Presentation Abstract

Pesticides are widely used throughout the Puget Sound region and are frequently detected as complex mixtures in aquatic habitats. As a result, pesticide mixture toxicity is an important component of risk assessments performed within the Salish Sea region. Here we describe a process for assessing toxicity of three categories of pesticide mixtures; formulated products (one product containing multiple active ingredients), tank mixes (multiple pesticides applied simultaneously), and environmental mixtures (resulting from unrelated pesticide use over the landscape). Mixtures were assumed to be either dose-additive or response-additive, depending on the modes of action of the individual pesticide components. Toxicity estimates utilized two main pieces of information - exposure concentrations and taxa-specific toxicity values. Exposure concentrations were either generated using EPA’s Pesticide Water Calculator (PWC), which incorporates chemical and application-specific parameters to calculate anticipated water concentrations over different durations, or utilized directly from routine monitoring studies. Standard measures of toxicity (typically the LC50, or the concentration that is lethal to 50% of the test organisms) were used to represent the sensitivity of different taxa groups to a given pesticide. We predicted toxicity for formulated products containing multiple pesticides, tank mixtures based on co-applications reported in California’s Pesticide Use Reporting System, and environmental mixtures identified in ambient water quality monitoring data from Washington State. Results show that estimating mixture toxicity is possible with currently available information, and these predictions can be used effectively in ecological risk assessments. Importantly, failing to consider mixtures may underestimate pesticide risk, leading to erroneous risk conclusions and ineffective protections for aquatic species and habitats.

Session Title

Posters: Fate, Transport, & Toxicity of Chemicals

Keywords

pesticides, mixtures, management

Conference Track

SSE18: Posters

Conference Name

Salish Sea Ecosystem Conference (Seattle, WA : 2018)

Document Type

Event

SSEC Identifier

SSE18-66

Start Date

5-4-2018 11:30 AM

End Date

5-4-2018 1:30 PM

Type of Presentation

Poster

Contributing Repository

Digital content made available by University Archives, Heritage Resources, Western Libraries, Western Washington University.

Geographic Coverage

Salish Sea (B.C. and Wash.)

Rights

This resource is displayed for educational purposes only and may be subject to U.S. and international copyright laws. For more information about rights or obtaining copies of this resource, please contact University Archives, Heritage Resources, Western Libraries, Western Washington University, Bellingham, WA 98225-9103, USA (360-650-7534; heritage.resources@wwu.edu) and refer to the collection name and identifier. Any materials cited must be attributed to the Salish Sea Ecosystem Conference Records, University Archives, Heritage Resources, Western Libraries, Western Washington University.

Type

text

Language

English

Format

application/pdf

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Apr 5th, 11:30 AM Apr 5th, 1:30 PM

A framework for incorporating the toxicity of pesticide mixtures into ecological risk assessments

Pesticides are widely used throughout the Puget Sound region and are frequently detected as complex mixtures in aquatic habitats. As a result, pesticide mixture toxicity is an important component of risk assessments performed within the Salish Sea region. Here we describe a process for assessing toxicity of three categories of pesticide mixtures; formulated products (one product containing multiple active ingredients), tank mixes (multiple pesticides applied simultaneously), and environmental mixtures (resulting from unrelated pesticide use over the landscape). Mixtures were assumed to be either dose-additive or response-additive, depending on the modes of action of the individual pesticide components. Toxicity estimates utilized two main pieces of information - exposure concentrations and taxa-specific toxicity values. Exposure concentrations were either generated using EPA’s Pesticide Water Calculator (PWC), which incorporates chemical and application-specific parameters to calculate anticipated water concentrations over different durations, or utilized directly from routine monitoring studies. Standard measures of toxicity (typically the LC50, or the concentration that is lethal to 50% of the test organisms) were used to represent the sensitivity of different taxa groups to a given pesticide. We predicted toxicity for formulated products containing multiple pesticides, tank mixtures based on co-applications reported in California’s Pesticide Use Reporting System, and environmental mixtures identified in ambient water quality monitoring data from Washington State. Results show that estimating mixture toxicity is possible with currently available information, and these predictions can be used effectively in ecological risk assessments. Importantly, failing to consider mixtures may underestimate pesticide risk, leading to erroneous risk conclusions and ineffective protections for aquatic species and habitats.