Aguilar-Miranda et al. 2024 — Total mercury in canned tuna sold in Quito, Ecuador
This study quantified total mercury (tHg) in 60 cans of tuna in water purchased from supermarkets in Quito, Ecuador, representing the three most widely consumed brands, using cold vapor atomic fluorescence spectrometry (CVAFS). Only tHg was measured; MeHg speciation was not performed, though the authors followed US EPA guidance treating THg as equivalent to MeHg for risk assessment purposes. Results found 96.7% of samples below the 1.0 mg/kg limit set by the EU (Commission Regulation 2023/915), FAO, and Ecuador’s NTE INEN 184:2013, with one batch from Brand B (intermediate price tier, most consumed in Ecuador) exceeding that limit at 1.98 mg/kg; non-carcinogenic risk calculations showed Brand B’s mean concentration yields an hazard quotient above 1 for children consuming 40 g weekly. The study provides a rare Latin American dataset on canned tuna Hg with brand-level variation and species-linked discussion, though tuna species were not consistently labeled on packaging.
Key numbers
- Brand A (lowest price): mean tHg 0.14 ± 0.11 mg/kg w.w., range 0.02–0.37 mg/kg; n=20 cans (30 samples per year × 2 years, reported as combined 60)
- Brand B (intermediate price, most consumed): mean tHg 0.41 ± 0.42 mg/kg w.w., range 0.12–1.98 mg/kg; n=20 cans; one lot reached 1.98 ± 0.42 mg/kg, exceeding EU/FAO/NTE INEN limits
- Brand C (highest price, labeled Thunnus albacares): mean tHg 0.25 ± 0.22 mg/kg w.w., range 0.04–0.78 mg/kg; n=20 cans
- EU/FAO/NTE INEN limit for tHg in tuna muscle: 1.0 mg/kg (fresh weight); FAO Codex limit: 1.2 mg/kg
- PTWI for MeHg (JECFA 2021): 1.6 µg/kg body weight/week
- Recommended maximum weekly intake per brand (based on highest THg, adults/children): Brand A: 306 g/63 g; Brand B: 57 g/12 g; Brand C: 144 g/30 g
- Non-carcinogenic risk (Rx) for children at mean Brand B tHg: 1.6 (exceeds threshold of 1); Brand A: 0.5; Brand C: 0.97
- Literature review reports THg range 0.005–1.4725 mg/kg in canned tuna across Latin America
- Approx. >89% of tHg in tuna muscle is in methylated form per cited references (Burger and Gochfeld 2004; Médieu et al. 2022), but MeHg was not independently measured in this study
Methods (brief)
Sixty cans (20 per brand) purchased from Quito supermarkets, March 2022–March 2023. Tuna meat homogenized, freeze-dried 48 h at −50 °C; microwave-assisted acid digestion (MARS 6, HNO3/H2O2/HClO4). THg quantified by Mercur Plus cold vapor atomic fluorescence spectrometer (Analytik Jena). Calibration curve 0.5–5 µg/L; LOD 0.10 µg/L; LOQ 0.34 µg/L. CRM IAEA-436A (tuna fish flesh homogenate): mean recovery 103% ± 5%. Results reported as wet weight (w.w.). Duplicate digestions per sample; Kruskal-Wallis and Wilcox pairwise tests for inter-brand comparison.
Note: only total mercury was measured. The authors explicitly did not speciate MeHg vs inorganic Hg; tHg was treated as MeHg for risk calculations per US EPA 2000 guidance. This is a conservative health-risk assumption, not a speciation result.
Implications
Certification: tHg data for canned tuna from Ecuador/eastern Pacific. Brand B’s one exceedance lot and its mean approaching the 0.5 mg/kg Ecuadorian limit are noteworthy, though most samples complied with international limits. The absence of species labeling on most brands limits HMT&C applicability without knowing species composition. EU limit (1.0 mg/kg) is relevant for tuna exported from Ecuador to the EU.
Courses: Illustrates within-product-category variance attributable to species, fish size, catch geography, and age; useful for supply-chain sourcing decisions.
App: tHg values in canned tuna from eastern Pacific (yellowfin, skipjack, bigeye): range 0.02–1.98 mg/kg w.w.; Brand-level mean range 0.14–0.41 mg/kg w.w.