For more than a half-century, North American farmers have been spraying atrazine, an herbicide, on their crops -- most notably corn -- in the millions of pounds per year.
This widespread use of the weed killer has also created no small amount of runoff, ensuring that atrazine winds up in lakes, streams and, on occasion, even drinking water, according to a recent report by Global News.
"Atrazine is the number one contaminant found in drinking water in the U.S. and probably globally[,] probably in the world," University of California-Berkeley scientist Tyrone Hayes told the news organization.
The prevalence of atrazine has, over time, gotten the attention of a number of groups -- and some government organizations -- regarding its use and, some say, overuse. One such organization is Health Canada, which confirmed recently that atrazine could indeed make its way into local drinking water. The agency says that, "because atrazine has been classified in Group III (possibly carcinogenic to humans)," it has set an acceptable amount of 5 parts per billion in drinking water; in the U.S., that level is 3 parts per billion.
But the problem is that atrazine levels in drinking water can vary from place to place, with agricultural regions obviously being more at risk (though not exclusively, as atrazine contained in runoff can travel for hundreds of miles).
'Most well-studied pesticide on the planet'
"In areas where atrazine is used extensively, it (or its dealkylated metabolites) is one of the most frequently detected pesticides in surface and well water. Atrazine contamination has been reported in British Columbia, Nova Scotia, Prince Edward Island, Quebec, Ontario and Saskatchewan," said Health Canada.
The compound is manufactured by Syngenta, the world's foremost agribusiness giant; the European Union banned atrazine in 2004.
Nevertheless, research on the compound and its effects has continued, and not just on humans: The effects of atrazine on amphibian and other wildlife are also being studied.
"Atrazine is probably the most well studied pesticide on the planet, perhaps only rivaled by DDT," University of South Florida Prof. Jason Rohr, told Global News.
There is less information, however, regarding the herbicide's effects on humans. Some studies have found a potential link between atrazine and ovarian, breast and prostate cancers, as well as birth defects including smaller male genitals and gastroschisis, which is a birth defect in the abdominal wall in which the infant's intestines can be outside of the belly.
"So for humans there are studies showing a correlation between atrazine exposure and low sperm count or low fertility, increased risk of breast cancer, increased risk of prostate cancer, deformities of the genitals," Hayes said.
For its part -- and perhaps expectedly -- Syngenta says such studies suggesting that atrazine is a carcinogen or is otherwise harmful to humans are scientifically flawed; the company says other experts have reviewed the research and have deemed it unreliable. The company says its herbicide is safe and has been approved for use both by Health Canada and the U.S. Environmental Protection Agency.
"Regarding other impacts of atrazine, the EPA stated very clearly in its presentation to the July 2011 Scientific Advisory Panel that the available data do not support any association between atrazine exposure and cancer," said Ann Bryan, a senior manager for Syngenta, in a statement.
The same panel criticized the EPA for listing all cancers into one category in its atrazine assessment.
"It would be useful and appropriate to make conclusions for individual cancers as opposed to making a blanket determination for cancer in general," the panel said, adding a list of cancers with "suggestive evidence of carcinogenic potential," to include ovarian cancer, non-Hodgkin's lymphoma, hairy cell leukemia and thyroid cancer.
The panel also recommended follow-up studies.
In 2012, as part of a class action lawsuit settlement, Syngenta paid $105 million to more than 1,000 municipal water systems in the U.S. to help pay for the removal of atrazine from drinking water. Syngenta denies any liability.