12 January - 20 June 2016

Mercury levels are up in Pacific yellowfin tuna

12 February 2015

An article published in the recent Journal of Environmental Toxicology and Chemistry addresses the issue of consumption of mercury-contaminated fish and the related neurological damage in humans. For example in the United States between 300 000 and 600 000 children are born annually with a mercury concentration in the cord blood over 5.8 µg/l, which is associated with significant loss of IQ (intelligence quotient). 

Humans are exposed to mercury primarily by consumption of fish that swim in waters polluted by industrial point-source water discharges and in the open ocean. The main source of mercury in the open ocean is believed to be atmospheric deposition resulting from human activity such as example fossil fuel combustion and artisanal gold mining.

Drevnick et al. report their analysis and interpretation of data on the mercury concentration in a yellow-fin tuna from waters near Hawaii (USA). The authors compiled already published data on mercury present in muscle tissues of fish caught in 1971, 1998 and 2008. The accurate analysis of the metal in fish samples was ensured by strict adherence to quality system and the use of atomic absorption spectrophotometry as an analytical technique. 

When analysing the data researchers took careful consideration of the size of tuna and analysed tuna that weight between 22-76 kg. This is due to the difference in the diet between big and small tuna and lower mercury concentration in young tuna (less than 22 kg). 

The outcome of the analysis by Drevnick et al. is that there is no change in tuna mercury between 1971 and 1998 which leads to the conclusion that the source of metal is natural and it comes from deep waters, which is in agreement with previous studies. However, there is also a body of evidence suggesting that natural sources of mercury are not strong enough to supply foodwebs, that fish get mercury from more shallow depths in the ocean and there is an increase in levels of mercury oceanwide. Drevnick and colleagues demonstrated an annual increase of 3.8% in mercury concentration in tuna between years 1998-2008. This follows the data reported by others who noticed rises in tuna mercury concentrations in years from 2002 to 2006 and from 1995 to 2006. 

Drevnick et al. suggest that the re-analysis of data compiled from previous years support the argument that mercury concentration in waters and fish is increasing as a result of human activity. Mercury contamination of fish is a serious global issue. For example the concentration of mercury in North Pacific Ocean is expected to double by 2050. United Nations Environment Programme called Minamata Convention on Mercury calls for reduction in atmospheric mercury emission.

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