Blanco et al. 2023 — Mercury in fish, Valencian Community, Spain, 2011–2017
This retrospective descriptive study analysed total mercury (THg) and methylmercury (MeHg) concentrations in 635 fish and seafood samples collected under the Generalitat Valenciana’s official food health surveillance programme between 2011 and 2017. Across all species and years, the median THg was 0.20 mg/kg wet weight and the median MeHg was 0.14 mg/kg wet weight. Swordfish/emperor (Xiphias gladius) was the highest-contaminated group (median THg 0.80 mg/kg), with 31.8% of swordfish samples exceeding the EU legal limit of 1 mg/kg; fresh tuna/albacore (median 0.46 mg/kg) and canned tuna (median 0.25 mg/kg) ranked second and third. Adjusted for the variable annual sampling weight of high-mercury species, the overall temporal trend was downward for THg; within swordfish specifically, THg declined approximately 7% per year. Mediterranean-origin fish showed higher THg than Atlantic- or Pacific-origin fish.
Key numbers
THg across all species, all years (n=560): median 0.20 mg/kg, geometric mean 0.18 (95% CI 0.16–0.20), range 0.01–2.70 mg/kg.
MeHg across all species, 2013–2017 (n=206): median 0.14 mg/kg, geometric mean 0.11 (95% CI 0.09–0.13), range 0.01–2.23 mg/kg.
THg by species group (all years, median and range):
- Swordfish/emperor: median 0.80, range 0.07–2.70 mg/kg; 31.8% exceeded EU limit (1 mg/kg)
- Fresh tuna/albacore: median 0.46, range 0.10–1.20 mg/kg; 2.8% exceeded EU limit
- Canned tuna: median 0.25, range 0.01–1.02 mg/kg; 1 sample exceeded limit (1.02 mg/kg)
- White fish: median 0.11 mg/kg; 1 rosada (Genypterus spp.) at 1.31 mg/kg exceeded 1 mg/kg limit
- Crustaceans: median 0.07 mg/kg
- Cephalopods: lower than crustaceans
- Mollusks, other blues, other canned/processed: lowest groups
Annual trend for THg (2011–2017): unadjusted trend appears variable; adjusted for proportion of swordfish in annual sampling, global trend is negative (decreasing). For swordfish specifically, beta = -0.07/year (95% CI -0.15; 0.01, p=0.09), corresponding to approximately 7% decrease per year.
THg annual medians (all species): 2011 = 0.06, 2012 = 0.23, 2013 = 0.32, 2014 = 0.49 (peak), 2015 = 0.07, 2016 = 0.15, 2017 = 0.35 mg/kg. Year-to-year variability was strongly influenced by sampling composition (swordfish proportion ranged 3.3%–59.3% of annual samples).
Geographic origin: fish from the Atlantic and Pacific showed significantly lower THg than Mediterranean-origin fish, adjusting for species type.
Values below LOQ (27% of total measurements) were imputed as LOQ/√2.
Methods (brief)
Official surveillance programme data from Generalitat Valenciana food safety laboratories (Valencia and Alicante). Sample collection 2011–2017. Methods: AAS (atomic absorption spectroscopy), CV-AAS (cold-vapour AAS), AAS-AMA-254 (advanced mercury analyser), and ICP-MS depending on year and laboratory. LOQ range: THg 0.02–0.10 mg/kg (variable by lab and technique); MeHg 0.01–0.02 mg/kg. Basis: wet weight throughout. Data follow EFSA chemical monitoring reporting guidance. Statistical analysis: multivariate linear regression on log2-transformed values; Kruskal-Wallis for non-parametric comparisons. MeHg available only from 2013 onward.
Implications
Certification: THg and MeHg data from 9 seafood categories, 2011–2017, Spanish market. Swordfish exceeds the EU 1 mg/kg limit in nearly a third of samples; this is the primary species of concern for consumer exposure. Tuna and canned tuna are lower-tier risks. The downward trend in swordfish THg from 2011–2017 is a positive signal, though still at high absolute levels. Mediterranean origin is a risk-amplifying factor. Relevant for seafood product-category pages and for any HMT&C seafood or meal-kit product categories.
Courses: Illustrates real-world regulatory limit exceedance rates, temporal trend methodology, and the importance of species-specific guidance for high-risk predatory fish.
App: Species-level THg values are directly applicable to seafood risk estimation. MeHg:THg ratio can be estimated from paired measurements (median THg 0.20, median MeHg 0.14 across all species, implying approximately 70% of THg as MeHg on average, but this average obscures wide species variation).
Microbiome: Not applicable.