Hydrological seasonality reshapes dissolved-metal exposure and health-ecological risk priorities in a semi-arid river...

Hydrological seasonality can influence the exposure patterns and risk priorities of dissolved heavy metals (HMs) in semi-arid river systems. In this study, operationally dissolved HMs, defined as the < 0.45 μm fraction, were investigated at 35 sampling sites in the Weihe River basin during low-flow, mean-flow, and high-flow seasons to characterize seasonal shifts in concentration patterns, metal associations, and human-health and ecological risks. Total operationally dissolved HM concentrations increased from 33.21 μg/L in the low-flow season to 40.16 and 43.35 μg/L in the mean-flow and high-flow seasons, respectively. Cr, As, and Hg were generally enriched during low flow, whereas Al, Zn, Cu, and Pb were elevated during high flow. Multivariate analyses revealed a relatively persistent V-Cr association, partly involving As and Cu, together with seasonally strengthened mixed-metal groupings during the mean-flow and high-flow seasons. Human-health risk was dominated by Cr and As through the drinking-water pathway and reached the highest value in children during the low-flow season (6.13 × 10^-6 yr^-1). Relative ecological priority was more strongly associated with Hg and Cu, which showed low HC5 values of 1.36 and 6.35 μg/L, respectively, although all PAF values remained below 5%. These findings indicate that hydrological seasonality can decouple human-health and ecological risk priorities, highlighting the need for season-specific exposure assessment and risk management.