Speciation of Mercury

Evaluation of the Form of Speciation of Mercury in Hackensack Meadowlands White Perch


As a result of a recent project in the Hackensack Meadowlands, the “Aquatic Animal Assessment and Inventory”, it was determined that white perch were probably unsafe for human consumption because of mercury and PCB contamination. This proposal is specifically for achieving more accurate data and understanding of the mercury problem. We propose to re-assess this issue by analyzing another 12 fish from the archived collection for methylmercury, because only 8 fish were analyzed so far (and methylmercury is much more toxic than inorganic mercury). Since this fish species is sought by local fishers, it is important that the state agencies responsible for protecting the citizenry have appropriate information on which to base their decisions.

During 2001-2003, personnel of the Meadowlands Environmental Research Institute (MRRI), along with investigators from Rutgers University and the University of Medicine & Dentistry of New Jersey (UMDNJ), in a multi-faceted project, the “Aquatic Animal Assessment and Inventory”, demonstrated that there is a healthy population of the white perch (Morone americana) in the Hackensack Meadowlands (HM). The UMDNJ part of the project involved analyzing the fish for toxic contaminants: a suite of trace metals including mercury (Hg). These were anticipated to be problematical because of the existence of a Superfund site with very high Hg contamination. The results of the analysis showed that there were substantial numbers of white perch in which the Hg level exceeded the FDA/EPA guideline for consumption of more than one meal per month (Weis, 2005). Furthermore, the Hg levels were higher in larger fish – those that would be likely to be kept by fishers – and higher during the summer months – when more people are out fishing in the HM. However, there are some uncertainties that should be cleared up.

The most toxic species of Hg found in aquatic organisms is the monomethylated form, methylmercury (meHg). The FDA/EPA guideline (USEPA, 1999) for Hg was determined using a risk assumption based on the then available information that virtually all the Hg in fish is meHg (Bloom, 1992). However, the 8 white perch that we had analyzed for meHg had much less of their total Hg methylated, just 18.1 ± 9.7%. This is low. Kannen et al (1998) analyzed Hg speciation in a large number of Florida fish species and found that meHg could be anywhere from 20% to 100% of the total Hg, but with most species having >80% (as anticipated in the federal consumption guidelines.) More relevant to this proposal, white perch in the Chesapeake have been found to have 28 ± 14% methylation (Mason, 2004), a value which is significantly different from ours (t = 2.327, P < 0.05). [It should be noted, however, that Mason (2004) found site differences in percent of methylation of Hg.] If most of the Hg in white perch is inorganic, then much of it would not be biologically available (Wallace et al, 2003), and thus not so much of a health risk. But the possibility of lifting a ban on white perch consumption should not be made on the basis of analysis of only 8 fish.

This study will analyze more white perch specimens for meHg so that there is a significant amount of samples on which to draw conclusions. The final product resulting from this study will be integrated with available MRRI data in a GIS format and used to predict percent methylation in neighboring unsampled areas via contour mapping.

University of Medicine & Dentistry of New Jersey

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