Correspondence Comment on “Sources and Variations of Mercury in Tuna” The authors make a good case that mercury levels in tuna caught in the vicinity of Hawaii have not changed significantly since the 1970s. However, one of their main inferences, that concentrations of mercury in tuna in general are not responding to atmospheric pollution, is unwarranted. Data support the authors’ assertion that, at the global level, mercury emissions have increased since the 1970s and that these increases have been driven largely by increased emissions from regions in eastern Asia. However, to assume that surface ocean waters as a whole in the region bounded by 30°N and 30°S and 75°W and 150°E will uniformly increase in mercury content to a degree corresponding to the increase in overall atmospheric emissions is to assume that the atmosphere over this region and the water in this region are well-mixed with respect to mercury. This assumption appears untenable. The evidence the authors present appears to relate specifically to the waters in which the fish were caught and thus does not support inferences about mercury increases in fish from other large-scale ocean areas that are more directly affected by regional Hg emissions. A recent modeling study (Dastoor, A. and Larocque, Y. Atmos. Environ. 2004, 38, 147-161) estimates that the deposition flux of total mercury in the Hawaiian Islands region * Corresponding author phone: michael.aucott@ dep.state.nj.us.
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is not greatly impacted by sources in Asia compared with many other ocean regions. Most of the Hg deposition associated with these sources, much of which is particlebound or reactive gaseous mercury, which have short atmospheric lifetimes, is predicted to occur much closer to the continent. Thus increased mercury emissions from sources in Asia would not be expected to impact waters in the Hawaiian Islands region. It is also likely that the surface ocean circulation in the vicinity of Hawaii brings in water from the relatively unpolluted western coast of North America, which could also contribute to relatively low levels of mercury in these waters now as well as in the 1970s. Therefore it would not be expected that the tuna caught near Hawaii would show a change in mercury concentrations, and the lack of such change would not provide useful information about Hg accumulation in tuna or other ocean fish in general. Samples of canned tuna have been shown to vary significantly in mercury content. Until data are available that can relate atmospheric emissions to ocean mercury concentrations in impacted areas and that can relate concentrations in tuna to mercury concentrations in those ocean areas, it is unwarranted to assume that tuna mercury concentrations are not responding to atmospheric pollution.
Michael Aucott* New Jersey Department of Environmental Protection P.O. Box 409, Trenton, New Jersey 08625-0409 ES0403817
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