Respondence And Degradation Of Three Marine Filter Feeders To Organophosphorus Pesticides

The effects of two widely used organophosphate insecticides (methamidophos and omethoate) on metabolic parametes (oxygen consumption rate, ammonia excretion rate and filtration rates) and metabolic enzymes (Na+-K+-ATPase and alkaline phosphatase) as well as antioxidant enzymes of three marine filter feeders Mactra chinensis, Mylitus edulis and Styela clava are studied in semi-static water system. The purpose is to discuss the toxic response of marine animals, as well as the detoxification mechanism under methamidophos and omethoate stess.When the concentrations of methamidophos and omethoate in sea water are higher than 50μgL-1, the O:N ratios of the three marine animals decline obviously. The O:N ratios decrease with the extension of time and concentration of pesticide exposure, and are below 30 when the concentrations exceed 100μgL-1, which suggests a dominance of protein used in the metabolism of the three animals.When M. chinensis and M. edulis are exposed to the methamidophos and omethoate of 1ugL-1 and 10μgL-1, their filtration rates decrease at the beginning 24 h, and then increase during 24-48 h, which indicates certain tolerance of methamidophos and omethoate. When the concentrations of methamidophos and omethoate are over 50μgL-1, the filtration rates of M. chinensis and M. edulis drop rapidly. When S. clava is exposed to organophosphate insecticides, its filtration rates drop to the lowest point in 24 hours and remain unchanged. In general, the filtration rates of the three animals decline with the increase of the concentration of two pesticides.As the inhibitors of acetylcholinesterase, the two insecticides reduce the activities of acetylcholinesterase of M. chinensis and S.clava by 7-96% with the time and doses. At the concentrations of 1μgL-1 and 10μgL-1, the acetylcholinesterase of M. edulis shows a tendency to increase after the first decline.The SOD activities in M. edulis and S. clava exposed to methamidophos and omethoate (1μgL-1 and 10μgL-1) increase to the maximum at 48 h which are higher than the control by 34 %-51%, which indicates that M. edulis and S. clava could activate the compounds in REDOX cycle and show the ability to resist oxidative stress. When M. chinensis, M. edulis and S. clava are exposed to higher concentrations of methamidophos and omethoate, the SOD activities decline and are lower than the control. This shows that the three marine animals have the ability of oxidation resistance and tolerance to the two pesticides.The peroxidase activities of M. chinensis and S. clava increased to the maximum at 24 h and 12 h, respectively, which indicated the induction of organophosphate pesticides on the peroxidase. The activity of peroxidase in M. edulis decrease to the lowest point at 24 h then increase slowly to the control at 96h.Polyphenol oxidase activities of three marine animals increase gradually with the extension of exposure time, and reach the highest at 48 h, and then remain about the same levels.Exposed to low concentrations (1μgL-1 and 10μgL-1) of the two pecticides, all the acitivities of glutamic-pyruvic transaminase(GPT) inM. chinensis, M. edulis and S. clava are increased. After 36 h exposure, the GPT of M. edulis and S. clava decline obviously indicating the degenerate of hepatopancreases of two animals. After 72 h exposure the GPT of the three animals increase gradually, indicating the regeneration of liver cell.When the concentrations of methamidophos and omethoate are below 50μgL-1, the activities of alkaline phosphatase (APT) of the three marine animals are promoted. When the concentrations are over 100μgL-1, all the APT activities drop in the three organisms.At the concentration of 1μgL-1, Na+-K+-adenosine triphosphatase (ATP) activities of the three animals increase quickly. The ATP activities decline with the exposure time at the concentrations over 50μgL-1 which reflect the osmotic adjustment based on ion is interferred seriously.It was found that M. chinensis, M. edulis and S. clava can degradate the methamidophos and omethoate, the degradation rate is 7-12% in 24-48 h and then decreases to 1-3%. The biological accumulation coefficient of methamidophos and omethoate in the three animals is 76-98, and the values show positively correlated with fat content and negatively with the nominal concentration of pescticides in sea water.