Mary Anna Bogle

Form of mercury in stream fish exposed to high concentrations of dissolved inorganic mercury

The form of mercury predominating in mercury-contaminated fish from both pristine and industrialized waters in North America and Europe has almost universally been methylmercury. Sunfish (Lepomis auritus) living in a stream contaminated with 0.5-1 micrograms/L dissolved inorganic mercury accumulated greater concentrations of total mercury at headwater sites, where the dissolved mercury concentrations were greatest, than they did at downstream sites. However, despite evidence from laboratory studies that dissolved inorganic mercury is rapidly accumulated by fish without transformation to methylmercury, methylmercury constituted 85% or more of the total mercury concentration in fish at all sites.

Response of mercury contamination in fish to decreased aqueous concentrations and loading of inorganic mercury in a small stream.

Approximately 250 000 kg of mercury was lost towater and soils at the U.S. Dept. of Energy Y-12 Plantin Oak Ridge, Tennessee in the 1950s and early 1960s. A creek originating within the plant receivedcontinuous inputs of waterborne mercury, predominantlyas dissolved inorganic mercury, from groundwater,streambed contamination, and sump and process waterdischarges to the contaminated storm sewer network.These produce aqueous total mercury concentrations of1–2 μg L-1 in the upper reaches of the stream,decreasing to about 0.1–0.2 μg L-1 in its lowerreaches. A program to reduce mercury concentrationsin the creek identified specific sources (buildingsumps, contaminated springwater seeps, foundationdrains, and contaminated piping) and rerouted wateraround contaminated portions of the drain system orcollected and treated mercury-contaminated waterbefore discharging it. As a result, waterbornemercury concentrations in the creek and total mercuryloading were reduced from 1.8 μg L-1 to0.6 μg L-1 and 100 to 20 g d-1, respectively, in the last 5 yr.Mean mercury concentrations in fish nearest sourceareas in the creek headwaters decreased at roughly thesame rate as waterborne total mercury concentrationsover the past five years, but at the facility boundarydownstream the decline in mercury bioaccumulation wasmuch less. At sites 5–15 km farther downstream, nodecrease was evident. Dissolved methylmercury tendedto increase with distance downstream in a patterninverse to that noted for its dissolved inorganicmercury precursor.Improvements in water quality and modification ofweirs to allow the passage of fish have resulted inthe establishment of large populations of fish inmercury-contaminated headwater areas previously devoidof fish. It may be that the accumulation, retention,and eventual downstream transport of this reservoir ofbiologically incorporated methylmercury has acted tobuffer against expected reductions in mercury in fishat downstream sites.

Bioaccumulation Factors for Mercury in Stream Fish

The bioaccumulation of methylmercury in fish is a complex process affected by many site-specific environmental factors. The US Environmental Protection Agency (USEPA) recently recommended changing the basis for expressing the ambient water quality criterion for mercury from an aqueous concentration to a measure of the methylmercury concentration in fish. This change would make the regulation of mercury in surface waters a site-specific exercise in which fish-based bioaccumulation factors (BAF; the ratio of mercury concentration in fish to the concentration of mercury in water) are used to calculate aqueous concentration limits for total mercury. These limits would then be used to allocate mercury loading among various point and nonpoint sources and guide regulatory actions. In order for this approach to succeed, it is critical that the site-specific BAFs and methylmercury:total mercury conversion factors be independent of aqueous total mercury concentration (HgT). We investigated this relationship by measuring aqueous methylmercury and HgTs and mercury in fish in ecologically similar warm-water streams in the southeastern United States. Bioaccumulation factors based on HgT in water were found to decrease with increasing HgT, primarily as a consequence of the reduction in the ratio of aqueous methylmercury to total mercury with increasing HgT. Methylmercury-based BAFs did not vary as a function of HgT. The implication of this relationship is that site-specific determination of aqueous HgT limits at contaminated sites may use BAFs that would be underestimates of the appropriate BAFs to describe mercury bioaccumulation in the system after mercury inputs have been reduced. In such cases, regulatory limits set using site-specific BAFs might not achieve their intended purpose of reducing mercury contamination in fish to acceptable concentrations.

Airborne Emissions of Mercury from Municipal Solid Waste. I: New Measurements from Six Operating Landfills in Florida

Abstract Mercury-bearing material enters municipal landfills from a wide array of sources, including fluorescent lights, batteries, electrical switches, thermometers, and general waste; however, the fate of mercury (Hg) in landfills has not been widely studied. Using automated flux chambers and downwind atmospheric sampling, we quantified the primary pathways of Hg vapor releases to the atmosphere at six municipal landfill operations in Florida. These pathways included landfill gas (LFG) releases from active vent systems, passive emissions from landfill surface covers, and emissions from daily activities at each working face (WF). We spiked the WF at two sites with known Hg sources; these were readily detected downwind, and were used to test our emission modeling approaches. Gaseous elemental mercury (Hg0) was released to the atmosphere at readily detectable rates from all sources measured; rates ranged from ∼1–10 ng m−2 hr−1 over aged landfill cover, from ∼8–20 mg/hr from LFG flares (LFG included Hg0 at μg/m3 concentrations), and from ∼200–400 mg/hr at the WF. These fluxes exceed our earlier published estimates. Attempts to identify specific Hg sources in excavated and sorted waste indicated few readily identifiable sources; because of effective mixing and diffusion of Hg0, the entire waste mass acts as a source. We estimate that atmospheric Hg releases from municipal landfill operations in the state of Florida are on the order of 10–50 kg/yr, substantially larger than our original estimates, but still a small fraction of current overall anthropogenic losses.

Airborne Emissions of Mercury from Municipal Solid Waste. II: Potential Losses of Airborne Mercury before Landfill

Abstract Waste distribution and compaction at the working face of municipal waste landfills releases mercury vapor (Hg0) to the atmosphere, as does the flaring of landfill gas. Waste storage and processing before its addition to the landfill also has the potential to release Hg0 to the air if it is initially present or formed by chemical reduction of HgII to Hg0 within collected waste. We measured the release of Hg vapor to the atmosphere during dumpster and transfer station activities and waste storage before landfilling at a municipal landfill operation in central Florida. We also quantified the potential contribution of specific Hg-bearing wastes, including mercury (Hg) thermometers and fluorescent bulbs, and searched for primary Hg sources in sorted wastes at three different landfills. Surprisingly large fluxes were estimated for Hg losses at transfer facilities (∼100 mg/hr) and from dumpsters in the field (∼30 mg/hr for 1,000 dumpsters), suggesting that Hg emissions occurring before landfilling may constitute a significant fraction of the total emission from the disposal/landfill cycle and a need for more measurements on these sources. Reducing conditions of landfill burial were obviously not needed to generate strong Hg0 signals, indicating that much of the Hg was already present in a metallic (Hg0) form. Attempts to identify specific Hg sources in excavated and sorted waste indicated few readily identifiable sources; because of effective mixing and diffusion of Hg0, the entire waste mass acts as a source. Broken fluorescent bulbs and thermometers in dumpsters emitted Hg0 at 10 to >100 μg/hr and continued to act as near constant sources for several days.

Lead in vegetation, forest floor, and soils of the Great Smoky Mountains National Park☆☆☆

Abstract The scarcity of lead toxicity data for forest plant species and the increasing concern over the possible role of metals in the decline of forests in western Europe and thet Eastern United States necessitate that lead and other metals be closely monitored in these important forest ecosystems. Samples of vegetation, forest floor material, and soil were collected at five spruce-fir sites and two hardwood sites in the Great Smoky Mountains National Park (GSMNP). Mean forest floor lead concentrations were lower than average values reported in an earlier EPA study of lead levels in the GSMNP, and lower than recently published values for similar sites in the northeastern United States and western Europe. As expected, lead concentrations increased (1) with increasing age of coniferous foliage, (2) with increasing site elevation for foliage and forest floor material, and (3) with increasing degree of decomposition of forest floor material.

Mercury source zone identification using soil vapor sampling and analysis

Development and demonstration of reliable measurement techniques that can detect and help quantify the nature and extent of elemental mercury (Hg(0)) in the subsurface are needed to reduce uncertainties in the decision-making process and increase the effectiveness of remedial actions. We conducted field tests at the Y-12 National Security Complex in Oak Ridge, Tennessee, USA, to determine if sampling and analysis of Hg(0) vapors in the shallow subsurface (< 0.3 m depth) can be used to as an indicator of the location and extent of Hg(0) releases in the subsurface. We constructed a rigid polyvinyl chloride push probe assembly, which was driven into the ground. Soil gas samples were collected through a sealed inner tube of the assembly and were analyzed immediately in the field with a Lumex and/or Jerome Hg(0) analyzer. Time-series sampling showed that Hg vapor concentrations were fairly stable over time, suggesting that the vapor phase Hg(0) was not being depleted and that sampling results were not sensitive to the soil gas purge volume. Hg(0) vapor data collected at over 200 push probe locations at 3 different release sites correlated very well to areas of known Hg(0) contamination. Vertical profiling of Hg(0) vapor concentrations conducted at two locations provided information on the vertical distribution of Hg(0) contamination in the subsurface. We conclude from our studies that soil gas sampling and analysis can be conducted rapidly and inexpensively at large scales to help identify areas contaminated with Hg(0).

Natural and Accelerated Bioremediation Research (NABIR) Field Research Center (FRC), Oak Ridge Tennessee

The Field Research Center (FRC) in Oak Ridge (Fig. 1), Tennessee supports the U.S. Department of Energys (DOEs) Environmental Remediation Sciences Program (ERSP) goal of understanding the complex physical, chemical, and biological properties of contaminated sites for new solutions to environmental remediation and long-term stewardship. In particular, the FRC provides the opportunity for researchers to conduct studies that promote the understanding of the processes that influence the transport and fate of subsurface contaminants, the effectiveness and long-term consequences of existing remediation options, and the development of improved remediation strategies. It offers a series of contaminated sites around the former S-3 Waste Disposal Ponds and uncontaminated sites in which investigators and students conduct field research or collect samples for laboratory analysis. FRC research also spurs the development of new and improved characterization and monitoring tools. Site specific knowledge gained from research conducted at the FRC also provides the DOE-Oak Ridge Office of Environmental Management (EM) the critical scientific knowledge needed to make cleanup decisions for the S-3 Ponds and other sites on the Oak Ridge Reservation (ORR).