RESUMEN
To reveal the hydrochemical characteristics of karst wetland located in a subtropical area and at lower elevations in China, 27 surface water samples were collected during three periods (wet, normal, and dry) in the Huixian karst wetland to investigate the distributions, pollution, and irrigation application of 12 inorganic ions and 10 heavy metals. Based on their concentrations, the Nemerow index and the four evaluation systems of the sodium adsorption ratio (SAR), sodium concentration (SC), permeability index (PI), and residual sodium carbonate (RSC) were applied to evaluate the pollution characteristics and irrigation application. It was found that the water type in this area was Ca2+-HCO3- and weakly alkaline. Regarding the 12 inorganic ions and 10 heavy metals, NH4+ exceeded the Chinese standards for drinking water with an exceedance rate of 25.93%, and the exceedance rates of Al, Mn, and Hg were 11.11%, 44.44%, and 37.04%, respectively. The spatiotemporal scaling effect on inorganic ions was lower than that of heavy metals, and the distributions of the inorganic ions and heavy metals were in the order of wet period > normal period > dry period. However, the surface water quality in the Huixian karst wetland was generally well-protected based on the pollution assessment. The Nemerow index ranged from 0.75 to 2.69, which recognized the main pollution contributors as NH4+, Mn, Al, and Hg with the contamination grade from slight pollution to moderate pollution, especially in the core area during the wet period. According to the limits of standards for irrigation water quality and environmental quality for surface water, as well as the evaluation results of the SAR, SC, PI, and RSC, the surface water in the Huixian karst wetland was generally suitable for irrigation, and the water quality in the dry period was better than that in the wet and normal periods. The surface water from site PH1 during the normal period with 19.1 µg·L-1 of Hg and site FH8 during the wet period with 13.7 mg·L-1 of NH4+ were not suitable for agricultural irrigation.
RESUMEN
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 â ¥ in the wet season, while Cd, Al, Zn, and Fe pollution were at the level of â ¢. Only the Hg pollution level reached level â ¥ while Al pollution reached the level of â ¢ 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.