Integrated assessment of microplastic and organochlorine pesticide contamination in the Nworie River, Southeastern Nigeria

Abstract Microplastic and organochlorine pesticide pollution of freshwater water systems is widespread in tropical Africa. Hence, this study assessed microplastic and organochlorine pesticide (OCP) contamination in the Nworie River, a critical urban freshwater body in Southeastern Nigeria. Systematic sampling was conducted across six sites representing varied land-use types, with water samples analyzed using Fourier-transform infrared spectroscopy (FTIR) and gas chromatography–flame ionization detection (GC-FID). The health risk assessment was evaluated using United States Environmental Protection Agency (USEPA) methods for hazard quotient (HQ), average daily dose (ADD), and cancer risk (CR). FTIR identified 54 microplastic spectral signatures across four major polymer types: polyethylene (PE), polypropylene (PP), polystyrene (PS), and polyvinyl chloride (PVC), linked to functional groups such as alkyl halides, carboxylic acids, aliphatic amines, and isothiocyanates. Site 5, an urban transit zone, recorded the highest polymer diversity (20 functional groups), followed by suburban Site 4 (17 groups), highlighting significant anthropogenic inputs. Surprisingly, Site 2 (industrial zone) showed moderate microplastic presence, potentially reflecting containment measures. GC-FID revealed the presence of multiple organochlorine pesticides. g-Chlordane recorded the highest concentration (0.1704 mg/L), while Lindane (0.0007 mg/L) was found with the lowest. Additionally, g-chlordane was detected in more than 60% of the sampling sites at concentrations above the Federal Ministry of Environment limits, indicating the most occurring OCP in the study area. Sites 4 and 5 emerged as dual hotspots of microplastic and OCP contamination, indicating a synergistic pollution pattern. The co-occurrence of microplastics and hydrophobic organic pollutants such as OCPs suggests enhanced pollutant persistence and bioavailability due to adsorption mechanisms. Additionally, the hierarchical clustering analysis provided strong evidence that multiple anthropogenic activities, including crop cultivation, pesticide storage, and runoff from cultivated lands collectively govern the observed OCP distribution. The HQ values (children) were less than the USEPA recommended limit of 1 in more than 95% of the OCPs detected, while CR values for the target population were below the acceptable limit of 10 − 6 . These findings align with SDGs 6, 12, and 14, reinforcing the call for integrated pollution management strategies in the urban freshwater systems of developing regions.