Mercury In Streams Research Articles

Landscape characteristics govern the impacts of beaver ponds on surface water methylmercury concentrations in boreal watersheds

Studies in boreal regions concerning the bioaccumulative neurotoxin methylmercury (MeHg) in natural wetlands and experimental reservoirs have shown that these waterbodies contribute to high MeHg levels in underlying sediments, inundated vegetation, and aquatic organisms. Beaver ponds are natural reservoirs that are ubiquitous in the Canadian boreal region and have been reported to increase downstream MeHg concentrations. However, the reported impacts of beaver ponds on stream MeHg vary widely across a limited number of studies, and factors influencing this variation are not well understood. To quantify the effect of beaver ponds on stream mercury concentrations, water samples were taken upstream and downstream of 10 in-channel beaver impoundments in northwestern Ontario, Canada. The downstream:upstream MeHg concentration ratios were related to pond and landscape characteristics to examine potential factors that play a role in determining the effect of beaver ponds on stream MeHg concentrations. Overall, MeHg concentrations were 1.6 times greater downstream of the beaver ponds, though this increase was not consistent; downstream concentrations up to 12 times greater and up to 5 times less were also observed. Landscape characteristics that can be readily obtained from existing spatial datasets or quantified using remote sensing techniques emerged as better predictors of downstream:upstream MeHg concentrations than site-specific stream chemistry parameters or pond characteristics that are more difficult to ascertain, with drier landscapes indicative of lower background MeHg export being more likely to exhibit greater increases in MeHg downstream of a beaver pond. These results suggest that the effects of beaver ponds on surface water MeHg concentrations are generally small but highly variable, and that the magnitude of the pond’s influence on stream MeHg are lessened in landscapes already conducive to higher MeHg concentrations.

Controls on methylmercury concentrations in lakes and streams of peatland‐rich catchments along a 1700 km permafrost gradient

AbstractPermafrost thaw may increase the production of neurotoxic methylmercury (MeHg) in northern peatlands, but the downstream delivery of MeHg is uncertain. We quantified total mercury (THg) and MeHg concentrations in lakes and streams along a 1700 km permafrost transect in boreal western Canada to determine the influence of regional permafrost extent compared to local lake and catchment characteristics. In lakes, we assessed sediment microbial communities and modeled potential rates of water column photodemethylation (PD). Regardless of permafrost conditions, peatlands were the primary sources of MeHg across the transect as MeHg concentrations in streams increased with aromatic dissolved organic carbon (DOC), iron, and lower pH. Higher DOC and greater catchment peatland extent were further associated with higher stream %MeHg (MeHg/THg). Peatland lakes were potential MeHg sinks, with lower MeHg concentrations than streams (mean ± 1SD: 0.19 ± 0.23 and 0.47 ± 0.77 ng MeHg L−1, respectively), and larger stream catchments had lower %MeHg where PD may occur in abundant small lakes. Microbial communities in lake sediments showed that abundance of Hg reducing genes (merA) predominated over Hg methylating (hgcA) and MeHg demethylating (merB) genes. The effects of permafrost extent on MeHg processes in lakes were secondary to the influence of local catchment characteristics, but lakes in regions with less permafrost had higher DOC concentrations, higher %MeHg, and lower potential rates of PD. Our study highlights a need to understand the impacts of climate change on MeHg source and sink processes, particularly as mediated through changes to peatland DOC, to improve projections of future MeHg concentrations in northern catchments.

Decontamination of Mercury-Containing Aqueous Streams by Electrochemical Alloy Formation on Copper

Mercury in aqueous streams poses severe health and environmental concerns and requires improved techniques for decontamination. One such technique is electrochemical alloy formation on platinum, which can effectively decontaminate mercury-containing aqueous streams at concentrations relevant for both industrial and natural waters. This study examines the viability of copper as an alternative to platinum. Mercury removal is faster on copper and works both with and without an applied cathodic potential. Without it, however, copper dissolution becomes a problem. Copper dissolution is preventable in neutral pH and in sulfuric acid solutions under potential control, and dissolved copper ions can be plated back onto the electrode. In the presence of nitrate or chloride anions, copper electrodes degrade rapidly even under potential control. Thus, there are practical restrictions for mercury decontamination via electrochemical alloy formation on copper, but it can be applied to solutions where copper is stable under potential control.

Quantification and speciation of mercury in streams and rivers sediment samples from Paracatu, MG, Brazil, using a direct mercury analyzer®

This paper describes the application of a method for the direct speciation of Hg in sediment samples by thermal desorption using a Direct Mercury Analyzer®. The different thermal behavior of the Hg species allowed direct chemical speciation by DMA. The set of temperature steps was as follows: 50 °C, 100 °C, 150 °C, 200 °C, 250 °C, 300 °C, 400 °C, 500 °C, 600 °C and 700 °C. Sediment samples presented total Hg concentrations varying over a range of 36 to 1996 μg·kg−1, with 78% of the samples being over of the TEL (threshold effect level). According to the speciation analysis, a prevalence of oxidized Hg was observed. This method was efficient, simple and adequate for determining the Hg speciation in sediment samples. The great advantage is that the method does not require pretreatment of the samples, and it is applicable to homogeneous solid samples.

Stream Mercury Export in Response to Contemporary Timber Harvesting Methods (Pacific Coastal Mountains, Oregon, USA).

Land-use activities can alter hydrological and biogeochemical processes that can affect the fate, transformation, and transport of mercury (Hg). Previous studies in boreal forests have shown that forestry operations can have profound but variable effects on Hg export and methylmercury (MeHg) formation. The Pacific Northwest is an important timber producing region that receives large atmospheric Hg loads, but the impact of forest harvesting on Hg mobilization has not been directly studied and was the focus of our investigation. Stream discharge was measured continuously, and Hg and MeHg concentrations were measured monthly for 1.5 years following logging in three paired harvested and unharvested (control) catchments. There was no significant difference in particulate-bound Hg concentrations or loads in the harvested and unharvested catchments which may have resulted from forestry practices aimed at minimizing erosion. However, the harvested catchments had significantly higher discharge (32%), filtered Hg concentrations (28%), filtered Hg loads (80%), and dissolved organic carbon (DOC) loads (40%) compared to forested catchments. MeHg concentrations were low (mostly <0.05 ng L-1) in harvested, unharvested, and downstream samples due to well-drained/unsaturated soil conditions and steep slopes with high energy eroding stream channels that were not conducive to the development of anoxic conditions that support methylation. These results have important implications for the role forestry operations have in affecting catchment retention and export of Hg pollution.

Prediction of fish and sediment mercury in streams using landscape variables and historical mining

Widespread mercury (Hg) contamination of aquatic systems in the Sierra Nevada of California, U.S., is associated with historical use to enhance gold (Au) recovery by amalgamation. In areas affected by historical Au mining operations, including the western slope of the Sierra Nevada and downstream areas in northern California, such as San Francisco Bay and the Sacramento River–San Joaquin River Delta, microbial conversion of Hg to methylmercury (MeHg) leads to bioaccumulation of MeHg in food webs, and increased risks to humans and wildlife. This study focused on developing a predictive model for THg in stream fish tissue based on geospatial data, including land use/land cover data, and the distribution of legacy Au mines. Data on total mercury (THg) and MeHg concentrations in fish tissue and streambed sediment collected during 1980–2012 from stream sites in the Sierra Nevada, California were combined with geospatial data to estimate fish THg concentrations across the landscape. THg concentrations of five fish species (Brown Trout, Rainbow Trout, Sacramento Pikeminnow, Sacramento Sucker, and Smallmouth Bass) within stream sections were predicted using multi-model inference based on Akaike Information Criteria, using geospatial data for mining history and landscape characteristics as well as fish species and length (r2=0.61, p<0.001). Including THg concentrations in streambed sediment did not improve the model's fit, however including MeHg concentrations in streambed sediment, organic content (loss on ignition), and sediment grain size resulted in an improved fit (r2=0.63, p<0.001). These models can be used to estimate THg concentrations in stream fish based on landscape variables in the Sierra Nevada in areas where direct measurements of THg concentration in fish are unavailable.

Removal of Elemental Mercury by Coconut Pith Char Adsorbents

Coconut pith (CP), which is abundantly available and cheap, has the potential of being used as low-cost adsorbents for elemental mercury removal. In this study, the preparation of chars was carried out through the carbonization of CP at three different environment conditions: (a) open reactor under nitrogen flow; (b) closed reactor under nitrogen environment; and (c) closed reactor under ambient environment; at the temperature of 700°C. The results show that the chemical, physical, morphological and spectral properties of the adsorbents greatly influenced by the environment of carbonization used. The highest Hgo adsorption capacity was observed for CCA700 (2395.98 μg/g), followed by CCN700 (2052.49 μg/g), and CFN700 (1416.92 μg/g). These results demonstrated that coconut pith derived chars could be potential as low-cost adsorbent alternatives for the removal of elemental mercury in gas streams.

Parsimonious Model for Simulating Total Mercury and Methylmercury in Boreal Streams Based on Riparian Flow Paths and Seasonality.

The complexity of mercury (Hg) biogeochemistry has made it difficult to model surface water concentrations of both total Hg (THg) and especially methylmercury (MeHg), the species of Hg having the highest potential for bioaccumulation. To simulate THg and MeHg variation in low-order streams, we have adapted a conceptual modeling framework where a continuum of lateral flows through riparian soils determines streamflow concentrations. The model was applied to seven forest catchments located in two boreal regions in Sweden spanning a range of climatic, soil, and forest management conditions. Discharge, and simulated riparian soil water concentrations profiles, represented by two calibrated parameters, were able to explain much of the variability of THg and MeHg concentrations in the streams issuing from the catchments (Nash Sutcliffe (NS) up to 0.54 for THg and 0.58 for MeHg). Model performance for all catchments was improved (NS up to 0.76 for THg and 0.85 for MeHg) by adding two to four parameters to represent seasonality in riparian soil water THg and MeHg concentrations profiles. These results are consistent with the hypothesis that riparian flow-pathways and seasonality in riparian soil concentrations are the major controls on temporal variation of THg and MeHg concentrations in low-order streams.

Mercury in streams at Grand Portage National Monument (Minnesota, USA): Assessment of ecosystem sensitivity and ecological risk

Mercury (Hg) in water, sediment, soils, seston, and biota were quantified for three streams in the Grand Portage National Monument (GRPO) in far northeastern Minnesota to assess ecosystem contamination and the potential for harmful exposure of piscivorous fish, wildlife, and humans to methylmercury (MeHg). Concentrations of total Hg in water, sediment, and soil were typical of those in forest ecosystems within the region, whereas MeHg concentrations and percent MeHg in these ecosystem components were markedly higher than values reported elsewhere in the western Great Lakes Region. Soils and sediment were Hg-enriched, containing approximately 4-fold more total Hg per unit of organic matter. We hypothesized that localized Hg enrichment was due in part to anthropogenic pollution associated with historic fur-trading activity. Bottom-up forcing of bioaccumulation was evidenced by MeHg concentrations in larval dragonflies, which were near the maxima for dragonflies sampled concurrently from five other national park units in the region. Despite its semi-remote location, GRPO is a Hg-sensitive landscape in which MeHg is produced and bioaccumulated in aquatic food webs to concentrations that pose ecological risks to MeHg-sensitive piscivores, including predatory fish, belted kingfisher, and mink.

Mercury cycling in aquatic ecosystems and trophic state-related variables — Implications from structural equation modeling

Structural equation modeling (SEM) provides a framework that can more properly handle complex variable interactions inherent in mercury cycling and its bioaccumulation compared to more traditional regression-based methods. SEM was applied to regional data sets for three different types of aquatic ecosystems within Florida, USA – lakes, streams, and the Everglades – to evaluate the underlying nature (i.e., indirect and direct) of the relationships between fish mercury concentrations and trophic state related variables such as nutrients, dissolved organic carbon (DOC), sulfate, and alkalinity. The modeling results indicated some differences in key variable relationships — for example, the effect of nutrients on fish mercury in lakes and streams was uniformly negative through direct and indirect pathways consistent with biodilution or eutrophication-associated effects on food web structure. Somewhat surprisingly, however, was that total phosphorus did not serve as a meaningful variable in the Everglades model, apparently because its effects were masked or secondary to the effects of DOC. What is perhaps a more important result were two key similarities across the three systems. First, the modeling clearly indicates that the dominant influence on fish tissue mercury concentrations in all three systems is related to variations in the methylmercury signal. Second, the modeling demonstrated that the effect of DOC on fish mercury concentrations was exerted through multiple and antagonistic pathways, including facilitated transport of total mercury and methylmercury, enhanced rates of methylation, and limitations imposed on bioavailability. Indeed, while the individual DOC pathways in the models were all highly significant (generally p<0.001), the net effect of DOC in each model was greatly reduced or insignificant. These results can help explain contradictory results obtained previously by other researchers in other systems, and illustrate the importance of SEM as a modeling tool when studying systems with complex interactions such as the aquatic mercury cycle.

Mercury proxies and mercury dynamics in a forested watershed of the US Northeast.

Although many studies focus on mercury (Hg) and methylmercury (MeHg) dynamics in streams, challenges remain in identifying the relative importance of land cover and seasonality at regulating Hg and MeHg dynamics at the watershed scale. Developing robust proxies for Hg and/or MeHg determination also remains a challenge. Our study used Hg, MeHg, and dissolved organic carbon (DOC) concentration measurements and various DOC fluorescence indices to characterize Hg and DOC dynamics in a forested watershed of the US Northeast. Principal component analysis indicated that land cover/landscape position (i.e., headwater vs. wetland-influenced area vs. lake-influenced area) explained 44% of the variance in Hg, MeHg, DOC concentrations, and DOC quality during the snow-free season, while seasonality (i.e., air temperature and discharge) explained only 21% of the variance in the results. Furthermore, finding a good proxy for Hg that is valid across a range of landscape positions remains a challenge; however, regression analysis indicated that the fluorescence peak Humic C (excitation = 350nm; emission = max (420-480)), which corresponds to the presence of melanoidins in water, explained 21% of the variability in MeHg concentrations across both space and time (p = 0.001), and thus appears to be a possible proxy for MeHg determination in our study watershed. From a management perspective, land cover modifications (lake, reservoir, and wetland) are likely to play more important roles at regulating Hg, MeHg, and DOC exports at the watershed scale than long-term changes in the climate of this region.

Forest harvest effects on mercury in streams and biota in Norwegian boreal catchments

Forest harvesting practices can potentially increase mercury run-off from catchments. A paired catchment experiment was conducted in a boreal forest in southern Norway, to test effects of forest harvest operations on (i) concentrations and fluxes of methylmercury (MeHg), total mercury (HgT), nutrients and dissolved organic matter (TOC), and on (ii) MeHg bioaccumulation in stream foodwebs.Thirty percent of a catchment was harvested in winter time with snow cover but no soil frost, resulting in wheel tracks and soil compaction. Pre-harvest differences included higher streamwater MeHg, HgT and TOC, and lower pH in the treated catchment compared to the reference.No significant treatment effects on concentrations of MeHg, HgT and TOC were detected, whereas concentrations of nutrients (ammonium, nitrate, phosphorus (P)) increased significantly. Estimated catchment export of nitrate and ammonium increased fourfold, as a combined effect of changed discharge and concentrations. Export of MeHg and HgT increased weakly, primarily because of an increase in discharge.Levels of MeHg in stream invertebrates mirrored differences in aquatic MeHg between the two streams, resulting in higher MeHg in biota in the harvest catchment in pre-harvest conditions. After harvest, MeHg levels in primary consumers (herbivorous stoneflies) were no longer different between the two streams, despite continued exposure to higher aqueous MeHg in the harvested catchment. Simultaneously, dietary biomarkers (δ15N signature, lipid- and algal fatty acid content) in the stoneflies had changed significantly, consistent with higher nutrient loadings and associated higher diet availability in the harvested stream.The results of our experiment do not support that forest management has a strong impact on catchment MeHg production. Catchment disturbance through forest harvesting may decrease MeHg in aquatic biota, because of higher stream productivity and associated higher quality of dietary sources, at least in the short-term. Other studies on catchment MeHg production to disturbance have shown a range in responses, from strong to none. So far, no factor has emerged to explain such range in responses. Predictions of forest management effects on MeHg in streamwater and aquatic food webs are hampered by limited understanding of catchment controls on MeHg production.

Economical and reliable mercury reduction in refinery and power plant discharge wastewater with robust microfiltration membrane technology

Environmental concerns and risks to bioaccumulation of mercury components among aquatic organisms, thus finally through the food-chain, and therefore exposing human health potentially, lead to more stringent regulations over the last years in several regions across the globe. Mercury (Hg) is a key contaminant in several crude oils and coal. Most of the mercury appears to exist in suspended and adsorbed forms and there is also the dissolved component in the form of methylmercury and salts. As an example, the United States EPA’s Great Lakes region initiative targets limiting the total mercury in lakes and streams to 1.3 nanogram/l (ppt). Many states in the USA along the Great Lakes and the Ohio valley limit total mercury in discharge wastewater to 12 nanogram/l (ppt) already. Western Europe and parts of Asia are most likely to implement similar mandates in the next few years. This paper describes in the first case a lengthy and successful plant trial performed by Pall Corporation on discharge wastewater generated at a refinery in the USA. Microfiltration (MF) systems were employed to treat the end of pipe wastewater after it goes through conventional treatment processes such as API separator and biological reactor treatment. The total mercury was reduced to below 5 ppt in the permeate from the MF process without the aid of additives or post treatment, thus reducing 90% of the total mercury in the feed to the MF system. The target levels were met consistently and the automated system ran smoothly. Independent of huge variability of the feed turbidity and changing mercury levels, the hollow-fiber system showed stable and reliable operation for more than 12 months under “real” site conditions. Above innovative approach eliminates the need for further mercury polishing steps while reaching target levels with a very solid and proven high-crystalline PVDF hollow fiber, that collect solids and contaminations only on the outer membrane side, which enable easy regeneration and cleanability all the time. The second case study refers to the power generation industry. Wet flue gas desulfurization (FGD), used primarily to control SOx in coal-fired power plants, also captures the Hg in its various forms. The wastewater generated in this process is contaminated accordingly, thus needing treatment for Hg removal before discharge to the environment. This second case study discusses experimental work done by Pall for the removal of Hg from FGD wastewater as a final polishing step, with and without chemical precipitation followed by MF to remove the Hg captured in the precipitate. Stable and positive results from both case studies could be obtained, hence proving that high crystalline PVDF in hollow fiber membranes is a simple, reliable, long-term and cost economic solution for the reduction of mercury compounds in wastewaters.

Using River Distance and Existing Hydrography Data Can Improve the Geostatistical Estimation of Fish Tissue Mercury at Unsampled Locations

Mercury in fish tissue is a major human health concern. Consumption of mercury-contaminated fish poses risks to the general population, including potentially serious developmental defects and neurological damage in young children. Therefore, it is important to accurately identify areas that have the potential for high levels of bioaccumulated mercury. However, due to time and resource constraints, it is difficult to adequately assess fish tissue mercury on a basin wide scale. We hypothesized that, given the nature of fish movement along streams, an analytical approach that takes into account distance traveled along these streams would improve the estimation accuracy for fish tissue mercury in unsampled streams. Therefore, we used a river-based Bayesian Maximum Entropy framework (river-BME) for modern space/time geostatistics to estimate fish tissue mercury at unsampled locations in the Cape Fear and Lumber Basins in eastern North Carolina. We also compared the space/time geostatistical estimation using river-BME to the more traditional Euclidean-based BME approach, with and without the inclusion of a secondary variable. Results showed that this river-based approach reduced the estimation error of fish tissue mercury by more than 13% and that the median estimate of fish tissue mercury exceeded the EPA action level of 0.3 ppm in more than 90% of river miles for the study domain.

Streamwater fluxes of total mercury and methylmercury into and out of Lake Champlain

From 2000 to 2004, we sampled for total mercury (THg) and methylmercury (MeHg) in inlet streams to Lake Champlain, targeting high flow periods to capture increases in THg and MeHg concentrations with increasing flow. We used these data to model stream THg and MeHg fluxes for Water Years 2001 through 2009. In this mountainous forested basin with a high watershed-to-lake area ratio of 18, fluvial export from the terrestrial watershed was the dominant source of Hg to the lake. Unfiltered THg and MeHg fluxes were dominated by the particulate fraction; about 40% of stream THg was in the filtered (<0.4 μm) phase. THg flux from the watershed to the lake averaged 2.37 μg m −2 yr −1, or about 13% of atmospheric Hg wet and dry deposition to the basin. THg export from the lake represented only about 3% of atmospheric Hg input to the basin.

Transport and fate of mercury under different hydrologie regimes in polluted stream in mining area

Abstract Seepage from Hg mine wastes and calcines contains high concentrations of mercury (Hg). Hg pollution is a major environmental problem in areas with abandoned mercury mines and retorting units. This study evaluates factors, especially the hydrological and sedimentary variables, governing temporal and spatial variation in levels and state of mercury in streams impacted by Hg contaminated runoff. Samples were taken during different flow regimes in the Wanshan Hg mining area in Guizhou Province, China. In its headwaters the sampled streams/rivers pass by several mine wastes and calcines with high concentration of Hg. Seepage causes serious Hg contamination to the downstream area. Concentrations of Hg in water samples showed significant seasonal variations. Periods of higher flow showed high concentrations of total Hg (THg) in water due to more particles being re-suspended and transported. The concentrations of major anions (e.g., Cl −, F −, NO 3 − and SO 4 2-) were lower during higher flow due to dilution. Due to both sedimentation of particles and dilution from tributaries the concentration of THg decreased from 2100 ng/L to background levels (< 50 ng/L) within 10 km distance downstream. Sedimentation is the main reason for the fast decrease of the concentration, it accounts for 69% and 60% for higher flow and lower flow regimes respectively in the upper part of the stream. Speciation calculation of the dissolved Hg fraction (DHg) (using Visual MINTEQ) showed that Hg(OH) 2 associated with dissolved organic matter is the main form of Hg in dissolved phase in surface waters in Wanshan (over 95%).

The effect of mercury contaminants in major gas developments

Over the past ten years the region has witnessed the unforeseen presence of mercury during gas production which has affected projects not only in southeast Asia but more recently in Australian waters. This has caused major operational challenges and has often involved costly production impairment, loss of condensate sales value and major brownfield modifications. Today–s awareness of mercury has seen a new vigilance in well testing programmes intended to address the identification of mercury in gas streams during the early appraisal and concept development phases of an asset lifecycle. This paper looks at the ways in which operating companies have resolved the issue of unforeseen mercury production to date, and the operational experience and lessons learned. The paper describes some of the fundamental testing programmes as well as the available technologies for treatment and removal of mercury from production and effluent streams. It also identifies the impact of mercury on the design and operation of specific parts of the process as well as the overall impact on facility topsides. The impact of mercury on a development is shown to be manageable and least costly where identified and addressed during the conceptual stage of a project development. Technical, environmental, safety and regulatory issues associated with mercury can be tackled, minimising risk of production deferment, and the costs incurred can be quantified and incorporated into economic models.

Elevated Concentrations of Methyl Mercury in Streams after Forest Clear-Cut: A Consequence of Mobilization from Soil or New Methylation?

Concentrations of inorganic, mercuric mercury (Hg(II)), methyl mercury (MeHg) and ancillary chemistry measured in first-order streams draining 0-4 (N = 20) and 4-10 (N = 27) year-old clear-cuts of former Norway Spruce Picea abies (Karst.) forest stands were compared with concentrations in streams draining >70 year-old Norway Spruce reference stands (N = 10). Concentrations of MeHg, and ratios of MeHg TOC(-1) and Hg(II) TOC(-1), were significantly (p < 0.01) elevated in 0-4 year-old clear-cuts, as compared to references. The only ancillary variable showing a significant elevation for 0-4 year-old clear-cuts was Mn (p < 0.02). The 4-10 year-old clear-cuts showed intermediate concentrations with nonsignificant differences as compared to references. pH, nitrate, sulfate, Ca, Fe, TOC, TON, and the aromaticity of TOC (SUVA(254 nm)) showed nonsignificant differences between clear-cut age classes and references. Assuming that MeHg and Hg(II) are mobilized from soil to stream to a similar relative extent as a consequence of clear-cutting, a calculation showed that (1)/(6) of the elevated MeHg concentration was due to enhanced mobilization from soil and (5)/(6) was due to new methylation of Hg(II) 0-4 years after clear-cut. New methylation after clear-cut is suggested to be stimulated by an increased availability of electron donors for methylating bacteria, as a consequence of degradation of logging residue ("slash") and soil organic matter. A subdivision of sites situated above and below the highest postglacial coastline (HC) revealed a significant elevation of MeHg, MeHg TOC(-1) and Hg(II) TOC(-1) (p < 0.05) beyond their references in 0-4 year-old clear-cuts above (but not below) the HC. This suggests that postglacial deposits of FeS(s) and FeS(2)(s) were not an important factor for elevation of MeHg after clear-cut.

Potential Flue Gas Impurities in Carbon Dioxide Streams Separated from Coal-Fired Power Plants

For geological sequestration of carbon dioxide (CO2) separated from pulverized coal combustion flue gas, it is necessary to adequately evaluate the potential impacts of flue gas impurities on groundwater aquifers in the case of the CO2 leakage from its storage sites. This study estimated the flue gas impurities to be included in the CO2 stream separated from a CO2 control unit for a different combination of air pollution control devices and different flue gas compositions. Specifically, the levels of acid gases and mercury vapor were estimated for the monoethanolamine (MEA)-based absorption process on the basis of published performance parameters of existing systems. Among the flue gas constituents considered, sulfur dioxide (SO2) is known to have the most adverse impact on MEA absorption. When a flue gas contains 3000 parts per million by volume (ppmv) SO2 and a wet flue gas desulfurization system achieves its 95% removal, approximately 2400 parts per million by weight (ppmw) SO2 could be included in the separated CO2 stream. In addition, the estimated concentration level was reduced to as low as 135 ppmw for the SO2 of less than 10 ppmv in the flue gas entering the MEA unit. Furthermore, heat-stable salt formation could further reduce the SO2 concentration below 40 ppmw in the separated CO2 stream. In this study, it is realized that the formation rates of heat-stable salts in MEA solution are not readily available in the literature and are critical to estimating the levels and compositions of flue gas impurities in sequestered CO2 streams. In addition to SO2, mercury, and other impurities in separated CO2 streams could vary depending on pollutant removal at the power plants and impose potential impacts on groundwater. Such a variation and related process control in the upstream management of carbon separation have implications for groundwater protection at carbon sequestration sites and warrant necessary considerations in overall sequestration planning, engineering, and management.

Ultraviolet absorbance as a proxy for total dissolved mercury in streams

Stream water samples were collected over a range of hydrologic and seasonal conditions at three forested watersheds in the northeastern USA. Samples were analyzed for dissolved total mercury (THg d), DOC concentration and DOC composition, and UV 254 absorbance across the three sites over different seasons and flow conditions. Pooling data from all sites, we found a strong positive correlation of THg d to DOC ( r 2 = 0.87), but progressively stronger correlations of THg d with the hydrophobic acid fraction (HPOA) of DOC ( r 2 = 0.91) and with UV 254 absorbance ( r 2 = 0.92). The strength of the UV 254 absorbance–THg d relationship suggests that optical properties associated with dissolved organic matter may be excellent proxies for THg d concentration in these streams. Ease of sample collection and analysis, the potential application of in-situ optical sensors, and the possibility for intensive monitoring over the hydrograph make this an effective, inexpensive approach to estimate THg d flux in drainage waters.