COMPARATIVE ANALYSIS OF HYDROGEOCHEMISTRY IN WET AND DRY SEASONS IN LAGOS STATE

This study investigates hydrogeochemical variability and health risks associated with groundwater quality across five distinct land-use zones in Lagos State, Nigeria. A total of 25 groundwater samples were collected following strict sampling protocols, representing residential, industrial, commercial, agricultural, and dumpsite areas. The samples were analyzed for physicochemical parameters in situ, while trace metals were determined in the laboratory using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma-optical emission spectrometry (ICP-OES). Measured physicochemical parameters showed variations with pH ranging from 5.13±0.46 to 7.10±0.16, electrical conductivity (EC) from 114.28±14.11 to 303.62±92.67 µS/cm, salinity from 0.01±0.00 to 0.10±0.04 ppt, total dissolved solids (TDS) from 42.25±4.55 to 131.05±40.29 mg/L, and temperature from 26.06±0.31°C to 26.28±0.11°C. Heavy metals such as arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and mercury (Hg), among others, were detected in varying concentrations. Notably, elevated levels of lead (up to 0.22±0.21 mg/L), arsenic (up to 0.04±0.00 mg/L), and nickel (up to 0.03±0.02 mg/L) were found, particularly in samples from dumpsites and agricultural areas. These elevated concentrations are attributed to leachate from waste deposits and agrochemical usage. Health risk assessment was conducted using the Estimated Daily Intake (EDI) and Hazard Quotient (HQ) models. The EDI values for most metals were below the United States Environmental Protection Agency’s (US EPA) reference dose (RfD), except for calcium, which showed elevated intake levels. HQ values indicated a low non-carcinogenic risk across all land-use zones. Furthermore, carcinogenic risk assessment revealed no significant threat from ingestion of groundwater in the study area. The results highlight the influence of land-use activities on groundwater quality and emphasize the importance of regular monitoring and adaptive management. These findings support the development of targeted groundwater protection policies and public health interventions to mitigate contamination risks in urban and peri-urban areas of Lagos