The growth response of the green algaChlorella vulgaris to combined divalent cation exposure

Abstract
Using the growth response of the green algaChlorella vulgaris as a model system, the effects of combinations of the environmentally active cations Cd, Co, and Cu were evaluated. The 96-h static EC50 for these cations toC. vulgaris were, respectively, 0.89 μM, 9.0 μM, and 2.8 μM, yielding a toxicity series such that Cd>Cu>Co. The cation combinations of Cd+Cu, and Cu+Co acted synergistically, while Cd + Co, and the tri-metallic combination Cd + Cu + Co resulted in antagonistic interactions. Examination of these toxic combinations at 24, 48, 72, and 96 h indicate that the cellular response is not a uniform one. Failure of energy dispersive X-ray spectrophotometric analysis to demonstrate any intracellular incorporation of these cations (except for a weak cytoplasmic Cu peak at the 8.0 KEV position) suggests that the toxic actions of these cations at EC50 concentrations are exerted at the level of the plasma membrane.

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