Study On Speciation Characteristics And Risk Assessment Of As In Dongping Lake

Dongping Lake,as the second largest freshwater lake in Shandong Province,is the last stage of the east line of the“South-to-North Water Deliver project”,also bear the important function of the water source of“West-to-East Water Deliver project”in Shandong province.It plays an important role in supply water,aquatic products,maintaining an ecological balance,and tourism.Heavy metal pollution and ecological environment in this area has attracted a lot of attention of many researchers in recent years.This paper dealt with Dongping Lake water body as the research subject,and indoor analysed based on field surveys and sampling.The contents of total arsenic（As）and speciation of arsenic in the overlying water-sediment-aquatic products were analyzed and determined,and the occurrence characteristics of arsenic in the water ecosystem of Dongping Lake were discussed,and comprehensively and systematically evaluated the environmental and ecological risks of arsenic in Dongping Lake waters.Furthermore,the effects of changes in the environmental conditions of the water body and the input of exogenous substances on the release of arsenic in the sediment were studied by designing ifnoldlooowr i nsig:mulation experiments.Based on the research above,the main conclusions as（1）The average concentration of total arsenic in the overlying water was 1.97±0.51μg·L^-1,which was spatially described as higher in the north and lower in the south,and the Laohu Wharf had the highest concentration.From the speciation characteristics,the dissolved arsenic content was higher than the granular arsenic content,with the highest As（Ⅴ）content and the lowest As（Ⅲ）content.The evaluation results show that the health risk level of arsenic in overlying water was within an acceptable range.（2）The average content of total arsenic in the sediment was 15.82±2.59 mg·kg^-1,which was spatially described as the highest value in the Laohu Wharf and the lowest value in the Dawen River and lake entrance.The content decreased vertically with increasing depth,and the highest value was in the sub-surface layer.Pollution evaluation results showed that the arsenic in the sediments was basically a slightly enriched,slightly ecologically harmful degree,and the potential harm was small.（3）From the valence characteristics of arsenic in the sediment,As（Ⅴ）was significantly higher than As（Ⅲ）in the surface and columnar sediments,and organic arsenic was not detected.At the level,the highest As（Ⅴ）was in the Laohu Wharf and the lowest in the Southwest Lake District;the highest As（Ⅲ）was in the middle of the Lake District and the lowest at the Dawen River and lake entrance.Vertically,the highest value of As（Ⅴ）appeared in the surface layer or sub-surface layer,and the lowest value appeared in the bottom layer.The variation of As（Ⅲ）was not obvious vertically,the lowest value was mostly at the bottom.From the fractionation distribution of the sediments,arsenic mainly existed in residual fraction,and the arsenic content in different extract states mostly fluctuates reduced as the depth increases.The morphological evaluation of arsenic pollution showed that the arsenic pollution in the sediment was relatively low,and the direct harm to the environment and the potential risk were relatively small.（4）The total arsenic content in aquatic products was as follows:shellfish>fish>shrimp,and the inorganic arsenic content was as follows:shellfish>shrimp>fish.Fish and shrimp in September were not detected in organic arsenic.The evaluation results showed that the health risk level of total arsenic in aquatic products was within an acceptable range,and the pollution level of shellfish inorganic arsenic was the most serious.Residents should appropriately reduce the intake of shellfish aquatic products.（5）Changed the environmental conditions of water bodies would affect the release of arsenic from sediments.The amount of arsenic released from the sediment increased with the increase of the Potamogeton crispus biomass,and showed a decreasing and rising and decreasing trend with the increase of time.Under different hydrodynamic conditions,the release amount of sediment in both areas turned into an increase with the disturbance velocity decrease.And with the increase of time,the release amount of the low-speed and medium-speed groups were increased in the first 1 h and then fluctuated and decreased,while the high-speed group was increased slowly in the first 16 h and then reduce.Under redox conditions,the release of arsenic in the two areas showed a trend of first increase and then decrease.There was a slight difference in different areas.It always showed that aerobic group>control group>anaerobic group in Potamogeton crispus area,while there was not much difference between the group samples in Phragmites communis area.（6）The input of foreign substances would affect the release of arsenic in the sediment.After the addition of sodium oxalate,the release of arsenic in the two areas increased with the increase of sodium oxalate concentration.The release of the high-concentration group in the first 24 h had the most significant change.The release from the high-concentration group in the Potamogeton crispus area was higher than that in Phragmites communis area,and there was not much difference between the releases in the two areas of the other groups.After the addition of glucose,the arsenic release amount of each concentration group was not significantly different,and all showed an upward decreasing fluctuation trend,and the arsenic release amount of each concentration group in Phragmites communis area was higher than that of the same concentration group in Potamogeton crispus area.After the addition of PO₄^3-,the release amount of arsenic in the sediment increased with the increase of the concentration of PO₄^3-in the water body.The release amount of arsenic in the sediments of each concentration group in the two areas increased sharply in the first0.5 h,and then the fluctuations decreased.The difference in arsenic release amount was small between the same concentration groups in different areas.