Comparative sub-lethal and lethal acute toxicity of copper to the freshwater crayfish, Cambarus robustus (Cambaridae, Decapoda, Crustacea) from an acidic metal-contaminated lake and a circumneutral uncontaminated stream

Comparative toxicological responses to Cu concentrations ranging from 0.61 to 24.06 mg 1−1 by Cambarus robustus (Girard) intermoult adult males, trapped from Wavy Lake, an acid-stressed (pH 4.6) metal-contaminated freshwater reservoir near Sudbury, Ontario [Cu, Ni, Pb and Cd body burden in whole crayfish (mean x ± SD) 89.94 ± 30.69, 2.60 ± 2.07, 42.82 ± 8.08, 4.08 ± 0.60 μg g−1 dry wt] and Pike Creek, a circumneutral (pH 6.2) uncontaminated fast-flowing stream [Cu, Ni, Pb and Cd body burden in whole crayfish (mean x ± SD) 43.68 ± 24.98, 1.76 ± 1.42, 13.53 ± 8.52, 11.40 ± 0.91 μg g−1 dry wt, respectively] in northeastern Ontario, were quantified using replicate standard 96-h static acute toxicity tests. In EC50 comparisons, crayfish from the contaminated Wavy Lake were significantly more tolerant to all Cu concentrations during 24-h exposures than were those from Pike Creek; no significant differences (P > 0.05) in the response between the two populations were observed with increases in exposure periods beyond 24 h. In LC50 comparisons, Pike Creek crayfish had a significantly lower mortality rate in 48-h exposure than did decapods from Wavy Lake; no significant differences (P > 0.05) in the response between the two populations were observed with increases in exposure periods beyond 48 h. The two populations, on the whole, did not show significant differences in their EC50-LC50 values at various periods they were exposed to the toxicant. However, there were significant differences (P < 0.05) in Cu concentrations that caused behavioural impairment and mortality in animals from the two sites. In general, individuals from the contaminated Wavy Lake were better suited to resist short-term (≤ 24 h) behavioural impairment than were crayfish from the uncontaminated Pike Creek, possibly because of the ability of the former to detoxify Cu at a comparatively quicker rate than the latter. However, once their behaviour was impaired, the crayfish from the contaminated lake were unable to withstand further Cu intake. The reason for the phenomenon may lie in the early saturation and subsequent failure of their copper regulatory mechanism because of comparatively high Cu body burdens associated with living in a metal-contaminated environment.