This story was updated at 1:20 p.m. EDT.
An updated human health risk assessment for a 1960s-era insecticide has few supporters, with environmentalists saying the study is too lax and manufacturers claiming it is too restrictive.
At issue: The registration for chlorpyrifos is up for review this year.
Environmental groups have fought to ban the chemical for nearly two decades, saying it can cause neurological developmental delays that lead to autism, attention deficit disorder and lowered IQ in children exposed in utero and in their early years.
Stakes are high for green groups and the pesticide industry. Even if the chemical is not suspended completely, the risk assessment could signal new restrictions.
"This [human health risk assessment] has the potential to establish precedents that could impact the [risk assessment] process for other pesticide active ingredients relating to EPA’s review processes and policies, particularly, how and what data is considered with respect to regulatory decision making," the pest control trade group CropLife America wrote in its comments to EPA.
The new risk assessment could lead to changes in labels for the pesticide, requiring applicators to use more protective clothing. In some cases, the period of time after application during which a field is off-limits could extend to 10 days. For most crops, the period of restricted entry lasts 24 hours (E&ENews PM, Jan. 5).
Chlorpyrifos and other insecticides in the organophosphate family can suppress an enzyme that affects how nerve impulses are regulated. The inhibition of the enzyme can lead to the overstimulation of nerves, causing headaches, nausea, dizziness and, in some cases, convulsions or death.
Under the Food Quality Protection Act, EPA must take additional precautions when assessing risk for more vulnerable populations, like children or pregnant women, unless there are sufficient data to demonstrate that children are not at greater risk to the product. This often means multiplying the normal risk factor by 10.
EPA shrunk the margin of safety from tenfold to four- or fivefold for the general population. The agency also eliminated a tenfold safety factor to extrapolate rodent studies to human safety, a coalition of eight environmental and farmworker rights groups wrote in formal comments to the agency.
On the positive side, the groups said, EPA did apply the tenfold safety factor for women of child-bearing age. But the lack of a risk margin for children is troubling, they wrote.
"What EPA gave with one hand … it took away with the other, and then some," the groups wrote. "The result — EPA will allow chlorpyrifos exposures to be an order of magnitude higher for pregnant women and even higher still for children."
What was only a bittersweet benefit for environmental groups was heavily criticized by Dow AgroSciences, the manufacturer of chlorpyrifos. The proposed application of the "10x" factor for pregnant women is based on epidemiological studies, or studies on population groups, which are more difficult to control than laboratory experiments.
In its comments to the agency, Dow slammed these epidemiological studies, specifically the Columbia University Center for Children’s Health research program to observe chlorpyrifos’s health effects by measuring levels of the chemical in the umbilical cords of pregnant women and maternal blood.
Other epidemiological studies came from the Mount Sinai School of Medicine and the University of California, Berkeley. The Columbia study is the most concerning to EPA, with a recent paper in the study finding that chlorpyrifos could change the structure of a fetus’s brain (Greenwire, May 1, 2012).
But the Columbia study should not be relied on for a number of reasons, Dow wrote. The adverse outcomes reported in the research program’s participants — low-income children in New York City — can’t be extrapolated to the general population, the sample size was too small, and the mode of action suggested by other scientists unaffiliated with the study is not "biologically plausible," Dow said.
"The Columbia Study is rife with limitations and uncertainties that diminish its scientific validity," Dow said.
Environmentalists, however, claim these population-based studies aren’t used enough. As a result, the more serious potential effects of chlorpyrifos are ignored.
‘Safely, effectively and efficiently’
EPA’s assessment relies on a model developed by Dow. The model tries to determine at which point exposure will inhibit the necessary enzyme for nerve function by 10 percent. That sets a "safe" limit for chlorpyrifos levels that EPA can then use to guide restrictions on the pesticide’s label.
But the model doesn’t take into account the neurological impacts to fetuses, said Jennifer Sass, a senior scientist with the Natural Resources Defense Council.
"It’s not that the model is so bad inherently, it’s that it misses the mark," Sass said. EPA should have included the epidemiological studies in the model.
"Protecting the mother from 10 percent [of enzyme inhibition] is not protecting the fetus, we know that for sure," she added.
Dow Agrosciences spokesman Garry Hamlin said epidemiological studies generally have a "qualitative" value but should not trump experimental data when devising a numerical limit for exposure.
The debates over the risks of chlorpyrifos are not new. EPA banned most household uses of chlorpyrifos in 2000. But instead of quelling environmentalists’ concerns, the move ignited a push for more restrictions. A household ban decreased urban children’s exposure, but use in agriculture continued.
"That just raised the flag of an obvious double standard that rural kids and farmworker kids were exempt from that," said Margaret Reeves, a scientist at the Pesticide Action Network North America (PANNA).
In 2007, PANNA and NRDC petitioned EPA to suspend all registered uses for the pesticide, and eventually took the agency to the U.S. Court of Appeals for the 9th Circuit. In response to the petition, EPA said it would study chlorpyrifos and other organophosphates further and expedited the review from the original deadline of 2022.
In 2012, the agency instituted no-spray buffer zones around public spaces.
Five decades after its initial approval, chlorpyrifos is still widely used on a number of crops, including fruit and nut trees, vegetables, wheat, alfalfa, and corn.
"Available alternatives to chlorpyrifos are less effective and cost significantly more," James Cranney Jr., president of the California Citrus Council, wrote in comments submitted last year.
One crop that is particularly dependent on the chlorpyrifos is Michigan’s tart cherries. With an estimated economic impact of $800 million, chlorpyrifos is a "critical component" of pest management for the industry, wrote Kevin Robson, a horticulture specialist with the Michigan Farm Bureau. The insecticide works well on many agricultural pests and works well in a rotation with other pesticides to avoid insect resistance.
"It is important to note the entire crop is mechanically harvested, resulting in the minimization of worker exposure," Robson wrote. "Chlorpyrifos can be used safely, effectively and efficiently."
The Fish and Wildlife Service is also required to undertake a new endangered species assessment for chlorpyrifos, along with four other pesticides (E&ENews PM, July 29, 2014).