Spatiotemporal Variability of Contaminants in Lake Water and Their Risks to Human Health: A Case Study of the Shahu Lake Tourist Area, Northwest China

Shahu Lake is a well-known tourist lake in Ningxia, northwest China. This study analyzed the general hydrochemical characteristics of the lake water to determine the spatiotemporal variability of contaminants and to assess the potential health risk associated with the surface water. Lake water was monitored at three stations each month throughout 2013. Samples were analyzed for pH, total dissolved solids, temperature, EC, major ions (Na+, K+, Ca2+, Mg2+, SO42-, Cl-, HCO3 (-), and CO3 (2-)), ammonia nitrogen (NH4-N), fluoride (F-), phenol, and heavy metals (As, Hg, and Cr6+). The results suggest that Na+ is the dominant cation in the lake water, and Cl- and SO4 (2-) are the dominant anions, resulting in a primary water type of Cl center dot SO4-Na. Contaminant levels (NH4-N, F-, As, Hg, Cr6+, and phenol) vary through time and space (spatiotemporal variations). As and F- are high in the summer season; Cr6+ and Hg do not significantly change over the year; and the NH4-N and phenol concentrations also remain relatively stable. Concentrations of all these substances are within the acceptable limits for recreational water use (1.5, 1.5, 0.1, 0.001, 0.05, and 0.01 mg/L for NH4-N, F-, As, Hg, Cr6+, and phenol, respectively). An assessment model recommended by the Ministry of Environmental Protection of the P.R. China was used in the study to conduct the health risk assessment. While workers do experience higher non-carcinogenic and carcinogenic risks than tourists, the risks are low and negligible. As and Cr6+ contribute the most to total carcinogenic and non-carcinogenic risks.