To investigate the presence of metal elements and assess their health risk for the populace in the Nandong Underground River Basin (NURB), we conducted an analysis of eleven common heavy metals in the water body. A Health risk assessment (HRA) model was employed to analyze 84 water samples from the NURB. The detection results revealed the following order of heavy metals concentrations: Fe > Al > Mn > Zn > As > Cd > Pb > Cr > Ni > Cu > Hg. Correlation analysis indicated a certain similarity in material source and migration transformation among these eleven metal elements. Our study identified that the health risks for local residents exposed to metal elements in the water of NURB primarily stem from carcinogenic risk (10⁻⁶–10⁻⁴ a⁻¹) through the drinking water pathway. Moreover, the health risk of heavy metal exposure for children through drinking water was notably higher than for adults. The maximum health risks of Cr in both underground and surface water exceeded the recommendation standard (5.0×10⁻⁵ a⁻¹) from ICRP, surpassing the values recommended by the Swedish Environmental Protection Agency, the Dutch Ministry of Construction and Environment and the British Royal Society (5.0×10⁻⁶ a⁻¹). The results of the health risk assessment indicate that Cr in the water of NURB is the primary source of carcinogenic risk for local residents, followed by Cd and As. Consequently, it is imperative to control these three carcinogenic metals when the water was used as drinking water resource.

Accurate estimate of carbonate weathering and the related carbon sink flux induced by anthropogenic H₂SO₄ is of great significance for improving understanding of the hydrogeochemical evolution and the global carbon cycle. Here, to quantitatively evaluate the influence of anthropogenic H₂SO₄ on different lithological carbonate weathering and the related carbon sink budget, karst spring water in the typical limestone and mixed limestone–dolomite catchments in Yaji and Beidiping affected by acid precipitation in southwest China were sampled monthly for the analysis of hydrochemical and δ¹³C_DIC characteristics. Results show for the period of sampling (August 2013 to December 2014) that the average contribution rates of atmospheric inputs and carbonate weathering to total dissolved cations are 2.24% and 97.8%, and 3.09% and 96.9% in Yaji and Beidiping, respectively. The δ¹³C_DIC values (−17.0% to −14.7‰) and the [Ca²⁺ + Mg²⁺]/[HCO₃⁻] (0.98 to 1.25) and [Ca²⁺ + Mg²⁺]/[HCO₃⁻ + SO₄²⁻] (approximately 1) equivalent ratios of samples prove that H₂CO₃ and H₂SO₄ simultaneously participate in carbonate weathering. The contribution rates of H₂SO₄ to [Ca²⁺ + Mg²⁺] and [HCO₃⁻] produced by carbonate weathering in Yaji and Beidiping are 0–30% and 0–18%, and 0–37% and 0–23%, with average values of 14% and 7%, and 19% and 11%, respectively, suggesting that the influence of H₂SO₄ on different lithological carbonate weathering is different. H₂SO₄ precipitation participating in carbonate weathering increases the weathering rate by 14–19%, whereas it decreases the flux of karst carbon sink by 7–11% in Southwest China. Therefore, anthropogenic acids have influenced the global carbon cycle and climate change by carbonate weathering due to the large karst areas in the world, and their influences on different lithological carbonate weathering should not be ignored in the regional and global carbon cycles in future studies.

As a result of their tendency to enter various ecosystems, bioavailable heavy metals (HMs) have become major human public health concerns. The diverse characteristics and variations in the bioavailable forms of various HMs can cause a range of specific health risks. To verify this, sources of HMs in the sediments of the Yixun river basin were identified, with a focus on studying the aggregation and risks of HMs in various speciation forms. The results showed that the HMs in the sediments were, in order of concentration: Ti > Mn > Zn > Ni > Cu > Pb. The major sources of pollution in the sediments were mining (39.86%), industrial activities (18.24%), and agricultural activities (12.32%). For adults and children, the non-carcinogenic hazard indexes were 0.37 and 1.88, respectively—thus indicating significant non-carcinogenic health impacts on children. These impacts were mainly attributed to the enrichment of Pb bound to Fe–Mn oxides in sediments from agricultural pollution, leading to a hazard quotient of > 1 for children through dermal exposure pathways. Given that industrial pollution contributed the most to the total carcinogenic risk index value, the carcinogenic risks for both adults and children were relatively significant. However, although mining represents the primary source of HMs in river sediments, it is not the main source of health risks in the Yixun river basin, owing to the low bioavailability of the HMs forms in the region. This study confirmed that mining activities can lead to HMs enrichment in river basin sediments, but that the health risks arising from agricultural and industrial sources also merit enhanced monitoring.

Wastes from social economic activities had great impact on water quality thereby limiting water usability for domestic purposes. Sewages discharge from people activities, usually consist of undesirable concentrations of soluble chemicals that infiltrate into the surrounding surface and underground water, and then constitute health risk to the populace. In order to investigate the concentration characteristics and health risk for the local residents in Nandong Underground River Watershed (NURW), eleven common heavy metals in the water body analysis were conducted. Health risk assessment (HRA) was taken to analyze eleven heavy metals of 84 water samples from surface and underground waters in NURW: 36 samples underground water and 48 samples surface water. Our results showed that the heavy metals concentration order is that of Fe > Al > Mn > Zn > As > Cd > Pb > Cr > Ni > Cu > Hg. Correlation analysis indicates that these eleven metal elements have certain similarity on material source and migration transformation. The health risks for local residents exposed to metal elements in the water of NURW mainly from carcinogenic risk (10−6～10−4 a−1) through drinking way, and the health risk of heavy metals exposed to children through drinking way was much higher than adults. The maximum exposing health risks of Cr in both underground and surface water were higher than the recommendation standard (5.0×10-5 a-1) from ICRP, and all the values over the standard (5.0×10-6 a-1) recommended by the Swedish Environmental Protection Agency and the Dutch Ministry of Construction and Environment and the British Royal Society. The results of health risk assessment shows that Cr in the water of NURW was the mainly source of carcinogenic risk for the local residents, following by Cd and As. Consequently, it is necessary to control the three carcinogenic metals when the water was used as drinking water source.