CHECK STUDIES WITH HYALELLA-AZTECA AND CHIRONOMUS-TENTANS IN SUPPORT OF THE DEVELOPMENT OF A SEDIMENT QUALITY CRITERION FOR DIELDRIN

The development of sediment quality criteria (SQCs) for nonpolar compo unds using equilibrium partitioning theory (EqP) requires three critic al data elements for the compound of interest: (a) a reliable, measure d K-ow; (b) an acceptable minimum data set for the development of the final acute and final chronic values necessary to calculate a water-qu ality criterion (WQC); and (c) ''check'' experiments with appropriate freshwater and marine benthic organisms to ensure that their responses in spiked-sediment tests are in agreement with responses predicted ba sed on EqP. This study presents the results of dieldrin check experime nts with two freshwater species: the amphipod Hyalella azteca and the chironomid Chironomus tentans. Ten-day, flow-through, water-only dield rin LC50 values for the amphipod and chironomid were 7.6 and 1.1 mu g/ L, respectively. The LC50 values for the two species based on organic carbon-normalized sediment concentrations of dieldrin were generally l ess variable than values based on dieldrin concentrations in sediments on a dry-weight basis. Ten-day LC50 values for H. azteca and C. tenta ns based on measured pore-water concentrations of dieldrin were greate r than those based on EqP-predicted pore-water concentrations of dield rin. An increase in the apparent water solubility of dieldrin as a res ult of binding to dissolved organic carbon appeared to account for thi s phenomenon. Ten-day LC50 values for H. azteca and C. tentans based o n EqP-predicted pore-water concentrations of dieldrin were within a fa ctor of 25 and 3 of their respective 10-d, water-only dieldrin LC50 va lues. Avoidance of the dieldrin-spiked sediments may offer a partial e xplanation for the concentration-response results observed with H. azt eca and the greater difference observed for this species between water -only and predicted pore-water 10-d LC50 values for dieldrin. Inhibiti on of growth in C. tentans was also a sensitive end point with effects observed at pore-water 10-d LC50 values for dieldrin. Inhibition of g rowth in C. tentans was also a sensitive end point with effects observ ed at pore-water concentrations of dieldrin as small as 5.5 mu g/g org anic carbon. Based on these results, it appears that EqP based upon se diment organic carbon content is an appropriate model for converting W QC for dieldrin to SQC. These results also highlight the importance of using multiple benthic test species (including at least one infaunal species), end points, and sediments in SQC sediment-spiking check stud ies.