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The toxic effect of hexavalent chromium on the growth rate of ten species of estuarine phytoplankton was examined in a defined growth medium. The concentration causing 50% inhibition of growth rate varied by a factor of more than 50 among the species. Three possible causes of interspecific variation in the sensitivity were examined: detoxification by extracellular reduction, interspecific differences in growth rate, and interspecific differences in chromium (VI) uptake. Results indicate that none of these hypotheses explains the interspecific variation in chromium sensitivity.
The chromium (VI) sensitivity of each algal species was also tested at two different sulfate concentrations. In every case, the toxicity of chromium (VI) was greater in the medium with lower sulfate concentrations. This confirms and extends previous results showing that chromate sensitivity in algae is closely correlated to the sulfate concentration of the growth medium.
algae, chromium, phytoplankton, toxicity testing, aquatic toxicology
Postdoctoral research associate, Academy of Natural Sciences, Benedict Estuarine Research Laboratory, Benedict, MD