Kangre 2024 — Lead and tin in canned tomato mix, Ghana (storage display conditions)
An MPhil thesis from the University of Education, Winneba (Ghana) examined Pb and Sn in 32 canned tomato mix samples (Tasty Tom brand) under two marketing display models: sunlight-exposed outdoor stalls vs enclosed shops. Samples were collected from the Effutu Municipality and analysed by ICP-MS at the Ghana Standard Authority. Both metals were within regulatory limits, but Pb was significantly higher in sunlight-exposed products (0.052 ± 0.12 mg/kg) than enclosed shop products (0.038 ± 0.02 mg/kg). Tin concentrations were consistent between display conditions. A dietary survey of 400 university students measured consumption patterns; the incremental lifetime cancer risk (ILCR) for Pb exceeded acceptable thresholds (3.28×10⁻⁶ to 6.29×10⁻⁶) at maximum and 95th percentile consumption levels, raising concern about long-term exposure even at sub-regulatory concentrations.
Key numbers
Pb and Sn concentrations (mg/kg) by display condition:
| Parameter | Sunlight-exposed | Enclosed shop |
|---|---|---|
| Pb mean ± SD | 0.052 ± 0.12 | 0.038 ± 0.02 |
| Sn (range) | consistent | consistent |
Analytical performance:
- LOD: Pb = 0.0002 mg/kg; Sn = 0.0005 mg/kg
- LOQ: Pb = 0.01 mg/kg; Sn = 0.10 mg/kg
- CRM recovery: Pb 107.6% (target 0.447 ± 0.161 mg/kg; found 0.481 mg/kg); Sn 95.6% (target 0.181 ± 0.26 mg/kg; found 0.173 mg/kg)
Exposure (chronic daily intake of Pb):
- Sunlight-exposed: males 0.00052 mg/kg-d, females 0.00063 mg/kg-d
- Enclosed shops: lower values (consistent with lower Pb concentrations)
Hazard quotient (HQ) for Pb: Higher in sunlight-exposed products for both males (0.052) and females (0.093) vs enclosed shop products.
Incremental lifetime cancer risk (ILCR) for Pb: Maximum and P95 values 3.28×10⁻⁶ to 6.29×10⁻⁶. US EPA acceptable threshold is 1×10⁻⁶; values above this threshold indicate elevated theoretical long-term cancer risk from chronic Pb consumption.
Consumption survey (n=400 students, Winneba campus):
- Canned tomato mix consumed primarily in Jollof rice (highest rate), stew, and soup
- Mean daily consumption (all dishes combined): 510 g/day (enclosed), 530 g/day (exposed), 410 g/day (both models combined)
- Females consumed more per day than males
- Total daily consumption across all respondents: 1,450 g/day; annual total 2,332 kg/year
Study population comparison: Mean Pb concentrations well below most international regulatory limits (EU: 0.1 mg/kg for processed tomato products; Codex/WHO: 0.1 mg/kg). ILCR concerns arise from high consumption frequency and serving volumes, not from regulatory exceedance.
Methods (brief)
Cross-sectional analytical study with dietary survey component. Sampling: systematic sampling from Winneba community market, 16 cans from sunlight-exposed shops and 16 from enclosed shops (all Tasty Tom brand). Chemical analysis: Perkin Elmer NexION 2000P ICP-MS at Ghana Standard Authority; BS EN 15763:2009 method; microwave digestion (HNO3 + H2O2, Milestone MA079, 170°C, 1000W, 50 bar). Student survey: multi-stage cluster sampling, 400 undergraduates, validated questionnaire. Statistical analysis: comparative analysis between display models by t-test or equivalent; Monte Carlo Simulation for health risk uncertainty quantification.
Limitations: single brand (Tasty Tom), single municipality (Winneba), student population not representative of general Ghanaian adult population, only Pb and Sn measured (other metals not assessed), convenience sampling of student consumers.
Implications
Certification: Demonstrates that retail display conditions (sunlight vs enclosed storage) measurably affect Pb concentration in canned tomato products. Sunlight exposure increases Pb, likely through temperature acceleration of metal migration from can linings. While concentrations remain below regulatory limits, the ILCR analysis shows that high-volume consumers may face elevated long-term risk. Relevant for certification programs considering packaging handling and storage requirements upstream of retail.
Courses: Useful for illustrating how post-manufacture storage conditions can affect heavy metal migration — a supply-chain and retail environment angle that complements processing-stage contamination discussions. The ILCR calculation methodology is a teaching case for probabilistic risk assessment in developing country contexts.
App: Canned tomato mix Pb: mean ~0.038–0.052 mg/kg (38–52 µg/kg) depending on storage conditions; Sn within regulatory limits but not numerically reported in abstract. Note: B-tier (thesis, single brand, single site, West Africa context).