Xu et al. 2025 — Heavy metal risks in aquatic foods: global assessment (Environment International)
This landmark open-access study in Environment International represents the first comprehensive global-scale assessment of heavy metal contamination in aquatic foods, analysing 138,281 records from the WHO FOSCOLLAB database covering mercury, cadmium, lead, and arsenic in fish, molluscs, crustaceans, and cephalopods. Authors include FAO Fisheries and Aquaculture Department researchers and Johns Hopkins Center for a Livable Future, giving the study strong institutional backing. The headline findings are: 97.6% of aquatic food products met safety standards globally; mercury is the primary non-cancer health risk (95% of global Targeted Hazard Quotient from aquatic foods); and cadmium and arsenic are the predominant contributors to cancer risk. Mercury is biomagnified through the food chain (high trophic-level fish accumulate more), while cadmium, lead, and arsenic exhibit biodilution (benthic/filter-feeding molluscs and crustaceans accumulate more). Critically, the risk-benefit assessment showed that for all aquatic species, the cardiovascular and cognitive benefits of EPA+DHA consumption exceed the heavy metal-associated risks — current global consumption is below the risk-based safe consumption limits for all species.
Key numbers
Compliance rates with safety standards (n = 138,281):
- Overall: 97.6% compliant
- Mercury: 96.2% compliant
- Cadmium: 97.2% compliant
- Lead: 99.6% compliant
- Arsenic: 99.5% compliant
- Species below 90% compliance: bream, flounder, mackerel, salmon, sharks (mercury); scallops, crabs, squid (cadmium); bream, rays (arsenic)
Health risk at national/regional level:
- 69 countries: mercury THQ exceeded non-cancer risk threshold
- 20 countries: cadmium cancer risk exceeded threshold
- 16 countries: arsenic cancer risk exceeded threshold
- 152 countries: within acceptable health risk thresholds overall
Trophic-level patterns (key findings from Random Forest model):
- Mercury: trophic level is the dominant predictor; large, long-lived top predators accumulate most (sharks, rays, tuna)
- Cadmium, Pb, As: benthic/low-trophic species accumulate most; scallops, oysters, squids highest Cd; clams, oysters, mussels highest Pb and As
- For fish specifically, resilience is the most important predictor followed by body size and trophic level
Species and geographic differences (from compliance analysis):
- Southern European countries (Spain, Italy, Greece, Malta): cadmium compliance rates 91.7–96.1%, below global average
- Northern European countries (Denmark, Norway, Sweden, Finland): compliance 98.5–100%
- Spain and Hong Kong: cadmium compliance below 90%
- China and Singapore: lead compliance in aquatic products above 90% but far below global average
Consumer guide (risk-based limits for selected species):
- Scallops: risk-based consumption limit 2.5 g/day (cadmium-driven FIRCR)
- Sharks: risk-based consumption limit 14.1 g/day (mercury-driven FIRTHQ)
- 71.4% of aquatic food production: “Best Choices” (recommended daily max ≥ 40 g/day)
- 17.6%: “Good Choices” (20–40 g/day)
- 11.0%: “Choices to Control” (< 20 g/day, high risk)
Global intake estimates (annual):
- Mercury intake from aquatic foods: 12.1 tonnes (95% CI: 11.7–12.5)
- Cadmium intake: 1.7 tonnes (95% CI: 1.6–1.8)
- Lead intake: 1.8 tonnes (95% CI: 1.6–2.0)
- Arsenic (inorganic) intake: 0.4 tonnes (95% CI: 0.2–0.9)
Risk-benefit: Cancer mortality from aquatic food heavy metal intake is roughly 1/1,000 the cardiovascular mortality prevented by EPA+DHA. All countries achieve net positive benefit from aquatic food consumption.
Methods (brief)
Data source: WHO FOSCOLLAB database, 138,281 records; standardized collection protocols and quality assurance. Species classified per FAO/WHO framework. FAO global aquatic food consumption data used for intake estimates. Random Forest models for ecological trait analysis. Monte Carlo simulation for population-level risk scenarios. Received May 2025; accepted September 2025; published online October 2025. CC BY licence, open access. LOD handling and speciation: arsenic reported as total arsenic (tAs) in most records; inorganic fraction estimated using published iAs/tAs ratios by species category. Hg treated as MeHg for fish consumption purposes (consistent with regulatory frameworks) but note that the primary measurement is total Hg.
Implications
Certification: This is the most comprehensive global aquatic food heavy metal dataset available, drawn from WHO FOSCOLLAB. Key certifiable findings: molluscs and cephalopods are Cd-risk categories; large predatory fish are Hg-risk categories; 97.6% global compliance rate means most aquatic products are within safety limits, but tail-end species (sharks, scallops, bivalves) present elevated risk. Consumer guidance metrics (species risk classifications) are directly applicable to HMT&C product-category assessments for seafood.
Courses: Essential reference for the seafood module — biomagnification vs biodilution distinction, trophic level predictors, the risk-benefit framework showing benefits outweigh risks for almost all consumption levels. Kiribati mercury example is a compelling case study for high-consumption island nations.
App: Species-level risk classification directly applicable: app should flag shark, tuna, mackerel, flounder for mercury; scallops, squid, crab for cadmium; clams, oysters, mussels for arsenic and lead. Risk-based consumption limits can inform “how much is too much” messaging.