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Evaluating the relative sensitivity of the “P&T” in EPT: Implications for standardized toxicity testing
Citation:
Sibley, P., M. Raby, J. Wirtz, M. McCoole, L. Lagadic, D. Soucek, T. Norberg-King, AND I. Roessink. Evaluating the relative sensitivity of the “P&T” in EPT: Implications for standardized toxicity testing. SETAC North America, Sacramento, CA, November 04 - 08, 2018.
Impact/Purpose:
Clean Water Act (CWA) implementation starts with the development of water quality criteria to protect uses, such as aquatic life. While aquatic life is exposed to innumerable chemical mixtures in the nation’s waters, EPA has developed just 45 numeric aquatic life criteria for use in National Pollution Discharge Elimination System (NPDES) permits and assessment of the nation’s waters. There is an urgent need to better protect aquatic life (including species federally-listed per the Endangered Species Act, or ESA) by establishing additional test methods for sensitive aquatic life. Historically, the choice of invertebrate species used in most current water and sediment toxicity test protocols represent a combination of practical and ecological considerations. This has led to the development of widely applied toxicity test protocols that incorporate reliable, though not necessarily highly sensitive, test species. Early exploration of candidate species for toxicity testing included evaluation of EPT (Ephemeroptera, Plecoptera, Trichoptera) taxa. However, many of these were found to be difficult to culture (e.g., many EPT taxa require flowing water), biological requirements were not well known, most would not reproduce under laboratory conditions, and many were sensitive to the laboratory environment (often failing to meet control test acceptability criteria during tests). In recognition of recent advances in culturing and application in aqueous and sediment-based toxicity testing of EPT species, a project was initiated to report on the state of the science for the application of mayflies in ecotoxicity testing. Key goals of the project include the identification and prioritization of knowledge gaps that can serve as areas for future research, the assessment of the prospect for routine incorporation of mayflies in toxicity testing, and the creation of standardized toxicity test protocols followed by a mayfly workshop in September. When we have additional methods available, they can be used by EPA, state, and tribal NPDES permitting programs and can support the completion of ecological risk assessments conducted in accordance with the CWA, ESA and other laws.
Description:
The EPT (Ephemeroptera, Plecoptera, and Trichoptera) group of insects are widely applied as indicators of water quality in biomonitoring because they contain some of the most sensitive species to environmental pollutants. This widespread application in the field has not translated into standardized lab-based toxicity tests, in part, because many of the taxa tested in the early days of test development were difficult to culture due to unique biological requirements (e.g., flowing water), most would not reproduce under laboratory conditions, and some were sensitive to the lab environment (often failing to meet control test acceptability criteria). In the past few years, however, interest in developing standard toxicity test protocols using EPT taxa has been renewed due to improved methods for culturing, development of novel exposure systems for obligate flowing water species, and an improved understanding of biological requirements. To date, much of this effort has focused on European and North American species within the Ephemeroptera (mayflies) but recent testing with both Plecoptera (stoneflies) and Trichoptera (caddisflies) with neonicotinoid insecticides indicates that standardized exposure protocols may be possible. In this presentation, we will review historical and recent applications of Plecoptera and Trichoptera in toxicity testing with the goal of evaluating their suitability for lab-based chemical assessments. In addition to practical considerations, we examined the relative sensitivity of EPT taxa based on studies derived from the literature and the application of Species Sensitivity Distributions developed for hazard assessments with neonicotinoid insecticides. We show that Ephemeropteran species, on average, are more sensitive than Plecopteran and Trichopteran species but that there is wide variation within and between the orders depending on genus, life history characteristics, and chemical class.