| Chlorella vulgaris was grown in the presence of environmentally-realistic concentrations of arsenic and chromium, 10--50 microg/L, to better understand the role that freshwater algae play in the speciation of these elements in surface waters. Arsenic (As) and chromium (Cr) in the culture medium and in algal cells was determined using AEC-ICP-MS and ICP-DRC-MS. Cultures were exposed to arsenate [As(V)], at 10 microg/L and multiple phosphorus (as phosphate) concentrations to test the effect of the macronutrient phosphorus on arsenic biotransformation. Evidence is presented for the competition between arsenate and phosphate for uptake by Chlorella vulgaris and of two scenarios of arsenic biotransformation. At low As-uptake the algal cells excreted predominantly methylated species while at high As-uptake the cells predominantly excreted arsenite, at much higher concentrations than the methylated form. Cultures were also completed with chromate and Chlorella vulgaris, and the algal cells reduced significant portions of chromate [Cr(VI)]. Toxicity in the form of reduced growth was found with Cr(VI) and As(III) but not in cultures of As(V) and DMAs(V). These results help explain the observations seen in freshwater systems of arsenic and chromium speciation.;Keywords: Arsenic, Chromium, Freshwater systems, Metabolism, Chlorella vulgaris, Speciation, Accumulation, Biotransformation, Ecotoxicity... |
