Mercury Exposure from Fish - Effects and Prevention

Environmental and Occupational Health Pearls - June 2017: Mercury Exposure from Fish

A bi-monthly feature providing clinical information and resources from Public Health Ontario on matters relating to environmental and occupational health. This edition considers the most important questions for family physicians about mercury exposure from fish.

What's important for family physicians to know?

  • How are people exposed to mercury? For most people diet, and fish in particular, is the most significant source of mercury exposure.

    The half-life of mercury is approximately two to three months in humans.  In utero, transfer via the placenta can occur.  Mercury is also excreted in breast milk.  

  • What are the health effects? Fetal exposure to high levels of mercury has been linked with psychomotor and developmental delays, intellectual deficits, seizures, deafness, and blindness. (1-3)

  • What should I do? Discuss the benefits of fish intake with your patients and suggest they choose low mercury fish such as salmon or tilapia for frequent consumption.

    Routine testing of blood mercury levels is not necessary. 

    However, if patients report consuming fish that is high in mercury, e.g.,  fresh/frozen tuna, shark, swordfish, three or more times per week for several months, you might consider blood mercury testing in order to guide your advice about changing consumption patterns to lower mercury fish. 

  • What fish have the highest mercury levels?

    The amount of mercury in various fish species vary greatly by region. Your local public health unit can provide you with information on mercury levels in sport fish. For additional information and recommended servings, see Health Canada’s Consumption Advice: Making Informed Choices About Fish5

[1] Clarkson TW, Magos L, Myers GJ. The toxicology of mercury—current exposures and clinical manifestations. New England Journal of Medicine. 2003 Oct 30;349(18):1731-7.

[2] Holmes P, James KA, Levy LS. Is low-level environmental mercury exposure of concern to human health? Science of the total environment. 2009 Dec 20;408(2):171-82.

[3] Abadin HG, Hibbs BF, Pohl HR. Breast-feeding exposure of infants to cadmium, lead, and mercury: a public health viewpoint. Toxicology and industrial health. 1997 Jul 1;13(4):495-517.

[4] Statistics Canada.  Lead, mercury, and cadmium concentrations in Canadians, 2012 and 2013.  Statistics Canada Health Fact Sheets (82-625-X); 2015.  Available from:

[5] Bureau of Chemical Safety, Food Directorate, Health Canada, Government of Canada.  Making Informed Choices About Fish.  Ottawa, ON: Publications, Health Canada; 2017.  Available from: