Heavy Metal Index
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Heavy metal exposure risk associated with ingestion of Oreochromis niloticus and Coptodon kottae harvested from a lacustrine ecosystem

This study quantified heavy metal concentrations (As, Cd, Co, Cu, Cr, Fe, Mn, Ni, Pb, Zn) in water, sediment, muscle, gut, and bone of two fish species — Oreochromis niloticus (Nile tilapia) and the endemic and endangered Coptodon kottae — from Lake Barombi Kotto, a crater lake in Cameroon.

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Overview

This study quantified heavy metal concentrations (As, Cd, Co, Cu, Cr, Fe, Mn, Ni, Pb, Zn) in water, sediment, muscle, gut, and bone of two fish species — Oreochromis niloticus (Nile tilapia) and the endemic and endangered Coptodon kottae — from Lake Barombi Kotto, a crater lake in Cameroon. Metal concentrations in lake water were generally low and below permissible standards; sediment concentrations ranged from 0.86 ± 0.03 mg/kg for Cd to 560.1 ± 11.15 mg/kg for Fe. In fish, the organ distribution followed bones > gut > muscle for most metals, with bioconcentration factors ranging from 1.6 (Fe) to 1,568 (Mn). Consumption of both fish species contributes less than 1.0% of the permissible tolerable daily/weekly intake (PTDI/PTWI) for most metals, but Pb has the potential to exceed permissible exposure levels under high-consumption scenarios for adults.

Key numbers

  • Sediment Cd range: 0.86 ± 0.03 mg/kg (dry weight)
  • Sediment Fe: 560.1 ± 11.15 mg/kg (dry weight)
  • Bioconcentration factors: 1.6 (Fe) to 1,568 (Mn) in fish tissues
  • Organ Cd distribution: bones > gut > muscle for both species
  • All metals contributed < 1.0% of PTDI/PTWI from fish consumption at typical rates
  • Pb has potential to exceed permissible levels at high-consumption scenarios (adults)
  • n = 10 samples per species (20 fish total); 6 water and sediment sampling sites
  • Metals not detected above LOD at routine fish consumption levels for most analytes

Methods (brief)

Fish muscle, gut, and bone dissected and analyzed separately. Wet digestion in aqua regia; metal analysis by ICP-MS or ICP-OES (method not specified for all metals). Water samples by standard methods. Total metals reported (no speciation). Health risk assessment: PTDI/PTWI approach per WHO/FAO guidelines.

Implications

Certification: Demonstrates Pb as the analyte of greatest dietary concern from freshwater lake fish even in non-industrialized African settings; organ distribution data supports bone/whole-fish products as higher-risk than muscle-only. Courses: Lacustrine fish as an understudied contamination pathway; Mn bioconcentration data notable. App: Freshwater tilapia contamination data point for sub-Saharan Africa.

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