ARSENATE SENSITIVITY IN MARINE PERIPHYTON COMMUNITIES ESTABLISHED UNDER VARIOUS NUTRIENT REGIMES

Arsenate sensitivity to carbon dioxide fixation was measured in marine periphyton communities established under different nutrient regimes in flow-through aquaria. An increase of the phosphate concentration in the incubation media from 0.1 to 0.8 μM did not cause any immediate changes in sensitivity to arsenate. However, after 72 h of phosphate enrichment, sensitivity to arsenate had decreased > 3000-fold (EC20 values increased from 0.3 μM to > 1 mM). Decreases in sensitivity to arsenate were also seen during natural and simulated upwelling episodes when both the phosphate and nitrate concentrations increased. The sensitivity to arsenate correlated with the phosphorus status of the communities, measured either as total phosphorus or surplus phosphorus, but not with their nitrogen or chlorophyll contents. The role of internal or external competition between arsenate and phosphate is discussed in relation to possible mechanisms for the phosphate-dependent tolerance. The key role of nutrient prehistory in modifying periphyton sensitivity to arsenate is stressed. The time of the year and current nutrient situation will affect the phosphorus status of the algae, and should therefore be considered, both when performing toxicity tests and when making hazard assessments for arsenate. © 1990.