Integrating Water Quality Index (WQI) and Multivariate Statistics for Regional Surface Water Quality Evaluation: Key Parameter Identification and Human Health Risk Assessment

Assessing regional water quality and evaluating the associated risks to human health posed by aquatic contaminants are paramount for conserving and managing surface water resources and formulating effective local policy decisions. This study utilizes 17 water quality parameters collected monthly from nine national monitoring stations in Nanning City, China, from January 2021 to March 2023, i.e., water temperature (WT), pH, dissolved oxygen (DO), permanganate index (CODMn), chemical oxygen demand (COD), five-day biochemical oxygen demand (BOD5), ammonia nitrogen (NH3-N), total phosphorus (TP), copper (Cu), zinc (Zn), fluoride (F-), selenium (Se), arsenic (As), mercury (Hg), cadmium (Cd), chromium (Cr), and lead (Pb). Analyses were performed utilizing the Water Quality Index (WQI) and multiple stepwise regression to ascertain seasonal and spatial variations in water quality and to identify key water quality parameters. Human health risks were evaluated, focusing on eight heavy metals. The results indicated that the average WQI for the designated area was 94.1, with individual monitoring stations displaying WQIs ranging from 93.22 to 96.44, categorizing the water quality as “excellent”. The WQI exhibited seasonal fluctuations, peaking in spring and winter while decreasing in summer and autumn. All measured parameters met national standards for Class I and II surface waters. The stepwise regression analysis facilitated the construction of minimized WQI models (WQImin) derived from three different training and testing datasets, with a WQImin model incorporating six key parameters, i.e., DO, CODMn, NH3-N, Hg, WT, and Se. The concentration of heavy metals in the water exhibited a sequence of Zn (3.35 µg/L) > Cr (2.00 µg/L) > Cu (1.36 µg/L) > As (1.29 µg/L) > Se (0.32 µg/L) > Pb (0.17 µg/L) > Cd (0.03 µg/L) > Hg (0.01 µg/L), with all metals adhering to the Class I standard. Children are more susceptible to the adverse effects of heavy metal contamination than adults, exhibiting a total environmental health risk of 1.28 times greater. Cr was identified as the predominant contributor to the aggregate health risk, accounting for over 80% of the risk in adults and children, followed by As (19.1%). Future protection efforts are recommended to prioritize the control of Cr and As concentrations in Nanning City.