Pesticides and Endangered Species

Posted on Behalf of  Katie Gibbs


The Endangered Species Act (ESA) of 1973 was passed to “protect and recover imperiled species and the ecosystems upon which they depend” (FWS, 2017). According to the Center for Biological Diversity, >2,000 species are listed as threatened or endangered under the ESA, with 1,618 of these species in the U.S (Figure 1; Center for Biological Diversity). The U.S. Fish and Wildlife Services (FWS) is primarily responsible for the terrestrial and freshwater organisms, and the National Marine Fisheries Service (NMFS) is responsible for marine wildlife. Under the ESA, a species can be listed as either endangered, defined as “in danger of extinction throughout all or a significant portion of its range,” or threatened, defined as “likely to become endangered within the foreseeable future” (FWS, 2017).

Figure 1. Summary of endangered species in the US (Center for Biological Diversity).

The ESA protects endangered and threatened plants and animals by:

  • prohibiting the harassment, harming, pursuing, hunting, shooting, wounding, killing, trapping, capturing, or collecting of any listed species without a federal permit; and
  • Prohibiting the federal actions that are likely to jeopardize the continued existence of listed species or adversely modify the species’ designated critical habitat (FWS, 2017).

These federal actions include those overseen by the Environmental Protection Agency (EPA).

Assessing Pesticides under the ESA

More than1.1 billion pounds of pesticides are used in the U.S. each year according to some estimates (Alavanja, 2009; EPA, 2017). The EPA treats pesticides as a particular concern to endangered species. Under the ESA, the EPA’s Endangered Species Protection Program (ESPP) determines whether pesticide use may affect any threatened or endangered species, or cause harmful modification of designated critical habitat (EPA, 2016a). When registering a pesticide or assessing the potential ecological risks of a currently registered pesticide, the EPA conducts an ecological risk assessment to evaluate extensive environmental fate and toxicity data in order to determine how the pesticide both moves through and breaks down in an environment. The risk assessment also evaluates whether potential exposure to the pesticide will result in adverse effects to wildlife and vegetation (EPA, 2016b).  

As part of its evaluation, ESPP relies upon the EPA’s Office of Pesticide Programs (OPP), which reviews information on exposure and effects for pesticides in order to derive the estimated environmental concentrations (EECs) and to estimate pesticide exposure and risk for various species (Figure 2). For most chemicals, effects characterization is based on a deterministic approach, using one point on a concentration-response curve. This approach involves the risk quotient (RQ) method, which compares exposure over toxicity. The calculated RQs are compared to the Levels of Concern (LOCs) summarized in Table 1 (EPA, 2004; EPA, 2007; EPA, 2016c).

Figure 2. Summary of information reviewed by OPP to derive pesticide’s EECs, exposure, and risk to various species.

Table 1. Summary of LOCs (unitless) used in risk assessment (EPA, 2004; EPA, 2007).


LOC (Species)


0.5 (aquatic animals, mammals, and birds)

Acute (restricted use)

0.1 (aquatic animals); 0.2 (mammals and birds)

Acute (endangered species)

0.05 (aquatic animals); 0.1 (mammals and birds)

Acute (plants)

1 (non-endangered and endangered plants)


1 (all species)

Upon completing its risk assessment, the EPA classifies a pesticide as having either “no effect” (NE), or that it “may affect” (MA) the species or designated critical habitat. In the event of an MA determination, the EPA will refine its assessment to determine whether the pesticide’s use “may affect, but is not likely to adversely affect” (NLAA), or “may affect and is likely to adversely affect” (LAA) the species or designated critical habitat. The NLAA determination is made when the effects are: 1) extremely unlikely to occur and cannot be evaluated; 2) would never reach a scale at which unintended injury or killing of an individual listed species would occur; or 3) are wholly beneficial (EPA, 2016b). In March, 2020, the EPA released the Revised Method for National Level Listed Biological Evaluations (BEs) of Conventional Pesticides, which evaluated carbaryl, methomyl, atrazine, propazine, simazine, and glyphosate. Part II of this blog (Recent Developments to Evaluating Conventional Pesticides) provides additional details and examples.

Cardno ChemRisk scientists have extensive professional experience evaluating the possible human and environmental hazards and risks posed by chemicals, including pesticides. Specifically, we have experience conducting risk assessments, evaluating product safety, and assuring regulatory compliance. For more information on Cardno ChemRisk’s capabilities, please contact Dr. Andrey Massarsky or Dr. Jordan Kozal.