Effects of Cd2+ and Pb2+ on Growth and Photosynthesis of Two Freshwater Algae Species

Microalgae are biological indicators of heavy metal pollution. Cadmium (Cd) and lead (Pb) are extremely toxic metals to aquatic organisms. In the present study, single and combined toxicity of Cd2+ and Pb2+ to Scenedesmus acutus and Schroederia sp. collected from the famous Xin'an River (Huangshan City) were evaluated. Treatments with 0.5-2.0 mg/L Cd2+ significantly reduced S. acutus population growth, and treatment with 2.0 mg/L Cd(2+ )significantly decreased Schroederia sp. population growth rate, suggesting a higher tolerance of Schroederia sp. than S. acutus to Cd2+ pollution. In addition, Cd2+ treatments significantly decreased chlorophyll a, carotene contents, and photosynthetic fluorescent parameters rETR(max) and I-k, demonstrating that the harms on photosynthesis might be the underlying mechanism of Cd2+ toxicity to algae. Treatments with 5.0-15.0 mg/L Pb2+ did not significantly affected population growth and photosynthetic pigment content. However, combined exposure to Cd2+ and Pb2+ revealed antagonistic effects on both species. Overall, these results provide basic information to the ecological risk assessments of heavy metal pollution in the Xin'an River Basin.