Selenate bioaccumulation and toxicity in Chlamydomonas reinhardtii: Influence of ambient sulphate ion concentration

The aim of the present study was to investigate selenate toxicity in the unicellular green algae Chlamydomonas reinhardtii as a function of sulphate ion concentration and the relationship with intracellular bioaccumulation. The toxicity of selenate was evaluated by measuring the effect of different selenate concentrations on algal growth during a 96 h exposure period. A non-linear regression according to the Hill model was used to describe the dose–effect relationship and estimate the effect concentrations (EC) of selenate. EC50 values of 0.40 [0.24–0.52] μmol L−1 and of 3.10 [1.65–4.86] μmol L−1 of ambient selenate were obtained, at 8 and 80 μmol L−1 of sulphate ions in the medium, respectively. For non-toxic and low-level ambient selenate concentrations, bioaccumulation in presence of 80 μmol L−1 was one tenth that of 8 μmol L−1 of sulphate ions. When expressed as intracellular selenium burden, EC50 values determined at 8 and 80 μmol L−1 of sulphate ions were not significantly different (126 and 67 nmol Se·109 cells−1, respectively). In conclusion, toxicity appeared to be correlated to selenate bioaccumulation which suggests that toxicity must be linked to intracellular selenium accumulation that is directly dependent on ambient sulphate ions that may compete with selenate for transport sites.