Overview
Onyegeme-Okerenta and West measured five potential toxic elements (As, Cd, Cr, Pb, Ni) in three shellfish species — shrimp (Penaeus monodon), oyster (Crassostrea rhizophorae), and periwinkle (Tympanostomus fuscatus) — from three rivers in the Niger Delta region of Nigeria (Buguma, Krakrama, Bonny Rivers), which are heavily impacted by oil and gas exploration and illegal artisanal refining. Concentrations in several species from the Buguma River exceeded FAO/WHO and EU regulatory limits for Cd and Cr. Dietary intake calculations for children showed Cd exposure from P. monodon and T. fuscatus from Buguma exceeds the tolerable daily intake, and Pb EDI for both age classes frequently exceeded TDI from several shellfish/river combinations. Hazard index (HI) values were above 1 for all species due primarily to elevated chromium, and total cancer risk (TCR) values for all species from all rivers exceeded the 1×10−4 priority risk threshold.
Key numbers
All concentrations in mg/kg dry weight (dw):
Cd:
- P. monodon from Buguma: 3.62 mg/kg (highest; FAO/WHO limit 0.5 mg/kg; EU limit 0.05 mg/kg for bivalves per text)
- Range across all samples: 0.05–3.62 mg/kg
Cr (total):
- P. monodon from Krakrama: 9.1 mg/kg (highest; EU limit for shellfish: 0.5 mg/kg cited)
- Range: 1.38–9.1 mg/kg; Cr was highest THQ contributor (84–92% of single-metal non-carcinogenic risk)
Pb:
- P. monodon from Buguma: 9.15 mg/kg (highest)
- C. rhizophorae from Bonny: 0.47 mg/kg (lowest)
As (total):
- C. rhizophorae from Buguma: 1.61 mg/kg (highest total As)
- P. monodon from Bonny: 0.01 mg/kg (lowest)
- iAs assumed as 3% of total As for EDI calculation
Ni:
- C. rhizophorae from Bonny/Buguma: 9.81 mg/kg (highest)
- T. fuscatus from Buguma: 2.56 mg/kg (lowest)
Health risk:
- Cd EDI for children (P. monodon Buguma): 4.6×10−3 mg/kg/day (5.75× above TDI of 8.0×10−4)
- Pb EDI: exceeds TDI for most species/river combinations for both age classes
- HI (sum THQ): range 3.2–39 for children; range 1.4–17 for adults; all >1
- TCR: 8.69×10−4 to 2.47×10−3 (children), 1.86×10−3 to 5.30×10−3 (adults); all above 1×10−4
Methods (brief)
AAS (atomic absorption spectrophotometry) on wet acid digestion (H2SO4:HNO3:HClO4 = 40:40:20). All results expressed as mg/kg dry weight. Triplicate analysis; RSD <5%. Calibration against multi-element standards. No speciation performed for As; iAs estimated as 3% of total (a conservative assumption for shellfish). Health risk assessment following US EPA and FAO/WHO frameworks.
Implications
Certification: High-evidence exceedance data from a heavily industrialized region. Cd in shrimp from Buguma River reaches 72× EU maximum for shellfish. Demonstrates that geographic sourcing is critical for shellfish Cd and Cr risk; Niger Delta sourcing is a significant risk signal.
Courses: Case study in how industrial pollution (oil/gas) translates to shellfish contamination, relevant to supply chain risk screening.
App: For shellfish ingredients, Niger Delta or similar West African industrialized-delta origin is a flag for elevated Cd, Cr, Pb, and Ni. High HI from chromium warrants attention even in “low-As” contexts.
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Update history
The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and 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.
| Commit | Date | Change | Description |
|---|---|---|---|
| a8052bb | 2026-08-09 | major | 6 sections added; narrative text revised |