An evaluation of a short-term chronic effluent toxicity test using sheepshead minnow (Cyprinodon variegatus) larvae

In response to recent changes in National Pollutant Discharge Elimination System (NPDES) permit regulations, rapid (7-day) static renewal toxicity tests have been developed to detect chronic (sublethal and lethal) effect concentrations of municipal and industrial effluents on freshwater and marine/estuarine organisms. This paper evaluates results from short-term (7-day) chronic effluent tests measuring effects on the growth and survival of the larvae of estuarine sheepshead minnow (Cyprinodon variegatus). Growth was the more sensitive endpoint in 52% of the effluent tests; survival was most sensitive in 7% of the tests. Growth and survival were equally sensitive endpoints in 26% of the tests, while there was no effect on either endpoint at the highest test concentration in 15% of the tests. Four short-term chronic tests were conducted concurrently with early life stage (ELS) tests using a common effluent. Effect concentrations were generally (two of three) within one dilution (a factor of three). Comparison of short-term chronic and ELS tests were also conducted with reference single chemicals and the results were slightly better than the effluent comparisons. A series of ten intralaboratory tests and seven interlaboratory tests were conducted to assess the variability among tests results. Toxicity in these tests varied by no more than one test concentration interval. We concluded that this sheepshead minnow test is suitable to estimate chronic values for complex effluents discharged to marine/estuarine environments within the NPDES permit regulations.