Groups of Pesticides in Registration Review

In conducting the registration review program, EPA generally will review pesticides in chronological order; that is, older cases will be reviewed first. However, we also plan to review certain related groups of pesticides at the same time. Pesticide cases may be related by chemical class or structure, mode of action, use, or for other reasons.

During previous reviews of pesticides (reregistration and cumulative risk assessments), we gained experience and efficiencies in simultaneously reviewing related pesticides in groups like the organophosphates, N-methyl carbamates, triazines, and chloroacetanilides, as well as the rodenticides and soil fumigants. Similarly, EPA expects to increase program efficiencies and promote other benefits by continuing the practice of grouping related pesticides during registration review. For example:

  • Resolution of technical and regulatory issues looking across an entire chemical class or group;
  • Optimization of use of resources within EPA, among stakeholders, and within other federal agencies;
  • Facilitation of new research findings;
  • Assurance of a "level playing field" in developing decisions among chemicals in the group.

The following groups of related pesticides have started registration review or are scheduled to begin registration review from 2012 to 2015

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Organophosphates (OP) and N-methyl Carbamates

EPA completed cumulative risk assessments and risk management decisions for the organophosphate pesticides in August 2006 and the N-methyl carbamate pesticides under the reregistration program in September 2007. The registration review of the organophosphates began in 2008, and the N-methyl carbamate review began in 2010. As we move forward with these reviews, we will be paying special attention to effects on endangered species, based on the better understanding of these classes of pesticides that we and stakeholders have developed.

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Pyrethroids, Pyrethrins and Synergists (PPS)

During fiscal year 2008, EPA completed reregistration eligibility decisions for the last individual pyrethroids, pyrethrins and synergists  that were subject to reregistration. Meanwhile, other PPS were not subject to reregistration; they are new active ingredients first registered after November 1, 1984. The PPS pesticides have similar uses and issues but have never before been considered together.

  • Many have residential uses that may result in urban runoff, potentially contaminating surface water and sediment, and posing ecological risks.
  • Most of these pesticides require endangered species risk assessments.

Because these pesticides may be used as alternatives for one another, it makes sense to consider them together and assess and manage their risks within a similar timeframe. EPA, therefore, is considering them during registration review. The various pesticides in this group began registration review in FY 2010 to FY 2012.

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Sulfonylureas (SU)

To increase efficiencies, EPA began reviewing the sulfonylurea herbicides as a group during registration review in 2011. These are herbicides that control weeds through inhibition of the enzyme acetolactate synthase. They are used as pre- and post-emergent herbicides to control a variety of weeds on cereal grains, pasture and rangeland, industrial sites, and turf grass.

Many of the sulfonylurea herbicides were first registered in the 1980s or later and so have not undergone reregistration. Consequently, the oldest group of these chemicals began registration review in 2011. Dockets opened in 2012 and 2013 for two groups of more recently registered sulfonylurea herbicides.

Registration Review of the sulfonylureas will include:

  • evaluation of the need for endangered species risk assessments; and
  • examination of the potential for adverse reproductive effects of sulfonylureas on off-site non-target plant species, such as may result from spray drift.

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The neonicotinoids are a class of insecticides with a common mode of pesticidal action that affects the central nervous system of insects, causing paralysis and death. All of the neonicotinoids were registered after 1984 and were not subject to reregistration.

Some uncertainties have been identified since their initial registration regarding the potential environmental fate and effects of neonicotinoid pesticides, particularly as they relate to pollinators. Data suggest that neonicotinic residues can accumulate in pollen and nectar of treated plants and may represent a potential exposure to pollinators.

Adverse effects data as well as beekill incidents have been reported, highlighting the potential direct and/or indirect effects of neonicotinic pesticides. Therefore, among other refinements to ecological risk assessment during registration review, we will consider potential effects of the neonicotinoids to honeybees and other pollinating insects.

The registration review docket for imidacloprid opened in December 2008, and the docket for nithiazine opened in March 2009. To better ensure a “level playing field” for the neonicotinoid class as a whole, and to best take advantage of new research as it becomes available, we moved ahead the docket openings for the remaining neonicotinoids on the registration review schedule (acetamiprid, clothianidin, dinotefuran, thiacloprid and thiamethoxam) to FY 2012.

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Fumigants share the characteristics of being volatile and mobile in the environment. We found soil fumigants eligible for reregistration in 2008; several other fumigant pesticides completed reregistration a few years earlier. EPA decided to move the fumigants forward in registration review from 2017 to 2013 so we can consider new data and new technologies sooner, as well as determine whether mitigation included in our earlier decisions is effectively addressing risks as we believe it will. The registration review will also include more recently registered fumigants.

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EPA decided to review all pesticides in the triazines group within the same time frame and to move these pesticides ahead in the registration review schedule to begin the process in 2013. Recent reevaluations should reduce the scope and resources needed to complete the atrazine registration review.


Imidazolinones are low-dose, high-potency herbicides that work by inhibition of the acetolactate synthase enzyme in plants. Their pesticidal mode of action is similar to that of the sulfonylurea family of herbicides, for which registration review dockets opened between FY 2011 and FY 2013. In addition, imazapyr was the only one of the imidazolinones to be subject to reregistration; registration review will provide the first opportunity to consider the six herbicides in this family in a common timeframe, starting in FY 2014.

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Isothiazolinones (or isothiazolones) are a group of compounds known for biocidal activity that are registered with EPA as antimicrobial agents and have similar uses and use patterns. Some of the isothiazolinones have conventional pesticide uses, as well. EPA has adjusted the registration review schedule for the isothiazolinones so that all of the uses of this family of pesticides can be considered in a common timeframe, starting in FY 2014.


Pyridine herbicides, which are used to control a number of broadleaf plants, have been identified in previous risk assessments as posing a potential risk to non-target plants. In particular, some herbicides in this family appear in reported incidents to have persisted in manure or compost later applied to planted fields. As with the imidazolinones, only a portion of the pyridine family was subject to reregistration, and registration review affords the Agency the opportunity to consider all the herbicides in this family in a common timeframe, starting in FY 2014.

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