Origins And Health-Risk Assessment Of Nitrate In Groundwater In Typical Alluvial-Pluvial Fans,North China Plain

Nitrate（NO₃^-）pollution in groundwater is a global environmental problem,which is widely concerned because it is harmful to human health.In recent decades,the distribution and source of nitrate in groundwater have been fully recognized all over the world,while the research on human health risk assessment of nitrate in groundwater is in the development stage.Taking the groundwater of typical alluvial-pluvial fans in North China Plain as the research object,this paper aims to study the main hydrogeochemical effects of groundwater of typical alluvial-pluvial fans in North China Plain by means of hydrochemical diagram,Schukarev classification and ion ratio method,and to evaluate the groundwater quality in the study area;to investigate the spatial distributions of nitrate in various aquifers and in areas with different land-use types in the study area,and to identify dominant sources and factors using principal component analysis and stable isotope method;and to conduct health risk assessment of groundwater nitrate in various aquifers and in areas with different land-use types in typical alluvial-pluvial fans in North China Plain using the models recommended by USEPA,as well as expand the theory of groundwater nitrate health risk assessment.The main results are as follows:（1）The major hydrochemical types of groundwater in the research region are HCO₃-Ca.The hydrochemical formation of groundwater is largely affected by rock weathering,in which the weathering and dissolution of silicate and carbonate minerals contributes more to the hydrochemical components,while the dissolution of evaporated salt rock contributes less.The results of water quality evaluation show that class I,class II,class III,class IV and class V water account for 45.99%,14.17%,15.78%,22.19%and1.87%,respectively,Among them,nitrate is the main impact index of groundwater quality in the study area.（2）The proportion of high-NO₃^-（>88.6 mg/L）groundwater in fissured aquifers is about 3.8 times that of those in granular aquifers.In fissured aquifers,the proportion of high-NO₃^-groundwater（PHNG-China）in peri-urban areas and farmland was about 1.8 times that in urban areas.And in shallow granular aquifers,the PHNG-China in urban areas was slightly higher than that in other areas.By contrast,there is no distribution of high-NO₃^-groundwater in deep granular aquifer.The spatial distribution of nitrate in groundwater in the research region decreases gradually from the piedmont to the plain.（3）Nitrogen and oxygen isotope information indicates that manure and sewage are the main sources of nitrate in groundwater in the study area,with an average contribution rate of 66.4%,followed by soil nitrogen and atmospheric deposition,with contribution rates of 22.1%and 11.5%,respectively.Groundwater nitrogen transformation process in the study area is mainly nitrification,while denitrification is weak.（4）Risk assessment of groundwater nitrate indicated about 43.3%,45.6%and 54.2%of the groundwater samples showed unacceptable non-carcinogenic risk to adult males,adult females and children,respectively.The average non-carcinogenic risk caused by nitrate in groundwater of shallow granular aquifers is about 3.0 times that of deep granular aquifers,indicating that deep granular aquifers have higher significance of water supply.The proportion of samples with health risks had a significant positive correlation with the urbanization level.Our study indicates that several effective measures for pollution prevention,such as strengthening sewage treatment and prohibiting groundwater over-exploitation,must be adopted so as to ensure the sustainable management of groundwater and the safety of drinking water.