Microplastic Contamination of Marine and Freshwater Fish in Nigeria: Occurrence, Particle Characteristics, Distribution, Ecological Implications and Human-health Concerns

Nigeria combines a large burden of mismanaged plastic waste with strong dietary reliance on fish, which makes the contamination of fish by microplastics a question of ecological and public-health relevance. Field studies on Nigerian fish have multiplied since the first report from a municipal water-supply lake, yet earlier syntheses either predate most of this evidence or pool fish with water, sediment, salt and other matrices. This critical narrative review evaluates what the fish-specific evidence supports. Literature published from 2004 onward was identified through international bibliographic databases, a regional African journal platform, institutional sources and citation tracking, and each study was appraised qualitatively for sampling design, contamination control, polymer confirmation, reporting units, taxonomic reliability and exposure assumptions. Microplastics have been reported in fish from coastal waters, lagoons, estuaries, rivers, reservoirs, burrow pits and markets across most geopolitical zones, with fibres, filaments and fragments of polyethylene, polypropylene and polyethylene terephthalate recurring most often. Reported burdens span several orders of magnitude, a spread driven at least as much by differences in tissue analysed, lower size limits, units and identification practice as by environmental gradients. Several high values rest on visual counting without spectroscopic confirmation or procedural blanks, and some studies report taxa whose occurrence in the sampled waters requires verification. Links between particle burdens and habitat, feeding guild, season and trophic position are plausible but inconsistent and derive mainly from small, single-season samples. Laboratory work on African catfish demonstrates oxidative, hepatic, haematological and behavioural responses at exposures far above most field concentrations, whereas field biomarker studies remain correlative and confounded by co-occurring contaminants. Dietary intake estimates differ by about six orders of magnitude because they rest on incompatible assumptions about edible tissue, consumption and normalisation. The evidence supports the conclusion that Nigerian fish are widely exposed to microplastics, but claims of population-level ecological harm or quantifiable human-health risk remain unsubstantiated. Harmonised, spectroscopically confirmed monitoring of edible tissues, processed fish and aquaculture products is the most pressing need.