Are mercury levels in commonly eaten fish getting worse over time?
Mixed. Mercury levels in some fish species have improved since 1990s regulations. But levels in other species, particularly large predatory fish, remain high and some are increasing as ocean mercury pollution continues.
What's actually in it
Mercury enters the ocean from industrial pollution and natural volcanic sources. It's converted to methylmercury by bacteria in sediment. Fish absorb it through their food, and it accumulates up the food chain. Big, long-lived predatory fish like swordfish, shark, king mackerel, and bigeye tuna have the highest levels because they eat many smaller fish over decades.
Pregnant women and young children are advised to limit high-mercury fish because methylmercury is a potent neurotoxin that crosses the placenta and damages developing brains.
What the research says
A 2026 Bayesian analysis of mercury levels and trends in fish from 2011-2021 found that trends varied significantly by species. Some fish showed declining mercury levels over the decade. Others, particularly larger open-ocean predators, showed stable or increasing levels despite global emission reduction efforts. Ocean mercury accumulation takes decades to respond to emission reductions.
The practical guidance from this research: fish choice matters more than reducing fish consumption overall. Low-mercury fish (salmon, sardines, tilapia, trout, shrimp, catfish) provide nutritional benefits without significant mercury risk. Limiting swordfish, shark, king mackerel, and fresh/frozen tuna to once a month or less is the relevant risk-reduction strategy.
The research at a glance
| Study | Journal | Year |
|---|---|---|
| Mercury levels and trends in fish (2011-2021): A Bayesian approach with multi-group GAMM models | Environ Sci Technol | 2026 |
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