Frontier GeoSciences, Inc. - Research And Consulting

Due to the release of potentially harmful gasses, municipal waste landfills have been experiencing increased public attention. The Urban Air Toxic Strategy currently classifies municipal waste landfills as a hazardous air pollutant source due to the identification of over 100 volatile organic compounds found in landfill gasses (LFG). Of particular concern are mercury and methylated mercury species, persistent bioaccumulative toxins and a common component of LFG.

Legislation and increased public awareness has lead to a decline in the introduction of mercury to landfills, but the historical utilization of mercury by industry and in common household products means that all landfills have potential mercury contamination issues.

Waste contaminated by mercury containing products, particularly batteries and light bulbs, releases mercury into the atmosphere throughout the collection, crushing, consolidation, and transportation processes prior to it being deposited in a landfill. Once disturbances have ceased and the contaminated waste has been effectively covered, direct emissions of mercury to the atmosphere essentially stop. However, the anaerobic environment rich with methane producing bacteria desirable by landfill waste management results in a more complicated fate for mercury.

Bacteria transform elemental mercury into more toxic methylated mercury species that tend to escape the landfill via normal gas emissions. To understand the fate and toxicity of mercury in LFG, it is necessary to determine the species of the mercury being released. Frontier GeoSciences has developed the sampling and analytical methods to accurately determine monomethyl, dimethyl, total, and elemental mercury emissions in LFG.

Monomethylmercury (MMHg) is usually present in LFG in a halide or hydroxide form which are stable and soluble in a hydrochloric acid solution. To collect samples for the determination of MMHg, a new ultra-clean Teflon line is inserted directly into the area of interest and connected to a series of 60mL Teflon impingers charged 40-45mL 0.001 M HCl dept in an ice-bath to reduce the moisture content of the gas stream. To prevent the photodecomposition of MMHg, all exposed sections of the sampling train are shielded from direct sunlight.

After an adequate amount (~30L) of gas is pulled through the sampling train, measured by a flow meter with a gas volume totalizer unit, the impinger solutions are consolidated into an amber glass bottle and shipped on ice to our laboratory for analysis.

EPA Method 1630, developed by Frontier GeoSciences for the determination of methylated mercury species, is very sensitive and highly selective. Upon receipt, samples are distilled to remove interferents and prepared for analysis. Distilled aliquots are reacted with sodium tetraethylborate in a sparging vessel before volatile mercury species are purged from the solution with a dry nitrogen gas stream and collected on analytical Carbotraps^TM.

The analytical trap is connected to an analytical train whereby MMHg is quantified by thermal desorption, gas chromatography, and cold vapor atomic fluorescence spectroscopy (TD-GC-CVAFS). The output of the GC passes through a pyrolytic cracking column held at 700°C to convert organomercury compounds to an elemental form which can be quantified by CVAFS. The analytical system is calibrated by purging precise quantities of MMHg in methanol from deionized water onto analytical traps and injected into the instrument. MMHg is identified by retention time and quantified by peak height.

To collect samples for the determination of dimethylmercury (DMHg), a new ultra-clean Teflon line is inserted directly into the area of interest. To reduce the moisture content of the gas stream an ultra-clean impinger is placed in-line and kept in an ice-bath. A Carbotrap^TM, which allows unoxidized elemental mercury to pass through while capturing most DMHg, is connected to the exhaust of the impinger. A guard column (OV-3 on Chromasorb WAW-DMCS 80/100 mesh) is attached to selectively prevent heavy semi-volatile organics from reaching the trap.

To prevent the photodecomposition of DMHg, all exposed sections of the sampling train are shielded from direct sunlight. After an adequate amount (300-1000mL) of gas is pulled through the sampling train, measured by a fixed-volume hand pump, the traps are conditioned with dry nitrogen (~300mL/min.) to drive off any remaining water vapor. Upon the completion of sampling the traps wrapped in foil, refrigerated, and shipped to our laboratory for analysis.

EPA Method 1630, developed by Frontier GeoSciences for the determination of methylated mercury species, is very sensitive and highly selective. Immediately prior to analysis the foil is removed from the sample trap, it is connected to an identical clean analytical Carbotrap^TM, and heated with an argon flow to transfer and focus the DMHg onto the analytical trap.

The analytical trap is connected to an analytical train whereby DMHg is quantified by thermal desorption, gas chromatography, and cold vapor atomic fluorescence spectroscopy (TD-GC-CVAFS). The output of the GC passes through a pyrolytic cracking column held at 700°C to convert organomercury compounds to an elemental form which can be quantified by CVAFS. The analytical system is calibrated by purging precise quantities of DMHg in methanol from deionized water onto analytical traps and injected into the instrument. DMHg is identified by retention time and quantified by peak height.

To collect samples for the determination of total mercury (THg), which is comprised of all gas-phase and particulate atmospheric species, a new ultra-clean Teflon line is inserted directly into the area of interest. A Fluegas Sorbent Total Mercury (FSTM) dry sorbent trap, specially designed and developed by Frontier GeoSciences, is heated to prevent moisture condensation and attached to the sampling line followed by a silica gel moisture trap to protect the flow meter and gas volume totalizer unit which pull gas through the trap. The FSTM trap is then shipped to our laboratory for analysis.

EPA Method 1631 for the determination of ultra-trace mercury was developed, co-authored, and validated by Frontier GeoSciences. Upon receipt, the FSTM traps are leached of mercury using hot-refluxing HNO₃/H₂SO₄and oxidized with a 0.01 N BrCl solution. An aliquot of the leachate is placed in a sparging vessel with SnCl₂ to reduce the mercury to volatile species and purged with a stream of dry nitrogen onto a gold trap which is placed in an analytical train. Via thermal desorption, mercury is captured by an analytical gold trap which is then heated to release the mercury for measurement by cold vapor atomic fluorescence spectroscopy (CVAFS).

Frontier GeoSciences also possesses the capability to measure the concentration of elemental mercury in the field in real time. The Lumex RA915+ Elemental Gaseous Mercury analyzer has been used to characterize fugitive landfill emissions across the country. We have performed sweeps across landfill grounds to determine if and where elemental mercury emissions occur. Measurements are performed across both the active and closed areas of the landfill including leachate ponds, groundwater holding ponds, and drainage ditches.

Data is recorded as three ten-second averages with an average value for the entire thirty-second period. In addition to these capabilities, the Lumex can be set up to determine mercury fluctuations from a single area over a long period. This is useful in the study of a single location such as a transfer station where the potential for mercury emissions is high. It is also possible to configure the instrument to determine complex flux measurements, allowing the calculation of the rate of mercury emission from a given point source.