Study On Impacts Of Compound Pollution Of PFOA And Ni To Enzyme Activities In Earthworms

Perfluorinated compounds(PFCs)are broad range of perfluorinated organic compounds which hydrogen atoms are completely substituted by fluorine atoms.PFCs are being used as surfactants in various industry sectors due to their unique chemical properties,such as high chemical stability,extremely low surface tension and lipophilic characteristics.Toxicological studies have focused on the toxicity of PFOA which has hepatotoxicity,embryo toxicity,reproductive toxicity,neurotoxicity and carcinogenicity.PFOA interfere with endocrine,change the instinctive behavior of animals,especially for infants,which may has potential development neurotoxicity.Nickel is a natural metal element.Trace amounts of nickel can stimulate biological growth and excessive nickel will change the cell structure and physiological processes,hinder biological growth and development.Recently,despite much effort directed to PFOA in soil and its impacts on the ecology,but the relationship between the damage of the antioxidant enzymatic system of E.fetida and PFOA-polluted soils and PFOA and heavy metal combined pollution in earthworms remains unknown.In this paper,we investigated effects of PFOA exposure and PFOA and heavy metal Ni combined pollution on the physiological indexes of earthworms,which were used by the OECD artificial soil method under standard laboratory conditions,which provide a strong basis for organic pollutant and heavy metals combined pollution of soil ecological risk assessment and early warning.The main test conclusions are as follows:(1)The effect of PFOA on activities of SOD in earthworms showed a tendency of stimulate first and inhibit latter.The activity of SOD was significantly increased at 14 days after exposure.The activity of SOD was significantly decreased after 21-28 days exposure.SOD activity decreased which indicated that the earthworm antioxidant system can’t tolerate excess ROS produced by PFOA stress,and excessive ROS lead to cell dysfunction in earthworms.CAT and POD activity were consistent,PFOA exposure increased significantly after 14-21 days and decreased after 28 days of exposure.GST activity was significantly increased after 14-28 days of exposure.The contents of MDA in earthworms increased significantly after 28 days of exposure,and reached the highest level in 40 mg/kg treatment group.This suggests that with increased PFOA dose and exposure times,the antioxidant enzymes cannot cope with the excessive free radicals,leading to lipid peroxidation and increased MDA contents.(2)At the early stage of exposure,the effect of PFOA and Ni combined pollution on the antioxidant enzyme system(SOD,POD,CAT)in earthworms was synergistic,and then showed slight antagonistic effect.This suggests that with added Ni,the toxicity of PFOA to antioxidant enzymes in earthworms were reduced.The contents of MDA in low concentration of PFOA(5,10 mg/kg)combined pollution groups were synergistic compared with the single groups,in high concentration of PFOA(20,40 mg/kg)combined pollution groups showed antagonistic effects.During the whole exposure time,MDA content in the combined pollution group showed an increasing trend with increased PFOA dose and exposure times.