Evidence of the cheap herbicide’s danger to biological functions and the environment continues to mount. Why are U.S. regulators not listening?
Chemicals giant Bayer AG is reeling after a jury awarded $2 billion in damages to people who say they contracted cancer after years of using Roundup, a popular weed killer manufactured by Bayer subsidiary Monsanto Co. Bayer probably won’t pay out the full $2 billion. But more than 10,000 further cases are pending, worrying Bayer investors as well as farmers who rely on the product as a cheap, effective herbicide.
Cancer may only be part of the story. Studies over the past decade suggest that glyphosate — the active ingredient in Roundup — pollutes water sources, hangs around in soil far longer than previously suspected, and routinely taints human food supplies. In both the U.S. and Europe, the supposedly safe limits for human ingestion are based on long-outdated science. Research also points to serious adverse consequences for the environment, and there are indications glyphosate can cause disease in mammals even several generations removed from the initial exposure.
Glyphosate isn’t as safe as its manufacturers would like us to believe, and steep reduction in its use is probably long overdue.
Monsanto patented glyphosate in the early 1970s, and it rapidly became the global go-to chemical for weed control as the commercial product Roundup. Executives at Monsanto encouraged the spread of Roundup by engineering genetically modified seeds for corn and other crops that can tolerate glyphosate.
Glyphosate manufacturers — which now include many companies around the world; Monsanto’s patent expired in 2000 — have long argued that glyphosate is completely safe for humans, animals and indeed all non-plant life. It works by inhibiting a biochemical pathway that plants need to grow, and animals don’t share that pathway, which is superficially reassuring. But it only means that glyphosate shouldn’t starve animals to death, as it does plants. Chemicals can exert effects on organisms in myriad ways.
Interpreting the evidence for cancer isn’t easy, because different panels have come to contrasting conclusions by using different procedures. In 2015, the International Agency for Research on Cancer, part of the World Health Organization, concluded that glyphosate is likely carcinogenic. But both the U.S. Environmental Protection Agency and the European Food Safety Authority have declined to do the same. Both the EPA and the EFSA relied on information provided by researchers linked to the industry and considered studies provided by the industry that were not peer-reviewed or made public. The IARC relied solely on publicly available peer-reviewed research.
An international team of biologists reviewed the IARC and EFSA studies, concluding that the latter were significantly flawed and departed from standard hazard-assessment practices.
There are plenty of other reasons to be concerned about glyphosate. An independent group of biologists in 2016 tried to clarify what we really know about the chemical. Their paper makes for grim reading. It noted that studies in the previous decade found significant traces of glyphosate-based herbicides in drinking water and groundwater, probably routinely exposing millions of people across the planet to the chemical. Toxicity studies in rodents have found that glyphosate can damage the liver and kidneys, even for doses in the range generally considered safe for humans. Young pigs fed soybeans contaminated with glyphosate herbicide residues have exhibited congenital malformations, not unlike birth defects observed for people living in and near farming regions with intensive glyphosate use.
The study points to many other troubling findings, from the disruptive impact of glyphosate on hormone signaling in mammals to how the chemical binds to metals such as zinc, cobalt and manganese, reducing the supplies of these crucial micronutrients for people, crops and other plants, and wildlife. Most of these effects would probably not be detected by the traditional toxicology test guidelines currently favored by pesticide regulators.
In April, a different study found another worrying effect: Glyphosate might disrupt biological functions for generations. One of the hottest topics in biology in recent years has been epigenetics — the study of how offspring inherit not only the genes of their parents, but also certain patterns of chemical activity written onto those genes by other signaling molecules. This offers a means by which environmental factors that affect an organism during its life can be passed down to its offspring. In experiments with rats fed glyphosate, Michael Skinner of Washington State University and colleagues found that malign effects of treatment did not show up in the organism eating glyphosate, or even in its offspring, but in the next two generations of offspring. These rats, without ever being exposed to glyphosate, nevertheless showed a prominent tendency toward prostate disease, obesity, kidney disease, ovarian disease and birth abnormalities.
Glyphosate is clearly not a benign herbicide warranting no concern, its link to cancer aside. It may be causing many other serious disruptions to human biology, and to organisms and plants in the environment, currently invisible to today’s outdated regulatory systems. It’s about time our regulators updated their science.
(Deletes reference to Roundup’s percentage of global pesticide use in fourth paragraph of article published June 4.)
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