On the Fourth of July, 1985, as the sun shone and the temperatures rose, people celebrated by eating watermelon. Then they got sick — becoming part of one of the nation’s largest episodes of foodborne illness caused by a pesticide. The outbreak began with a few upset stomachs in Oregon on July 3; by the next day, more than a dozen people in California were also doubling over with nausea, diarrhea, and stomach pain. A few suffered seizures.
Today’s toxicologists are finding adverse effects that their earlier counterparts could only have imagined.
All told, the CDC estimated that more than 1,000 individuals from Oregon, California, Arizona and other states, along with two Canadian provinces, became ill from eating melons, picked from a field in California, contaminated with a breakdown product of aldicarb — one of the most toxic pesticides on the market. There were the usual calls for the pesticide to be banned. While it was eventually scheduled to be phased out, now the chemical is back — albeit with more restrictions on its use.
Banning a pesticide is tricky business once it’s made its way onto the market and into fields and orchards. Consider the Environmental Protection Agency’s flip-flopping on a ban on the insecticide chlorpyrifos. In 2000, the EPA deemed chlorpyrifos too dangerous for home use, and allowances for food residues were reduced as well. Yet it remained popular — and legal — for agricultural use. In 2015 the agency concluded the chemical was too toxic to use on our fruits and vegetables. Then in 2017, the EPA flipped, granting the insecticide, introduced and widely sold by Dow Chemical, clemency. Finally, last Thursday, in a decision lauded by environmental groups, a federal court nullified the agency’s decision and ordered chlorpyrifos to be banned within the next two months.
In its ruling, the court did what the EPA wouldn’t, stating that there was no justification for maintaining “a tolerance for chlorpyrifos in the face of scientific evidence that its residue on food causes neurodevelopmental damage to children.”
For many, it’s hard to fathom why such a decision couldn’t have been reached years ago. After all, the EPA is directed to consider the costs and benefits of chemical use on the environment, and the potential health impacts on humans weigh heavily in the decision — particularly when establishing how much pesticide may remain in our food from fruit to grains, the exposure must be deemed “safe.” Though we might not recognize it, EPA regulations are currently responsible for protecting our daily safety in numerous ways. Every time we choose conventional foods over organic, for example, we are putting our trust in the agency’s decisions. Often, that trust is warranted. But recent advances in toxicology, the workhorse science of the EPA, suggest that regulations based on earlier testing may not protect consumers from harmful exposures.
Indeed, today’s toxicologists are finding adverse effects that their earlier counterparts could only have imagined. One striking recent discovery, for example, showed that pesticides and industrial contaminants can impact not only the individuals initially exposed, but also their offspring, grandoffspring, and possibly even great-grandoffspring. Another demonstrated how chemicals like bisphenol A — or BPA, used to make some plastics — causes subtle but irreversible damage to developing brains.
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But changing regulations to reflect these new findings is complicated; as is evident from the corporate interests in chlorpyrifos, any new law has complex social, political, and economic impacts, making it a high stakes game. Chemical regulation and testing requirements simply can’t keep pace with science. Take for example, testing for chemicals like BPA. These so-called hormone-disrupting chemicals were known to be problematic since before the turn of this century, yet approved tests for these chemicals have only recently emerged.
Recognizing that standard toxicity tests may lag behind the science, the EPA reviews registered pesticides every 15 years or so, providing an opportunity to reconsider old chemicals in light of more recent data. New findings of toxicity can also prompt a review, which is what happened with the insecticide chlorpyrifos. A series of epidemiological studies suggested the chemical had adverse impacts on children’s brains, causing the Pesticides Action Network North America and the Natural Resources Defense Council to circulate a petition prompting an EPA review. In 2015, the agency determined that, based on the new science, chlorpyrifos was so toxic that no trace of the chemical should remain on fruits and vegetables — essentially an all-out ban.
Over the past few decades, multiple studies have shown that other chemicals known to be neurotoxic, like mercury and lead, can alter brain development and impact children’s behavior. As a result, acceptable thresholds for exposure to these chemicals have also been lowered. Previous toxicity tests on animals often failed to reveal these kinds of impacts, in part because, somewhat obviously, lab rats aren’t children. “We’re using behavioral paradigms that aren’t exactly the same,” Deborah Cory-Slechta, a neurotoxicologist at University of Rochester who studies both lab animals and humans, told me, “so they aren’t measuring the same thing [in animals] we are measuring in humans.”
Previous toxicity tests on animals often failed to reveal potential human impacts, in part because lab rats aren’t children.
Humans, in other words, are complicated: We eat odd foods, drink, take drugs, and stress out. All of these things can affect our response to toxic chemicals, yet none are included even in today’s animal testing. So it is not surprising that past chemical evaluations may have missed some critical toxic responses.
Chlorpyrifos is one of those chemicals for which traditional studies now appear to be insufficient. The insecticide kills the bugs it’s intended to deter by interfering with nerve signaling. Nerve cells constantly chatter with one another, sending chemical messages from nerve to nerve, or nerve to muscle. One such messenger is acetylcholine. Once a muscle cell, for example, is activated by acetylcholine it begins contracting. To stop the activity, the acetylcholine message must then be deactivated, much like the ringer on your phone turning off once you answer so you can hear to talk. In this case, the enzyme acetylcholinesterase normally deactivates the messenger acetylcholine. But chlorpyrifos inhibits the enzyme, causing unabated signaling and potentially deadly overstimulation. (This is also how the lethal chemical warfare poison Novichok works.)
Toxicologists and regulators can measure the chemical’s effect on signaling to evaluate the impact of exposure to it. The EPA has used these results, along with other information, like when and how a chemical is used, to set food tolerances. Concentrations that don’t cause signaling inhibition, have historically been considered safe.
But part of the problem with setting these kinds of tolerances is that not everyone is affected equally. Studies over the last several decades suggest that infants and children — who have developing brains, maturing metabolic systems, and tend to eat a higher proportion of fruits and vegetables — may be more sensitive to some chemicals than adults. The Food Quality Protection Act of 1996 addressed some of these concerns directing regulators to set standards for children’s health, and to consider the effects of cumulative chemical exposures. These include the additive effects of exposure to chlorpyrifos or similar pesticides, for example, by eating produce like peaches, snap peas, and bell peppers — crops that may be treated with the pesticide.
As the ability to study more subtle impacts of chemicals, particularly in the very young has improved, scientists began questioning if tolerances for chlorpyrifos should be reduced or eliminated because of its impacts on developing brains. “Growing cells are more vulnerable to toxins, and the brain forms over a longer period than do other organs,” wrote Bruce Lanphear, an epidemiologist at Simon Fraser University, in a 2015 paper published in the Annual Review of Public Health. Lanphear argued that to continue to regulate all chemicals as if they have a safe level no longer makes sense, particularly when it comes to protecting children from chemicals that impact brain development. We were taught that “low levels are of no consequence,” says Lanphear, “and we now know that’s not true.”
We were taught that “low levels are of no consequence,” says Lanphear, “and we now know that’s not true.”
Chemicals that affect children’s brains, unlike those that injure organs like livers or hearts, affect not just our bodies but who we are, and early deficits are difficult to regain, unless there are serious interventions, says Cory-Slechta. Studies both in the laboratory and in children exposed in utero, suggested that the most recent restrictions on chlorpyrifos were not strict enough. One series of studies by Columbia University perinatal epidemiologist Virginia Rauh and her colleagues revealed an association between chlorpyrifos and intelligence and memory deficits. The researchers used MRI imaging to find structural changes linked to exposure in the children’s brains. Some of those effects were found at concentrations below those causing acetylcholinesterase inhibition. These studies were just a few of those that convinced EPA regulators in 2015 that chlorpyrifos residues on fruits and vegetables could no longer be considered acceptable.
And then there was a national presidential election, and a new head administrator, Scott Pruitt, was appointed to the EPA. Bedeviled by scandal, Pruitt was forced to resign this summer, but not before postponing a decision on chlorpyrifos regulations until 2022, citing a return to “sound science,” emphasizing uncertainty and trading on doubt. Prior to the agency’s turn-around, former administrator Pruitt met with the CEO of Dow Chemical, which produces chlorpyrifos. Earlier in the year the company had donated $1 million dollars to President Trump’s inaugural activities and spent a total $13.6 million lobbying in 2016.
In May of this year, the state of Hawaii decided not to wait for the EPA, and banned chlorpyrifos. California also began taking another look. Then, this month in a case brought by the original petitioners along with a number of labor groups, the U.S. Court of Appeals for the 9th Circuit, citing the EPA’s failure to determine that exposures through food were safe and the agency’s “patent evasion” of it duties, ordered the agency to do its job and ban the pesticide.
Chemical regulation combines toxicology and other sciences with economics and politics. This is always a tricky process. But our health, and the health of the next generation, require an agency that is receptive to the best available science incorporating new insights into toxic chemicals and values health over profit. Toxicology has certainly advanced, but the federal body responsible for its application, the EPA, currently appears to be in retreat. Pruitt’s departure provides a modicum of hope, as do the federal courts — for now. But, should the agency continue to turn its back on its citizens — and its raison d’être — it will fall to the states, the courts and us, as concerned citizens, to step up.
Emily Monosson is a member of the Ronin Institute for Independent Scholarship, and an adjunct professor of environmental toxicology at the University of Massachusetts, Amherst. Her latest book, “Natural Defense,” was published by Island Press in 2017, and her writing has also been published in The Scientist, Aeon, American Scientist, and Environmental Health Perspectives, among other publications.