Mercury in seafood: what level of toxins are we really ingesting?

Is seafood really part of a healthy diet? This is the question we should all be asking ourselves as seafood can contain methylmercury – a harmful neurotoxin that builds up in tissues over time, appearing in alarming numbers amongst some commercially fished species.

A study by Maine’s Biodiversity Research Institute in 2013 found that a staggering 84% of all fish contain unsafe levels of mercury. Monomethylmercury and dimethylmercury, which are frequently found in ecological systems as a residue of human activity, may severely contaminate marine ecology and consequently filter into the food chain. This became evident during the Minamata Disease epidemics in Japan that resulted from the daily intake of mercury-contaminated fish and shellfish.

So how toxic is the seafood that ends up in today’s markets? A study published in 2014 in the American Journal of Clinical Nutrition, found that in a sample of 10,673 adults who consumed seafood; the blood mercury concentration increased as the frequency of seafood consumption increased, more so in the case of tuna and wild salmon. These apex predators that feed on smaller, already contaminated fish, have even higher levels of mercury than oysters, lobsters and scallops. An average serving of one can of light tuna (Ahí or Yellowfin) contains around 20μg, white tuna (Albacore or Longfin tuna) contains around 50μg and red tuna (Bluefin) contains a whopping 100μg of Hg per serving. The Joint FAO/WHO Expert Committee on Food Additives considers the tolerable weekly intake to be 1.6μg/kg of body weight. That means a 70kg person will be exceeding this limit by consuming 2 cans of light tuna a week.

Common symptoms of mercury poisoning include peripheral neuropathy (presenting as itching, burning, pain, swelling, peeling of skin and formication - a sensation that resembles small insects crawling under the skin) and metabolic effects (that cause profuse sweating and salivation, tachycardia and hypertension). Other symptoms may include kidney failure, psychiatric symptoms, hypersensitivity to light and even hair, teeth and nail loss in children.

When you consider the benefits to the world’s oceans – and your own health, the decision to alter your consumption of fish seems fantastic. By simply changing our diets we can make a huge impact. Ready to try some plant-based seafood?