Mercury Level

Methylmercury (MeHg) is produced by sulfate-reducing bacteria methylating inorganic mercury in aquatic sediments and bioconcentrates approximately 1–10 million-fold between water and top predators. Biomagnification means each trophic step increases tissue concentrations by a factor of ~10. Short-lived, planktivorous species (sardines, anchovies, wild salmon) typically contain <0.1 ppm MeHg; long-lived apex predators (swordfish, shark, bigeye tuna) often exceed 1 ppm. The FDA/EPA advises pregnant women to avoid high-mercury fish and limit albacore tuna to 170g per week. Selenium in fish tissue partially counteracts methylmercury toxicity by forming a seleno-protein complex, explaining why high-selenium fish (tuna) may pose less risk than predicted by mercury content alone.