[Metal Pollutions and Human Health Risks in Groundwater from Wet, Normal, and Dry Periods in the Huixian Karst...

The concentrations of 10 metals (Cd, Cr, As, Al, Cu, Pb, Zn, Mn, Hg, and Fe) in 27 groundwater samples collected during different periods (wet, normal, and dry) in the Huixian Karst wetland, the largest subtropical low-altitude karst wetland in China, were detected and analyzed to investigate pollution and health risks. The pollution characteristics, distribution, and health risks of the metals in groundwater were revealed by a comprehensive pollution assessment, multivariate statistical analysis, and health risk assessment model, respectively. The results showed that the average concentrations of metals in groundwater were followed the order of Mn > Fe > Zn > Al > Hg > Cr > Cu > Cd > As > Pb. The maximum concentration of Mn (1022.00 μg·L^-1) was found in the wet season, while that of Hg (42.40 μg·L^-1) was found in the normal season, and both were over the corresponding standard limits. The results of the pollution assessment indicated that only Mn pollution reached level Ⅵ in the wet season, while Cd, Al, Zn, and Fe pollution were at the level of Ⅲ. Only the Hg pollution level reached level Ⅵ while Al pollution reached the level of Ⅲ in the normal water period. According to the above results, the water quality in the dry season was better than that in the wet and normal seasons in terms of the 10 metals. The concentrations of Zn, Cd, Mn, and Al in groundwater were affected by human activities, while the time-scale characteristics of these were not obvious. The concentrations of As, Fe, Cu, and Cr were all affected by human activities and the time-scale, while the concentrations of Hg and Pb were mainly manifested in time-scale characteristics. The results of the health risk assessment of the water due to drinking and the skin penetration pathway indicated that the total health risks followed the order of normal season > the wet season > the dry season. The carcinogenic risks caused by Cr for adults and children through drinking pathway in the wet season (8.03×10^-5 a^-1 and 8.76×10^-5 a^-1), normal season (1.15×10^-4 a^-1 and 1.26×10^-4 a^-1),and dry season (8.72×10^-5 a^-1 and 9.51×10^-5 a^-1) exceeded the maximum allowed level (5.0×10^-5 a^-1) in all periods. Hence, Cr was the main metal element that caused carcinogenic risks. For the sake of drinking water safety, the concentrations of Mn, Hg, and Cr in groundwater should be controlled before drinking.