Method Development for a Short-Term 7-d Toxicity Test with Unionid Mussels


US Environmental Protection Agency's short-term freshwater effluent test methods include a fish (Pimephales promelas), a cladoceran (Ceriodaphnia dubia), and a green alga (Raphidocelis subcapitata). There is a recognized need for additional taxa to accompany the 3 standard species for effluent testing. An appropriate additional taxon is unionid mussels because mussels are widely distributed, live burrowed in sediment and filter particles from the water column for food, and exhibit high sensitivity to a variety of contaminants. Multiple studies were conducted to develop a relevant and robust short-term test method for mussels. We first evaluated the comparative sensitivity of 2 mussel species (Villosa constricta and Lampsilis siliquoidea) and 2 standard species (P. promelas and C. dubia) using 2 mock effluents prepared by mixing ammonia and 5 metals (cadmium, copper, nickel, lead, and zinc) or a field-collected effluent in 7-d exposures. Both mussel species were equally or more sensitive (>2 fold) to effluents compared to the standard species. Next, we refined the mussel test method by first determining the best feeding rate of a commercial algal mixture for 3 age groups (1-, 2-, and 3-wk old) of L. siliquoidea in a 7-d feeding experiment, and then used the derived optimal feeding rates to assess the sensitivity of the 3 ages of juveniles in a 7-d reference toxicant (NaCl) test. Juvenile mussels grew substantially (30 to 52% length increase) when the 1- or 2-wk-old mussels were fed 2 mL twice daily and the 3-wk-old mussels were fed 3 mL twice daily. 25% inhibition concentrations (IC25s) for NaCl were similar (314 to 520 mg Cl/L) among the 3 age groups, indicating that an age range of 1- to 3-wk-old mussels can be used for a 7-d test. Finally, using the refined test method, we conducted an interlaboratory study among 13 laboratories to evaluate the performance of a 7-d NaCl test with L. siliquoidea. Eleven laboratories successfully completed the test, with >80% control survival and reliable growth data. IC25s ranged from 296 to 1,076 mg Cl/L, with a low (34%) coefficient of variation, indicating that the proposed method for L. siliquoidea has acceptable precision. This article is protected by copyright. All rights reserved.



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Interlaboratory variability, NaCl, Species sensitivity, Test methods, Whole effluent toxicity

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Environmental toxicology and chemistry