Prediction of permissible concentrations of copper from microcosm toxicity tests

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Abstract
Microcosm toxicity tests using naturally derived protozoan communities were used to estimate permissible concentrations of copper. In tests with copper sulfate, taxonomic richness of communities was adversely affected at concentrations ≧12.7 μg/L after 21 days. Colonization was also affected at ≧12.7 μg Cu/L. Concentrations affecting taxonomic composition, chlorophyll and biomass concentrations, and nutrient retention ranged from ≦6.6 to ≧59.5 μg Cu/L. A Cu concentration expected to affect only 5% of taxa (EC05) adversely was predicted from test data as 3.2 (1.6–4.8) μg Cu/L. A similar estimate of a 5% effect level based on single‐species chronic toxicity test data was 4.9 (2.2ndash;7.1) μg Cu/L. Results of a test with combined effluents containing Cu were similar, with differences in colonization apparent at ≧18.0 μg Cu/L. Reductions in individual populations were apparent at 8.7 μg Cu/L. Estimates of permissible concentrations derived from these tests were reasonable when compared to the revised numerical water quality criteria (8.2 μg Cu/L at a hardness of 65 ppm). In addition, they fell above selected literature reports of Cu levels in clean systems (23 μg/L), thus seeming to be a reasonable basis for management decisions.