Venant et al. 2025 — Cadmium and lead in Lake Victoria sardine, Tanzania
This cross-sectional study assessed Cd and Pb concentrations in 279 samples of the small pelagic sardine Rastrineobola argentea collected from three regions of the Tanzanian Lake Victoria basin (Mwanza, Kagera, Mara), alongside a community-awareness survey of 425 sardine processors. All 279 samples fell below the FAO/WHO limit of 0.3 mg/kg for both metals. Median concentrations were low: Cd 0.012 ± 0.005 mg/kg and Pb 0.081 ± 0.057 mg/kg on a dry-weight basis. Health risk metrics (THQ, HI, cancer risk) were all well below thresholds of concern. Community awareness of heavy metal contamination was extremely low (96.2% unaware), though most processors had adopted raised drying racks that reduce contact with contaminated substrates.
Key numbers
n = 279 sardine samples; regions: Mwanza 114 (41.2%), Kagera 78 (27.8%), Mara 87 (31.1%).
Cd: overall mean 0.012 ± 0.005 mg/kg, median 0.012 mg/kg (dry weight). No regional difference (Kruskal-Wallis p = 0.1756). Dried sardine mean 0.013 ± 0.006 mg/kg; fresh sardine mean 0.010 ± 0.003 mg/kg (dry-weight-adjusted: 0.031 ± 0.009 mg/kg).
Pb: overall mean 0.082 ± 0.057 mg/kg, median 0.081 mg/kg (dry weight). No significant regional difference. Dried sardine mean 0.096 ± 0.054 mg/kg; fresh sardine mean 0.038 ± 0.044 mg/kg (dry-weight-adjusted: 0.119 ± 0.138 mg/kg).
All samples below FAO/WHO limit of 0.3 mg/kg for both Cd and Pb.
Estimated Daily Intake (EDI): Cd 1.043–1.175 × 10−5 mg/kg/day; Pb 2.704–3.047 × 10−6 mg/kg/day.
Target Hazard Quotient (THQ): Cd 0.0027–0.0031; Pb 0.0026–0.0029. Both far below 1.0.
Hazard Index (HI = sum of THQs): 0.0053–0.0060. Well below 1.0.
Target Cancer Risk (TR): Cd 1.70 × 10−5 to 1.92 × 10−5; Pb 1.03 × 10−9 to 9.99 × 10−5. Cd TR falls in the range requiring “attention” (10−6 to 10−4) but is near the lower bound.
Drying method effect on Pb: sand-dried and rock-dried sardines had higher Pb than rack-dried (rock median Pb 0.142 mg/kg vs. buti median 0.100 mg/kg). Cd was elevated in rack-dried (mean 0.016 mg/kg) vs. buti-dried (0.012 mg/kg), which was attributed to accumulation on surfaces rather than environmental contamination.
Dried sardines had Cd and Pb concentrations approximately 1.3× higher than fresh sardines on a raw-weight basis; after moisture correction (68% moisture in fresh), dried concentration was approximately 3× the fresh value.
Methods
Flame Atomic Absorption Spectrophotometry (FAAS; AAS 280 FS Varian). Microwave digestion (Milestone Ethos Easy) with nitric acid and hydrogen peroxide; 7.5 mL each, 180°C for 20 min. Samples filtered through Whatman No. 42, diluted to 50 mL. Air-acetylene flame; wavelengths 228.8 nm (Cd) and 324.7 nm (Pb). Calibration with Sigma Aldrich standards; R2 = 1.0. Spike recoveries: 93.5% (Cd), 102% (Pb). Fresh samples moisture-corrected to dry weight using 68% moisture content. Community survey: 425 participants, semi-structured questionnaire via KoboToolbox. Statistical analysis: Kruskal-Wallis nonparametric test for between-group comparisons; significance at p < 0.05.
Limitation: FAAS reports total Cd and Pb without speciation. The FAO/WHO 0.3 mg/kg limit used as comparator (from 1972) is less stringent than some current standards; the authors do not benchmark against EU or US limits. Study is dry-weight basis; wet-weight comparison with EU limits (which typically apply wet-weight) would require adjustment. Survey-based awareness data from self-selected processors at landing stations may not generalize to all consumers.
Implications
Certification: Lake Victoria sardine Cd and Pb levels are low relative to regulatory limits, consistent with the general finding that freshwater small pelagic fish from sub-Saharan lakes tend not to accumulate Pb and Cd at concerning concentrations under current conditions. The drying-method effect on Pb (sand vs. rack) is a supply-chain mitigation point relevant to sourcing and post-harvest handling guidance.
Courses: the community-awareness finding (96.2% unaware) is relevant to training material for food safety educators and public health officers in East Africa. The moisture-correction methodology (fresh to dry weight) is a useful worked example for analytical method modules.
App: the contamination profile for sardine/freshwater fish should reflect these low Cd/Pb levels, noting that drying method and proximity to mining/industrial inputs are variance drivers.