Using Hexagenia in sediment bioassays: methods, applicability, and relative sensitivity.

The majority of sediment toxicity and aquatic bioaccumulation assessments are conducted using standardized species, such as Hyalella azteca, Chironomus dilutus, and Lumbriculus variegatus. The burrowing mayfly, Hexagenia sp., may serve as an ideal supplemental organism for both toxicity and bioaccumulation studies for several reasons. Hexagenia are recognized as sensitive species, have a long aquatic life stage (up to 2 yr), and have large bodies, which aid in retrieval from sediments and for residue analysis. The present study outlines the authors' established method for collecting and hatching eggs, raising nymphs, and using these animals for toxicity testing. Furthermore, the relative sensitivity of 3 size classes of Hexagenia to a representative contaminant (bifenthrin) was examined and compared with laboratory-derived median lethal concentrations for the more traditionally used Hyalella and Chironomus. Finally, sublethal end points, including immobilization and suspended solids, were defined for this species. This provides guidance for the use of this species in toxicological bioassays.