Study On Bioaccumulation And Toxicity Assessment Of Copper To Juvenile Anodonta Woodiana

Copper（Cu）is one of the essential trace elements of organisms,which plays an irreplaceable role in enhancing immunity,promoting growth and development,and maintaining normal metabolism of organisms.Meanwhile,as a kind of heavy metal,it can cause serious toxic damage to aquatic animals when it accumulates in excess of a certain threshold.With the rapid development of China’s economy,the environmental pollution of heavy metal is gradually aggravated,and frequent industrial and agricultural activities lead to serious pollution of heavy metals in soil and water.At present,copper pollution has become the most serious heavy metal pollution in fishery environment.This is bound to be a serious threat to the safety of aquatic organisms and human health.Therefore,it is particularly important to study the bioaccumulation and toxicity-assessment of Cu by suitable indicators for freshwater fishery ecological environment in China.Anodonta woodiana（Mollusca:Bivalvia:Unionoida:Unionidae）,a mussel native to the Yangtze River and Heilongjiang Province of China,has become an invasive species widely distributed in almost all freshwater environments around the world.A.woodiana has the characteristics of small range of movement,high accumulation of heavy metals and low excretion rate,and therefore,it is very suitable for the monitoring and evaluation of heavy metal pollutants in water.The sensitivity to heavy metal toxicity of A.woodiana at different life cycle stages was significantly different,and juvenile mussels were more sensitive to heavy metal toxicity than adult mussels.In recent years,there have been many reports on the monitoring and evaluation of freshwater environment by this mussel as a biological indicator for"Freshwater Mussel Watch".The aim of this study was to screen target organs of juvenile A.woodiana for monitoring and evaluating Cu bioaccumulation from freshwater environment.In order to further improve the"Freshwater Mussel Watch"system,this study also hopes to provide scientific basis and technical support for the toxicity-assessment of Cu by juvenile A.woodiana as a model animal.The main results of this dissertation are as follows:In order to explore the toxic effects of Cu on the tissues of the gill,digestive gland,mantle and hatchet-shaped foot of juvenile A.woodiana the Cu concentration gradients were set at 2.0,1.0,0.1,0.01 and 0.005 mg/L in the present study,according to the corresponding values of 96 h-EC₅₀ and the Cu limit in China’s Fisheries Water Quality Standard（GB11607-89）.The water samples before and 24 h of exposure were taken respectively,and the Cu content in the water was determined by ICP-MS,and then the absorption efficiency and removal efficiency were calculated according to the formula.The results showed that the Cu absorption efficiency increased rapidly with the increase of exposure concentration,and the highest value was 0.69±0.11μg/g/h in 2.0 mg/L exposure group.The Cu removal efficiency showed a trend of decreasing first and then increasing,in which the removal efficiency of 0.005 mg/L exposure group was the highest,84.8%,and the removal efficiency of 1 mg/L exposure group was the lowest,28.9%.After the exposure,the gills,foot,mantle,digestive glands and other tissues of young mussels were dissection and removed respectively.After drying,the tissues were digested by microwave digestion,and the concentration of Cu in each tissue of young mussels was analyzed by ICP-MS.The results showed that the concentration of Cu in tissues of different exposed groups was significantly higher than that of control group.The concentration of Cu in the whole soft tissue increased with the increase of exposure concentration and the extension of exposure time.The maximum concentration of Cu in the mantle was 669.2μg/g.Gill and mantle were the most sensitive tissues,and the Cu content increased significantly at 24 h exposure,which was significantly higher than that of the foot and digestive glands,and then increased gradually with the extension of exposure time.The concentration of Cu in gill and mantle reached the maximum at 96and 72 h,respectively.At 96 h,the concentration of Cu was the highest in the digestive gland and the axopod,which were the potential target organs for Cu accumulation.This study provides a theoretical basis for the characteristics of heavy metal concentration in tissues of A.woodiana as an indicator organism for"Freshwater Mussel Watch",and provides technical support for the screening of biomarkers for monitoring and evaluating Cu pollution in freshwater environment.In addition,the gill,mantle,foot and digestive gland of the juvenile mussel were dissected and observed by histological section technique.The results showed that 0.005mg/L Cu did not cause obvious tissular damage.After 96 hours of exposure,the gills of the 0.01 mg/L exposed group began to have a significant increase in pigment cells and vacuolization of the cells.In the gills of the mussels exposed to 0.1 mg/L,macrophages began to increase and cilia fell off.In the group exposed to 2.0 mg/L,gill cell necrosis,filament atrophy,connective tissue erosion could be observed.Cell vacuolation and epithelial damage of the foot occurred in the mussels exposed to 1.0mg/L,and this effect obviously aggravated when exposed to 2.0 mg/L.Significant increase in pigment cells and macrophages of the mantle could be found for the mussels exposed to 0.01 mg/L,while the epithelial layer was damaged at the 2.0 mg/L.In addition,the digestive glands even presented tubular epithelial cell deformation,lymphatic area enlarged,and connective tissue atrophy at the level of 0.1 mg/L.The aforementioned results suggested that the gill was the most sensitive tissular of the mussel to tissular Cu toxicity,and could be used as a target tissue for Cu contamination monitoring and toxicity assessment of freshwater fishery ecological environment.