PW20 New Approaches to Determining Soil and Sediment Exposures
Exhibit Hall
8:00 AM - Wednesday
(PW294) Toxicity and bioavailability of sediment-associated copper to Daphnia magna.
Gillis, Patricia 1, Chow-Fraser, Patricia1, Ranville, James2, Ross, Phillip2, Wood, Chris1, 1 McMaster University, Hamilton, Ontario, Canada2 Colorado School of Mines, Golden, Colorado, USA
ABSTRACT- In aquatic environments with elevated levels of sediment-associated metals, organisms may be exposed to metals through both the dissolved and particulate phases (suspended and settled). Daphnia magna were used to assess Cu toxicity and bioavailabilty from a mining-impacted stream (Clear Creek, CO, USA) with elevated sediment Cu (2.5 mg/g) levels. To distinguish metal accumulation and toxicity originating from the particulate phase with that from the dissolved phase, it was necessary to remove or at least to significantly reduce, the amount of metal that would readily dissociate from the sediment and move into the dissolved phase. Repetitive rinsing (washing) of sediments reduced dissolved Cu concentrations by 60% and resulted in significantly greater D. magna survival compared to exposure to unwashed sediments. Once the majority of easily-mobilized metals had been removed, D. magna were exposed to filtered (0.45
m) and unfiltered overlying water. Removal of suspended particles by filtration did not significantly affect survival or tissue Cu concentration suggesting that the Cu that remained associated with the particles was not bioavailable. D. magna survival could be predicted by dissolved Cu concentration (r2=0.71, p=0.0001) but not by particle-associated Cu. The relationship between tissue Cu and dissolved Cu (r2=0.62, p=0.0003) was stronger than that between tissue Cu and particulate Cu (r2=0.27, p=0.04). The presence of sediment particles in the gut indicated that D. magna ingested sediment during the exposure. We found that D. magna exposed to metal-contaminated sediment will clear their gut of sediment particles when allowed to feed on algae for eight hours. Tissue Cu concentration, and thus Cu bioavailability would have been overestimated by 128% if gut contents were not purged at all or by 85% if D. magna were held in water alone to gut clear. These data indicate that although there is substantial metal associated with these sediments, the easily-mobilized portion is the main source of bioavailable metal, rather than metals that remain adsorbed to the particles. (Supported by CSME, USEPA)
Key words: Sediment toxicity, Metal bioavailability, Daphnia magna, Copper