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Refining culturing and effluent testing methods for the mayfly, Neocloeon triangulifer
Citation:
Soucek, D., A. Dickinson, AND T. Norberg-King. Refining culturing and effluent testing methods for the mayfly, Neocloeon triangulifer. SETAC North America, Toronto, ON, CANADA, November 03 - 07, 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. As such, whole effluent toxicity (WET) methods are used to assess whether chemical mixtures of effluents and ambient waters are causing toxicity to aquatic life, thereby filling a key role in meeting the CWA goal of “no toxics in toxic amounts.” Currently, EPA primarily relies on short-term chronic toxicity testing methods for only two animals and one plant species in the NPDES WET program to assess whether effluents or waters comply with this “no toxics” provision of the CWA. 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. Mayflies are sensitive to pollutants and are a good candidate as a new toxicity test organism. The work in this study aims to identify the best age of mayfly and optimized diet and culture conditions to obtain an optimized, healthy organism to use for development of a sensitive WET test.
Description:
For decades, toxicity tests with aquatic invertebrates have been conducted and yet a small number of model organisms are routinely used. Test organisms are usually easily cultured in the laboratory, have rapid life-cycles, exhibit sensitivity to a variety of pollutants with reproducible results, and are generally available year-round. The US EPA effluent testing program uses short-term chronic freshwater tests (4d to 8d) with cladocerans (Cladocera, Ceriodaphnia dubia), green algae (ýSphaeropleales, Raphidocelis subcapitata) and fish (Cypriniformes, Pimephales promelas). EPA also has standardized Hyalella azteca (Amphipoda) and Chironomus dilutus (Diptera) test methods for sediments; yet EPA’s effluent and ambient testing manuals do not provide acute or short-term test methods for H. azteca, C. dilutus or mayflies (Ephemeroptera). Because mayflies have been shown to be among the most sensitive species to major ions, metals, and pesticides, we have focused on effluent method development for the mayfly, Neocloeon triangulifer, a parthenogenetic species with a short life cycle (~30d at 25C). While methods for conducting acute 4d and chronic (~25-30d) toxicity tests with this mayfly have been published, a need exists to extend and standardize the methodology for applicable methods for testing in short-term exposures (e.g., 7d or 10d). Studies began with identifying an optimal starting age, test duration, and optimal sublethal endpoint for whole effluent toxicity testing. We found that chronic values from tests using <24-h-old organisms were ~4-fold more sensitive than those using 7-d-old organisms. Survival was never a more sensitive endpoint than either calculated weight or biomass. Efforts to refine the various aspects of diatom culture technique on food quality and therefore mayfly growth are underway and optimizing the diet for these organisms may be critical for achieving consistently high growth rates with low intra-treatment variability. We also determined the influence of amendments to culture water and food, and temperature on sensitivity to reference contaminants and effluents. Results of the study should provide data needed to guide the development of a toxicity test method to support NPDES permit decision-making.