Groundwater quality assessment, health risk assessment, and source apportionment in the Xin’an River Basin, China, during the wet season

Abstract

To analyze groundwater quality and its influencing factors in the Xin'an River Basin and to support the pilot ecological compensation mechanism, 150 groundwater samples were collected in the wet season from May to June, 2021. This study investigated groundwater quality during the wet season in the Xin'an River Basin through integrated application of groundwater quality assessment, health risk assessment, and source apportionmen. The results showed that iodine was the most frequently exceeded parameter, with 69 samples (46%) exceeding the drinking water standard, while other parameters generally met regulatory limits with only isolated anomalies. Overall groundwater quality was satisfactory, with more than 95% of samples having EWQI values below 100; only 7 samples exhibited EWQI > 150, all attributable to single-point anomalies. Health risk assessment revealed relatively low overall risks, though children faced higher risks than adults, primarily driven by long-term chronic cumulative effects. Notably, iodine was the only groundwater constituent for which the non-carcinogenic health risk exceeded the threshold within the 90% confidence interval, and it also contributed the highest non-carcinogenic risk (45.01% for adults and 44.61% for children), thus warranting particular attention. Water–rock interaction is the dominant factor influencing the hydrochemical characteristics of groundwater in the study area. The genesis of naturally occurring high-iodine groundwater is jointly governed by hydrogeological conditions and hydrogeochemical processes in red bed regions: sluggish groundwater flow facilitates solute accumulation, while reductive dissolution of iron-bearing minerals releases adsorbed iodine into groundwater. Source apportionment also indicated a non-negligible influence of agricultural activities. Long-term monitoring of iodine concentrations—particularly in red bed areas—and improved guidance on fertilization and pesticide practices are recommended.