华北平原典型山前冲洪积扇高硝态氮地下水分布特征及健康风险评价

Occurrences and health risks of high-nitrate groundwater in typical piedmont areas of the North China Plain

地下水硝态氮污染受到世界的广泛关注,但是,高集约农业生产的山前冲洪积扇地下水中高硝态氮分布特征及其对不同人群的健康危害尚未完全清楚。本研究于华北平原北京和石家庄地区两组冲洪积扇采集了144件地下水样,在研究地下水化学成分形成控制因素的基础上,探究地下水中高硝态氮的分布规律与成因机制以及健康风险。结果表明地下水为中性至弱碱性。84%地下水样品的硝态氮浓度超出我国饮用水标准值10 mg/L,北京地区地下水硝态氮平均浓度高于石家庄地区。两地区总体浅层地下水硝态氮浓度高于深层地下水,西南部地区地下水硝态氮高于东部和北部地区。高硝态氮地下水水化学类型以HCO_(3)-Ca-Mg型为主。地下水化学形成作用主要受矿物溶解、岩石风化和蒸发结晶的影响。离子比例系数和主成分分析(PCA)表明,农业活动、离子交换和硝化作用是高硝态氮地下水形成的主要原因。深层地下水水质优良且熵权水质指数(EWQI)多处于1或2等级,优于浅层地下水。人类健康风险评价(HHRA)模型对4类人群(婴儿、儿童、成年男性、成年女性)风险计算结果显示:地下水硝态氮的潜在非致癌风险对婴儿表现严重,浅层地下水潜在非致癌风险都要高于深层地下水,石家庄地区地下水潜在非致癌风险低于北京地区。平面上,北京地区地下水硝态氮对4类人群均存在潜在风险,高风险区域主要分布在北京西南部和中部,东部风险相对较低。石家庄地区地下水硝态氮潜在风险整体表现为西高东低,东部大部分区域地下水适宜全部人群饮用。因此,控制浅层地下水硝态氮的输入、根据不同人群差别取水、对婴儿群体多提供深层地下水源是保障居民饮水安全的关键。

Nitrate pollution in groundwater is a global concern,yet the distribution characteristics of high-nitrate groundwater and its health risks to different populations in the agricultural intensive piedmont alluvial fans are not fully understood.In this study,we carried out comprehensive hydrogeochemical analysis on 144 groundwater samples collected from two sets of piedmont aquifers(Beijing and Shijiazhuang areas)in the North China Plain to determine the distribution pattern,formation mechanism,and health risks of high-nitrate groundwater in the region.The regional groundwater was neutral to slightly alkaline,and 84%of the samples had nitrate concentrations exceeding the national standard(10 mg/L)for drinking water.The average nitrate concentration in groundwater was higher in Beijing than in Shijiazhuang areas,and in both areas higher in shallow than in deep aquifers.Planarly,high-nitrate groundwater was more commonly distributed in the southwestern region as compared to the eastern and northern regions.High-nitrate groundwater was mainly characterized by HCO_(3)-Ca-Mg hydrochemical facies,controlled mainly by mineral dissolution,rock weathering,and evaporative crystallization,according to ion ratio and principal component analyses.Agricultural activities,ion exchange,and nitrification were the main causes of nitrate enrichment in groundwater.Water quality of deep groundwater was better compared to shallow groundwater,with EWQI values mostly between 1 and 2.According to health risks assessments of four population groups(infants,children,women,and men)using HHRA model,the potential non-carcinogenic risk of high-nitrate groundwater was high for infants,and shallow groundwater posed a greater health risk in both areas.Overall,the potential non-carcinogenic risks were lower in Shijiazhuang than in Beijing where high-nitrate groundwater posed a health risk to all populations.In Beijing,the high risk areas were mainly located in the southwest and central part,and the east was at relative low risk.In Shijiazhuang,the potential health risk was high in the west and low in the east,and most of the groundwater in the east was suitable for drinking by all populations.We concluded,therefore,that controlling nitrate input from shallow groundwater,selecting drinking water sources according to population groups,and providing deep groundwater to infants were crucial for ensuring safe drinking water for local residents.