Atrazine, an endocrine-disrupting herbicide banned in Europe, is widely used in the U.S.

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Atrazine is the second-most widely used weed killer in the United States, with more than 70 million pounds are applied across the nation each year, according to the U.S. Geological Survey. It is an endocrine disruptor and also linked to various cancers, premature birth and birth defects.

The herbicide has been banned for use in the European Union since 2004. In the U.S., it is one of the most commonly reported contaminants in groundwater and public drinking water, according to the EPA.

While atrazine is applied to a wide range of crops, it is primarily used on sugarcane, soy, sorghum, and corn; the USDA notes that more than 65 percent of all corn crops in the U.S. have been treated with the herbicide. It is also a weed killer for golf courses, fields, and residential and commercial lawn spaces across the United States.

Atrazine is among the most prevalent herbicides used in Canada and Australia, as well.

The primary manufacturer of atrazine is Syngenta, a Swiss-based corporation owned by the Chinese state-owned company ChemChina.

Studies of atrazine suggest health dangers

Endocrine disruption

A significant body of scientific research suggests that atrazine is an endocrine disruptor. An endocrine disruptor is a general term for a chemical that impedes normal functioning of the endocrine system, which “regulates all biological processes in the body from conception through adulthood and into old age, including the development of the brain and nervous system, the growth and function of the reproductive system, as well as the metabolism and blood sugar levels,” according to the EPA.

Endocrine disruption in humans

In humans, atrazine has been linked to irregular estrogen levels and menstrual cycles, abnormal birth weight and unexplained infertility.

In a 2011 study published in the journal Environmental Research, scientists compared women’s menstrual cycles in areas of Illinois, where atrazine was widely used on crops, with Vermont, where it was used rarely. The public drinking water in Illinois had double the amount of atrazine than in Vermont, though both places were within the legal limits. Researchers found that the women in agricultural areas of Illinois were five times more likely to report having irregular menstrual cycles than those in Vermont. The Illinois women were also more likely to report lower estrogen levels. The researchers wrote: “We present preliminary evidence that atrazine exposure, at levels below the US EPA [Maximum Contaminant Level], is associated with increased menstrual cycle irregularity, longer follicular phases, and decreased levels of menstrual cycle endocrine biomarkers of infertile ovulatory cycles.”

Research published in 2004 in the American Journal of Epidemiology sought to examine the cross-sectional association between pesticides and the menstrual cycles of women living on farms in North Carolina and Iowa. The researchers found that “women who used pesticides experienced longer menstrual cycles and increased odds of missed periods compared with women who never used pesticides.” And specifically when they used probable endocrine-disrupting pesticides, including atrazine, women “had a 60 to 100% increased odds of experiencing long cycles, missed periods, and intermenstrual bleeding compared with women who had never used pesticides.”

In a study published in 2001 in Environmental Health Perspectives, researchers collected and analyzed self-reported information from about 2,000 couples living on farms regarding the effects of various pesticides on the risk of spontaneous abortion in a farm population in Ontario, Canada. They found that preconception exposure to atrazine was among the pesticides associated with a 20 to 40 percent relative increase in risk of spontaneous abortion in pregnancies less than 20 weeks gestation. Researchers wrote: “Our findings of an association between preconception exposure and an early abortion may imply that for some pesticides, preconception exposures lead to gross chromosomal anomalies. On the other hand, our finding of an association between late abortions and postconception exposure may suggest that postconception exposure to specific pesticides tends to damage the fetus or fetus–placenta complex rather than cause chromosomal anomalies.”

In a 2007 study published in Environmental Health Perspectives, researchers compared steroidogenic factor 1 (SF-1) expression in atrazine responsive and non-responsive cell lines and transfected SF-1 into nonresponsive cell lines to assess SF-1’s role in atrazine-induced aromatase. They found that “atrazine-responsive adrenal carcinoma cells (H295R) expressed 54 times more SF-1 than nonresponsive ovarian granulosa KGN cells. Exogenous SF-1 conveyed atrazine-responsiveness to otherwise nonresponsive KGN and NIH/3T3 cells. Atrazine induced binding of SF-1 to chromatin and mutation of the SF-1 binding site in ArPII eliminated SF-1 binding and atrazine-responsiveness in H295R cells.” Researchers concluded that the findings “are consistent with atrazine’s endocrine-disrupting effects” in aquatic life, along with the links between mammary and prostate tumors in rats and reproductive cancers in humans. Researchers wrote, “This study highlights the importance of atrazine as a risk factor in endocrine disruption in wildlife and reproductive cancers in laboratory rodents and humans.”

Endocrine disruption in mammals

Animal studies have shown that atrazine may affect reproductive function in mammals, including estrous cycles, sperm motility, testosterone levels, and prolactin, luteinizing and follicle-stimulating hormone levels.

In a comprehensive review published in the journal Toxics in 2015, researchers examined 20 years of animal studies that focused on atrazine exposure and reproductive dysfunction. They were particularly interested in how the herbicide affected the hypothalamic-pituitary-gonadal (HPG) axis, which is vital for maintaining proper reproductive function. For female animals, researchers concluded: “Female mammalian models have addressed the effects of atrazine at numerous life stages. Gestational and prenatal studies have demonstrated a significant delay in vaginal opening and a controversial effect on mammary gland epithelium. Adult exposure studies report robust alterations in reproductive hormones. … In combination, atrazine is reported to elicit a prolonged estrous cycle and histological alterations of ovarian tissue including an increase in atretic follicles.” For males, the researchers wrote: “Prenatal and adult studies show decreased levels of testosterone and altered testicular morphology in response to atrazine exposure. In addition, numerous steroidogenic genes and upstream regulators are altered due to atrazine exposure in both granulosa and Leydig cells.”

In a meta-analysis published in 2021 in Environmental Science and Pollution Research, researchers analyzed the results of 36 relevant studies related to male rats exposed to atrazine. They found that, when compared to rats that were not exposed to atrazine, those exposed experienced a significant decrease in the weight of the testis, seminal vesicles, epididymis, and other organs. The serum testosterone concentration was also reduced in atrazine-exposed rats. Researchers wrote that atrazine may significantly reduce the number of sperm in the epididymis, along with daily sperm production. Rats had worse sperm motility, and they produced more dead sperm than non-exposed rats. The researchers concluded: “Atrazine exposure may have toxic effects on many aspects of [the] rodents’ male reproductive system, and has a cross-species effect and a dose-dependent trend. … Pathways related to oxidative stress and apoptosis may be responsible for the toxicity of the male reproductive system.”

In a study published in 2020 in Frontiers in Endocrinology, researchers examined the effects of long-term exposure to atrazine beginning in utero in male mice and how it affected their metabolic and reproductive traits. Researchers then examined whether mating these males to females unexposed to atrazine changed in vitro embryo characteristics. The scientists wrote: “Atrazine exposure caused a decrease in liver weight and changes in both liver and testis gene expression, specifically in genes involved in lipid uptake and fatty acid metabolism in the liver, as well as androgen conversion in the testis. Notably, atrazine exposure decreased epididymal sperm concentration and subsequent embryo cell numbers generated from the 12-week cohort males.”

A study published in 2012 in Toxicology and Applied Pharmacology found that atrazine acts as an endocrine disruptor by inhibiting cAMP levels in cultured rat pituitary and testicular Leydig cells. Researchers wrote: “Atrazine-induced changes in cAMP levels were sufficient to stimulate prolactin release in pituitary cells and androgen production in Leydig cells, indicating that it acts as an endocrine disruptor both in cells that secrete by exocytosis of prestored hormones and in cells that secrete by de novo hormone synthesis.”

In a study published in 2017 in Scientific Reports, French researchers examined the effects of atrazine exposure on meiosis. They found that “embryonic exposure to atrazine increases the level of 8-oxo-guanine in the nucleus of meiotic cells, reflecting oxidative stress and affecting meiotic double-strand break repair, chromosome synapsis and crossover numbers. Finally, embryonic exposure to atrazine reduces the number of primordial follicles and increases the incidence of multi-oocyte follicles in adult mice. Our data demonstrate that embryonic exposure to atrazine disrupts prophase I of meiosis and affects normal follicle formation in female mice.”

A 2019 study conducted by researchers at the University of Melbourne and published in the journal Reproduction, Fertility and Development, found that, when male mice were exposed to atrazine, at levels permitted in public drinking water in Australia, they experienced reduced sperm viability and increased weight gain. The herbicide also altered the expression of key metabolic genes in the liver and testis. Researchers concluded that “a chronic reduction in sperm quality and increased weight gain could have negative consequences on the reproductive capacity of males, and further studies should consider the effects of long-term atrazine exposure on male reproductive health.”

In a comparison study published in 2000 in the journal Toxicological Sciences, researchers conducted a variety of experiments on female rats to examine estrogen-induced surges of luteinizing hormone (LH) and prolactin when exposed to atrazine. They found that atrazine changed these levels in the animals by modifying the hormones’ hypothalamic control. The scientists wrote that the results “support the hypothesis that the effect of atrazine on LH and prolactin secretion is mediated via a hypothalamic site of action.”

In a study published in 1994 in the Journal of Toxicology and Environmental Health, researchers evaluated the effects of atrazine exposure in two types of female rats, Sprague-Dawley and Fischer 344. They examined their body, ovaries, uterus, and adrenal weights, estrous cycle stages, vaginal cytology, along with plasma hormone estradiol, progesterone, prolactin, and corticosterone levels. The scientists found that both types of rats experienced significant decreases in body weights of both Sprague‐Dawley and Fischer 344 female rats when exposed to atrazine. They also had a significant reduction in ovarian and uterine weights, and a decrease in circulating estradiol levels. Both types of female rats also had a longer estrous cycle. Researchers wrote: “These findings suggest that treatment with doses of triazine at or above the MTD may result in prolonged exposure to endogenous estrogen in the Sprague‐Dawley but not the Fischer 344 rat. These changes may account for the observed earlier onset and/or increased incidence of mammary tumors in chlorotriazine‐treated female Sprague‐Dawley rats.”

In a research article published in 1996 in Toxicology Letters, Croatian researchers assessed the effects of atrazine exposure in low doses in female pigs by examining the biochemical and histopathological parameters of the ovarian function. They specifically examined serum 17β-oestradiol (17β-E) and progesterone (P) concentrations. When compared with pigs not exposed to atrazine, the researchers found that the atrazine-treated pigs had a significantly higher serum P concentration and significantly lower serum 17β-E concentration before the next expected oestrus, which then did not occur. The pigs exposed to atrazine also experienced more multiple ovarian follicular cysts and benign cysts.

A 2020 study conducted by researchers at the University of Melbourne and published in the journal Reproduction, Fertility and Development examined the effects of atrazine on marsupials, which have experienced significant population decline throughout Australia over the last several decades. Scientists found that, when adult female wallabies were exposed to high levels of atrazine throughout pregnancy, birth and lactation, the expression of genes required for normal testis function was altered in their male offspring. The researchers also found that the male offspring also had “a significant reduction” in penis length. The researchers wrote: “These results demonstrate that atrazine exposure during gestation and lactation can significantly affect the development of male young by affecting virilisation. Given the known vulnerability of macropodid marsupials to endocrine disruption, as well as their overlapping distribution with agricultural areas, these data raise major concerns for the use of pesticides in areas with fragile marsupial populations.”

Birth defects

Scientific research has linked atrazine to several birth defects, including choanal atresia, stenosis, gastroschisis, and more.

In a 2013 study published in Pediatrics, researchers at the University of Texas School of Public Health found that, “compared to [children] of mothers with low levels of estimated residential atrazine exposure, those with high levels had nearly a two-fold increase in risk for choanal atresia or stenosis.” This congenital condition is caused by a narrowing or blocking of the back of the nasal passage, which can lead to life-threatening respiratory symptoms.

A 2012 study published in Maternal and Child Health Journal examined maternal exposure to atrazine and the risk of gastroschisis, a rare birth defect where an opening in the newborn’s abdomen wall causes the intestines to spill outside the body. Researchers examined birth data in Texas between 1999 and 2008. They found the risk of gastroschisis in newborns significantly increased in mothers who were less than 25 years old and exposed to high levels of residential atrazine exposure compared to low exposure. Interestingly, the association was not seen in mothers over 25 years old who were also exposed to high levels of atrazine.

Research presented in 2010 at the 30th Annual Meeting of the Society for Maternal-Fetal Medicine found, by using data from the Washington State Birth Certificate and U.S. Geological Survey databases, that gastroschisis was more common in mothers who lived within 25 kilometers of an area with elevated exposure to atrazine and other agrichemicals. The researchers concluded, “Maternal exposure to surface water atrazine is associated with fetal gastroschisis, particularly in spring conceptions.”

In a study published in 2011 in Environmental Health Perspectives, researchers at the University of Rennes in France assessed the link between adverse birth outcomes and urinary biomarkers of prenatal atrazine exposure before the 19th week of gestation. After collecting urine samples from 579 pregnant women, scientists found that pregnant women who had a positive biomarker for atrazine had an association with reduced fetal growth and small head circumference, when compared with women who did not have atrazine biomarkers in their urine samples. Researchers concluded, “Evidence of associations with adverse birth outcomes raises particular concerns for countries where atrazine is still in use.”

Preterm delivery

In a 2017 study published in Environmental Research and conducted by scientists at the University of Illinois at Chicago, researchers found that exposure to atrazine in public drinking water was associated with an increased rate of preterm delivery. The study examined more than 130,000 single births between 2004 and 2008 in 46 counties in the midwest that were part of the EPA’s Atrazine Monitoring Program (AMP). The study authors wrote: “Our findings do raise concerns about the potential adverse effects of these common water contaminants on human development and health, and the adequacy of current regulatory standards.”

Abnormal birth weight and unexplained infertility

In a 2008 study published in the journal PLoS ONE, researchers from the University of California at San Francisco tested the effects of atrazine on human placental cells in vitro. They found that the herbicide “increased the activity of a gene associated with abnormal human birth weight when over-expressed in the placenta. Atrazine also targeted a second gene that has been found to be amplified in the uterus of women with unexplained infertility.”

Breast cancer

In a study conducted by scientists at China’s Jilin University who examined cells in vitro and in vivo, findings showed that atrazine suppressed immune cell function, and in turn promoted tumor proliferation and migration in triple-negative breast cancer. Researchers concluded that “this study demonstrated that atrazine accelerated the cell cycle and encouraged the proliferation and invasion of breast cancer tumor cells.” The research was published in Ecotoxicology and Environmental Safety in March 2023.

In a 1997 study published in Environmental Health Perspectives, researchers at the University of Kentucky College of Medicine analyzed low, medium, and high exposure levels of atrazine in Kentucky counties, alongside data on county breast cancer rates in the state registry. The results showed a “statistically significant increase in breast cancer risk with medium and high levels of triazine exposure. The results suggest a relationship between exposure to triazine herbicides and increased breast cancer risk, but conclusions concerning causality cannot be drawn, due to the limitations inherent in ecologic study design.”

Neurotoxicity

In a review published in 2021 in the journal Toxics, scientists wrote, “There is evidence of crosstalk between systems that can be affected by atrazine exposure, causing widespread dysfunction and leading to changes in behavior even with no direct link to the hypothalamus. The hypothetical mechanism of toxicity of atrazine endocrine disruption and neurotoxicity can therefore be described as a web of pathways that are influenced through changes occurring in each and their multiple feedback loops with further research needed to refine [no-observed-adverse-effect-levels] for neurotoxic outcomes.”

In a 2023 study published in Food and Chemical Toxicology, researchers examined the toxic effects of atrazine on the hippocampus and examined whether lycopene offers protective benefits of atrazine-induced impairment in male mice. The researchers wrote: “Atrazine can cause spatial learning and memory impairments by inducing histopathological changes in the hippocampus and ferroptosis in the hippocampal cells.”

Low birthweight

In a study published in 2018 in the International Journal of Environmental Research and Public Health, researchers examined adverse birth outcomes between 2006 and 2008 in Ohio communities with high atrazine contamination in public drinking water. The researchers wrote: “Significantly increased odds of term low-birthweight birth was associated with atrazine exposure over the entire gestational period and second trimesters of pregnancy.” They continued: “Our results suggest that atrazine exposure is associated with reduced birth weight among term infants and that exposure to atrazine in drinking water in early and mid-pregnancy may be most critical for its toxic effects on the fetus.” They concluded: “These results suggest that the current maximum contaminant level for atrazine may not be protective against some adverse birth outcomes such as term low birth weight.”

A 2005 study published in Occupational and Environmental Medicine examined the link between atrazine levels in public drinking water in France and various adverse reproductive outcomes. Researchers found that atrazine levels were slightly associated with premature births. They also found that atrazine levels were linked to an increased risk of small-for-gestational-age (SGA) status when the third trimester was around the same time as the summer season, when atrazine levels in drinking water were highest. “Findings point to the third trimester of pregnancy as the potential vulnerable period for an increased risk of SGA birth.”

Slowed metabolism and weight gain

In a 2009 study published in PLoS ONE, researchers examined the effects of chronic atrazine exposure on mitochondrial dysfunction and insulin resistance in rats. Researchers fed the rats drinking water with low concentrations of atrazine for five months. They found that the rats exposed to atrazine had a “decreased basal metabolic rate, and increased body weight, intra-abdominal fat and insulin resistance without changing food intake or physical activity level.” They concluded: “These results suggest that long-term exposure to the herbicide ATZ might contribute to the development of insulin resistance and obesity.”

Gestational diabetes

A small study published in 2007 in the journal Diabetes Care examined data from the Agricultural Health Study to see whether exposure to certain pesticides, including atrazine, put pregnant women in their first trimester at higher risk of gestational diabetes. Researchers found that risk of gestational diabetes was “significantly associated” when women self-reported ever having used atrazine. The exposure of three other herbicides (2,4,5-T; 2,4,5-TP; atrazine; or butylate) and three insecticides (diazinon, phorate, or carbofuran) were also significantly associated with increased risk of gestational diabetes.

Renal failure

A 2016 study published in Occupational and Environmental Medicine examined the link between end-stage-renal disease (ESRD) and dozens of pesticides from data in the Agricultural Health Study, a prospective cohort study of licensed pesticide applicators in Iowa and North Carolina. The results showed that farmers who were chronically exposed to atrazine and other pesticides throughout their lives were at higher risk of kidney failure. The more significant use of atrazine was associated with a higher risk of the disease. The researchers wrote: “Our findings support an association between ESRD and chronic exposure to specific pesticides and suggest pesticide exposures resulting in medical visits may increase the risk of ESRD.”

Respiratory issues

In a 2002 study published in American Journal of Respiratory and Critical Care Medicine, researchers examined the risk of wheeze among applicators of various pesticides by examining the data of a large cohort of certified pesticide applicators in Iowa and North Carolina from the Agricultural Health Study. They found that atrazine was associated with wheeze. Researchers specifically noted that “atrazine had a significant dose–response trend with participants applying atrazine more than 20 days [per] year having an odds ratio of 1.5.”

Endocrine disruption in aquatic life

In amphibians and various fish, atrazine has been shown to damage reproductive organs and systems.

In 2010, Dr. Tyrone Hayes of the University of California, Berkeley conducted research published in Proceedings of the National Academy of Sciences (PNAS) that showed African clawed frogs experienced “complete feminization and chemical castration” when living in water contaminated with atrazine, at levels within the legal limit in public drinking water in the United States. Hayes writes: “Our study showed that atrazine-induced females are indeed genetic males. Furthermore, we showed that feminization is persistent and complete, resulting in reproductively functional females capable of producing viable eggs.”

Prior to his 2010 study, Hayes published several other studies with similar results. In a 2002 study published in Nature, Hayes examined the effects of atrazine contamination in water on wild leopard frogs in various regions of the U.S. He found that, in males, atrazine was linked to significant gonadal abnormalities, including incomplete development. Hayes wrote, “these results are supported by laboratory observations, which together highlight concerns over the biological effects of environmental atrazine on amphibians.”

A 2011 review published in the Journal of Steroid Biochemistry and Molecular Biology, which included Hayes along with 21 co-authors around the world presented “a state of the art summary of the mechanisms by which atrazine acts as an endocrine disruptor to produce these effects.” The researchers wrote, “Atrazine demasculinizes male gonads producing testicular lesions associated with reduced germ cell numbers in teleost fish, amphibians, reptiles, and mammals, and induces partial and/or complete feminization in fish, amphibians, and reptiles. These effects are strong (statistically significant), consistent across vertebrate classes, and specific.”

A 2009 qualitative meta-analysis of atrazine effects on aquatic life found evidence that atrazine “can have indirect and sublethal effects.” Specifically, the research, which was published in the journal Environmental Health Perspectives and conducted by scientists at the University of South Florida noted, “the relationship between atrazine concentration and timing of amphibian metamorphosis was regularly nonmonotonic, indicating that atrazine can both accelerate and delay metamorphosis.” Furthermore, “atrazine reduced size at or near metamorphosis in 15 of 17 studies and 14 of 14 species. Atrazine elevated amphibian and fish activity in 12 of 13 studies, reduced antipredator behaviors in 6 of 7 studies, and reduced olfactory abilities for fish but not for amphibians. Atrazine was associated with a reduction in 33 of 43 immune function end points and with an increase in 13 of 16 infection end points. Atrazine altered at least one aspect of gonadal morphology in 7 of 10 studies and consistently affected gonadal function, altering spermatogenesis in 2 of 2 studies and sex hormone concentrations in 6 of 7 studies.”

In a 2008 animal study published in PLoS One, researchers at the University of California at San Francisco found atrazine affects “hormone signaling and endocrine transcriptional networks in zebrafish and in mammalian cells.” Scientists wrote, “We propose that this pervasive and persistent environmental chemical alters hormone networks via convergence of NR5A activity and cAMP signaling, to potentially disrupt normal endocrine development and function in lower and higher vertebrates.”

What is atrazine?

Source: American Chemical Society

Atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) is a chlorinated herbicide that is derived from triazine. It is water soluble and used to kill broadleaf and grassy weeds. In broadleaf and grassy weeds, the chlorotriazine herbicide works by interfering with photosynthesis by disrupting the electron transport chain.

Scientists at Swiss-based CIBA-GEIGY (now Novartis AG) invented atrazine in 1958 and has been widely used in the U.S. since the 1960s. It is usually applied to crops to preemptively ward off weeds, but it can also be used post-emergently. Only people who have been trained with the product can now apply atrazine in the U.S.

Manufactured by Swiss-based, China-owned Syngenta

The Syngenta Group is a multinational agricultural corporation based in Basel, Switzerland. In May 2017, state-owned Chinese corporation ChemChina bought Syngenta for $44 billion, the largest foreign purchase ever by a Chinese state-owned company. The U.S. Department of Defense has listed ChemChina among companies that are “‘Chinese military companies’ operating directly or indirectly in the United States.”

Syngenta’s main products include herbicides, pesticides, and seeds; it is the primary manufacturer of atrazine. The company reported $33.4 billion in sales in 2022.

Why did the EU ban atrazine?

In 2004, the EU banned the use of atrazine after it was found to surpass the regulatory limits of pesticide (0.1µg/L) in groundwater, according to the European Chemicals Agency (ECHA).

In the EU Commission’s decision letter regarding atrazine in 2004, the commission wrote: “The Committee is … of the opinion that available monitoring data does not demonstrate that concentrations of atrazine or its breakdown products will not exceed 0,1 μg/l in groundwater and it expects that for soils with pH above six concentrations of atrazine and its breakdown products will not exceed 0,1 μg/l.”

The letter continued: “In particular, available monitoring data were insufficient to demonstrate that in large areas concentrations of the active substance and its breakdown products will not exceed 0,1 μg/l in groundwater. Moreover it cannot be assured that continued use in other areas will permit a satisfactory recovery of groundwater quality where concentrations already exceed 0,1 μg/l in groundwater. These levels of the active substance exceed the limits in Annex VI to Directive 91/414/EEC and would have an unacceptable effect on groundwater.”

In other words, the EU committee found that atrazine not only regularly exceeded the maximum limits in groundwater but also deemed there were insufficient monitoring and measures in place to mitigate such excess.

On its Substance Infocard, the ECHA warns about atrazine: “According to the harmonised classification and labelling (CLP00) approved by the European Union, this substance is very toxic to aquatic life, is very toxic to aquatic life with long lasting effects, may cause damage to organs through prolonged or repeated exposure and may cause an allergic skin reaction.”

In the EU, atrazine is also subject to export notification and explicit consent requirements of the prior informed consent regulation (PIC), the ECHA told U.S. Right to Know. In other words, any exporting of atrazine from the EU to third countries requires consent from the receiving end before the export takes place. In 2012, Switzerland also banned atrazine. The country is not an EU member state, but it is where the primary manufacturer of atrazine, Syngenta, is headquartered.

The persistence of atrazine in groundwater

For decades, research has demonstrated atrazine persistence in groundwater and surface water, even long after it has been used; it is among the most frequently detected contaminants in public drinking water in the U.S.

The herbicide’s “chemical properties make it susceptible to leaching and runoff, especially during heavy rains,” according to the USDA. Research has shown that atrazine can remain in soil and groundwater for decades.

A study published in 2014 in the journal Water Research found that in Germany, “even 20 years after the ban of atrazine, the groundwater concentrations of sampled [observation wells] remain on a level close to the threshold value of 0.1 μg l−1 without any considerable decrease.”

In a commentary piece published in 2010 regarding atrazine’s persistence, scientists in Germany wrote in the journal Environmental Science and Pollution Research that, “even more than 18 years after it was banned in Germany, atrazine remains the most abundant pesticide in groundwater samples.” They continued: “That, after decades of weathering, atrazine is still detectable, and metabolites (apparently with triazine ring intact) are still abundant in soil, underscores the need to assess the environmental behavior of this herbicide on longer time scales.”

Click here to see a map from the U.S. Geological Survey of estimated atrazine use across the United States in 2019.

What are the legal levels of atrazine in drinking water?

In the U.S., the maximum contaminant level (MCL) of atrazine is 3 µg/L (parts per billion) in public drinking water. In the European Union, atrazine is banned for use, but the EU’s Water Directive Framework has set a general precautionary standard level for pesticides in groundwater at 0.1µg/L, 30 times lower than the U.S. limit on atrazine.

According to the EU’s 2006 Groundwater Directive, the decision to set the level at 0.1µg/L “includes the objective to achieve water quality levels that do not give rise to significant impacts on, and risks to, human health and the environment.”

Atrazine contamination in groundwater

A 2018 report published by the Environmental Working Group found that around 30 million Americans in 28 states have some level of atrazine in their drinking water. In general, levels of atrazine in tap water are highest in the late spring and early summer, when farmers typically spray their crops with the herbicide. The report also found that several locations monitored in the EPA’s Atrazine Monitoring Project had, at times, particularly during the late spring and summer months, tested for atrazine three to seven times above the legal limit in public drinking water. Furthermore, the dispatch noted that officials did not report the contamination levels to people living in those communities.

A study published in 2010 in the Journal of Agricultural and Food Chemistry tested soils in Belgium and Germany and found that “atrazine application history dramatically influences its degradation and mineralization.” Their soil tests also suggested that “atrazine is not completely mineralized and remains extractable even in adapted soils, and … appears to be conserved on long time scales after the last application.

A study conducted by scientists at the U.S. Geological Society and published in 2021 in the journal Environmental Science and Technology found that, of the 442 U.S. streams tested, atrazine contaminated 55 percent of surface water and 70 percent of the groundwater.

Atrazine-related lawsuits

In 2012, dozens of U.S. water-utility companies hit Syngenta with a federal class-action lawsuit, alleging that the company knew the herbicide was contaminating local drinking water supplies. The lawsuit also cited atrazine’s potential danger it posed to the environment and pregnant women. Syngenta agreed to a settlement and paid $105 million, which was split between the water utility companies.

In 2020, advocacy groups sued the EPA after it reapproved the use of atrazine, claiming that the government agency failed to uphold its duties to monitor and confirm the herbicide did not pose risks to public health through water contamination.

California

In 2016, the state of California added atrazine to its Prop 65 list of toxic chemicals, and listed the herbicide as causing developmental toxicity and reproductive toxicity.

Recent changes proposed by the EPA

In June 2022, the EPA proposed, for public comment, changes to atrazine use in the United States in order to reduce runoff and leaching. As shown on the EPA website, they are as follows:

  • Prohibit application when soils are saturated or above field capacity (i.e., the soil’s ability to retain water);
  • Prohibit application during rain or when a storm event, likely to produce runoff from the treated area, is forecasted to occur within 48 hours following application;
  • Prohibit aerial applications of all formulations; and
  • Restrict annual application rates to 2 pounds of active ingredient or less per acre per year or less for applications to sorghum, field corn, and sweet corn.
  • Farmers choose from a “picklist” of EPA-approved counter-measures to reduce leaching and runoff
  • Boost record-keeping by atrazine-users to ensure safe practices

In an email statement to U.S. Right to Know, the U.S. EPA wrote: “EPA expects to make a final decision on atrazine in mid- to late-2024, after the Scientific Advisory Panel (SAP) meeting on August 22 to 24. Currently, the Agency is working on the upcoming SAP meeting, as well as reviewing and considering more than 500 comments received on the proposal. Once the final decision is released, the new mitigation measures would appear on labels within 1 to 2 years.”

Dispute between Syngenta and scientist Tyrone Hayes

Dr. Tyrone Hayes, a professor of integrative biology of University of California, Berkeley, has studied atrazine for decades. In 1997, Hayes was recruited to conduct research for the herbicide on an expert committee for Syngenta (then Novartis). While conducting his research, he discovered that, when exposed to atrazine, male frogs underwent significant reproductive changes and developed abnormal gonads.

Hayes explained to Mother Jones in 2012 that, for decades, scientists had been sounding the alarm about decreasing amphibian populations all over the world. “We’re asking, ‘How come there aren’t any new frogs?’ Atrazine isn’t killing the frogs. But if they’re reproductively impaired, that’s killing the population.”

When he brought his findings to Syngenta, Hayes said executives did not appear concerned and even questioned the veracity of his findings. Eventually Hayes quit working for the corporation, and then repeated the experiment multiple times and found similar results. He published several peer-reviewed research papers over the course of the following decade.

Syngenta representatives began attending Hayes’ academic talks and testimonies; sometimes Hayes would get into arguments about his research with the attending representatives. Other times, they would insult one another on professional and personal levels, Nature reported in 2010. Hayes continuously expressed concern that Syngenta was spying on him and trying to ruin his reputation. In 2013, unsealed court documents related to the federal class-action lawsuit against Syngenta revealed that the corporation had put forward a multi-million-dollar public relations strategy to discredit atrazine critics, and specifically singled out Hayes.

Syngenta document shows “discredit Hayes” as the first action item under “science.”

As Rachel Aviv described the conflict in the New Yorker in 2014, “The company documents show that, while Hayes was studying atrazine, Syngenta was studying him, as he had long suspected. Syngenta’s public-relations team had drafted a list of four goals. The first was ‘discredit Hayes.’ In a spiral-bound notebook, Syngenta’s communications manager, Sherry Ford, who referred to Hayes by his initials, wrote that the company could ‘prevent citing of TH data by revealing him as noncredible.’”

In a perspective piece published in the journal Environmental Toxicology and Chemistry in 2020, biologist Jason Rohr of the University of Notre Dame offered a timeline of the most important events in the “atrazine saga” between Syngenta and Hayes. Rohr argued, “The atrazine controversy must be … used as an example of how manufacturing uncertainty and bending science can be exploited to delay undesired regulatory decisions and how greed and conflicts of interest—situations where personal or organizational considerations have compromised or biased professional judgment and objectivity—can affect environmental and public health and erode trust in the discipline of toxicology, science in general, and the honorable functioning of societies.”

Syngenta’s defense of atrazine

Syngenta stands by atrazine as a safe and effective product, and the corporation estimates that the herbicide, along with simazine, saves U.S. consumers between $4.3 billion to nearly $6.2 billion yearly. On Syngenta’s website, it states: “Governments and international agencies continue to approve atrazine because there is no credible connection between the herbicide and any health problem in humans.”

In a recent webinar moderated by Dr. Tyrone Hayes, U.S. Right to Know co-founder Stacy Malkan presented her 2022 report Merchants of Poison, which investigated and demonstrated the various strategies pesticide manufacturers have used to discredit scientists.

One of these ways is to make use of organizations like the American Council on Science and Health (ACSH). The agency refers to itself as a “pro-science consumer advocacy organization” but is a front organization that solicits money in exchange for dispensing research and communications that champions and advocates for controversial products.

An example of this was in 2011, when the ACSH funded the publication of a book by Jon Entine about “chemophobia,” or the unfounded fear of chemicals. The book maintained that atrazine was safe. Today, Entine is the executive director of the Genetic Literacy Project, a nonprofit group similar to ACSH that works with Monsanto.

Internal company files obtained by the Center for Media and Democracy in the midst of the major 2012 lawsuit against Syngenta demonstrated that the chemical giant channeled millions of dollars toward strategies to get external allies to influence public opinion of atrazine.

In a 2009 email, ACSH staff requested an additional $100,000 from Syngenta – “separate and distinct from general operating support Syngenta has been so generously providing over the years” – to create a “consumer-friendly booklet” on atrazine to educate journalists and scientists.

The ACSH staffer continued in the email: “We will widely distribute the report to the media, and use it as the basis for Op-eds, letters to the editors, media appearances etc. … In the course of the project, we would bring our 400 scientists up to the date on the subject.”

EPA review of atrazine studies

In early 2010, the EPA announced it would be conducting a new scientific review of the risk of atrazine. That same year, the Huffington Post Investigative Fund reported that the EPA relied heavily on industry-backed research in its assessment, with studies funded by Syngenta, its affiliates, or Syngenta-backed researchers.

Research on Syngenta’s website

On its website, Syngenta links to several studies that demonstrate a lack of association between atrazine and various health risks, including cancer, hyperthyroidism, and breast cancer. Still, other research linked on its website does indeed demonstrate risk, including a study that found an increased risk of gestational diabetes mellitus among women who had exposure to pesticides (including atrazine) in their first trimester, and another study that showed pesticides, including atrazine, might lead to respiratory problems in farmers.

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