• Kevin Elliott

Atrazine: Widely used and controversial herbicide


Considered the second-most used herbicide in the United States and one that has been found in drinking water in thousands of communities across the country, atrazine is viewed as an invaluable weedkiller to corn, soybean and specialty farmers across the Midwest.

In Michigan, nearly 6.4 million combined gallons and pounds of atrazine have been sold in liquid and solid form from 2005 to September of 2018, according to the Michigan Department of Agriculture and Rural Development (MDARD), which tracks sales of more than 100 different restricted-use products that contain the herbicide.

While essentially banned in the European Union since 2004 due to its strong potential to contaminate groundwater, atrazine has been widely used in the United States since 1959. Domestically, it's estimated between 60 and 80 million pounds of atrazine are used in the United States each year, with about 75 percent of stream water and 40 percent of groundwater samples from agricultural areas testing positive for atrazine, according to a study by the United States Geological Survey.

In the United States, atrazine is registered for use against broadleaf weeds and grassy weeds. It's used on various foods, including corn, sorghum and sugar cane. It's also used for some non-food crops, including pine tree farms, turf for sod production, and some other turfs, including golf courses, roadsides and residential areas, such as playgrounds, parks and recreational areas.

Atrazine is considered a restricted-use product, meaning only certified applicators are able to buy or apply the herbicide. As such, MDARD tracks all sales of atrazine. Records provided by MDARD to Downtown Newsmagazine show a total of 59,799 combined gallons and pounds of atrazine were sold, and assumed to have been applied, from 2005 to 2018 in Oakland County. Records show 50,978 pounds and gallons sold in Macomb County; 65,003 in Livingston County; 66,522 in Genesee County; 176,051 in Monroe County; and 8,513 in Wayne County. As can be anticipated, rural counties with a higher percentage of agricultural land had vastly greater sales, such as Lenawee County (293,990), Eaton County (313,364), Cass County (524,256), and Washtenaw County (163,675).

While tens of thousands of pounds of atrazine have been used in Oakland County over the past decade, it appears most has been used for agricultural purposes.

The question is, what effect has there been upon the residents of these counties?

Rob Morosi, spokesman for the Michigan Department of Transportation (MDOT), said the state doesn't use atrazine for weed control along any state-maintained roadways in the state. Likewise, Craig Bryson, spokesman for the Road Commission for Oakland County (RCOC), said the county doesn't use atrazine along any roads serviced by the county.

Inquires into atrazine use with local school districts and municipalities also show no atrazine use, which includes the cities of Birmingham, Rochester and Rochester Hills; Bloomfield Township; Birmingham Public Schools; Bloomfield Hills Schools; and Rochester Hills Community School District.

As one of the most studied, widely-used and controversial pesticides on earth, the weedkiller has been linked to multiple effects on freshwater organisms, including fish and amphibians. Multiple studies show atrazine as a potential disruptor of sexual development in frogs, causing males to develop as females and even mate with male frogs. It has also been considered a possible human carcinogen, and a possible endocrine disruptor, effecting organs and hormones, and developing reproductive systems.

Syngenta, one of the largest producers of atrazine, insists the herbicide is safe for the environment and humans. While it has been detected in thousands of drinking water systems, Syngenta says it's almost always below the threshold set by the United States Environmental Protection Agency (EPA). A 2011 study by the U.S. National Cancer Institute concluded atrazine has no consistent link to cancer. Further, the manufacturer has rejected studies that have linked it to being harmful to animals or humans.

Adding to the controversy of atrazine is evidence of a multi-million dollar smear campaign by Syngenta to discredit scientists publishing findings critical of atrazine's safety. That evidence includes internal memos, notebooks and emails that were released in a court case that Syngenta settled for $105 million with more than 1,000 public water systems which claimed they had to remove atrazine from their water supply. In settling the case, Syngenta admitted no wrongdoing or negligence.

Currently, atrazine is in the midst of a pesticide registration review by the EPA. In 2016, the EPA's ecological risk assessment for the herbicide found "risk concerns for mammals, birds, reptiles, plants and plant communities across the country for many atrazine uses," with some recommending changes to the amount of atrazine allowed to be used on crops. More recently, the EPA released a human health assessment draft.

Tim Pastoor, CEO of Pastoor Science Communications, and a former principal scientist for Syngenta Crop Protection, said the most recent assessment is good news for both the agriculture and herbicide industry, as well as for the public.

"Atrazine is one of the best tested, best regulated and best understood pesticides on the planet, and I don't say that lightly – there are many out there," Pastoor said, speaking on behalf of Syngenta. "It's been on the market for over 50 years. It's been through multiple rounds of data, development and regulatory reviews in a very transparent way. The data is showing atrazine is at extra low levels when found, or virtually non-existent in the environment. The EPA has gone through yet another round of review in gaining a degree of certainty in the safe use of atrazine. In the latest round, the EPA has done a remarkable job of turning over every stone of how best to regulate the product."

As part of the most recent assessment process, the EPA conducted a cumulative health risk assessment. As a chemical, atrazine is closely related to two other herbicides, simazine and propazine, which together are called "triazines." Because triazines have a common mechanism of toxicity, they are often evaluated together in cumulative risk assessments, according to the EPA.

In July 2018, as part of the EPA's registration review process, the agency released a cumulative human health risk assessment for triazines, as well as atrazine. The assessment also includes published toxicity and epidemiology literature. Overall, the assessment identifies potential risks to children who crawl and play on lawns and playgrounds treated with atrazine; workers who mix, load or apply atrazine; and workers who enter a triazine treated field after application to certain crops.

Those opposed to the current use of atrazine see the EPA's current review in a different light.

Nathan Donley, senior scientist with the Center for Biological Diversity, said while the EPA did a good analysis of the ecological assessment of atrazine under the Obama administration, the most recent assessment is a return to industry-influenced findings.

"The ecological risk assessment, or draft assessment, was done under the Obama administration. I thought that was a pretty good analysis. I thought they might have gone further, but they took into account a lot of studies, and recommended lowering the levels," Donley said. "Now, under the Trump administration, I think things have gone quite a bit different. This human health assessment – it's a typical assessment – they take the guideline studies, and these are done by the pesticide industry in support of their (own) product."

Donley said he was disappointed the EPA didn't take into account studies that found harm to human health at lower levels, and discounted or gave less weight to some studies done by independent researchers and university studies that have been published in peer-reviewed journals.

"The EPA typically ignores researchers at a university and focuses instead on these experiments that are required to be submitted by the pesticide companies," he said. "That's pretty typical."

Donley said the models favored by the pesticide industry and given the most weight by the EPA are physiologically based pharmacokinetic models, or PBPK modeling, which is a mathematical modeling technique for predicting the absorption, distribution, metabolism and excretion of chemicals in humans or other animals. Because tests can't be conducted on actual humans, the tests utilize concentrations that harm lab animals, such as a rat, and use the model to determine what exposure would be harmful to a person.

"Let's say you have a concentration of 10 micrograms per liter that would harm a rat. To convert that for humans, the agency adds what are called 'uncertainty factors,'" Donley said. "Typically, the agency adds a 10-times uncertainty factor due to the fact they are testing a different species than humans. Then, they usually add another 10 times because lab rats are a genetically homogeneous group, or have no genetic difference... so that reduces the harmful dose by about 100. That's what the agency typically identifies as a safety threshold for humans."

Donley said the newer PBPK models instead allows researchers to take the toxicity in an animal and convert it to what might be toxic in a human, rather than adhering to a standard uncertainty factor.

"They are trying to get a better grasp on it than just a 10-times factor, but that model was partially developed by Syngenta, and they have quite a bit of incentive here to make a model that is beneficial to them," he said.

Pastoor, who serves as president of the Health and Sciences Institute, has specialized in human health risk assessment for three decades, as well as in product development with DuPont, ICI, Zeneca, Novartis and Syngenta. Pastoor said the PBPK modeling gives greater certainty to the results of an assessment.

"In this case, what they knew from using this computer-based model is that they have a greater degree of certainty, to 30 fold from 100 fold," he said. "The analogy I like to use is: if we are standing by a bonfire, and we know that everyone within five feet of it will be burnt, so to be certain we will stand 10-fold farther, so we go to 50 feet. Then, we say, let's go another 10-fold, so we are 500 feet away. That's what the EPA does in its regulation. But, with a greater degree of certainty, we have a greater sense of risk, so they say you can be closer than originally set because we know more."

Pastoor said that even with a reduction in what is considered harmful to humans, the EPA has still maintained retaining the maximum contaminant level (MCL) in drinking water for atrazine at three micrograms (ug/L), or about one part-per billion (ppb). The MCL threshold serves as a benchmark for potential human health concerns, rather than a regulatory standard.

While atrazine is one of the most commonly detected herbicides in drinking water, the United States Geological Survey (USGS) states that about 95 percent of the nation's agricultural areas have less than a 10 percent chance of exceeding the threshold.

"The highest probabilities are predicted for shallow groundwater in agricultural areas where substantial atrazine use is combined with natural conditions of permeable soils and high groundwater recharge, such as parts of eastern Nebraska," the USGS said in a 2012 study. "Probabilities of high concentrations are lower across much of the Corn Belt, where atrazine use is greatest, but soils tend to be poorly drained and often require artificial drainage that diverts recharge from groundwater to nearby streams."

The EPA's Atrazine Monitoring Program monitors about 150 community drinking water systems, primarily in the Midwest. The program has been required since 2004, following a reregistration of the herbicide. Under the monitoring program, selected community drinking water systems are monitored on a weekly basis during peak atrazine use season, and bi-weekly during the rest of the year. The program doesn't monitor any locations in Michigan.

The EPA also maintains an Atrazine Ecological Exposure Monitoring Program, which monitors atrazine levels in streams in watersheds exposed to atrazine runoff from corn and sorghum production. That program also doesn't include any monitoring locations in Michigan.

Public drinking water suppliers are required to monitor periodically for unregulated contaminants. Those public drinking water suppliers include the Great Lakes Water Authority (GLWA), which supplies water to the majority of southeast Michigan communities.

The GLWA said monitoring for atrazine and other pesticides occurs every three years during the second and third quarters. Monitoring for atrazine last occurred in 2017, and none was detected. Previous monitoring by the Detroit Water and Sewerage Department (the precursor to GLWA) also found no detection of atrazine in previous tests.

Robert Pigg, with the groundwater monitoring program within the Michigan Department of Agriculture, said the state receives some funding from the EPA to conduct testing for pesticides in private and domestic wells.

Pigg, who has been with the program for more than two decades, said the presence of atrazine in private water wells has dropped since the introduction of glyphosate, or Roundup.

"We look in places that aren't normally tested. We do look for atrazine and other leachers that tend to move with water," he said. "Roundup tends to bind to soil well, and not leach."

While atrazine has been one of the more commonly detected pesticides, Pigg said it has only been found to exceed the maximum contaminant level set by the EPA once or twice in the past 20 years.

"We probably saw atrazine more than others, but usually it doesn't exceed the drinking water standards when it is present. Maybe one or two times in the 20-plus years that I've been here," he said. "One of those times was from improper disposal – we know for sure. There was an arial applicator, who isn't around anymore, and he got rid of some by dumping it down a dry well."

A baseline study of MDARD's groundwater monitoring program tested 391 random wells between 1997 and 2000. Of the 75 different pesticides tested, atrazine was detected at just one well. That finding was at a level of two ppb, while the EPA threshold is about three ppb. Overall, the study found less than 1.75 percent of rural wells tested had a detectable level of pesticides.

The one well that did test positive for atrazine was located in St. Joseph County, which had the eighth highest amount of atrazine sales in the state from 2005 to 2018.

Despite the lack of atrazine presence, it's possible that the presence of contaminants may be seen many years in the future.

"It's important to remember that groundwater quality in general, and domestic well water quality in particular, are lagging indicators," Pigg wrote in the report. "Infiltration and percolation of water from the surface to domestic well screens can take generations in some cases. The impacts of land use may not be reflected in domestic well water quality for several decades or longer.

"For example, research carried out at the USGS in southeast Michigan indicated that 10 to 28 domestic supply wells (36 percent), which had been selected essentially at random, supplied water older than 47 years, based on tritium dating. This evidence, albeit limited, that the water quality of a significant fraction of domestic supply wells in Michigan has not yet been impacted by post Second World War and Green Revolution land use practices."

Even if increases in contaminated wells is found, Pigg said there must be greater cooperation among agencies and others to mitigate the problem.

"There's little point to searching for contaminated groundwater if nothing will be done once it's found," he wrote. "The Michigan Groundwater Stewardship Program has provided state-wide leadership in tackling many of the problems that can lead to groundwater contamination. The MDA and other organizations need to continue to work to prevent groundwater contamination and to mitigate it when it's found."

The spread of atrazine to groundwater and drinking water starts at the surface. Because atrazine doesn't bind well to soil and is soluble in water, it's easily spread by rainwater and other runoff from farm fields and other areas where it's applied. The herbicide can then be carried to streams, rivers, lakes and other surface water. Even without entering groundwater, surface water may serve as a drinking water source, providing yet another avenue for atrazine to enter a system. And, because atrazine breaks down slowly in rivers and lakes, it may persist for a long time.

Atrazine may also drift when applied as a spray or in dust when it's eventually removed from the air by rainfall. In dust form, it's possible for atrazine to travel more than 100 miles from its application area.

A 2012 study by the International Association for Great Lakes Research conducted a modeling study to determine if atrazine persisted in Lake Michigan, and if it poses a threat to algae, the foundation of the fishery's food chain.

According to the study, researchers forecasted atrazine concentrations to increase from about .048 ug/L to about .67 ug/L by 2057, if current usage continues into the future. While the projection is below the known criteria for the established protection of algae, the model shows atrazine to be decaying very slowly, or about .9 percent of the inventory each year.

In addition to the EPA's maximum contaminant level for drinking water, Michigan maintains a surface water quality value for atrazine, which is set at 7.3 (ug/L) micrograms per liter.

Oakland County Water Resources Commissioner Jim Nash said the department doesn't test surface water for atrazine in Oakland County.

A 2005 study conducted by the USGS, in cooperation with the Michigan Department of Environmental Quality (DEQ), sampled 23 sites across the state for atrazine and other pesticides. The study took 320 samples from March to November of 2005. In all, only one site – the Black River, near Jeddo, Michigan, in St. Clair County, exceeded the state's surface water limit for atrazine.

Sampling at the Black River site showed a maximum concentration of 10.55 ug/L, which is over the limit of 7.3 ug/L. Other sites and their maximum concentrations included: St. Joseph River, at St. Joseph (.9 ug/L); Kalamazoo River, at New Richmond (.16 ug/L); Grand River near Eastmanville (.86 ug/L); Muskegon River near Bridgeton (.25 ug/L); Pere Marquette River at Scottville (.1 ug/L); Cheboygan River (pond) at Cheboygan (.12 ug/L); Thunder Bay River near Alpena (.15 ug/L); Au Sable River near Au Sable (.14 ug/L); Saginaw River at Essexville (.71 ug/L); Clinton River at Mt. Clemens (.34 ug/L); River Rouge at River Rouge (.23 ug/L); Escanaba River at Wells (.15 ug/L); Shiawassee River, near Fergus (.97 ug/L); Deer Creek near Dansville (.48 ug/L); Grand River at Lansing (.88 ug/L); Shiawassee River at Owasso (.4 ug/L); Mill Creek near Avoca (.9 ug/L); Pine River near Marysville (1.75 ug/L); Belle River near Marine City (1.18 ug/L); and Clinton River at Sterling Heights (.24 ug/L).

Overall, atrazine concentrations ranged from a low of .0046 ug/L to the maximum of 10.55 ug/L, with a median for all samples of .15 ug/L.

While testing is typically done in areas where agricultural use is highest, sampling gave researchers with the USGS some varying results based on land use. Overall, the highest concentrations were from agricultural sites; however, a high percentage of agriculture wasn't consistently correlated with high pesticide concentrations.

"For example, the drainage area of Deer Creek, a small stream in the Grand River watershed, is 82 percent agriculture (corn and soybeans); however, herbicide concentrations at this site were similar to those at urban sites," the authors wrote. "This was the case for several agricultural sites.

"More detailed sampling – including sampling of storm runoff – and more information on site characteristics – such as the amount of tile drainage – would be needed to fully understand the effects of land use and pesticide application on water quality in streams."

Despite claims by Syngenta that levels of atrazine in drinking water have been and remain low, the company in 2013 paid out $105 million to settle a class-action lawsuit with 1,085 communities who said they spent millions over many years to filter the herbicide from their drinking water.

The suit, which claimed atrazine exposure could lead to low birth weights, birth defects and reproductive problems, ended without any admission of wrongdoing. In fact, Syngenta said no one has ever been or could be exposed to concentrations in drinking water high enough to affect their health.

The site included water systems from Illinois, Indiana, Kansas, Missouri and Ohio, serving about 52 million people. Payments ranged from $5,000 to more than $15 million, with an average payout of $50,000, according to the Associated Press, which stated the plaintiff's attorneys, Korein Tillery, received about $35 million in fees.