John Wiley & Sons, Ltd.

Cadmium accumulation and toxicity in the unicellular alga Pseudokirchneriella subcapitata: Influence of metal‐binding exudates and exposure time

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Predicting metal availability and toxicity for chronic (several hours or days) metal exposure scenarios, even for unicellular algae, is a major challenge to existing toxicity models. This is because several factors affecting metal uptake/toxicity, such as the release of metalbinding exudates, changes in the kinetics of metal uptake/toxicity over time and algal physiological acclimation to internalized metals, are still poorly understood. The present study assessed the influence of these factors on Cd uptake and toxicity in laboratory batch cultures of the freshwater alga, Pseudokircheneriella subcapitata. To do so, changes in the free Cd2+ concentrations due to the release of metal‐binding algal exudates were monitored, 109Cd accumulation in algal cells was measured and Cd‐ induced inhibition of algal growth as a function of exposure time (from 12 to 96 h) was followed. Our results indicate that metal‐binding exudates may decrease the proportion of the free Cd2+ ion in solution up to twofold, a decrease that affect Cd uptake and toxicity. Pseudokirchneriella subcapitata has the capacity to decrease net Cd uptake rate on short‐time scales (< 24 h), but this reduction in the Cd uptake rate disappeared after 24 h and Cd toxicity occurred at relatively high Cd concentrations in solution. These data illustrate some of the pitfalls of standard algal toxicity assays, which were designed for short‐term exposures, and suggest how robust chronic bioassays might be developed. This article is protected by copyright. All rights reserved

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