Tolerance of freshwater test organisms to formulated sediments for use as control materials in whole-sediment toxicity tests

A method is described for preparing formulated sediments for use in toxicit y testing. Ingredients used to prepare formulated sediments included commer cially available silt, clay, sand, humic acid, dolomite, and rw-cellulose ( as a source of organic carbon), alpha-Cellulose was selected as the source of organic carbon because it is commercially available, consistent From bat ch to batch, and low in contaminant concentrations. The tolerance of freshw ater test organisms to formulated sediments for use as control materials in whole-sediment toxicity testing was evaluated. Sediment exposures were con ducted for 10 d with the amphipod Hyalella azteca, the midges Chironomus ri parius and C. tentans, and the oligochaete Lumbriculus variegatus and for 2 8 d with H. azteca. Responses of organisms in formulated sediments was comp ared with a field-collected control sediment that has routinely been used t o determine test acceptability. Tolerance of organisms to formulated sedime nts was evaluated by determining responses to varying levels of alpha-cellu lose, to varying levels of grain size, to evaluation of different food type s, or to evaluation of different sources of overlying water. In the 10-d ex posures, survival of organisms exposed to the formulated sediments routinel y met or exceeded the responses of test organisms exposed to the control se diment and routinely met test acceptability criteria required in standard m ethods. Growth of amphipods and oligochaetes in 10-d exposures with formula ted sediment was often less than growth of organisms in the held-collected control sediment. Additional research is needed, using the method employed to prepare formulated sediment, to determine if conditioning formulated sed iments before starting 10-d tests would improve the growth of amphipods. In the 28-d exposures, survival of H. azteca was low when reconstituted water was used as the source of overlying water. However, when well water was us ed as the source of overlying water in 28-d exposures, consistent responses of amphipods were observed in both formulated and control sediments.