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Subject: Mercury in fish
From: John Sibert <[log in to unmask]>
Reply-To:Scientific forum on fish and fisheries <[log in to unmask]>
Date:Tue, 23 Dec 2008 16:56:29 -1000

text/plain (62 lines)

is a complex issue.

It seems to me that if you want to reduce the Hg content of fish, you 
are making the assumption that it has increased recently and that the Hg 
content of fish is amenable to human intervention. So, how does mercury 
get into marine fish fish?

 From Kraepiel, et al 2003, Sources and variations of mercury in tuna. 
Environ. Sci. Technol. 37: 5551-5558

> While the bulk of human exposure to mercury is through the consumption 
> of marine fish, most of what we know about mercury methylation and 
> bioaccumulation is from studiesof freshwaters. We know little of where 
> and how mercury is methylated in the open oceans, and there is 
> currently a debate whether methylmercury concentrations in marine fish 
> have increased along with global anthropogenic mercury emissions. 
> Measurements of mercury concentrations in Yellowfin tuna caught off 
> Hawaii in 1998 show no increase compared to measurements of the same 
> species caught in the same area in 1971. On the basis of the known 
> increase in the global emissions of mercury over the past century
> and of a simple model of mercury biogeochemistry in the Equatorial and 
> Subtropical Pacific ocean, we calculate that the methylmercury 
> concentration in these surface waters should have increased between 9 
> and 26% over this 27 years span if methylation occurred in the mixed 
> layer or in the thermocline. Such an increase is statistically 
> inconsistent with the constant mercury concentrations measured in 
> tuna. We conclude tentatively that mercury methylation in the oceans 
> occurs in deep waters or in sediments
Also the highest levels of mercury contamination are found in fresh 
water, downwind from coal fired power plants.

Is tuna safe to eat? It is hard to say. Tunas don't live in fresh water, 
and most places where they are caught are at long distances rom coal 
fired power plants (and everything else for that matter). I eat a lot of 
fresh tuna and swordfish here in Honolulu. Seafood safety depends the 
kind of seafood and what you take in with it, particularly selenium. It 
is a multidimensional problem without a simple answer. See So far 
regulatory agencies seem disinclined to consider multidimensional problems.

Happy Holidays,

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In theory, there is no difference between theory and practice. In practice there is. Yogi Berra

John Sibert, Manager
Pelagic Fisheries Research Program
University of Hawaii at Manoa
1000 Pope Road, MSB 313
Honolulu, HI 96822
United States

Phone: (808) 956-4109
Fax: (808) 956-4104
Skype: john.sibert

PFRP Web Site:
email: [log in to unmask]

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