Heavy Metal Toxicity and Algal Bioassays

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Abstract
Algal bioassays for heavy metals can detect low levels in the environment, for example, 0.01 ppm for silver. Algae respond to increasing levels of heavy metals such as copper, nickel, mercury, silver, or cadmium by reduction of growth rate. Occasionally, the response to nontoxic metals is an increase in growth rate. At very low concentrations some potentially toxic metals may be necessary micronutrients. Algal species differ quite markedly in their sensitivity to heavy metals. Combined effects of two or more metals at toxic concentrations may be synergistic (for example, copper-nickel) or antagonistic (for example, cadmium-selenium). The critical concentrations for toxicity of a particular metal may be different at different times during the growth of an algal culture, as well as being dependent upon other chemical and physical conditions. Algal cells appear to markedly concentrate metals from solution, even at concentrations of these metals in the medium which do not apparently inhibit cell division. Bioassays provide the only direct method for assessing the biological availability of metals in solution. Algae isolated from metal-polluted lakes appear to have evolved specific metal tolerances. These “tolerant” algae actually accumulate more of the metals concerned than do their “nontolerant” relatives. Correlations between fish toxicity tests and algal bioassays may allow the relatively expensive fish testing schemes to be replaced by simple and cheaper algal bioassays.