Chronic toxicity of zinc sulphate in Procambarus clarkii

Abstract

We evaluated the chronic toxicity of zinc sulphate in the crayfish Procambarus clarkii.Mature P.clarkii were exposed to 0,0.40,4.04,or 40.37 mg/L Zn2+ for 21 days.Each day,we randomly selected five crayfish in each group and collected samples of the hepatopancreas,gill,and muscle tissue from males and females and ovar-ian tissue from each female.The tissues were placed in Bouin's fixative for 24 h,sectioned in paraffin,and stained using H?E.We observed a number of brick red particles in the cytoplasm of cells from the hepatopancreas and antennal gland in animals exposed to Zn2+.The number of these particles was positively correlated with the con-centration of Zn2+ and exposure time.There was no obvious histopathology in the group exposed to 0.40 mg/L Zn2+.We observed bleeding and necrosis in hepatopancreas,antennal gland,and gills in the group exposed to 4.04 mg/L after 7 d.The proportion of necrotic cells increased as the concentration of Zn2+ and time of exposure in-creased.We observed spermatocyte necrosis after 14 d in exposure to 40.37 mg/L Zn2+.After 21 d,we observed bleeding of the spermary and ovary and necrosis of the ootid and spermatocyte cells.A large number of hepato-cytes exhibited necrosis and had dropped from the hepatic ducts.The connective tissue exhibited hyperplasia,with large numbers of cells blocking the hepatic ducts,resulting in macroscopical bulky grains in the hapatopancreas of the group exposed to 40.37 mg/L.Our results suggest that exposure to 4.04 mg/L Zn2+ for 21 d causes pathological changes in the hepatopancreas,antennal gland,gills,and gonad tissue of P.clarkii.Given that zinc sulphate inter-feres with the metabolic,respiratory,and reproductive systems,chronic exposure is likely to threaten the survival of P.clarkii populations.