Journal of Global Ecology and Environment

Aims: This study assessed the occurrence, characteristics, seasonal distribution and environmental associations of microplastics and an operationally defined submicron plastic fraction in the surface water of River Ngadda, Maiduguri, Borno State, Nigeria.

Study Design: A longitudinal field-based environmental monitoring study involving seasonal sampling and multivariate statistical analysis was employed.

Place and Duration of Study: The study was conducted in River Ngadda, Borno State, north-eastern Nigeria, across six sampling stations over eight months (March - October 2025), covering both the dry and wet seasons.

Methodology: Surface water samples were collected monthly from six sampling stations between March and October 2025, covering the dry and wet seasons. At each station, five 4 L subsamples were composited to obtain representative samples. Samples were processed using wet peroxide oxidation, followed by size separation with a 50 μm stainless-steel sieve and 0.45 μm membrane filtration. Microplastic particles were examined microscopically and confirmed by Fourier-transform infrared spectroscopy, while the retained submicron plastic fraction was characterised using pyrolysis gas chromatography-mass spectrometry. Physicochemical parameters, including temperature, pH, total dissolved solids, electrical conductivity, nitrate and sulphate, were also measured.

Results: All measured physicochemical parameters were within the permissible limits of the World Health Organization and the National Environmental Standards and Regulations Enforcement Agency. Microplastic abundance ranged from 29 ± 2.4 to 41 ± 1.6 particles/L during the dry season and from 27 ± 4.6 to 34 ± 8.3 particles/L during the wet season. Polymer-associated concentrations of the submicron plastic fraction ranged from 27.0 ± 1.4 to 38.0 ± 2.1 μg/L in the dry season and from 21.0 ± 0.3 to 34.0 ± 1.1 μg/L in the wet season. Fragments were the dominant microplastic form, while polyethylene, polypropylene, polystyrene, polyethylene terephthalate, polyamide and polyvinyl chloride were identified. Multivariate analyses indicated associations between plastic contamination and selected water-quality variables.

Conclusion: River Ngadda is contaminated with microplastics and submicron plastic particles, although physicochemical parameters remained within regulatory limits. The predominance of fragmented plastics and diverse polymer types suggests continuous anthropogenic inputs and ongoing degradation processes. Environmental variables, particularly water-quality parameters, influence the distribution and dynamics of plastic pollutants within the river system. Continuous monitoring and improved waste management strategies are therefore necessary to mitigate plastic pollution and protect aquatic ecosystem health.