Early Toxic Effects of Cd2+ on Photosynthetic Activity of Six Freshwater Algae Species

Cd2+ is a serious environmental pollutant. Previous studies have investigated the effects of Cd2+ on animals, plants and algae. However, the tested concentrations were generally higher than the actual environment level. The present study determined the effects of low concentrations of Cd2+ (0.05 to 0.20 mg/L) on the chlorophyll fluorescent parameters of six local algae species in order to investigate the early toxicity of Cd2+. The results showed that treatments with up to 0.20 mg/L Cd2+ did not significantly affect population growth rate of S. quadricauda, C. pyrenoidosa, S. obliquus, N. palea, S. minutum and S. acutus. Treatments with 0.05-0.20 mg/L Cd2+ significantly increased F-v/F-m in N. palea and S. minutum and decreased F-v/F-m in S. obliquus and S. acutus, but did not significantly affect F-v/F-m in C. pyrenoidosa. When exposed to Cd2+, rETR(max) was reduced in S. obliquus, C. pyrenoidosa, S. acutus and S. quadricauda, but was elevated in N. palea and S. minutum. Overall, trace Cd2+ still revealed early toxicity to green algae. N. palea, S. minutum and C. pyrenoidosa were more tolerant to Cd2+ than S. obliquus, S. acutus and S. quadricauda.