Uzomah et al. 2021 — Chemical contaminants in Nigerian fresh and marine fish: review
This narrative review synthesizes the Nigerian literature on chemical contaminants in fresh and marine fish, covering polycyclic aromatic hydrocarbons (PAHs), persistent organic pollutants (POPs), heavy metals, and microplastics across more than 104 commercially important species. The heavy metals section reports that iron and lead may reach potentially toxic concentrations in fish from specific contaminated sites in Nigeria, particularly near oil extraction, industrial effluent discharge, and urbanized waterbodies. The review provides geographic context for which species and regions present elevated metal risk but does not report pooled concentration statistics; it synthesizes primary studies conducted under varying analytical conditions.
Key numbers
The review does not report harmonized concentration tables. Key findings from cited primary studies:
- Lead (Pb): Potentially toxic levels flagged in fish from sites near industrial and oil-extraction activity; specific primary studies cited in the review report Pb concentrations exceeding WHO and EU guideline values in some freshwater species from the Niger Delta and Cross River regions.
- Cadmium (Cd): Reported in several primary studies; concentrations vary widely by species and site; no pooled range provided.
- Mercury (tHg) and arsenic (tAs): Present in review scope; specific concentrations for Nigerian fish not synthesized into a single summary table in the available text.
- Iron: Flagged as potentially toxic in fish from specific sites; this is a macro-mineral finding and not a standard heavy metals concern under HMT&C analyte vocabulary.
Analytical methods across cited studies: predominantly AAS (atomic absorption spectrometry) and ICP-MS; sample matrices and preparation protocols varied across primary studies.
Methods (brief)
Systematic review methodology; searches of Nigerian and international literature on chemical contaminants in Nigerian fish. Primary study quality and comparability explicitly noted as a limitation: studies used different analytical methods, different LODs, different tissue types (muscle vs whole fish), and different geographic and seasonal sampling windows. The review therefore synthesizes qualitative risk signals rather than pooled quantitative estimates. Evidence tier B because this is a review article synthesizing heterogeneous primary literature rather than reporting new primary measurements.
Implications
Certification: The review flags Pb contamination risk in fish from industrially contaminated Nigerian freshwater systems as a concern, but does not provide the concentration distributions needed for direct threshold comparison. Primary studies cited within this review would need individual evaluation as A-tier sources.
Courses: Useful for illustrating how geographic contamination gradients within a country (industrial vs non-industrial sites) create heterogeneous risk profiles that complicate country-level generalizations.
App: Insufficient quantitative granularity for contamination_profile use. Provides qualitative signal that Nigerian-origin fish warrants site-specific verification, particularly for Pb and Cd.
Microbiome: Not applicable.