Laoye et al. 2024 — Heavy metal contamination in fish, fruits, and vegetables in Southwest Nigeria

Laoye et al. (2024) present a PRISMA systematic review of 64 studies (from 10,212 initially identified) reporting heavy metal contamination in fish, fruits, and vegetables in Southwest Nigeria published between 2014 and 2024. The majority of research focused on fish (40 studies), followed by vegetables (20 studies) and fruits (4 studies). The most commonly studied fish species were Tilapia zilli, Chrysichthys nigrodigitatus (bagrid catfish), Clarias gariepinus (African catfish), and Oreochromis niloticus, with heavy metal concentrations in fish frequently exceeding WHO limits. Studies were predominantly from Lagos (30 studies), Ondo (8 studies), Ogun (7 studies), Osun (7 studies), Ekiti (6 studies), and Oyo (3 studies).

Key numbers

Studies: 64 included (of 10,212 screened), PRISMA methodology, databases: ResearchGate, Scopus, Google Scholar, ScienceDirect, PubMed.

Distribution: fish 40 studies, vegetables 20 studies, fruits 4 studies.

Dominant study locations: Lagos (30), Ondo (8), Ogun (7), Osun (7), Ekiti (6), Oyo (3).

Key fish species studied: Tilapia zilli, Chrysichthys nigrodigitatus, Clarias gariepinus, Oreochromis niloticus.

Key finding: Heavy metal concentrations in fish frequently exceeded WHO limits, driven by contamination from aquatic systems near industrial zones, agricultural runoff, and mining activities.

Metals discussed: Pb, Cd, Cr, Ni, Zn, Fe, Cu, tHg, tAs, Al, Co, and Mn across food matrices. Fish in rivers near industrial zones in Lagos found to contain high Pb and Cd concentrations (Olayinka and Adedeji, 2018, per review). Vegetables irrigated with contaminated water sources had high levels of arsenic (Ogundele et al., 2015, per review). The review states that Hg and As were less frequently detected or tested in fish.

Note: This is a B-tier systematic review (not all primary studies included are themselves A-tier; the review covers a broad range of study quality). Specific pooled concentration values are not provided in the review; qualitative summary of study findings is the primary output. Peer review status: 1 approved with reservations (F1000Research open peer review).

Methods (brief)

PRISMA systematic review. Databases searched: ResearchGate, Scopus, Google Scholar, ScienceDirect, PubMed. Search terms included keywords for heavy metals, food products, and Southwest Nigeria. Inclusion: studies reporting heavy metal contamination in fish, fruits, or vegetables in Southwest Nigeria, 2014–2024. Exclusion: studies outside the 10-year window or outside Southwest Nigeria. 10,212 → 64 studies after screening.

Implications

Certification: Contributes regional occurrence evidence for Nigerian freshwater fish, with tilapia and catfish species described as carrying documented Pb and Cd exceedances above WHO limits in aquatic systems near industrial zones.

Courses: Illustrates how industrialization and inadequate environmental regulation drive heavy metal contamination in staple protein sources in West African food systems.

App: Contextual regional signal for Nigerian-sourced freshwater fish (Pb/Cd), vegetables from irrigated sources (tAs), and less-characterized fruit contamination.

Wiki pages this source may touch

• lead
• cadmium
• arsenic-total
• mercury-total
• aluminum
• chromium
• nickel
• zinc
• iron
• copper
• cobalt
• manganese
• freshwater-fish
• vegetables
• fruit
• fresh-fish

Verification notes

• Cross-vendor audit (Codex, 2026-05-17) corrected the Ogun location typo to 7 studies, removed unsupported iAs, removed invalid tilapia and catfish slugs, and expanded the metal scope to match the review’s results sections.
• tilapia and catfish are source-level species descriptors in the review, but they are not current ingredient slugs; this page routes them through [[ingredients/freshwater-fish]].
• The review discusses arsenic and mercury without occurrence speciation; this page uses tAs and tHg rather than iAs or MeHg.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.