Benjamin et al. 2023 — Heavy metals in canned fish, Cape Coast market, Ghana
This study measured lead (Pb), zinc (Zn), iron (Fe), tin (Sn), manganese (Mn), and total mercury (tHg) in ten commercially available canned fish products from Cape Coast market in Ghana’s Central Region. Products covered three species groups: mackerel (n=4 brands), sardines (n=4 brands), and tuna (n=2 brands). All analyte concentrations fell below EU Regulation No. 1881/2006 limits where those limits apply, and a health risk assessment using US EPA criteria found no significant non-carcinogenic risk. The dataset is most useful for its Pb, Sn, and tHg values across three commercially important canned fish species in a West African retail context.
Key numbers
All values in µg/g wet weight (equivalent to mg/kg = ppm; multiply by 1000 for ppb).
Lead (Pb): EU Regulation 1881/2006 limit = 0.3 µg/g for canned fish
- Mackerel: mean 0.142 ± 0.017 µg/g (142 ppb)
- Sardine: mean 0.122 ± 0.034 µg/g (122 ppb)
- Tuna: mean 0.141 ± 0.006 µg/g (141 ppb)
- All three below EU limit of 0.3 µg/g (300 ppb); no significant difference across species types (ANOVA p=0.305)
Tin (Sn): No EU regulatory limit specific to canned fish; EU limit for canned fruits/vegetables = 200 µg/g used as reference; JECFA PTWI = 14 µg/kg bw/week
- Mackerel: mean 16.550 ± 3.700 µg/g (16,550 ppb)
- Sardine: mean 14.482 ± 10.202 µg/g (14,482 ppb)
- Tuna: mean 16.024 ± 0.195 µg/g (16,024 ppb)
- All values well below EU 200 µg/g reference; significant differences across species (ANOVA p=0.004)
- Note: the EU 200 µg/g limit for canned fruits/vegetables is not directly applicable to canned fish
Total mercury (tHg): EU Regulation 1881/2006 limit = 0.5 µg/g for canned fish
- Mackerel: mean 0.126 ± 0.017 µg/g (126 ppb)
- Sardine: mean 0.132 ± 0.012 µg/g (132 ppb)
- Tuna: mean 0.263 ± 0.006 µg/g (263 ppb)
- All below EU 0.5 µg/g limit; tuna highest mean; no significant difference across species (ANOVA p=0.990)
- Note: tHg reported; MeHg fraction not speciated in this study
Zinc (Zn): No EU regulatory limit for fish; significant variation across species (ANOVA p=0.024)
- Mackerel: mean 0.137 ± 0.048 µg/g; Sardine: 0.140 ± 0.039 µg/g; Tuna: 0.178 ± 0.022 µg/g
Iron (Fe): Significant variation (ANOVA p<0.001)
- Mackerel: mean 7.279 ± 6.832 µg/g; Sardine: 13.261 ± 9.945 µg/g; Tuna: 12.115 ± 1.985 µg/g
Manganese (Mn): No significant variation (ANOVA p=0.664)
- Mackerel: mean 0.017 ± 0.014 µg/g; Sardine: 0.024 ± 0.014 µg/g; Tuna: 0.022 ± 0.004 µg/g
Methods (brief)
Ten canned fish samples; 2 ± 0.001 g representative homogenized subsamples per product. tHg determined by Cold Vapor AAS using a Direct Mercury Analyzer. Pb, Sn, Zn, Mn, Fe determined by Flame AAS (UNICAM 969). Detection limits: Pb 0.010 µg/mL, Zn 0.002 µg/mL, Mn 0.002 µg/mL, Fe 0.005 µg/mL, Hg 0.001 µg/mL. Certified reference materials used for validation; method blanks performed. One-way ANOVA for species comparisons. Key limitation: n=10 products is small; sample duplication but no per-product replication reported; tHg not speciated to MeHg; Sn detection method not separately stated (likely FAAS, though CV-AAS used for Hg).
Implications
Certification: Pb levels of 122–142 ppb in canned mackerel, sardine, and tuna are relevant benchmarks for the canned fish product category. All are below EU 300 ppb limit and substantially below Codex/WHO concern levels. The Sn values (14,482–16,550 ppb) are characteristic of tinplate-canned seafood and are well below EU’s 200,000 ppb reference for canned vegetables; the wiki’s Sn page should note that canned seafood is a significant dietary Sn source even at compliant levels. The tHg data (126–263 ppb) capture total mercury; the HMT&C-relevant MeHg fraction was not measured. Tuna’s higher mean tHg (263 ppb) aligns with known biomagnification in higher-trophic-level species.
Courses: Illustrates species-level differences in Hg (tuna > sardine ≈ mackerel) even at regulatory-compliant concentrations, and the distinction between tHg and MeHg as a teaching moment for why speciation matters in consumer advisory context.
App: For canned fish as a product class in Ghana/West Africa market context: Pb ~120–140 ppb, tHg ~130–263 ppb with tuna at upper range. Sn ~14,000–16,500 ppb (canning-vessel contribution, not from fish biology).