You are here:
Development of short-term toxicity test methods to estimate chronic toxicity using the freshwater parthenogenic mayfly, Neocloeon triangulifer.-poster
Citation:
Norberg-King, T., D. Soucek, AND A. Dickinson. Development of short-term toxicity test methods to estimate chronic toxicity using the freshwater parthenogenic mayfly, Neocloeon triangulifer.-poster. Twin Ports Freshwater Folk Meeting, Duluth, MN, June 05, 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. To best accomplish this goal, WET methods for new species could be developed, validated, and promulgated at 40 CFR Part 136. Methods for conducting acute 4-day and full-life chronic (~25-30-d) toxicity tests with the mayfly (Neocloeon triangulifer) have been published, but there is a need to extend the methodology so that it is applicable for testing effluents and receiving waters in a short-term exposure (e.g., 7 or 10 d). Our studies involved identifying an optimal starting age, test duration, and sub-lethal endpoint for WET testing. Others have compared sensitivity of this species at 0, 3, and 5 d-old, and we sought to further investigate this question with independent experiments comparing 0-d and 7-d old organisms in 7 and 14-d tests. We also developed a length versus dry weight relationship for this species with the idea that while dry weight is a more sensitive endpoint than length, length is much easier to consistently and accurately measure with young instars of this species. The other objective of this study was to investigate and further refine various aspects of diatom culture technique on food quality and therefore mayfly growth. Optimizing diet for these organisms may be critical for achieving consistently high growth rates with low intra-treatment variability. Results of the study will provide further data needed to guide the development of a whole effluent toxicity test method for mayflies. Once the new methods have been demonstrated to be sensitive and reliable for effluents and receiving waters, they can be proposed for approval for use by EPA, state, and tribal NPDES permitting programs to support the completion of ecological risk assessments conducted in accordance with the CWA, ESA and other laws.
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). These species have been used extensively in acute and short-term toxicity tests using EPA standardized methods to assess the hazard of chemicals and effluents in freshwater environments. EPA has standardized Hyalella azteca (Amphipoda) and Chironomus dilutus (Dipteran) test methods for sediments; yet EPAs effluent and ambient testing manuals don’t provide acute or short-term test methods for H. azteca, C. dilutus or mayflies (Ephemeroptera,Hexagenia, Neocloeon).To add a sensitive insect, we have focused on using the mayfly, N. triangulifer, as it is parthenogenetic, has a short life cycle (~30d at 25C), and is sensitive to various toxicants. 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. While others have compared the sensitivity of this species at 0d, 3d, & 5d old, we sought to further investigate this question with independent experiments comparing 0d and 7d old organisms in 7d and 14d tests. We developed a length versus dry weight relationship for this mayfly; dry weight is a more sensitive endpoint than length, but length is easier to measure more consistently and accurately with young instars. 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. Results of the study should provide data needed to guide the development of a toxicity test method to support NPDES permit decision-making. T