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

Abstract

By use of continuous-culture techniques, populations of the freshwater diatom Asterionella formosa were exposed to various concentrations of arsenic or cadmium for periods of 6–23 days. Sorption of arsenic (as arsenate) was a linear function of ambient concentrations < 130 μg As∙L−1 but reached an apparent plateau at ambient values > 130 μg As∙L−1. In contrast, cadmium sorption was a complex function of ambient concentration and time. Cellular arsenic and cadmium was desorbed in some of the experiments, and there appeared to be an active regulatory mechanism that kept the cellular arsenic content at a nontoxic level. For arsenic, no detrimental effects on growth or on micronutrient utilization were observed over the range of ambient concentrations used (< 160 μg As∙L−1). For cadmium, however, an ambient concentration of ~2 μg Cd∙L−1 reduced the population growth rate by an order of magnitude, while populations exposed to > 10 μg Cd∙L−1 ceased growth and micronutrient utilization in 20–30 h. Fractionation experiments suggest that a large proportion of the cellular arsenic was associated with the organic layer surrounding the frustule, while most of the cellular cadmium was associated with the cell contents. Key words: arsenic, cadmium, toxicity, sorption, diatom, Asterionella formosa