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Method development for short-term effluent tests with a freshwater mussel (Fatmucket, Lampsilis siliquoidea)
Citation:
Wang, N., J. Kunz, D. Hardesty, J. Steevens, T. NorbergKing, E. Hammer, C. Bauer, T. Augspurger, D. Martinez, C. Barnhart, J. Murray, M. Bowersox, J. Roberts, R. Bringolf, R. Ratajczak, S. Ciparis, G. Cope, S. Buczek, D. Farrar, L. Rabalais, M. Garton, P. Gillis, J. Bennett, J. Salerno, B. Hester, R. Lockwood, C. Tarr, D. McIntyre, AND J. Wardell. Method development for short-term effluent tests with a freshwater mussel (Fatmucket, Lampsilis siliquoidea). Freshwater Mollusk Conservation Society, San Antonio, TX, April 14 - 18, 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. The fatmucket (Lampsilis siliquoidea) is found in six of the EPA Regions and Canada and has been demonstrated to be among the most sensitive of all aquatic species to some contaminants, including ammonia, chloride, sulfate, potassium, copper, nickel, and zinc. Studies with the fatmucket mussel to develop short-term 7-day testing procedures like those used determining effluent toxicity have been conducted to determine optimum feeding rates and the most sensitive stage of the juvenile mussels in 7- and 10-d exposures using survival and growth of different ages of the juvenile mussels. We are now starting an interlaboratory study to evaluate the performance and variability in the newly developed mussel testing method with 13 volunteer laboratories to test the method we have developed. 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:
Short-term freshwater toxicity testing methods have been promulgated by the USEPA for estimating chronic toxicity of effluent only using three standard species: a fish (Pimephales promelas; 7-d exposure), a cladoceran (Ceriodaphnia dubia; 6 to 8-d exposure), and a green alga (Raphidocelis subcapitata; 4-d exposure). Unionid mussels are among the most sensitive species to a variety of contaminants, including ammonia, some metals and major ion salts. Their sensitivity, ecological relevance, and conservation significance make mussels an attractive additional taxon for effluent toxicity assessments. Between 2012 and 2016, we evaluated the sensitivity of two mussel species (Villosa constricta and Lampsilis siliquoidea) and two standard species (C. dubia and P. promelas) to field-collected effluents and laboratory-prepared mock effluents in 7-d exposures. These studies showed that both mussels were more sensitive to the effluents compared to the two standard species. In 2017, we refined the mussel testing method using L. siliquoidea by determining optimum feeding rates and ages of juvenile mussels (1-, 2-, and 3-wk old) in a 7-d feeding study and by assessing the sensitivity of the three ages of mussels in 7-d reference toxicant (NaCl) tests. The 1- to 3-wk-old mussels increased in length by up to 50% over the 7-d feeding study, and the sensitivity to NaCl was similar among the three ages of mussels. Finally, an interlaboratory study was performed in 2018 by 13 volunteer laboratories from the USA and Canada to evaluate the performance of 1-wk-old L. siliquoidea in a 7-d NaCl toxicity test using the refined methods. All 13 laboratories met the test acceptability criterion of ¡Ý80% control survival, and the differences in 20% effect concentrations among laboratories were within a factor of 3, indicating that the proposed methods with L. siliquoidea have acceptable precision and can be performed routinely.