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PW08 Aquatic Ecotoxicology II
(PW106) Effects of hardness on the toxicity of zinc, cadmium and aluminum to Selenastrum capricornutum.
Condon, C1, Elphick, J2, 1 EVS Environment Consultants, North Vancouver, BC, Canada2 Nautilus Environmental, Tacoma, WA, USA
ABSTRACT- Zinc, cadmium, and aluminum were each evaluated for toxicity to the freshwater alga Selenastrum capricornutum under a range of hardnesses from 10 to 90 mg/L as CaCO3. Tests were conducted in microwell plates for 72 hours according to Environment Canada Guidelines. Consistent with widely published observations and the basis for the US EPA water quality guideline for this metal, cadmium toxicity decreased with increasing hardness. Conversely, zinc toxicity did not decrease in response to increases in water hardness within the range of hardnesses tested. This finding is unusual, and implies that toxicity of zinc to S. capricornutum is different mechanistically from that observed with most other aquatic organisms. Aluminum did not exhibit a substantial change in toxicity under different hardness regimes. Effects data for cadmium and aluminum occurred well above US EPA criteria values; however, effects associated with zinc fell below the criteria values at some hardnesses. This suggests that, within the range of hardnesses tested, US EPA criteria values are sufficient to protect S. capricornutum from toxicity caused by cadmium and aluminum, but not zinc. Interestingly, low concentrations of both cadmium and aluminum appear to exhibit a hormetic effect on cell growth. Since neither of these metals are essential nutrients for this species, the reason for this observation is unclear.
Key words: Selenastrum capricornutum, metals, hardness, hormesis
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