Scary facts on tuna

Tuna, a finfish belonging to the mackerel family, is a popular and inexpensive source of protein and widely served, from sandwiches, salads to gourmet dishes.  But a neurotoxin of extreme danger to human health, mercury, is plaguing our popular tuna dishes.  Recent years of marine and chemical research raised serious questions about the health risks associated with tuna, and there are certain facts about today’s commercial tuna that everyone ought to know.  Uneasy and scary facts, but everyone especially tuna lovers, ought to know.

Unsafe mercury levels

By consuming tuna, humans ingest small, but potentially harmful amounts of the metal mercury.  Unfortunately, the levels of mercury in tuna and other fish cannot be removed or reduced by any form of processing or food preparation.  The redflag was rasied when recent scientific research showed that mercury levels in tuna are higher, and potentially much higher than thought for many years.  This left the US Food and Drug Administration embarrassed  about their publishing of inaccurate and unreliable information, particularly as human health is involved.  But at what point of tuna consumption does mercury levels become considered as unsafe?

The US Mercury Policy Project reported that consuming two medium-sized portions of tuna per week can potentially result in mercury exposure up to six times higher than acceptable levels of mercury exposure.  The Mercury Policy Project issued a warning particularly for children: due to their low body mass, tuna consumption by children should be carefully monitored.  The ratio of lower body mass to mercury levels is of greater health concern.

Serious health concerns

Exposure to excessive levels of mercury can cause kidney failure and permanent brain damage in humans.  Furthermore, mercury exposure in young children, infants and fetuses is especially known for negatively impacts on neurological development.  The US National Institute of Health warns against exposing fetuses to even low levels of mercury from the mother’s diet as the brain and nervous system development can be severely affected.

Why the high mercury levels in tuna?

Anthropogenic mercury levels in the natural environment far exceed natural mercury levels – and human activities continue to vastly increase mercury levels.  Mercury level estimation due to human activities exceeds natural mercury levels by two to five fold.  Volcanoes are a natural source of atmospheric mercury emissions, but human activities since the Industrial Revolution has vastly contributed to unnaturally high levels of mercury in the natural environment.  Industrial activities including power plants, smelting plants, waste incinerators emit mercury particles into the atmosphere.  These particles soon contribute to land and water mercury pollution from rain or particle fall out.  The total mercury content in the world’s oceans is estimated at double the atmospheric mercury content.  When coming into contact with water, mercury is chemically converted into methylmercury.  Fish intake of methylmercury occurs directly from polluted ocean waters and so the food chain contamination begins.  And it is particularly this form of mercury, methylmercury, the most toxic form of this metal, which poses the greatest risk for biological matter as it bioaccumulates through the food chain aggressively.  Consider this figure of the mercury cycle:

Mercury Cycle (Source: teachers.yale.edu)

Do you need to avoid eating tuna?

The true safety of tuna is not easily determined as mercury levels can vary drastically, due to biological stock but also geographical origin of the tuna.  Avoiding chemical pollution through food sources is very much a personal decision – but there are certain guidelines in place for what is thought to be safe consumption of tuna.  For an average weight of 130lbs or 59kg, the recommendation is for no more than one can albacore tuna per two weeks and no more than one can of chunk tuna per five days.  More conservative tuna consumption is advised for high risk categories, including young children, infants and pregnant women.

Based on the scientific data mentioned before, a tuna calculator has been developed to calculate volumes of tuna for consumption.

Considering the type and geographical origin of the tuna consumed is strongly advised.  The larger White Albacore tuna species have mercury levels three times higher than smaller tuna species such as the skipjack.  For this reason, the US Food and Drug Administration recommended less frequent consumption of the White Albacore, but chunk light tuna can be consumed more regularly.  Tuna from certain waters have also been found to have higher mercury contamination.  Tuna from Asian or American waters is known for lower mercury levels than tuna from Latin American waters.

This situation might change in future as countries across the world continue to adopt more stringent environmental and pollution prevention legislation.  But for the time being, be sure to know your tuna!

 

A reader asked Word from the Savanna to explain the environmental induced health risks of tuna.  Do you have any environmental questions? Ask us!

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Sources: Mercury Alert: Is canned tuna safe to eat?; School tuna contains excessive mercury, environmentalists’ report say

Photo credits: some rights reserved by eFF-BKK, anthro_aya and Justin Woolford via flickr.

 

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