Distribution And Risk Assessment Of Heavy Metal Species In Soil Of Caohai Bird Habitat

Caohai is a plateau wetland in southwestern China,a national nature reserve that provides protection for endangered migratory birds such as the black-necked crane Grus nigricollis.In recent decades,Caohai Wetland has been facing more and more environmental problems.Although previous studies have investigated heavy metal pollution in this area,the distribution of heavy metal content in birds' resting and foraging grounds,potential environmental risks,possible sources,and factors affecting their spatial distribution have not been systematically explored.In addition,the study of heavy metal exposure to overwintering waterbirds has certain guiding significance for the risk management of heavy metals in Caohai and bird protection.To address these issues,we analyzed toxic metals in 20 surface sediment samples from 5 bird resting places,and 7 bird foraging areas investigated the heavy metal content of water,plants(Juncellus serotinus,Solanum tuberosum L,Daucus carota L,Shamrock,Perennial ryegrass,Vicia villosa Roth),soil,and benthic animals(C.Cathayensis,Anodonta).The results showed that the content of Cd,Hg and Sb in the night rest grounds and foraging grounds exceeded the background values of the five southwestern river systems,and the heavy metal pollution degree in the five night rest areas was: LJX > ZJW > YGS > HYL > WJY.The analysis of metal morphology showed that,with the exception of Cd and Pb,the main morphology of most heavy metals was the residue state.According to the geological accumulation index,potential ecological risk index,and risk assessment code,Cd and Hg are the most important pollutants,posing a medium to very high potential ecological risk to the Caohai Wetland Ecosystem,while other metals present no risk or low risk to the environment risk.In addition,in order to quantitatively estimate the relative contribution of man-made loads and environmental factors to the accumulation of heavy metals in the sediment,the enrichment factor(EF)index was included in the conventional regression analysis.The results show that the distribution patterns of Cu,Pb,Zn,Cd,Hg and Sb are mainly controlled by artificial loads.Sediment parameters(ie,TOC or p H)play a leading role in determining the concentration distribution of Cr and Ni.The distribution pattern of Be and V is a combination of artificial load control and environmental factors.The heavy metal pollution in the soils of the seven foraging areas was at the extreme level,with JJW and LJX being the most severe.The content of heavy metals in the benthic animal is greater than that of the Chinese garden snail(except Zn),and the total accumulation capacity of heavy metals in WJYX is the largest;the concentrations of Cd,Cr and Ni in plants exceed the normal range of plants but do not exceed phytotoxicity Level,green manure and sedges have a strong accumulation of heavy metals;overall,animals and plants have the highest absorption of Zn and the lowest absorption of Sb.An exposure model was used to assess the risk of heavy metal exposure to wintering waterbirds(black-necked cranes,bar-headed geese,and red ducks).The data show that the doses of heavy metals exposed through the drinking route are low and negligible.The exposure of Cd and Ni to black-necked cranes through soil is relatively safe.Bar-headed geese and red-duck ducks are at higher risk than black-necked cranes.LJX and JJW are the most heavily polluted areas.The exposure doses of Cr,Pb and Zn all exceeded mc TDI(the most conservative daily tolerated dose).Heavy metal pollution in this area may have adverse effects on birds.In order to protect this wetland ecosystem and many precious birds,combined with the results of this study,priority should be given to heavy metal pollution in LJX and JJW areas,and ryegrass or sedge grass should be used for in-situ treatment and priority control of Pb.