Excerpt from Mercury Study Report to Congress Volume Iii: Fate and Transport of Mercury in the Environment

This chapter first presents available measurement data for mercury in environmental media and biota. This is followed by a discussion of efforts to collect measurement data from remote locations and near anthropogenic sources of concern. Note that this chapter does include measured mercury concentrations in wildlife that function as vectors to humans but does not include measured concentrations in final receptors of concern (i.e., humans and selected wildlife receptors). Measurement data for people and wildlife are presented in Volumes IV and VI, respectively. A number of methods can be employed to determine mercury concentrations in environmental media. The concentrations of total mercury, elemental mercury, organic mercury compounds (especially methylmercury) and chemical properties of various mercuric compounds can be measured, although speciation among mercuric compounds is not usually attempted. Recent, significant improvements and standardizations in analytical methodologies enable reliable data on the concentration of methylmercury, elemental mercury and the mercuric fraction to be separated from the total mercury in environmental media. It is possible to speciate the mercuric fraction further into reactive, non-reactive and particle-bound components. It is generally not possible to determine which mercuric species is present in environmental media (e.g., HgS or HgCl). 2 One of the significant advances in mercury analytical methods over the past decade or so has been in the accurate detection of mercury at low levels (less than 1 µg/g). Over the past two decades mercury determinations have progressed from detection of µg levels of total mercury to picogram levels of particular mercury species (Mitra, 1986 and Hovart et al., 1993a and 1993b). Typical detection limits for data used or presented in this study are on the order of 1 to 2 ng/L for water samples (Sorensen et al., 1994), 0.1 ng/g for biota (Cappon, 1987; Bloom, 1992) and 0.1 ng/m for atmospheric samples (Lindberg 3 et al., 1992). Mercury contamination of samples has been shown to be a significant problem in past studies. The use of ultra-clean sampling techniques is critical for the more precise measurements required for detection of low levels of mercury. Based on the current understanding of the mercury cycle, mercury is thought to be transported primarily through the atmosphere and distributed to other compartments of the environment (Chapter 2). The primary source of mercury in terrestrial, aquatic and oceanic environments appears to be the wet or dry deposition of atmospheric mercury. Once deposited, the mercury may be revolatilized back to …