have been attributed to dioxin-like PCBs and PCDFs. Their daily intake

22446-520: The most statistically significant defect. The large discrepancy in RR between Vietnamese studies and those in the rest of the world has been ascribed to bias in the Vietnamese studies. Twenty-eight of the former U.S. military bases in Vietnam where the herbicides were stored and loaded onto airplanes may still have high levels of dioxins in the soil, posing a health threat to the surrounding communities. Extensive testing for dioxin contamination has been conducted at

22620-516: The most toxic of its type) found in the mixture have caused major health problems and deformities for many individuals who were exposed and for their children. Agent Orange was produced in the United States beginning in the late 1940s and was used in industrial agriculture, and was also sprayed along railroads and power lines to control undergrowth in forests. During the Vietnam War, the U.S. military procured over 20,000,000 U.S. gal (76,000,000 L; 17,000,000 imp gal), consisting of

22794-469: The mountainous area along Truong Son (Long Mountains) and the border between Vietnam and Cambodia. The affected residents are living in substandard conditions with many genetic diseases . In 2006, Anh Duc Ngo and colleagues of the University of Texas Health Science Center published a meta-analysis that exposed a large amount of heterogeneity (different findings) between studies, a finding consistent with

22968-465: The official history of Australia's involvement in the Vietnam War to acknowledge that Australian soldiers were exposed to defoliants used in Vietnam. New Zealand was even slower to correct their error, with the government going as far as to deny the legitimacy of the Australian reports in a report called the "McLeod Report" published by Veterans Affairs NZ in 2001 thus infuriating New Zealand veterans and those associated with their cause. In 2006 progress

23142-574: The other toxic herbicides to which they had been exposed in Vietnam. U.S. Veterans began to file claims in 1977 to the Department of Veterans Affairs for disability payments for health care for conditions they believed were associated with exposure to Agent Orange, or more specifically, dioxin, but their claims were denied unless they could prove the condition began when they were in the service or within one year of their discharge. In order to qualify for compensation, U.S. veterans must have served on or near

23316-641: The perimeters of military bases in Thailand during the Vietnam Era, where herbicides were tested and stored outside of Vietnam, veterans who were crew members on C-123 planes flown after the Vietnam War, or were associated with Department of Defense (DoD) projects to test, dispose of, or store herbicides in the U.S. By April 1993, the Department of Veterans Affairs had compensated only 486 victims, although it had received disability claims from 39,419 soldiers who had been exposed to Agent Orange while serving in Vietnam. In

23490-469: The physical properties of the spray solution and the overall phytotoxicity of the herbicide, increasing translocation. Herbicide safeners enhance the selectivity by boosting herbicide resistance by the crop but allowing the herbicide to damage the weed. Selectivity is determined by the circumstances and technique of application. Climatic factors affect absorption including humidity , light, precipitation, and temperature. Foliage-applied herbicides will enter

23664-580: The plant's ability to survive in other ways, but over time, the least costly mutations tend to dominate in weed populations. Recently, incidences of non-target site resistance have increasingly emerged, such as examples where plants are capable of producing enzymes that neutralize herbicides before they can enter the plant's cells – metabolic resistance . This form of resistance is particularly challenging, since plants can develop non-target-site resistance to herbicides their ancestors were never directly exposed to. Resistance to herbicides can be based on one of

23838-654: The potency, but qualitatively the effects remain similar. Therefore, a simple sum of different dioxin congeners is not a meaningful measure of toxicity. To compare the toxicities of various congeners and to render it possible to make a toxicologically meaningful sum of a mixture, a toxicity equivalency (TEQ) concept was created. Each congener has been given a toxicity equivalence factor (TEF). This indicates its relative toxicity as compared with TCDD. Most TEFs have been extracted from in vivo toxicity data on animals, but if these are missing (e.g. in case of some PCBs), less reliable in vitro data have been used. After multiplying

24012-469: The present low exposures. While the affinity of dioxins and related industrial toxicants to the Ah receptor may not fully explain all their toxic effects including immunotoxicity, endocrine effects and tumor promotion , toxic responses appear to be typically dose-dependent within certain concentration ranges. A multiphasic dose–response relationship has also been reported, leading to uncertainty and debate about

24186-445: The production of reactive metabolites that are mutagenic and carcinogenic. This enzyme induction can be initiated by many natural or synthetic compounds, e.g., carcinogenic polycyclic hydrocarbons such as benzo (a) pyrene , several natural compounds, and dioxins. Secondly, AH receptors are involved in the activation or silencing of genes that lead to the toxic effects of high doses of dioxins. Because TCDD at high doses can influence

24360-447: The regular use of a sequence incorporating mecoprop , a herbicide with a different mode of action. The term organic herbicide has come to mean herbicides intended for organic farming . Few natural herbicides rival the effectiveness of synthetics. Some plants also produce their own herbicides, such as the genus Juglans ( walnuts ), or the tree of heaven ; such actions of natural herbicides, and other related chemical interactions,

24534-458: The remote risks of dioxins. A general conclusion may be that safety margins are not very great concerning developmental effects, but toxic effects are not likely at the present population levels of dioxins. A number of cross-sectional studies have shown associations between type 2 diabetes and several POP compounds including dioxins. Such observational studies cannot prove causality, i.e. there may be an association which does not prove that one

24708-1129: The request of the Veterans Administration, the Institute Of Medicine evaluated whether service in these C-123 aircraft could have plausibly exposed soldiers and been detrimental to their health. Their report Post-Vietnam Dioxin Exposure in Agent Orange-Contaminated C-123 Aircraft confirmed it. Publications by the United States Public Health Service have shown that Vietnam veterans, overall, have increased rates of cancer, and nerve, digestive, skin, and respiratory disorders. The Centers for Disease Control and Prevention notes that in particular, there are higher rates of acute/chronic leukemia, Hodgkin's lymphoma and non-Hodgkin's lymphoma, throat cancer, prostate cancer, lung cancer, colon cancer, Ischemic heart disease , soft tissue sarcoma, and liver cancer. With

24882-424: The rise. In Missouri, 43% of waterhemp samples were resistant to two different herbicides; 6% resisted three; and 0.5% resisted four. In Iowa 89% of waterhemp samples resist two or more herbicides, 25% resist three, and 10% resist five. As of 2023, Palmer amaranth with resistance to six different herbicide modes of action has emerged. Annual bluegrass collected from a golf course in the U.S. state of Tennessee

25056-444: The same species, with the most notable disparity being between the seemingly similar species of hamster and guinea pig . The oral LD 50 for guinea pigs is as low as 0.5 to 2 μg/kg body weight, whereas the oral LD 50 for hamsters can be as high as 1 to 5 mg/kg body weight. Even between different mouse or rat strains there may be tenfold to thousandfold differences in acute toxicity. Many pathological findings are seen in

25230-439: The scope of the biological systems affected and in the range of dosage needed to bring these about. Acute effects of single high dose dioxin exposure include reduced feed intake and wasting syndrome , and typically a delayed death of the animal in 1 to 6 weeks. By far most toxicity studies have been performed using 2,3,7,8-tetrachlorodibenzo- p -dioxin . The LD 50 of TCDD varies wildly between species and even strains of

25404-433: The selection pressure on weeds to evolve resistance can be lowered. Researchers warn that if herbicide resistance is combatted only with more herbicides, "evolution will most likely win." In 2017, the USEPA issued a revised Pesticide Registration Notice (PRN 2017-1), which provides guidance to pesticide registrants on required pesticide resistance management labeling. This requirement applies to all conventional pesticides and

25578-441: The seriousness of the problems of dioxin. The companies involved have often said that the campaign against dioxin is based on "fear and emotion" and not on science. Most intake of dioxin-like chemicals is from food of animal origin: meat, dairy products, or fish predominate, depending on the country. The daily intake of dioxins and dioxin-like PCBs as TEQ is of the order of 100 pg/day, i.e. 1-2 pg/kg/day. In many countries both

25752-661: The site of action of the herbicide is preferable as herbicide resistance management can be handled more effectively. Classification by mechanism of action (MOA) indicates the first enzyme, protein, or biochemical step affected in the plant following application: Complementary to mechanism-based classifications, herbicides are often classified according to their chemical structures or motifs. Similar structural types work in similar ways. For example, aryloxphenoxypropionates herbicides ( diclofop chlorazifop , fluazifop ) appear to all act as ACCase inhibitors. The so-called cyclohexanedione herbicides, which are used against grasses, include

25926-416: The timing, dose, application method, soil and climatic conditions are optimal for good activity. In the UK, partially resistant grass weeds such as Alopecurus myosuroides (blackgrass) and Avena genus (wild oat) can often be controlled adequately when herbicides are applied at the 2-3 leaf stage, whereas later applications at the 2-3 tiller stage can fail badly. Patch spraying, or applying herbicide to only

26100-566: The transactivation domain structure of the AH receptor for different genes. Some of these low-dose effects can in fact be interpreted as protective rather than toxic (enzyme induction, aversion to novel foods). High doses. Toxicity of dioxins at high doses has been well documented after accidents, deliberate poisonings, food contamination episodes, and high industrial exposures. Three women in Vienna, Austria, were poisoned with large doses of TCDD in 1998. The highest concentration of TCDD in fat tissue

26274-517: The transcription of perhaps hundreds of genes, the genes crucial for the multitude of toxic effects of dioxins are still not known very well. Binding of dioxin-like compounds to the AH receptor has made it possible to measure total dioxin-like activity of a sample using CALUX (Chemical Activated LUciferase gene eXpression) bioassay. The results have been comparable to TEQ levels measured by much more expensive gas chromatography-high resolution mass spectrometry in environmental samples. Dioxin toxicity

26448-591: The true role of dioxins in cancer rates. The endocrine disrupting activity of dioxins is thought to occur as a down-stream function of AH receptor activation, with thyroid status in particular being a sensitive marker of exposure. TCDD, along with the other PCDDs, PCDFs and dioxin-like coplanar PCBs are not direct agonists or antagonists of hormones, and are not active in assays which directly screen for these activities such as ER-CALUX and AR-CALUX. These compounds have also not been shown to have any direct mutagenic or genotoxic activity. Their main action in causing cancer

26622-683: The unit supervised the aerial spraying of 2,4,5-T in Kenya to assess the value of defoliants in the eradication of tsetse fly . In Malaya , the local unit of Imperial Chemical Industries researched defoliants as weed killers for rubber plantations . Roadside ambushes by the Malayan National Liberation Army were a danger to the British Commonwealth forces during the Malayan Emergency , several trials were made to defoliate vegetation that might hide ambush sites, but hand removal

26796-414: The use of alternative herbicides such as dicamba or glyphosate. The use of two or more herbicides which have differing modes of action can reduce the selection for resistant genotypes. Ideally, each component in a mixture should: No mixture is likely to have all these attributes, but the first two listed are the most important. There is a risk that mixtures will select for resistance to both components in

26970-588: The variation in responses is clearly seen in a study following the Seveso disaster indicating that sperm count and motility were affected in different ways in exposed males, depending on whether they were exposed before, during or after puberty. In occupational settings many symptoms have been seen, but exposures have always been to a multitude of chemicals including chlorophenols , chlorophenoxy acid herbicides , and solvents . Therefore, definitive proof of dioxins as causative factors has been difficult to obtain. By far

27144-656: The war had continued. In the years after the war, the U.S. tested 1,100 compounds, and field trials of the more promising ones were done at British stations in India and Australia, in order to establish their effects in tropical conditions, as well as at the U.S. testing ground in Florida. Between 1950 and 1952, trials were conducted in Tanganyika , at Kikore and Stunyansa, to test arboricides and defoliants under tropical conditions. The chemicals involved were 2,4-D, 2,4,5-T, and endothall (3,6-endoxohexahydrophthalic acid). During 1952–53,

27318-565: The widespread use of herbicides, cultural controls , such as altering soil pH , salinity, or fertility levels, were used to control weeds. Mechanical control including tillage and flooding were also used to control weeds. In the late 19th and early 20th centuries, inorganic chemicals such as sulfuric acid , arsenic, copper salts, kerosene and sodium chlorate were used to control weeds, but these chemicals were either toxic, flammable or corrosive and were expensive and ineffective at controlling weeds. The major breakthroughs occurred during

27492-556: The wrong field or plants may be sprayed due to error. Although herbicidal warfare uses chemical substances , its main purpose is to disrupt agricultural food production or to destroy plants which provide cover or concealment to the enemy. During the Malayan Emergency , British Commonwealth forces deployed herbicides and defoliants in the Malaysian countryside in order to deprive Malayan National Liberation Army (MNLA) insurgents of cover, potential sources of food and to flush them out of

27666-418: Was 144,000 pg/g, the highest ever reported in human beings. The main feature was chloracne , a serious skin disease. The victim survived, and other symptoms were modest after initial gastrointestinal symptoms and amenorrhea . Another acute incident was the deliberate poisoning of Victor Yushchenko , then presidential candidate of Ukraine, in 2004. TCDD concentration in fat was 108,000 pg/g. Also in this case

27840-399: Was continuously and heavily relied upon for weed control. This caused incredibly strong selective pressure upon weeds, encouraging mutations conferring glyphosate resistance to persist and spread. However, in 2015, an expansive study showed an increase in herbicide resistance as a result of rotation, and instead recommended mixing multiple herbicides for simultaneous application. As of 2023,

28014-531: Was difficult (or impossible) in many areas. Many defoliated forest areas were quickly invaded by aggressive pioneer species (such as bamboo and cogon grass ), making forest regeneration difficult and unlikely. Animal species diversity was also impacted; in one study a Harvard biologist found 24 species of birds and 5 species of mammals in a sprayed forest, while in two adjacent sections of unsprayed forest there were, respectively, 145 and 170 species of birds and 30 and 55 species of mammals. Herbicide In

28188-517: Was ever said is hard to find). Roundup is toxic and has resulted in death after being ingested in quantities ranging from 85 to 200 ml, although it has also been ingested in quantities as large as 500 ml with only mild or moderate symptoms. The manufacturer of Tordon 101 ( Dow AgroSciences , owned by the Dow Chemical Company ) has claimed Tordon 101 has no effects on animals and insects, in spite of evidence of strong carcinogenic activity of

28362-588: Was first used by British Commonwealth forces in Malaya during the Malayan Emergency . It was also used by the U.S. military in Laos and Cambodia during the Vietnam War because forests near the border with Vietnam were used by the Viet Cong . The active ingredient of Agent Orange was an equal mixture of two phenoxy herbicides – 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) – in iso-octyl ester form, which contained traces of

28536-561: Was found cheaper. A detailed account of how the British experimented with the spraying of herbicides was written by two scientists, E. K. Woodford of Agricultural Research Council 's Unit of Experimental Agronomy and H. G. H. Kearns of the University of Bristol . After the Malayan Emergency ended in 1960, the U.S. considered the British precedent in deciding that the use of defoliants was a legal tactic of warfare . Secretary of State Dean Rusk advised President John F. Kennedy that

28710-454: Was found in 2020 to be resistant to seven herbicides at once. Rigid ryegrass and annual bluegrass share the distinction of the species with confirmed resistance to the largest number of herbicide modes of action, both with confirmed resistance to 12 different modes of action; however, this number references how many forms of herbicide resistance are known to have emerged in the species at some point, not how many have been found simultaneously in

28884-483: Was found to be uncorrelated with any health issues like cancer in a massive US Department of Health study on 90,000 members of farmer families for over a period of 23 years. That is, the study shows lack of chronic toxicity, but cannot question the herbicide's acute toxicity. Some herbicides cause a range of health effects ranging from skin rashes to death. The pathway of attack can arise from intentional or unintentional direct consumption, improper application resulting in

29058-565: Was made in the form of a Memorandum of Understanding signed between the New Zealand government, representatives of New Zealand Vietnam veterans, and the Royal New Zealand Returned and Services' Association (RSA) for monetary compensation for New Zealand Vietnam veterans who have conditions as evidence of association with exposure to Agent Orange, as determined by the United States National Academy of Sciences. In 2008

29232-448: Was only recognized in the 1960s. It was marketed as Roundup in 1971. The development of glyphosate-resistant crop plants, it is now used very extensively for selective weed control in growing crops. The pairing of the herbicide with the resistant seed contributed to the consolidation of the seed and chemistry industry in the late 1990s. Many modern herbicides used in agriculture and gardening are specifically formulated to degrade within

29406-831: Was published in 2016, entitled Veterans and Agent Orange: Update 2014 . The report shows sufficient evidence of an association with soft tissue sarcoma; non-Hodgkin lymphoma (NHL); Hodgkin disease; Chronic lymphocytic leukemia (CLL); including hairy cell leukemia and other chronic B-cell leukemias. Limited or suggested evidence of an association was linked with respiratory cancers (lung, bronchus, trachea, larynx); prostate cancer; multiple myeloma; and bladder cancer. Numerous other cancers were determined to have inadequate or insufficient evidence of links to Agent Orange. The National Academy of Medicine has repeatedly concluded that any evidence suggestive of an association between Agent Orange and prostate cancer is, "limited because chance, bias, and confounding could not be ruled out with confidence." At

29580-432: Was sprayed at least once between 1965 and 1971. 90% of herbicide use was directed at defoliation. The U.S. military began targeting food crops in October 1962, primarily using Agent Blue ; the American public was not made aware of the crop destruction programs until 1965 (and it was then believed that crop spraying had begun that spring). In 1965, 42% of all herbicide spraying was dedicated to food crops. In 1965, members of

29754-526: Was the most important source of PCDD/Fs. PCB-compounds , always containing low concentrations of dioxin-like PCBs and PCDFs, were synthesized for various technical purposes (see Polychlorinated biphenyls ). They have entered the environment through accidents such as fires or leaks from transformers or heat exchangers, or from PCB-containing products in landfills or during incineration. Because PCBs are somewhat volatile, they have also been transported long distances by air leading to global distribution including

29928-483: Was ultimately destroyed. In some areas, TCDD concentrations in soil and water were hundreds of times greater than the levels considered safe by the EPA. The campaign destroyed 20,000 km (7,700 sq mi) of upland and mangrove forests and thousands of square kilometres of crops. Overall, more than 20% of South Vietnam's forests were sprayed at least once over the nine-year period. 3.2% of South Vietnam's cultivated land

30102-569: Was unloaded at Tan Son Nhut Air Base in South Vietnam, on January 9, 1962. U.S. Air Force records show at least 6,542 spraying missions took place over the course of Operation Ranch Hand. By 1971, 12 percent of the total area of South Vietnam had been sprayed with defoliating chemicals, at an average concentration of 13 times the recommended U.S. Department of Agriculture application rate for domestic use. In South Vietnam alone, an estimated 39,000 sq mi (100,000 km) of agricultural land

30276-562: Was up to 100,000 times higher than average intake presently. There were many skin problems, chloracne, swelling of eyelids, and hypersecretion of Meibomian glands in the eyes. Babies born to Yusho and Yu-cheng mothers were smaller than normal, they had dark pigmentation and sometimes teeth at birth and tooth deformities. Foetal deaths and miscarriages were common. Perhaps the best known dioxin accident occurred in Seveso, Italy, in 1976. A tank of chlorophenols released its contents to air including many kilograms of TCDD, and contaminated much of

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