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Method development for conducting effluent tests with the mayfly Neocloeon triangulifer.
Citation:
Soucek, D., A. Dickinson, AND T. Norberg-King. Method development for conducting effluent tests with the mayfly Neocloeon triangulifer. 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. 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:
Currently, USEPA relies on three freshwater species for short-term toxicity testing in a variety of programs and all tests are 8-d in duration or less. These methods are published in USEPA's Short-Term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms. The methods use a fish, a cladoceran, and an alga, but to date, there have been no EPA-approved methods to use sensitive invertebrates like mayflies, which are among the most sensitive species tested with metals and major ions, to support NPDES permit decision-making (i.e., via incorporation of whole effluent toxicity (WET) tests). 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 days-old, and we sought to further investigate this question with independent experiments comparing 0 and 7 day 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. This abstract does not necessarily represent the position or policy of the U.S. EPA.