Air-surface exchange of mercury with soils amended with ash materials

Air-surface exchange of mercury (Hg) was measured from soil low in Hg (0.013 mg/kg) amended with four different ash materials: a wood ash containing -10% coal ash (0.070 mg/kg Hg), a mixture of two subbituminous coal fly ashes (0.075 mg/kg Hg), a subbituminous coal ash containing -10% petroleum coke ash (1.2 mg/kg Hg), and an ash from incinerated municipal sewage sludge (4.3 mg/kg Hg) using a dynamic flux chamber. Ash was added to soil to simulate agricultural supplements, soil stabilization, and pad layers used in livestock areas. For the agricultural amendment, -0.4% ash was well mixed into the soil. To make the stabilized soil that could be used for construction purposes, -20% ash was mixed into soil with water. The pad layer consisted of a wetted 1-cm layer of ash material on the soil surface. Diel trends of Hg flux were observed for all of the substrates with significantly higher Hg emissions during the day and negligible flux or deposition of Hg during the night. Hg fluxes, which were measured in the summer months, were best correlated with solar radiation, temperature, and air O3 concentrations. Mean Hg fluxes measured outdoors for unamended soils ranged from 19 to 140 ng/m2 day, whereas those for soil amended with ash to simulate an agricultural application ranged from 7.2 to 230 ng/m2 day. Fluxes for soil stabilized with ash ranged from 77 to 530 ng/m2 day and for soil with pads constructed of ash ranged from -50 to 90 ng/m2 day. Simple analytical tests (i.e., total Hg content, synthetic precipitation leaching procedure, heating, and indoor gas-exchange experiments) were performed to assess whether algorithms based on these tests could be used to predict Hg fluxes observed outdoors using the flux chamber. Based on this study, no consistent relationships could be developed. More work is needed to assess long-term and seasonal variations in Hg flux from (intact and disturbed) substrates before annual estimates of emissions can be developed.     

Mercury accumulation in grass and forb species as a function of atmospheric carbon dioxide concentrations and mercury exposures in air and soil

The goal of this study was to investigate the potential for atmospheric Hg degrees uptake by grassland species as a function of different air and soil Hg exposures, and to specifically test how increasing atmospheric CO(2) concentrations may influence foliar Hg concentrations. Four common tallgrass prairie species were germinated and grown for 7 months in environmentally controlled chambers using two different atmospheric elemental mercury (Hg major; 3.7+/-2.0 and 10.2+/-3.5 ng m(-3)), soil Hg (<0.01 and 0.15+/-0.08 micro g g(-1)), and atmospheric carbon dioxide (CO(2)) (390+/-18, 598+/-22 micro mol mol(-1)) exposures. Species used included two C4 grasses and two C3 forbs. Elevated CO(2) concentrations led to lower foliar Hg concentrations in plants exposed to low (i.e., ambient) air Hg degrees concentrations, but no CO(2) effect was apparent at higher air Hg degrees exposure. The observed CO(2) effect suggests that leaf Hg uptake might be controlled by leaf physiological processes such as stomatal conductance which is typically reduced under elevated CO(2). Foliar tissue exposed to elevated air Hg degrees concentrations had higher concentrations than those exposed to low air Hg degrees , but only when also exposed to elevated CO(2). The relationships for foliar Hg concentrations at different atmospheric CO(2) and Hg degrees exposures indicate that these species may have a limited capacity for Hg storage; at ambient CO(2) concentrations all Hg absorption sites in leaves may have been saturated while at elevated CO(2) when stomatal conductance was reduced saturation may have been reached only at higher concentrations of atmospheric Hg degrees . Foliar Hg concentrations were not correlated to soil Hg exposures, except for one of the four species (Rudbeckia hirta). Higher soil Hg concentrations resulted in high root Hg concentrations and considerably increased the percentage of total plant Hg allocated to roots. The large shifts in Hg allocation patterns-notably under soil conditions only slightly above natural background levels-indicate a potentially strong role of plants in belowground Hg transformation and cycling processes.     

Transport of the insecticides chlorpyrifos,chlorfenvinphos, carbofuran,carbosulfan, and furathiocarb from soil into the foliage of cauliflower and Brussels sprouts plants grown in the field

In several field assays made in different locations in 1988 and 1989, cauliflower and Brussels sprouts plants were treated some days after plantation by pouring onto soil around the stem of the plant one of the insecticides chlorpyrifos, chlorfenvinphos, carbofuran, carbosulfan, or furathiocarb, for protection against the root fly. During plant growth, each of the insecticides (and their soil metabolites) was transported from soil into the plant foliage, where it could give—during a certain period of time—a secondary plant protection against the foliage insects. The foliage concentrations of the non systemic chlorpyrifos and chlorfenvinphos were equal or greater than 1 mg/kg fresh weight during a period of about 44 days after soil treatment in Brussels sprouts crops, and 35 days in cauliflower crops. Comparison of 1988 and 1989 however showed that these periods of time changed according to the weather conditions, especially rainfall. These periods of time were greater when the insecticide soil concentrations were greater—and thus when the rates of insecticide soil metabolism were smaller— and when the rainfall were greater—water transporting the insecticides from soil to the foliage. Similar relationships were observed with the systemic insecticides carbofuran, carbosulfan and furathiocarb; the weights per plant of insecticide compounds transported from soil into the foliage however were greater with these systemic insecticides than they were with the non systemic chlorpyrifos and chlorfenvinphos. The extreme values observed for the periods of time of insecticide foliage concentrations equal or greater than 1 mg/kg fresh weight thus were: 1. in cauliflower crops: 21 to 36 days for chlorpyrifos, and 23 to 39 days for chlorpyrifos + oxon; 24 to 37 days for chlorfenvinphos; 20 to 48 days for carbofuran; 2. in Brussels sprouts crops: 43 to 49 days for chlorpyrifos; 47 to 53 days for chlorpyrifos + oxon; 41 to 45 days for chlorfenvinphos; between 2 to 3 months for carbofuran, carbofuran + carbosulfan, and carbofuran + furathiocarb in the fields treated respectively with either carbofuran, carbosulfan, or furathiocarb. Moreover, in the spring and summer cauliflower crops made on fields onto which continuous cauliflower crops—with their soil insecticide treatments—had been made since a greater number of years (greater soil “history”), the insecticide compounds soil and foliage concentrations generally were lower.     

Evaluation of wetland methyl mercury export as a function of experimental manipulations

Mercury associated with natural enrichment, historic mining, and ore processing is a contaminant of concern in watersheds of the western USA. In this region, water is a highly managed resource and wetlands, known to be important sites of methyl mercury production, are often an integral component of watersheds. This study applied controlled manipulations of four replicated experimental wetland designs with different water and soil mercury concentrations to determine the potential impacts on methyl mercury export. Wetlands were manipulated by drying and wetting, changing hydraulic retention time, and adding sulfate and nitrate to influent waters. In a summer drying and wetting manipulation, an immediate increase in total methyl mercury release was observed with rewetting, however, concentrations decreased quickly. Drying all wetlands over the winter and rewetting in the spring resulted in high net methyl mercury output relative to that observed before drying. Net methyl mercury output was not influenced by changes in hydraulic retention time from 4 to 8 h or to 30 min, or by increasing the nitrate concentration from 0.1 to 10 mg L(-1). The addition of sulfate to the inlet waters of two mesocosms to increase concentrations from approximately 100 to 250 mg L(-1) did not result in a clear effect on methyl mercury output, most likely due to sulfate concentrations being higher than optimal for methyl mercury production. Despite the lack of response to sulfate amendments, the change in sulfate concentration between the inlet and outlet of the mesocosms and temperature were the parameters best correlated with methyl mercury outputs.     

An assessment of the significance of mercury release from coal fly ash

Some mercury (Hg) naturally present in coal is retained in the fly ash remaining after combustion. Concern has been raised regarding the potential for release of this Hg to the environment. The exchange of Hg between fly ash and the atmosphere was measured in the laboratory and in situ at a fly ash landfill. All samples of fly ash used in the laboratory study, with the exception of that derived from lignite-type coal, acted as a sink for atmospheric Hg. Deposition rates were found to increase as air Hg concentrations increased and to decrease with incident light and increased temperature. Addition of water to fly ash samples resulted in re-emission of deposited atmospheric Hg. Deposition was the dominant flux measured in situ at a fly ash landfill. Atmospheric Hg was deposited to all samples collected as part of two demonstration projects using carbon injection for enhanced Hg capture. Hg concentrations of extracts derived using U.S. Environmental Protection Agency Method 1312 (Synthetic Precipitation Leaching Procedure) were < or = 14.4 ng/L. Data developed demonstrate that fly ash, including that collected from Hg removal projects, will release little Hg to the air or water, and under certain conditions, absorbs Hg from the air.     

The influence of dynamic chamber design and operating parameters on calculated surface-to-air mercury fluxes

Dynamic Flux Chambers (DFCs) are commonly applied for the measurement of non-point source mercury (Hg) emissions from a wide range of surfaces. A standard operating protocol and design for DFCs does not exist, and as a result there is a large diversity in methods described in the literature. Because natural and anthropogenic non-point sources are thought to contribute significantly to the atmosphere Hg pool, development of accurate fluxes during field campaigns is essential. The objective of this research was to determine how differences in chamber material, sample port placement, vertical cross sectional area/volume, and flushing flow rate influence the Hg flux from geologic materials. Hg fluxes measured with a Teflon chamber were higher than those obtained using a polycarbonate chamber, with differences related to light transmission and substrate type. Differences in sample port placement (side versus top) did not have an influence on Hg fluxes. When the same flushing flow rate was applied to two chambers of different volumes, higher fluxes were calculated for the chamber with the smaller volume. Conversely, when two chambers with different volumes were maintained at similar turnover times, the larger volume chamber yielded higher Hg fluxes. Overall, the flushing flow rate and associated chamber turnover time had the largest influence on Hg flux relative to the other parameters tested. Results from computational fluid dynamic (CFD) modeling inside a DFC confirm that the smaller diffusion resistance at higher flushing flows contributes to the higher measured flux. These results clearly illustrate that differences in chamber design and operation can significantly influence the resulting calculated Hg flux, and thus impact the comparability of results obtained using DFC designs and/or operating parameters. A protocol for determining a flushing flow rate that results in fluxes less affected by chamber operating conditions and design is proposed. Application of this protocol would provide a framework for comparison of data from different studies.     

Atmospheric mercury concentrations and speciation measured from 2004 to 2007 in Reno, Nevada, USA

Atmospheric elemental, reactive and particulate mercury (Hg) concentrations were measured north of downtown Reno, Nevada, USA from November 2004 to November 2007. Three-year mean and median concentrations for gaseous elemental Hg (Hg⁰) were 1.6 and 1.5 ng m⁻³ (respectively), similar to global mean Hg⁰ concentrations. The three-year mean reactive gaseous Hg (RGM) concentration (26 pg m⁻³) was higher than values reported for rural sites across the western United States. Well defined seasonal and daily patterns in Hg⁰ and RGM concentrations were observed, with the highest Hg⁰ concentrations measured in winter and early morning, and RGM concentrations being greatest in the summer and mid-afternoon. Elevated Hg⁰ concentrations in winter were associated with periods of cold, stagnant air; while a regularly observed early morning increase in concentration was due to local source and surface emissions. The observed afternoon increase and high summer values of RGM can be explained by in situ oxidation of gaseous Hg⁰ or mixing of RGM derived from the free troposphere to the surface. Because both of these processes are correlated with the same environmental conditions it is difficult to assess their overall contribution to the observed trends.     

A passive sampler for ambient gaseous oxidized mercury concentrations

This paper reports on the development of a passive sampler for estimating gaseous oxidized mercury concentrations. Atmospheric gaseous oxidized mercury concentrations calculated from passive sampler data were correlated with those obtained using an automated analyzer (r² = 0.71, p < 0.01, n = 110 for one-week deployments; r² = 0.89, p < 0.01, n = 22 for two-week deployments). Sampler uptake was not significantly affected by changes in temperature, humidity, or ozone concentration, but it was slightly dependent on wind speed. As such, an equation for correcting data due to this factor was developed based on wind tunnel and field data. The detection limit for a two-week sampler deployment was ～5 pg m^?3. Field data collected in Nevada and the southeastern United States showed these samplers are useful for investigating spatial and temporal variability in gaseous oxidized mercury concentrations.     

MERCURY IN WATER AND SEDIMENT OF STEAMBOAT CREEK,NEVADA: IMPLICATIONS FOR STREAM RESTORATION1

ABSTRACT: The objective of this study was to characterize the sources, concentrations, and distribution of total and methylmer‐cury in water, and channel and bank sediments of Steamboat Creek, Nevada. This information was needed to begin to assess the potential impacts of stream restoration on mercury pollution in this tributary to the Truckee River. The Truckee River flows into Pyramid Lake, a terminal water body home to one endangered and one threatened fish species, where stable pollutants will accumulate over time. Mercury in Steamboat Creek was originally derived from its headwaters, Washoe Lake, where several gold and silver mills that utilized mercury were located. In the 100 plus years since ore processing occurred, mercury‐laden alluvium has been deposited in the stream channel and on streambanks where it is available for remobilization. Total mercury concentrations measured in unfiltered water from the creek ranged from 82 to 419 ng/L, with greater than 90 percent of this mercury being particle‐bound (> 0.45 (m). Mercury in sediments ranged from 0.26 to 10.2 μg/g. Methylmercury concentrations in sediments of Steamboat Creek were highest in wetlands, lower in the stream channel, and still lower in streambank settings. Methylmercury concentrations in water were 0.63 to 1.4 ng/L. A streambank restoration plan, which includes alterations to channel geometry and wetland creation or expansion, has been initiated for the creek. Data developed indicate that streambank stabilization could reduce the mercury loading to the Creek and that wetland construction could exacerbate methylmercury production.