Heavy metals in water and Macrobrachium prawns from the Benin River, Nigeria

Abstract

Water is the most vital natural resource, sustaining all life forms. Any alteration in its quality can disrupt ecological balance and render it unsuitable for use. Prawns, positioned delicately in the aquatic food chain, can bioaccumulate heavy metals at levels that may pose health risks to consumers. This study evaluated the concentrations of heavy metals (Fe, Zn, Cu, Pb, Cd, and Cr) in the prawns, Macrobrachium macrobrachion and M. vollenhovenii, and the physicochemical characteristics of water from the Benin River. Samples were collected monthly from four stations between October 2018 and May 2019. Physicochemical parameters, including temperature, pH, electrical conductivity (EC), salinity, turbidity, total suspended solids (TSS), total dissolved solids (TDS), dissolved oxygen (DO), biochemical oxygen demand (BOD), chemical oxygen demand (COD), and major ions were determined using standard methods, while heavy metals were analyzed by atomic absorption spectrophotometry. Data were processed using descriptive statistics, unpaired t-tests, and ANOVA (SPSS). Most parameters were within WHO/FMEnv limits, except EC, chloride, TDS, Fe, Pb, and Cd. Apart from pH and vanadium, seasonal variations were not significant (P > 0.05). Heavy metals in prawns were within permissible limits, with no significant seasonal differences. Estimated Daily Intake (EDI) values were below regulatory thresholds, while Target Hazard Quotient (THQ) values were < 1, indicating negligible non-carcinogenic risks. The Hazard Index (HI) also remained < 1 throughout the study. These findings suggest that prawns from the Benin River are currently safe for consumption, though increasing anthropogenic pressures could elevate future risks. Given their nutritional and economic importance, routine monitoring of prawns and aquatic systems is recommended to safeguard public health and ensure sustainable resource use.