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Calcium (Ca) and magnesium (Mg) in drinking water and the relevant health effects have been ignored for too long. This study aims to reveal the concentrations, spatial distributions, origins and contributions to the daily estimated average requirements of Ca and Mg in public drinking water. Using hydrochemical data of collected samples of public drinking water in 314 cities across China, the contributions of Ca and Mg intakes from public drinking water to their daily estimated average requirements (EARs) were assessed. And the significance of Ca/Mg ratio and total hardness (TH) was evaluated as well. The Ca and Mg concentrations of the samples were in the range of 2.5–155.1 mg/L and 0.2–81.9 mg/L, with an average of 40.4 mg/L and 12.4 mg/L, respectively. There exist obvious differences in Ca and Mg concentrations in different regions, under the impact of climate conditions and water–rock interactions. The intake of Ca via the consumption of public drinking water for adults may be twice as much as that for other age groups. In cities with high Ca levels in public drinking water, the Ca contributions to EAR could reach up to 51.59% for adults. By contrast, Mg in drinking water is an important and even the main pathway to ingest Mg for infants and children. Therefore, public drinking water is critical for Ca and Mg intake among urban residents of China. Besides, attention should be paid to the health effects of high Ca/Mg ratio and low TH in public drinking water, especially in southern China. This research is the first systematic and comprehensive national scale study of Ca and Mg in public drinking water and can provide an important reference to improve healthy public drinking water standards around the world. [ABSTRACT FROM AUTHOR]

Water resource is in high demand within the Yangtze River Delta, given its developed economy. Long-term exploitation of this resource has posed risks of artificial pollution and seawater intrusion to the shallow groundwater. This study aims to reveal the hydrochemical characteristics and health risks of shallow groundwater in the coastal plain of the Yangtze River Delta, as well as to discuss the possible factors affecting groundwater quality. Standard methods for hydrochemical parameter measurements, water quality assessment, and health risk models were applied to fulfill the objectives of the study. The results showed that the shallow groundwater was slightly alkaline, and the average values of total dissolved solids (TDS) and total hardness (TH) were 930.74 mg/L and 436.20 mg/L, respectively. The main hydrochemical types of groundwater were HCO3–Ca·Mg and HCO3–Ca·Na, accounting for 44.3% and 47.5%, respectively. In addition, As concentration was generally high, with a mean value of 0.0115 mg/L. The principal factors affecting the groundwater components include water-rock interactions (especially silicate), cation exchange, seawater intrusion, and human activities. The data also showed that As is strongly influenced by the redox of Fe, Mn, and NO3−. The results of the groundwater quality evaluation indicated that the shallow groundwater in some regions was unsuitable for drinking and agricultural irrigation. Health risk assessment showed that 44.3% of the water samples had significant health risks, which was attributed to the high As concentration. Therefore, it is urgent to establish long-term As monitoring to maintain sustainable groundwater management and drinking water safety. The results of this study provide essential data for water resource management and human health security in the Yangtze River Delta. [ABSTRACT FROM AUTHOR]

Rainfall represents one of the most significant cause of landslide hazards. With runoff in the saturated zone of shallow soil considered, an improved Green–Ampt model was proposed to depict the rainfall infiltration process. Furthermore, a formula for calculating the depth of wetting front was derived, and the slope stability was evaluated accordingly. Finally, a formula for calculating the safety factor of multilayer slopes above different surfaces was obtained via the limit equilibrium method. An illustration is a multilayer colluvial slope in Guangdong Province of China, the results indicated that the downward speed of wetting front decreases gradually within the same layer with continuous rainfall but increases significantly when it extends to the interfaces between the soil layers. Safety factor of the slope decreases sharply at the initial stage of rainfall but then more slowly. Slope failure is more likely to occur along the first interface between the soil layers than along the surface of wetting front. The result from the proposed model is closer to the result of the physical model test than from the existed Green–Ampt model. The improved Green–Ampt model for multilayer slopes can accurately evaluate the infiltration process and related stability of multilayer slopes under rainfall. [ABSTRACT FROM AUTHOR]

Due to the fact that strontium (Sr) is not involved in the scope of supervision of drinking water in China, the Sr concentration in public drinking water and its related health risks have been neglected for a long time. In this research, public drinking water samples were collected from 314 cities across the country to reveal the concentration and spatial distribution of Sr in public drinking water. In addition, the Monte Carlo method (a statistical simulation method) was applied to evaluate the Sr intake from drinking water and human health risks among different age groups and different regions. As shown in the results, the Sr was in the concentration range of 0.005–3.11 mg/L with a mean value of 0.360 mg/L. There were significant differences in the Sr concentration in different regions; in general, it was high in the north and low in the south. The Sr intakes of infants, children, teens, and adults from drinking water were 0.273, 0.503, 0.633, and 0.784 mg/day, respectively. There was a significant positive correlation between Sr concentration in drinking water and bone mineral density (BMD) in the elderly. Especially, the correlation coefficients (r) between Sr concentration and the BMD of the elderly whose age fell in the range of 60–70 years were 0.692 (male) and 0.483 (female). In addition, the Sr concentration in drinking water was positively correlated with the incidence of children's rickets (r = 0.411), while the Ca/Br ratio was negatively correlated with the incidence of children's rickets (r = − 0.410). According to the health risk assessment, among people of different ages, infants' hazard index (HI) value was the highest. The mean value and 95th percentile value were 0.066 and 0.247. Non-carcinogenic risk of Sr through drinking water among different people in different regions was less than 1, which meant no significant damage to human health. This study is the first time to systematically investigate Sr in public drinking water across the whole country. More importantly, the conclusions can be applied to risk control and management of public drinking water. [ABSTRACT FROM AUTHOR]

Rugao city is a typical longevity area taking shallow groundwater as the primary drinking water source. To determine the relationship between longevity and groundwater conditions, the hydrogeochemical characteristics and related causes of potable groundwater were investigated. On this basis, the water quality index (WQI) and hazard index (HI) of groundwater were evaluated. Meanwhile, the nutrient indicators beneficial to human health, like Ca and Mg concentrations, were also considered to explore the relationship. The results were as following: (1) 91.3% of water samples fell under the Ca/Mg–HCO 3 water type, which resulted from the dissolution of silicate rock. Na, Cl-, Br, B in groundwater emanated from seawater intrusion. The abnormal concentrations of NO 3 − and As also indicated that anthropogenic activities had exerted significant influences on groundwater quality. (2) The average WQI value was 30.19, which meant that the overall groundwater quality in Rugao city was pretty good. However, 8 water samples were found to have HI values above 1, which might be attributed to the high concentration of As (maximum value 0.0407 mg/L; mean value 0.0076 mg/L). In general, low WQI and HI values corresponded to towns with a high longevity population; what's more, WQI and HI values of Rugao city were lower than those of non-longevity areas. (3) Comparing with adjacent non-longevity areas, the potable groundwater in Rugao city had the characteristics of high Ca (mean value 123.57 mg/L), high Mg (mean value 50.33 mg/L) and high SO 4 2- (mean value 525.19 mg/L). The daily intake of Ca and Mg from drinking water could meet 12.4% and 22.4% of daily Ca and Mg requirements, respectively. Also, the areas where the Sr and B concentrations were higher usually had higher life expectancy. The high concentrations of Ca, Mg, SO 4 2-, Sr and B in drinking water, as well as low WQI and HI values, probably contribute to physical health and longevity. This research helps provide an insight into the relationship between groundwater quality and health and can serve as a reference for drinking water quality management. [Display omitted] • Water-rock interaction and seawater intrusion dictate groundwater composition. • Anthropogenic activities have affected groundwater quality. • Towns in Rugao city with high longevity usually have low WQI and HI values. • The potable groundwater in Rugao city has high levels of nutrient elements. [ABSTRACT FROM AUTHOR]

The trace elements in the public drinking water have a duality: on the one hand, trace elements play an important role in maintaining human metabolism; on the other hand, high trace elements levels lead to significant health risks. To determine the impacts of trace elements in the public drinking water on physical health in China, water samples were collected from 314 Chinese cities to analyze the concentrations and spatial distributions of trace elements on a national scale. On this basis, the non-carcinogenic health risk assessments and the nutrient-based scores of trace elements (NSTEs) were applied to evaluate the public drinking water quality in terms of safety and nutrition. Most of the water samples were weakly alkaline: pH values fell in the range of 6.62–8.54, with a mean of 7.80. The results indicated that Sr and F− had the highest concentrations in public drinking water, with averages of 0.3604 mg/L and 0.2351 mg/L, respectively. Moreover, hazard index (HI) values in different regions followed the order: northwest China (NWC) > northern China (NC) > Qinghai-Tibetan Plateau (QT) > southern China (SC). The percentages of water samples with HI > 1 in SC, NC, NWC, and QT were 5.49%, 16.82%, 25.81%, and 16.67%, respectively, indicating that the public drinking water in some cities had significant non-carcinogenic health risks. In addition, the intakes of Mn, Fe, Cu, and Rb through public drinking water made negligible contributions to their recommended nutrient intakes. In contrast, trace elements like Sr, F, B, Li, Mo, etc., contributed a lot. The NSTEs in NWC and most parts of NC were relatively high with averages of 8.0300 and 11.2082, respectively; however, the NSTEs in SC and the northeast part of NC were low with averages of 3.3284 and 5.2106, respectively. The results from this study provide a reference for establishing the public drinking water standards and improving drinking water quality. [Display omitted] • Significant differences in the distribution of trace elements in China exist. • The public drinking water in 37 cities has obvious non-carcinogenic health risks. • Intakes of Sr, F−, B, Li, Mo from public drinking water are important for health. • Intakes of Mn, Fe and Cu through drinking water can be ignored. • The nutrient-based scores of trace elements are high in NC and NWC but low in SC. [ABSTRACT FROM AUTHOR]

The southwest karst area is considered to have the most vulnerable groundwater environment in China. Groundwater quality is an important factor restricting sustainable economic development. In this study, traditional water chemistry method, water quality index (WQI), and hazard index (HI) were applied to comparatively analyze the hydrochemical characteristics of groundwater and the water quality in the exposed karst region (EKR) and buried karst region (BKR) in Bama, a typical karst area in southwest China. Generally, the main water type was Ca/Mg–HCO 3. Due to the predominance of dissolution of carbonate rocks in EKR and silicate rocks in BKR, higher total dissolved solids (TDS), Ca and HCO 3 − concentrations, and lower H 2 SiO 3 content were detected in groundwater in EKR compared with BKR. As affected by weathering of rocks such as lead-zinc ore, the maximum concentrations of Zn and Sr were 11.23 mg/L and 13.30 mg/L, showing that mineral water resources are widely distributed in Bama. The ion ratios and isotope abundances (δD and δ18O) in groundwater samples indicated stronger evaporation and rock-water interaction in EKR than BKR. Human activities exerted a more significant influence on the water quality in EKR compared to BKR. The mean WQI value also suggested that the groundwater quality was better in BKR (9.56) than EKR (12.17). Although 95.7% of the water samples in the study area were classified as excellent based on their WQI values, 4.3% of the water samples still had significant health risks (HI > 1) due to the high Sb, Zn, As, and Sr concentrations. It is recommended to reduce anthropogenic pollution in EKR and develop a plan for clean production of mineral water industry according to local conditions, which will help the sustainable development of the local economy. [Display omitted] • Groundwater hydrochemistry in exposed and buried karst regions is totally different. • Aquatic environment in exposed karst regions is more sensitive than buried ones. • Sb, As, and Zn are the main trace elements which may pose non-carcinogenic risks. • Groundwater quality assessment contributes to sustainable water management. [ABSTRACT FROM AUTHOR]