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 computerbased 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
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. ONE OF THOSE TIMES WAS FROM IMPROPER DISPOSAL...THERE WAS AN ARIAL APPLICATOR (WHO) GOT RID OF SOME BY DUMPING IT DOWN A DRY WELL. 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