Study On The Toxic Effects Of Lindane And Chlorpyrifos To Freshwater Algae

Pesticides are becoming widely used in agricultural production. Organochlorine and organophosphorus pesticide are two principal kinds of pesticides. Their residual in environment may pose a serious threat to ecosystem security. Because organochlorine and organophosphorus pesticides can enter surface water and easy bioaccumulation, their toxicity to aquatic organism is important basis to establish the water quality standard and guideline for pesticide in water. The present water quality standard of China referred to the criteria and standard from USEPA. To study the toxicity of pesticide to national aquatic organism such as freshwater algae is significant to establish the water quality criteria and standard of China for protecting water environment of China.In this study, the toxic effects of lindane (organochlorine pesticide) and chlorpyrifos (organophosphorus pesticide) on three freshwater algae (Microcystis aeruginosa, Chlorella vulgaris and Cyclotella meneghiniana) were investigated by algal growth inhibition test under laboratory-cultured conditions. The results are sa follows:The 96 h-50% of effect concentration (EC50), the lowest observed effect concentration (LOEC), no observed effect concentration (NOEC) and the maximum acceptable toxicant concentrations (MATC) for the toxicities of lindane to M. aeruginosa are 442,120,60 and 85 μg/L, respectively. The concentration of EC50, LOEC, NOEC and MATC for the toxicities of lindane to C. vulgaris are 524,128,61,88μg/L, respectively, and their toxicities data for C. meneghiniana are 11849, 1295,406 and 725 jig/L, respectively. The concentration of EC50, LOEC, NOEC and MATC for the toxicities of chlorpyrifos to M. aeruginosa are 2720,1026,615 and 794 μg/L, respectively, their toxicities data are 5374,1978,1172 and 1522 μg/L, respectively for C. vulgaris and 11109, 2792,1355 and 1945 μg/L, respectively for C. meneghiniana.With increasing concentrations of lindane, the growth inhibition of three algae M. aeruginosa, C. vulgaris and C. meneghiniana significantly increased but the protein contents and the activities of SOD significantly decreased. However, the MDA contents increased insignificantly. While at low concentrations of chlorpyrifos, the protein contents and the activities of SOD have slightly increased, but with the increase of the concentrations of chlorpyrifos, the protein contents and the activities of SOD decreased and the MDA contents increased. The results showed that toxicities of lindane to freshwater algae were higher than that of chlorpyrifos.When the initial algae cell population was 2.0 x 104 cells/mL, and the concentration of lindane was 400 μg/L, the BCF values of M. aeruginosa, C. vulgaris and C. meneghiniana to lindane were 340,350 and 10, respectively, and when the initial concentrations of chlorpyrifos were 1500 μg/L and 3000 μg/L, the BCF values of M. aeruginosa were 400 and 580.The EC50 did increase with an increase of pH, this result implies weak alkaline conditions could reduce the toxicity of lindane and chlorpyrifos to M. aeruginosa. Hydrolysis was also an important mechanism in the abiotic transformation of lindane and chlorpyrifos. The toxic effects of the two pesticides on M. aeruginosa decreased dramatically with increasing concentrations of HA, DOM has been reported to decrease the bioconcentration of organic chemicals in aquatic animals. These decreases in bioconcentration have been attributed to DOM interactions with chemicals.The cell surface hydrophobicity of M. aeruginosa increased with the increasing concentrations of lindane, the algal cells were more easily to contact with the substrate, thereby increasing the affinity between the algal cells and lindane. While exposed to chlorpyrifos the cell surface hydrophobicity of M. aeruginosa increased in lower concentration and then decreased in higher concentration. The cell hydrophobicity exposure of 5000 μg/L of chlorpyrifos was lower than the control, because the majority of dead cells occurred and resulted in the damage of cell wall. The zeta potential of M. aeruginosa decreased with the increasing concentrations of lindane and chlorpyrifos. More negative charge in the cell surface might increase the electrostatic repulsion and reduce affinity with pesticide. Moreover, the negative charge in cell surface could inhibit the absorption of anions nutrients and the growth of algal cells. The ultrastructural observations of M.aeruginosa by TEM indicated the toxic effects of of lindane and chlorpyrifos, and the destruction of the structure of algal cells.