Seasonal variations in heavy metal contamination and physicochemical properties of borehole water in Woreilu Town, Ethiopia

This study investigates the seasonal variations in heavy metal contamination and physicochemical properties of borehole water in Woreilu Town, South Wollo Zone, Ethiopia. Water samples were collected from five borehole sites during the dry and wet seasons and analyzed for key physicochemical parameters and concentrations of selected heavy metals, including iron (Fe 2+ / 3+ ), copper (Cu + / 2+ ), lead (Pb 2+ ), manganese (Mn 2+ / 4+ ), and zinc (Zn 2+ ). Standard procedures established by APHA (23rd edition) and WHO were followed for both sampling and analysis. The results revealed statistically significant spatial and seasonal variations in water quality parameters. Notably, lead (Pb 2+ ) levels exceeded the WHO and Ethiopian standard (0.01 mg l −1 ) at several sites, with a maximum concentration of 0.098 mg l −1 recorded during the wet season, indicating potential health risks. Spatial analysis showed turbidity levels at Jegola (7.00 ± 0.17 NTU) exceeded permissible limits in both seasons, while total hardness at Abazinab (264 ± 1.04 mg l −1 ) surpassed national standards. Seasonal variations revealed iron concentrations at Agamti increased from 0.403 mg l −1 (dry) to 0.642 mg l −1 (wet), exceeding safety limits. Temperature, turbidity, total hardness, alkalinity, phosphate, and sulphate exhibited notable differences across sites and seasons. Correlation analysis showed consistently strong positive relationships among Fe 2+ / 3+ , Cu + / 2+ , Pb 2+ , and Mn 2+ / 4+ across all sites and seasons (r > 0.85, p < 0.01), suggesting common geogenic or anthropogenic sources. In contrast, Zn 2+ exhibited strong negative correlations with all other metals (r < −0.98, p < 0.01), implying different geochemical behavior or sources. These findings underscore the impact of seasonal dynamics on groundwater quality and highlight the critical need for continuous monitoring and targeted public health interventions to ensure safe and sustainable drinking water.