[Seminar blog] Pesticide Ecological Risk Assessment at the USEPA

written by: Michael Adu-Brew and Leo M Kerner
​
​The United States Environmental Protection Agency (EPA) was instituted in 1970 and is tasked with matters of environmental protection. Its mandate is to provide clean air, land, and water, reduce environmental risk based on science, administer and enforce federal laws protecting human health and the environment, and promote environmental stewardship1 . As part of the UMD Department of Entomology seminar series, Mr. Keith Sappington – a Senior Science Advisor at EPA’s Office of Pesticide Programs – provided an overview on December 6 th , 2024 of the agency’s procedures for pesticide ecological risk assessment and how these procedures are used to assess risk to insect pollinators and endangered species.

What is the Office of Pesticide Programs?

The Office of Pesticide Programs (OPP) conducts all EPA’s pesticides review and oversight, thus regulating the manufacturing and usage of all pesticides in the US, ensuring they meet safety standards for human health and the environment2 . Every year, the OPP undertakes thousands of pesticide-related actions, including registration of new pesticide products and uses, reviewing registrations of existing pesticides, and conducting reviews on currently registered pesticide data and efficacy. OPP assesses the potential risk of pesticides to establish maximum safe levels of pesticide residue and implements various pesticide-related laws, including but not limited to, the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), and the Endangered Species Act (ESA). To achieve OPP’s mandate to ensure the environmental safety of pesticides , the agency depends on FIFRA and ESA, which provide a framework for regulating pesticide use and minimizing environmental risks. Before EPA may register a pesticide under FIFRA, the applicant must show, among other things, that using the pesticide according to specifications “will not generally cause unreasonable adverse effects on the environment”, taking into account the economic, social, and environmental costs and benefits of the use of any pesticide.3

​For existing pesticides, registration procedure follows a 15-year cycle beginning with the development of a Preliminary Work Plan, which lays the scientific foundation for evaluating the pesticide as seen in Figure 1. Following public comment and revision, the Final Work Plan identifies any data gaps which must be filled by the pesticide applicants by submitting additional data through issuance of a “Data Call-In”. After completion and review of the Draft Risk Assessment, proposed and final decisions are made regarding pesticide registration. The final ​stage may include measures such as label changes or usage restrictions to mitigate identified risks.4

Fig 1: US EPA registration review process

Ecological Risk Assessment Process
To support the evaluation of potential risks of an existing or proposed pesticide use to the environment, EPA conducts an ecological risk assessment (ERA). As part of the ERA, an exposure assessment is conducted in which different routes of exposure are examined, such as from spray drift and runoff into streams or contamination of dietary items like foliage, pollen and nectar. EPA scientists characterize the environmental fate of a pesticide based on submitted on how a pesticide interacts in the environment through process like hydrolysis (breakdown in water), photolysis (breakdown in contact with light), aerobic and anaerobic metabolism, and/or sorption (binding to solid particles in the environment). Exposure assessments also include how a pesticide is used agronomically and how climate and hydrological conditions affect exposure concentrations. The output from an exposure assessment includes a series of estimated environmental concentrations (EEC) in various environmental media. These EECs are then compared to various toxicological endpoints derived from studies of different taxa (e.g., plants, invertebrates, fish, birds, mammals). Such information is based on submitted data and suitable studies found in the scientific literature.

​Based on the exposure and effects data, a risk characterization is made which is the final phase of the ecological risk assessment. A risk characterization includes two components: a risk estimation and a risk description. The risk estimation component is quantitative in nature and usually determined by comparing exposure (EEC) and effects data (toxicity endpoint) in the form of a risk quotient (RQ). 

Risk Quotient (RQ) = Estimated environmental concentration (EEC) / Toxicity endpoint (LC50, LD50, NOAEC)

​The risk description component tends to be more qualitative and places the calculated RQs in context of other lines of evidence and evaluates key assumptions and uncertainties underlying the risk assessment. For example, environmental monitoring data are considered to help evaluate the appropriateness of the risk estimates. 

photo credit: Bonnie Smith, EPA

Assessing pesticide risk to honeybees
Mr. Sappington provided an example of how EPA agents assess the non-target effects of insecticides on honeybees. The first step of bee risk assessment process is determining the potential for exposure of bees to the pesticide through direct contact to spray droplets or through their diet (e.g., pollen and nectar). The extent to which bees are attracted to blooming crops is one component of this first step. The second step involves a “Tier 1” assessment where risks to individual bees are evaluated.

The Tier 1 risk assessment is based on toxicity data generated in the laboratory for adult and larval life stages of the honeybee. It also considers how much pollen and nectar different life stages and castes of bees consume. When necessary, the third and fourth step of the bee risk assessment process considers risk to bees at the colony level. A “Tier 2” risk assessment considers effects to honeybee colonies under partially controlled conditions of high exposure (e.g., colonies confined in mesh tunnels or fed contaminated diet). If necessary, a “Tier 3” risk assessment may be conducted. The Tier 3 assessment is based on so-called “full field studies” where colonies are placed in/adjacent to agricultural fields under actual pesticide use practices. Based on the risk assessment results, EPA can identify various options to mitigate risks to bees, such as reducing application rates, changing application methods, or adjusting the timing of applications relative to crop bloom.

Assessing Pesticide Risk to Federally Threatened or Endangered Species
Finally, Mr. Sappington concluded his seminar with a summary of how pesticide risks are evaluated for Federally threatened or endangered species. The Endangered Species Act (ESA) mandates that all federal actions must not cause jeopardy to the existence of federally listed species and their designated critical habitat. Based on 2022 species listing, nearly 100 terrestrial arthropod species are listed under ESA. As part of the ESA consultation process on listed species, the EPA first conducts Biological Evaluations (BEs) to assess the potential direct and indirect adverse effect of pesticides on individuals or populations of listed species and their habitat. The U.S. Fish and Wildlife Service (USFWS) and the National Marine Fisheries Service (NMFS) then use the BEs as the basis to construct “Biological Opinions”. Among other things, this opinion states whether the federal body involved has done enough to ensure that its proposed action is not likely to jeopardize the continued existence of a listed species or result in the destruction or adverse modification of critical habitat.

The EPA encounters several challenges in effect/risk assessments:
1. Identifying surrogate species for toxicological studies to represent listed species.
2. Obtaining standardized data from open literature, particularly regarding test designs.
3. Addressing challenges in exposure assessments.
4. Overcoming difficulties in risk characterization, including indirect effects and spatio-temporal scale considerations.
To address these challenges, the EPA is exploring advanced procedures, such as mechanistic-based assessment of species sensitivity using tools like Sequence Alignment to Predict Across Species Susceptibility (SeqAPASS), and retrospective analyses of non-target arthropods (NTA) to enhance the accuracy of their evaluations.

We’d like to extend a thank you to Mr. Keith Sappington for taking the time to come to our department and speak on the roles of the EPA in protecting endangered species and helping our country maintain clean air, land, and water. It’s because of people like him and the agency he works for that we can make informed decisions about pesticide restrictions that benefit not only ourselves, but the world around us.

About the authors: Leo M Kerner is a third year masters student studying conservation biocontrol using crop diversification techniques in the Hooks lab at University of Maryland. In the future he plans on working in extension, helping growers adopt sustainable pest management practices that help to promote arthropod diversity and ecological resilience.
Michael Adu-Brew is a second year master’s student working in the Krishnan Lab. His research focuses on assessing the toxicity and risk of pesticides on non-target insects, particularly monarch butterflies.

​Presenter’s Disclaimer: The views expressed in this presentation are those of the authors and do not necessarily reflect the views or policies of the U.S. EPA 

---

Photo credits:
Bonnie Smith, EPA
Reference:
​1. U.S Environmental protection Agency. Registration Review Process. Available from: https://www.epa.gov/pesticide-reevaluation/registration-review-process
2. United States Fish and Wildlife Service. 2024. Listed Animals. Available from: https://ecos.fws.gov/ecp0/reports/ad-hoc-species-report
3. Janicki, J. et al. (2023) Insect populations are declining at an unprecedented rate, Reuters. Available at: https://www.reuters.com/graphics/GLOBAL-ENVIRONMENT/INSECT-APOCALYPSE /egpbykdxjvq/ (Accessed: 17 December 2024).