WASHINGTON - Benefits of weed killer paraquat easily outweigh the risks, according to regulators at the U.S. Environmental Protection Agency (EPA).
A report they issued on Jan. 30 assigned no weight at all to a risk of Parkinson’s disease.
“EPA does not believe there is concern for Parkinson’s disease because the data do not support a connection between paraquat use as a pesticide and Parkinson’s disease,” they wrote.
They found no risk beyond irritation of skin and lungs.
Paraquat maker Syngenta and former paraquat maker Chevron provided a copy to Chief U.S. District Judge Nancy Rosenstengel of East St. Louis on Feb. 2.
She presides over more than 5,000 claims that paraquat caused Parkinson’s disease.
A judicial panel consolidated claims from many states in 2021 and assigned Rosenstengel to preside.
Also in 2021, the EPA issued an interim registration review decision finding no need to outlaw paraquat or change the label.
Plaintiffs in a California action challenged the decision and in 2022 the agency agreed to issue a supplement this January and a final decision next January.
Pesticide program director Edward Messina delivered the supplement on deadline with signatures of division directors Timothy Kiely, Anne Overstreet, and Dana Vogel.
Kiely’s division reviews evaluations, Overstreet’s division analyzes biology and economics, and Vogel’s division measures health effects.
They found the agency can register a pesticide if it won’t cause unreasonable adverse effects.
They added that federal pesticide law expressly requires consideration of a product’s benefits.
They offered as an example that respirators would involve buying them, replacing filters, adjusting the fit annually, and requiring breaks for relief from heat stress.
Regulators also found that if costs cancel out benefits, the agency can consider other options.
The Benefits
The EPA regulators provided a long list of the weed killer's benefits.
In this case, they found paraquat controls broadleaf and grass weeds and prepares crops for harvest.
They added that several chemical characteristics make it useful.
“Paraquat is rapidly absorbed into plant tissues which means that control of vegetation occurs even at cool temperatures when plants are not actively growing or when applied shortly before a rain event,” they wrote.
“Generally, alternatives either require plants to be actively growing or are not as rainfast as paraquat,” they added.
The regulators found growers treat nine million acres with paraquat every year.
It has high benefits for artichoke, cotton, peanuts, soybeans, bulb vegetables, alfalfa, orchards and vineyards.
On the other hand, It has low benefits for corn, winter wheat, sorghum, tomato, and pasture.
Cotton growers use it to burn weeds down before planting.
The regulators found that using other herbicides could reduce control of key weeds and cause yield loss.
Cotton growers in Texas, California and Arizona use paraquat as a fast acting harvest aid that makes leaves dry up and fall off plants.
“If paraquat were not available as a harvest aid, growers may have to wait longer between the application of a harvest aid and harvest,” they wrote.
The regulators found a longer wait would increase the possibility of rain that would delay harvest and reduce the quality of the lint.
Additionally, peanut growers use paraquat against weeds that could significantly limit yields.
“Paraquat offers growers flexibility in peanut weed management as it can be effectively used at multiple timings and for multiple purposes,” they wrote.
The regulators found paraquat necessary for peanut growers who practice conservation tillage, “to kill plant foliage to prepare fields prior to strip tilling and planting.”
They found multiple alternatives would be needed to replace paraquat at that time.
Paraquat limits weed competition after peanut plants emerge.
It offers flexibility in soil management and crop rotation cycles.
“Without paraquat more peanut growers would likely switch from conservation to conventional tillage,” they wrote.
They found conventional tillage increases erosion and decreases soil health.
Soybean growers use paraquat before crops emerge.
The regulators found alternative weed killer glyphosate is expensive, and weed resistance to it has resulted in more growers using paraquat.
They found that without paraquat, growers would have to combine two or more herbicides and would have fewer partners for rotation to reduce further resistance.
They added that their agency identified a need to enclose cabs of application vehicles but later decided not to pursue that option.
They found grower representatives reported that respirators were bulky and they inhibited the ability of applicators to look behind themselves.
Paraquat Studies
The EPA regulators opened their section on Parkinson’s disease by stating they reviewed more than 200 animal studies and found numerous limitations and deficiencies.
They found researchers directly injected paraquat into animals in 90% of studies, rather than using a relevant pathway.
They added that no one designed an animal study to evaluate hallmarks of the disease.
They wrote that the lack of data for hallmarks “introduces some uncertainty when characterizing the impact of long term exposure to paraquat on nervous system tissues.”
“However, there is a lack of evidence demonstrating changes in behavioral signs or neuropathology across multiple species in any of the reviewed studies,” they added.
“Petitioners suggest that there are several studies indicating that low level exposure significantly increases the risk of Parkinson’s disease,” they continued.
They found the overall body of epidemiologic evidence “too limited and insufficient to conclude that there is such a positive association.”
The agency received 13 reports of bystander incidents from 1998 to 2018 and no event involved multiple individuals.
Symptoms of subjects in those incidents resolved rapidly.
The regulators expressed an expectation that exposures to spray plumes resulted from misuse and they stated the agency doesn’t generally assess potential illegal use of a product.
They found brain tissue concentrations from skin exposure are unknown.
They found operations based on label directions didn’t indicate long term exposure should be expected for workers or bystanders.
They wrote that their balancing of risks and benefits took into account the fact that paraquat handlers are required to be certified and trained on its risks.