Mercury (Hg) is a toxic heavy metal with no beneficial biological role. Blood mercury testing measures the concentration of total mercury in whole blood, primarily reflecting recent or ongoing exposure to methylmercury (from fish consumption) or inorganic mercury (from industrial or dental sources). Methylmercury is the most bioavailable and neurotoxic form.
Mercury is a potent neurotoxin affecting the central and peripheral nervous system, kidneys, and immune system. The developing foetal brain is particularly vulnerable. Elevated blood mercury from regular high fish consumption (particularly large predatory fish such as shark, swordfish, and orange roughy) is the most common cause in developed countries including Australia.
FAQs
Which fish have the most mercury?
Shark (also sold as flake), swordfish, broadbill, marlin, orange roughy, gemfish, and southern bluefin tuna have the highest mercury levels. Salmon, sardines, herring, trout, flathead, and most prawns and shellfish are low in mercury and considered safe to eat regularly.
Should pregnant women avoid all fish because of mercury?
No. Australian guidelines recommend pregnant women eat 2-3 serves of low-mercury fish per week for omega-3 benefits, while limiting or avoiding high-mercury species (shark, swordfish, orange roughy). The benefits of fish consumption for foetal brain development outweigh mercury risks when low-mercury species are chosen.
Can dental fillings cause mercury poisoning?
Dental amalgam fillings release very small amounts of inorganic mercury vapour, well below levels associated with toxicity in most people. Blood and urine mercury may be marginally higher in people with many fillings but are generally within safe ranges.
Is hair mercury a better test than blood mercury?
Hair mercury reflects longer-term methylmercury exposure (months rather than weeks) and is useful for assessing dietary exposure patterns. Blood mercury reflects more recent exposure. Both have valid clinical applications depending on the clinical question.
