Sub-Lethal Effects of Copper on Salmonids: An Avoidance Evaluation Using a Direct Test Method.

Avoidance of copper (Cu) by rainbow trout (Oncorhynchus mykiss) was evaluated using a Y-maze exposure system, with data collected over a 1-h exposure period using a digital camcorder. In exposures to five measured concentrations of dissolved copper (<0.3, 1.2, 9.8, 48.3, and 98.6 µg Cu/L), plus control, significant avoidance behavior (p < 0.05) relative to the control was observed at ≥9.8 µg Cu/L, but not at 1.2 µg Cu/L. The chronic value (i.e., geometric mean of these concentrations) was 3.43 µg Cu/L. Estimates of EC50 values for avoidance of Cu ranged from 4.81 to 9.15 µg Cu/L over four 15-min time intervals of exposure to the metal. Based on water quality characterization of the control/diluent water, the U.S. Environmental Protection Agency (USEPA) water hardness- and biotic ligand model (BLM)-based chronic criteria for dissolved Cu were 8.03 and 2.26 µg Cu/L, respectively. This study suggested that enforcement of the BLM-based criterion would provide a higher level of protection of trout for this sensitive response than the hardness-based criterion.

Survival and Growth of the Marine Polychaete, Neanthes arenaceodentata, Following Laboratory Exposure to Copper-Spiked Sediment.

Juvenile marine polychaetes, Neanthes arenaceodentata, were exposed for 28 days to copper (Cu)-spiked sediment at six concentrations ranging from 48.3 to 2380 mg Cu/kg dry sediment, plus control. Survival was reduced (p ≤ 0.05) at concentrations ≥1190 mg Cu/kg. Growth was inhibited at Cu concentrations ≥506 mg Cu/kg. Dose-response relationships yielded LC10 and LC50 estimates of 514 and 1230 mg Cu/kg, respectively. The growth effect EC50 estimate was 409 mg Cu/kg. Ranges for the no observable effect concentration and lowest observable effect concentration were 506-1190 mg Cu/kg for survival, and 230-506 mg Cu/kg for growth. Pore water concentrations of Cu were 38.7-65.8 µg Cu/L in exposures where toxic effects were observed, compared to a range of 15.1-22.4 µg Cu/L in exposures where significant effects were not evident. The results of the study were compared with empirical and mechanistic sediment quality guidelines for the protection of benthic organisms.

Survival, Reproduction and Growth of the Marine Amphipod, Leptocheirus plumulosus, Following Laboratory Exposure to Copper-Spiked Sediment.

Leptocheirus plumulosus was exposed for 28 days to Cu-spiked sediment at mean concentrations ranging from 44.4 to 605 mg Cu/kg dry sediment in a sediment/water test system designed to simulate natural conditions. The NOEC (no observed effect concentration)-LOEC (lowest observed effect concentration) range for the most sensitive endpoint of growth was 199-414 mg Cu/kg sediment. An IC50 for reproduction was estimated at 187 mg Cu/kg sediment. Mean Cu concentrations in pore water (PW) where significant effects were observed were 25.8 and 59.0 µg/L, while their respective concentrations in overlying water (OW) were 22.1 and 28.0 µg Cu/L. Copper concentrations were ≤19.1 and <16.6 µg/L in PW and OW, respectively, at lower exposures where effects were not evident. Concentrations of Cu in marine sediment lower than sediment quality guidelines based on geochemical factors of acid volatile sulfide, organic carbon content (f OC), and sediment grain size (i.e., silt + clay) would appear not to result in adverse effects toward L. plumulosus.

Toxicity of silver in water and sediment to the freshwater amphipod Hyalella azteca.

Hyalella azteca was exposed to Ag as AgNO3 over a 10-d period in water and two lake sediments that were selected on the basis of their differences in metal-binding properties. The median lethal concentrations (LC50s) for waterborne exposures were 5.4 and 4.9 microg/L for total and dissolved Ag, respectively. In the sediment containing a lesser quantity of total Ag-binding ligands (i.e., Bond Lake, Douglas County, WI, USA, sediment), an Ag-amended sediment toxicity test resulted in a 10-d LC50 of 0.084 g (i.e., 84,000 microg) Ag/kg dry sediment or 8.6 microg Ag/L of pore water (PW). The no-observed-effect concentration (NOEC) to lowest-observed-effect concentration (LOEC) range was 0.012 to 0.031 g Ag/kg dry sediment, or less than 5.0 to 6.0 microg Ag/L of PW. In the sediment with a greater quantity of total Ag-binding ligands (i.e., West Bearskin Lake, Cook County, MN, USA, sediment), the 10-d LC50 was 2.98 g Ag/kg dry sediment, and the NOEC to LOEC range was 2.15 to 4.31 g Ag/kg dry sediment. Because "dissolved" concentrations of Ag in PW were less than 5.0 microg/L at the critical exposures in the latter test, the bioavailable and toxic form of Ag may have been a weakly associated coprecipitate or colloidal complex with hydrous iron oxides that competitively partitioned to the surface of the gills.