Assessment of Microbial Quality, Irrigation Suitability, and Human Health Risks of Surface Water Along the Middle Reaches of Rivers State, Nigeria

This study comprehensively assessed the microbiological content, Water Quality Index (WQI), agricultural irrigation suitability, and human health risks associated with surface water across Iwofe, Tombia, Bukuma, and Bakana along the Niger Delta river system. Field data from fifteen water samples were analyzed using standard analytical, mathematical, and probabilistic Monte Carlo simulation frameworks. The microbiological evaluation revealed dense total heterotrophic bacterial populations (averaging) sustained by organic loads and tropical conditions. Weighted arithmetic WQI values ranged from 948 at Iwofe to 1,464 at Bakana, classifying all sampled surface waters as entirely unsuitable for drinking purposes. Irrigation indices, including Sodium Percentage () and Sodium Adsorption Ratio (), coupled with Wilcox and USSL diagram classifications, indicated severe high-salinity and high-sodium hazards that threaten soil permeability. Furthermore, human health risk assessments demonstrated that cumulative Hazard Index values exceeded safe thresholds (), driven by extreme localized arsenic and chromium concentrations at Tombia (oral Hazard Quotient up to for children). Carcinogenic risks () severely exceeded US EPA safety standards, with pediatric cohorts exhibiting heightened vulnerability. The findings confirm that chronic anthropogenic pressures have severely degraded the river ecosystem, posing acute non-carcinogenic toxicity and lifetime cancer risks. Consequently, urgent regulatory interventions, restricted direct consumption, agricultural pre-treatment, and targeted bioremediation are imperative.