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Mayflies in ecotoxicity testing: methodological needs and knowledge gaps identified in a virtual workshop
Citation:
Sibley, P., I. Roessink, M. Raby, J. Wirtz, M. McCoole, L. Lagadic, D. Soucek, T. Norberg-King, AND T. Watson-Leung. Mayflies in ecotoxicity testing: methodological needs and knowledge gaps identified in a virtual workshop. SETAC Europe 2019, Helsinki, N/A, FINLAND, May 26 - 30, 2019.
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:
Among the sensitive EPT (Ephemeroptera, Plecoptera, Trichoptera) group of insects, mayflies (Ephemeroptera) have been applied most successfully in water and sediment toxicity testing. For example, the recent development of a culture-based, life-cycle test with Neocloeon triangulifer and the long-standing sediment test with Hexagenia in North America, and the routine application of field-collected Cloeon dipterum in European testing reflect commensurate advancements in understanding the biology of these organisms and their behaviour under lab holding and testing conditions. With growing interest in expanding the arsenal of mayfly species used in toxicity testing, a virtual workshop was held in September 2018 to identify and discuss knowledge gaps constraining advancements in the use of new mayfly species in culture-based or field-collected protocols for water and sediment toxicity testing. Participants from industry, government, and academic sectors, representing both Europe and North America, took part in the workshop. Discussions were guided by several questions: 1) Should the emphasis be placed on further development of lab-cultured species or on a more standardized use of field-collected species? 2) What criteria should be used to select suitable test species (e.g., relative sensitivity to chemicals and test conditions, ecological traits, culturability)? 3) Should regulatory requirements play a role in determining species selection? 4) In tests emphasizing field-collected species, how can holding, feeding, and testing conditions be improved to maximize organism health and successful use in testing? In this poster presentation, we summarize the outputs of the workshop using, where appropriate, a data-driven approach based on species sensitivity distributions comparing the relative sensitivity of mayflies to various chemical classes based on ecological traits classification.