Sorption of Arsenic and Cadmium and Their Effects on Growth, Micronutrient Utilization, and Photosynthetic Pigment Composition of Asterionella formosa

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Abstract
By continuous-culture techniques, populations of the freshwater diatom A. formosa were exposed to various concentrations of As or Cd for periods of 6-23 days. Sorption of As (as arsenate) was a linear function of ambient concentrations < 130 .mu.g As/l, but reached an apparent plateau at ambient values > 130 .mu.g As/l. Cd sorption was a complex function of ambient concentration and time. Cellular As and Cd was desorbed in some experiments, and there appeared to be an active regulatory mechanism that kept the cellular As content at a nontoxic level. For As no detrimental effects on growth or micronutrient utilization were observed over the range of ambient concentrations used (< 160 .mu.g As/l). For Cd an ambient concentration of .apprx. 2 .mu.g Cd/l reduced the population growth rate by an order of magnitude; populations exposed to > 10 .mu.g Cd/l ceased growth and micronutrient utilization in 20-30 h. Fractionation experiments suggest that a large proportion of the cellular As was associated with the organic layer surrounding the frustule; most of the cellular Cd was associated with the cell contents.