Use of the mayflyStenonema Modestum(Heptageniidae) in subacute toxicity assessments

Abstract

This study presents the results of subacute toxicity testing with the mayfly (Ephemeroptera), species Stenonema modestum (Heptageniidae). This species is ubiquitous to many streams in the eastern United States and Canada and is associated with unpolluted sediments and water. The results show that counts of molts or exuviae over a 7–14-d exposure period can be a sensitive indicator of chronic growth effects. Molt production was a more sensitive indicator of pollutant effects than length of organism or width of head capsule measurements. Tests using coal mine effluents indicated that the 7-d molt production end point was often more sensitive than the 14-d molt or survival end point. This was due to either a short-term stimulatory effect on molting or effluent variability over time. Molt stimulation was not observed in tests using NaCl or silver nitrate. Tests with these compounds and coal mine effluents demonstrated that the methods and end points provide repeatable and relatively sensitive data. Test precision was comparable to U.S. Environmental Protection Agency 7-d short-term chronic tests. Molt production of Stenonema modestum in laboratory tests proved to be a reliable predictor of instream effects due to a metal-finishing effluent. Furthermore, simultaneous tests of sediment elutriates and ambient samples from the stream pinpointed probable mechanisms behind the observed instream impact on Stenonema modestum. This method should be amenable to other mayfly species, making it a potentially useful tool in site-specific water quality and sediment quality studies.