US EPA releases updates on organophosphate pesticides dicrotophos, dimethoate, and tetrachlorvinphos

The U.S. Environmental Protection Agency (EPA) has released the Proposed Registration Review Interim Decisions (PIDs) for dicrotophos and dimethoate, as well as an Interim Registration Review Decision (ID) for tetrachlorvinphos (TCVP), three organophosphate (OP) pesticides.  

OPs are a group of pesticides used in agriculture (e.g. food crops) and non-agricultural sites (e.g., turf at golf courses, athletic fields, sod farms, industrial areas) that affect the nervous system, which makes them effective against insects but can also impact mammals, including humans, depending on the level of exposure. These pesticides are currently undergoing registration review, a process that reviews each registered pesticide every 15 years to ensure that the pesticide can carry out its intended functions without unreasonable adverse effects to human health and the environment.  

EPA has evaluated a large number of studies for the OPs to ensure that they continue to meet federal standards to protect human health and the environment. Toxicity tests supporting pesticide registration provide information on a wide range of potential health outcomes in major organ systems, such as the nervous, digestive, circulatory, and urinary systems, across different animal species, lifestages, durations, and routes. For OPs, neurotoxicity occurring through interaction with the acetylcholinesterase (AChE) enzyme has been found to be the most sensitive effect, and EPA has a long history of using a 10% change in AChE levels as a basis for its OP human health risk assessments. EPA also evaluated the potential of these OPs to cause developmental neurotoxicity (DNT), which is an impact on the normal development of the nervous system during pregnancy or childhood.  

For each OP, EPA examined the available epidemiological studies (investigation of human populations for patterns and causes of health outcomes), animal toxicity studies performed with laboratory animals, and a battery of 17 in vitro assays (testing with cells from the nervous system) that evaluate a wide range of potential impacts on processes critical to the development of the human nervous system (referred to as the DNT battery). Data from all three lines of evidence are used to evaluate DNT potential using a weight of evidence approach (WOE), which is a process that integrates all relevant evidence and considers the strengths and limitations of each line of evidence. 

EPA uses the WOE evaluations of DNT potential and other considerations--such as completeness of the toxicological database, evidence of neurotoxicity, evidence of sensitivity/susceptibility, and residual uncertainty in the exposure database--to determine an appropriate Food Quality Protection Act Safety Factor (FQPA SF) for each OP. The FQPA SF is intended to provide an additional 10X margin of safety to account for any additional developmental risk during pregnancy or childhood, but it can be reduced when reliable scientific information demonstrates that no such additional risk exists.

Dicrotophos 

Dicrotophos is used only on cotton for treating thrips, stink bugs, tarnished plant bugs, and other pests. The PID released today for dicrotophos relies on the 2015 ecological draft risk assessment and an updated human health draft risk assessment (HH DRA), which is also being released today. The 10X FQPA factor for dicrotophos was retained because EPA concluded that there was not sufficient evidence to support its reduction at the time of the PID.

The updated HH DRA identified potential health risks of concern for neurotoxicity for workers and bystanders.

EPA is proposing the following mitigation measures for dicrotophos products to address worker, bystander, and ecological risks: 

• Decreasing the single maximum application rate for aerial applications, 

• Updating labels to include more up-to-date information related to worker personal protective equipment, 

• Necessary and recommended drift mitigation, including buffers, 

• Necessary runoff mitigation to reduce off-field movement of pesticides into surface water, 

• Pollinator stewardship label language, including best management practices for pollinator protection, 

• A link on product labels to EPA’s Bulletins Live! Two, a web-based system for additional directions and restrictions to protect endangered species, and 

• Guidance to users on how to report an ecological incident. 

The PID and updated HH DRA are posted to www.regulations.gov on docket #EPA-HQ-OPP-2008-0440. Upon publication of the Federal Register notice, these documents will be open for public comment for 60 days.  

Dimethoate 

Dimethoate is used to treat pests such as aphids, mites, beetles, weevils, and leafhoppers on agricultural crops including broccoli, corn, cotton, oranges, and tomatoes. The PID released today for dimethoate relies on the 2015 ecological draft risk assessment, and an updated HH DRA, which is also being released today. The updated HH DRA concluded that there are reliable data to support reducing the FQPA SF from 10X to 1X. While EPA ‘s review of the epidemiological data, animal toxicity studies, and DNT battery found the potential for DNT to occur during pregnancy or childhood, this evidence also showed that the DNT effect would occur at concentrations approximately 270-5,400 times higher than those that cause changes to AChE levels. Therefore, protecting people from neurotoxicity (shown by changes in AChE levels) will also protect them from DNT.   

The updated assessment found there were no anticipated human health risks of concern when considering the protective measures currently in place on dimethoate labels.   

EPA identified ecological risks of concern, and is proposing the following mitigation measures for dimethoate products: 

• Cancellation of several agricultural and non-agricultural uses that have low benefits, including: asparagus, conifer seedling nurseries, cottonwood grown for pulp, pecans, wheat (spring and winter), broccoli, brussels sprouts, cantaloupe, cauliflower, corn, grapefruit, lemons, oranges, pears, soybeans, watermelon, honeydew melons, and other Brassicas (kale, mustard greens, turnip greens), as well as in nursery-grown ornamentals, 

• Updating labels to include more up-to-date information related to worker personal protective equipment,  

• Necessary and recommended drift mitigation, including buffers, 

• Necessary runoff mitigation to reduce off-field movement of pesticides into surface water, 

• Pollinator stewardship label language, including best management practices for pollinator protection, 

• A link on product labels to EPA’s Bulletins Live! Two, a web-based system for additional directions and restrictions to protect endangered species, and 

• Guidance to users on how to report an ecological incident. 

The PID and updated HH DRA are posted to www.regulations.gov on docket #EPA-HQ-OPP-2009-0059. Upon publication of the Federal Register notice, these documents will be open for public comment for 60 days. 

TCVP 

TCVP is used to treat fleas, ticks, lice, and flies in or on livestock animals and their facilities, pets, garbage piles, kennels, residential lawns, and recreational areas. Today, EPA is releasing an ID for TCVP product registrations. 

A PID for TCVP was released with an accompanying revised HH DRA in September 2023. The 10X FQPA factor for TCVP was retained because EPA concluded there was not sufficient evidence to support its reduction at the time of the HH DRA.  

Potential risks of concern for neurotoxicity were identified for workers from exposure during treatment of livestock and livestock premises. 

Ecological risks of concern were identified for birds, mammals, and freshwater invertebrates via runoff particularly from manure applications, and proposed mitigation measures were suggested. 

In the ID finalized today, EPA outlines the mitigation measures identified as necessary to address risks, which include: 

• Prohibiting application via foggers, misters, electrostatic dusters, and any other aerosolizing method,  

• Prohibiting down-the-drain disposal,  

• Increasing personal protective equipment requirements,  

• Requiring label statements on protecting non-target organisms and water,  

• A link on product labels to EPA’s Bulletins Live! Two, a web-based system for additional directions and restrictions to protect endangered species, and 

• Guidance to users on how to report an incident. 

Consistent with EPA’s commitment to improve the quality of pet product incident reporting sales data it receives from pesticide registrants, EPA is requiring updates to the terms and conditions of TCVP pet product registrations to include information on how to submit enhanced incident reports and annual sales information. These data collected for pet products will allow the Agency to review pet incidents across the most used registered pet products.  

The TCVP ID is available in the TCVP public docket #EPA-HQ-OPP-2008-0316 at www.regulations.gov.  

For more information on the registration review schedule for these and other organophosphate pesticides, please visit EPA’s website.