Evaluating the influence of seasonal stratification on mercury methylation rates in the water column and sediment in a contaminated section of a western U.S.A. reservoir.

Mercury methylation frequently occurs at the active oxic/anoxic boundary between the sediment bed and water column of lakes and reservoirs. Previous studies suggest that the predominant mercury methylation zone moves to the water column during periods of stratification and that high potential methylation rates (Km) in sediment require oxygenated overlying water. However, simultaneous measurements of methylmercury (MeHg) production in both the sediment and water column remain limited. Understanding the relative importance of sediment versus water column methylation and the impact of seasonal stratification on these processes has important implications for managing MeHg production. This study measured Km and potential demethylation rates (Kdm) using stable isotope tracers of unfiltered inorganic mercury and MeHg in sediments and water of the littoral and profundal zones of a shallow branch of the Nacimiento Reservoir in California's central coastal range. Field sampling was conducted once during winter (well-mixed/oxygenated conditions) and once during late summer (thermally stratified/anoxic conditions). The results showed very high ambient MeHg concentrations in hypolimnetic waters (up to 7.5 ng L-1; 79% MeHg/total Hg). During late summer, littoral sediments had higher Km (0.024 day-1) compared to profundal sediments (0.013 day-1). Anoxic water column Km were of similar magnitude to Km in the sediment (0.03 day-1). Following turnover, profundal sediment Km did not change significantly, but water column Km became insignificant. Summer and winter sediment Kdm were higher in profundal (2.35, 3.54 day-1, respectively) compared to the littoral sediments (0.52, 2.56 day-1, respectively). When modelled, Km in the water column could account for approximately 40% of the hypolimnetic MeHg. Our modelling results show that the remaining MeHg in the hypolimnion could originate from the profundal sediment. While further study is needed, these results suggest that addressing methylation in the water column and profundal sediment are of equal importance to any remediation strategy.

Investigation of an immobilization process for PFAS contaminated soils.

A two-phased bench-scale study was conducted to evaluate various sorbents for possible use as chemical stabilizing agents, along with cement solidification, for possible use in an in-situ solidification/stabilization (immobilization) treatment process for per- and polyfluoroalkyl (PFAS) contaminated soils. The first phase involved sorption experiments for six selected PFAS compounds diluted in a water solution, using five selected sorbents: granular activated carbon (GAC), activated carbon-clay blend, modified clay, biochar, iron (Fe)-amended biochar, and Ottawa sand as a control media. The second phase involved chemical stabilization treatment (via sorption), using the most effective sorbent identified in the first phase, followed by solidification of two soils from PFAS-contaminated sites. Physical solidification was achieved by adding cement as a binding agent. Results from the first phase (sorption experiments) indicated that GAC was slightly more successful than the other sorbents in sorption performance for a 3000 µg/L solution containing a mixture of the six selected PFAS analytes (500 µg/L concentration each of shorter- and longer-chain alkyl acids), and was the only sorbent used in the second phase of this study. While the GAC, activated carbon-clay blend, and modified clay sorbents showed similar sorption performance for the longer chain analytes tested, both the activated carbon-clay blend and modified clay, exhibited slightly less sorptive capacity than GAC for the shorter-chain alkyl acids. Immobilization effectiveness was evaluated by soil leachability testing using Environmental Protection Agency (EPA) Method 1312, Synthetic Precipitation Leaching Procedure (SPLP) on the samples collected from two PFAS-contaminated sites. For the majority of the PFAS soil analytes, the addition of GAC sorbent (chemical stabilization) substantially reduced the leachability of PFAS compounds from the contaminated soil samples, and the addition of cement as a physical binding agent (solidification) further decreased leachability for a few of the PFAS compounds. Overall immobilization of PFAS analytes that were detectable in the leachate from two PFAS contaminated soils ranged from 87.1% to 99.9%. Therefore, it is reasonable to consider that the laboratory testing results presented here may have application to further pilot or limited field-scale studies within a broader suite of PFAS-contaminated site treatment options that are currently available for treating PFAS contaminated soils.

Effect of organic matter concentration and characteristics on mercury mobilization and methylmercury production at an abandoned mine site.

Thousands of abandoned mines throughout the western region of North America contain elevated total-mercury (THg) concentrations. Mercury is mobilized from these sites primarily due to erosion of particulate-bound Hg (THg-P). Organic matter-based soil amendments can promote vegetation growth on mine tailings, reducing erosion and subsequent loading of THg-P into downstream waterbodies. However, the introduction of a labile carbon source may stimulate microbial activity that can produce methylmercury (MeHg)-the more toxic and bioaccumulative form of Hg. Our objectives were to investigate how additions of different organic matter substrates impact Hg mobilization and methylation using a combination of field observations and controlled experiments. Field measurements of water, sediment, and porewater were collected downstream of the site and multi-year monitoring (and load calculations) were conducted at a downstream gaging station. MeHg production was assessed using stable isotope methylation assays and mesocosm experiments that were conducted using different types of organic carbon soil amendments mixed with materials from the mine site. The results showed that >80% of the THg mobilized from the mine was bound to particles and that >90% of the annual Hg loading occurred during the period of elevated discharge during spring snowmelt. Methylation rates varied between different types of soil amendments and were correlated with the components of excitation emission matrices (EEMs) associated with humic acid fractions of organic matter. The mesocosm experiments showed that under anoxic conditions carbon amendments to tailings could significantly increase porewater MeHg concentrations (up to 13 ± 3 ng/L). In addition, the carbon amendments significantly increased THg partitioning into porewater. Overall, these results indicate that soil amendment applications to reduce surface erosion at abandoned mine sites could be effective at reducing particulate Hg mobilization to downstream waterbodies; however, some types of carbon amendments can significantly increase Hg methylation as well as increase the mobilization of dissolved THg from the site.

Supporting contaminated sites management with Multiple Criteria Decision Analysis: Demonstration of a regulation-consistent approach.

This study proposes a set of key decision-making features of the contaminated site remediation process to assist in selecting the most appropriate decision support method(s). Using a case study consistent with the requirements of the U.S. regulation for contaminated sites management, this article shows that suitable Multiple Criteria Decision Analysis methods can be selected based on a dynamic and evolving problem structuring. The selected methods belong to the family of PROMETHEE methods and can provide ranking recommendations of the considered alternatives using variable structures of the criteria, evaluation of the alternatives and exploitation of the preference model. It was found that in order to support a quick and up-to-date application of powerful decision support techniques in the process of remediation of contaminated sites, decision analysts and stakeholders should interact and co-develop the process. This research also displays how such interactions can guarantee a transparent and traceable decision recommendation so that stakeholders can better understand why some alternatives perform comprehensively better than others when a multitude of inputs is used in the decision-making process.

Comparison of the efficiency of chitinous and ligneous substrates in metal and sulfate removal from mining-influenced water.

Mining-influenced water (MIW) remediation is challenging, not only due to its acidity and high metal content, but also due to its presence in remotely located mine sites with difficult surrounding environments. An alternative to common remediation technologies, is the use of sulfate-reducing bacteria (SRB) to achieve simultaneous sulfate reduction and metal removal in on-site anaerobic passive systems. In these systems, the organic carbon source (substrate) selection is critical to obtaining the desired effluent water quality and a reasonable treated volume. In this study, we evaluated the use of two different substrates: a chitinous product obtained from crushed crab shells, and a more traditional ligneous substrate. We put the substrates, both with and without water pretreatment consisting of aeration and pH adjustment, in anaerobic experimental columns. The treatment with the chitinous substrate was more effective in removing metals (Al, Cu, Fe, Cd, Mn, Zn) and sulfate for a longer period (458 days) than the ligneous substrate (78 days) before suffering Zn breakthrough. The reactors fed with pretreated water had longer operational periods and lower metals and sulfate concentrations in the effluent than those with untreated influent water. Zn was consistently removed to levels <0.3 mg/L for 513 days in the chitinous substrate columns, while levels <0.3 mg/L were maintained for only 140 days in the ligneous substrate pretreated column. The highest sulfate removal rates achieved in this study were in the range of 5-6 mol/m3/d for the chitinous substrate and 1-2 mol/m3/d for the ligneous substrate. Overall, the chitinous substrate proved to be more efficient in the removal of all the aforementioned metals and for sulfate when compared to the ligneous substrate. This could be the determinant when selecting a substrate for passive systems treating acidic MIW, particularly when Zn and Mn removal is necessary.

The Challenges of PFAS Remediation.

Many military bases and their surrounding communities are impacted by contamination with per- and polyfluoroalkyl substances (PFAS) from Aqueous Film-Forming Foams (AFFFs). Soil sorption technologies provide a promising solution to immobilize PFAS in the soil and prevent groundwater and drinking water contamination. This article is the result of a collaborative effort between Battelle and the U.S. EPA's review of the most promising technologies.

Assessing the Impact of Removing Select Materials from Coal Mine Overburden, Central Appalachia Region, USA.

The exposure of readily soluble components of overburden materials from surface coal mining to air and water results in mineral oxidation and carbonate mineral dissolution, thus increasing coal mine water conductivity. A conductivity benchmark of 300 µS/cm for mine water discharges in the Appalachian region has been suggested to protect aquatic life and the environment. A USGS screening-level leach test was applied to individual strata from three cores collected from a surface mine site in the Central Appalachian region to generate preliminary conductivity rankings, which were used to classify strata for two disposal scenarios: (i) Unmodified Scenario, which included all extracted strata and (ii) Modified Scenario, which excluded 15% (by mass) of the overburden materials with the highest conductivities. We evaluated overburden leaching conductivity using EPA Method 1627 in 18 dry-wet cycles, generating conductivities of 1,020-1,150 µS/cm for the Unmodified Scenario and 624-979 µS/cm for the Modified Scenario. Hence, overburden segregation was successful in reducing the leachate conductivity, but did not reach the proposed benchmark. The leachate was dominated by sulfate in the first four cycles and by bicarbonates in cycles 5-18 in columns with higher sulfur content, while bicarbonates were dominant throughout experiments with lower sulfur content in overburden. The use of conductivity rankings, isolation of potentially problematic overburden strata, and appropriate materials management could reduce conductivity in Central Appalachian streams and other surface mining areas.

Water-level fluctuations influence sediment porewater chemistry and methylmercury production in a flood-control reservoir.

Reservoirs typically have elevated fish mercury (Hg) levels compared to natural lakes and rivers. A unique feature of reservoirs is water-level management which can result in sediment exposure to the air. The objective of this study is to identify how reservoir water-level fluctuations impact Hg cycling, particularly the formation of the more toxic and bioaccumulative methylmercury (MeHg). Total-Hg (THg), MeHg, stable isotope methylation rates and several ancillary parameters were measured in reservoir sediments (including some in porewater and overlying water) that are seasonally and permanently inundated. The results showed that sediment and porewater MeHg concentrations were over 3-times higher in areas experiencing water-level fluctuations compared to permanently inundated sediments. Analysis of the data suggest that the enhanced breakdown of organic matter in sediments experiencing water-level fluctuations has a two-fold effect on stimulating Hg methylation: 1) it increases the partitioning of inorganic Hg from the solid phase into the porewater phase (lower log Kd values) where it is more bioavailable for methylation; and 2) it increases dissolved organic carbon (DOC) in the porewater which can stimulate the microbial community that can methylate Hg. Sulfate concentrations and cycling were enhanced in the seasonally inundated sediments and may have also contributed to increased MeHg production. Overall, our results suggest that reservoir management actions can have an impact on the sediment-porewater characteristics that affect MeHg production. Such findings are also relevant to natural water systems that experience wetting and drying cycles, such as floodplains and ombrotrophic wetlands.

Metal contamination in environmental media in residential areas around Romanian mining sites.

Hard-rock mining for metals, such as gold, silver, copper, zinc, iron and others, is recognized to have a significant impact on the environmental media, soil and water, in particular. Toxic contaminants released from mine waste to surface water and groundwater is the primary concern, but human exposure to soil contaminants either directly, via inhalation of airborne dust particles, or indirectly, via food chain (ingestion of animal products and/or vegetables grown in contaminated areas), is also, significant. In this research, we analyzed data collected in 2007, as part of a larger environmental study performed in the Rosia Montana area in Transylvania, to provide the Romanian governmental authorities with data on the levels of metal contamination in environmental media from this historical mining area. The data were also considered in policy decision to address mining-related environmental concerns in the area. We examined soil and water data collected from residential areas near the mining sites to determine relationships among metals analyzed in these different environmental media, using the correlation procedure in the SAS statistical software. Results for residential soil and water analysis indicate that the average values for arsenic (As) (85 mg/kg), cadmium (Cd) (3.2 mg/kg), mercury (Hg) (2.3 mg/kg) and lead (Pb) (92 mg/kg) exceeded the Romanian regulatory exposure levels [the intervention thresholds for residential soil in case of As (25 mg/kg) and Hg (2 mg/kg), and the alert thresholds in case of Pb (50 mg/kg) and Cd (3 mg/kg)]. Average metal concentrations in drinking water did not exceed the maximum contaminant level (MCL) imposed by the Romanian legislation, but high metal concentrations were found in surface water from Rosia creek, downstream from the former mining area.

Mechanisms and effectivity of sulfate reducing bioreactors using a chitinous substrate in treating mining influenced water.

Mining-influenced water (MIW) is one of the main environmental challenges associated with the mining industry. Passive MIW remediation can be achieved through microbial activity in sulfate-reducing bioreactors (SRBRs), but their actual removal rates depend on different factors, one of which is the substrate composition. Chitinous materials have demonstrated high metal removal rates, particularly for the two recalcitrant MIW contaminants Zn and Mn, but their removal mechanisms need further study. We studied Cd, Fe, Zn, and Mn removal in bioactive and abiotic SRBRs to elucidate the metal removal mechanisms and the differences in metal and sulfate removal rates using a chitinous material as substrate. We found that sulfate-reducing bacteria are effective in increasing metal and sulfate removal rates and the duration of operation in SRBRs, and that the main mechanism involved was metal precipitation as sulfides. The solid residues provided evidence of the presence of sulfides in the bioactive column, more specifically ZnS, according to XPS analysis. The feasibility of passive treatments with a chitinous substrate could be an important option for MIW remediation.

Issues in the development of epidemiologic studies of workers exposed to engineered nanoparticles.

OBJECTIVE: Capitalizing on phenomena at the nanoscale may present great benefits to society. Nevertheless, until the hazards and risks of engineered nanoparticles are determined, the technological products and advances of nanotechnology may be impeded by the societal concerns. Although animal data provide the necessary first step in hazard and risk assessment, ultimately epidemiological studies will be required, especially studies of workers exposed to engineered nanoparticles. It may be too soon to conduct informative epidemiological studies but it is now appropriate to identify issues that will be pertinent and prepare strategies to address them. METHODS: The published scientific literature on incidental and engineered nanoparticles and air pollution were reviewed to identify issues in the conduct of epidemiological studies of workers exposed to engineered nanoparticles. RESULTS: Twelve important issues were identified-the most critical pertaining to particle heterogeneity, temporal factors, exposure characterization, disease endpoints, and identification of the study population. CONCLUSION: Consideration of these issues provides the foundation for initiating epidemiologic research on workers exposed to engineered nanoparticles.

Presence of tungsten-containing fibers in tungsten refining and manufacturing processes.

In tungsten refining and manufacturing processes, a series of tungsten oxides are typically formed as intermediates in the production of tungsten powder. The present study was conducted to characterize airborne tungsten-containing fiber dimensions, elemental composition and concentrations in the US tungsten refining and manufacturing industry. During the course of normal employee work activities, seven personal breathing zone and 62 area air samples were collected and analyzed using National Institute for Occupational Safety and Health (NIOSH) fiber sampling and counting methods to determine dimensions, composition and airborne concentrations of fibers. Mixed models were used to identify relationships between potential determinants and airborne fiber concentrations. Results from transmission electron microscopy analyses indicated that airborne fibers with length >0.5 microm, diameter >0.01 microm and aspect ratios > or =3:1 were present on 35 of the 69 air samples collected. Overall, the airborne fibers detected had a geometric mean length approximately 3 microm and diameter approximately 0.3 microm. Ninety-seven percent of the airborne fibers identified were in the thoracic fraction (i.e. aerodynamic diameter < or = 10 microm). Energy dispersive X-ray spectrometry results indicated that airborne fibers prior to the carburization process consisted primarily of tungsten and oxygen, with other elements being detected in trace quantities. Based on NIOSH fiber counting 'B' rules (length > 5 microm, diameter < 3 microm and aspect ratio > or = 5:1), airborne fiber concentrations ranged from below the limit of detection to 0.085 fibers cm(-3), with calcining being associated with the highest airborne concentrations. The mixed model procedure indicated that process temperature had a marginally significant relationship to airborne fiber concentration. This finding was expected since heated processes such as calcining created the highest airborne fiber concentrations. The finding of airborne tungsten-containing fibers in this occupational setting needs to be confirmed in similar settings and demonstrates the need to obtain information on the durability and associated health effects of these fibers.

Presence of airborne fibers in tungsten refining and manufacturing processes: preliminary characterization.

In tungsten refining and manufacturing processes, a series of tungsten oxides (WO(X)) are typically formed as intermediates in the production of tungsten powder. Studies in the Swedish tungsten refining and manufacturing industry have shown that intermediate tungsten refining processes can create WO(X) fibers. The purpose of the present study was to identify and provide a preliminary characterization of airborne tungsten-containing fiber dimensions, elemental composition, and concentrations in the U.S. tungsten refining and manufacturing industry. To provide the preliminary characterization, 10 static air samples were collected during the course of normal employee work activities and analyzed using standard fiber sampling and counting methods. Results from transmission electron microscopy analyses conducted indicate that airborne fibers with length > 0.5 microm, diameter > 0.01 microm, and aspect ratio > or = 3:1, with a geometric mean (GM) length of approximately 2.0 microm and GM diameter of approximately 0.25 microm, were present on 9 of the 10 air samples collected. Energy dispersive X-ray spectrometry results indicate that airborne fibers prior to the carburization process consisted primarily of tungsten and oxygen, with other elements being detected in trace quantities. Results from an air sample collected at the carburization process indicated the presence of fibers composed primarily of tungsten with oxygen and carbon, and traces of other elements. Based on National Institute for Occupational Safety and Health standard fiber counting rules, airborne fiber concentrations ranged from below the limit of detection to 0.14 f/cm(3). The calcining process was associated with the highest airborne fiber concentrations. More than 99% (574/578) of the airborne fibers identified had an aerodynamic diameter

Evaluation of a proposed area equation for improved exothermic process control.

Our understanding of heat transfer and meteorological theories and their applications for engineering control design have been refined since the collective work in ventilation engineering for manufacturing process was published by Hemeon in 1955. These refined theories were reviewed and used to develop a newly proposed equation to estimate buoyant plume area (A). The area is a key parameter in estimating the plume volumetric flow (Q=UA) required for exothermic process control. Subsequent to developing a theoretical equation for plume area (A), plume velocity and area data were collected in the laboratory using a thermal anemometer and a scale-model exothermic process. Laboratory results were compared to solutions provided by the proposed, American Conference of Governmental Industrial Hygienists (ACGIH) and Hemeon plume area equations to determine which equation most closely matched the laboratory data. To make this determination, either t-tests or Wilcoxon signed-rank tests were conducted (based on examination of data normality) to determine the difference between collected data and solutions from the proposed, ACGIH and Hemeon equations. Median differences and P-values from Wilcoxon signed-rank tests (non-parametric) indicate that the ACGIH and Hemeon plume area equations provide significantly lower values than the laboratory data. However, the proposed equation provided solutions that were not significantly different from the collected data. Results indicate that the plume area equations currently recommended by the ACGIH and Hemeon are not as accurate as the proposed equation over the range of parameters investigated.

Evaluation of a proposed velocity equation for improved exothermic process control.

Exothermic or heated processes create potentially unsafe work environments for an estimated 5-10 million American workers each year. Excessive heat and process contaminants have the potential to cause adverse health effects in exposed workers. Owing to the potential hazards, engineering controls are recommended for these processes. Our understanding of heat transfer and meteorological theories, and their applications for engineering controls have evolved since seminal work was published by Hemeon in 1955. These refined theories were reviewed and used to develop a proposed equation to estimate buoyant plume mean velocity. Mean velocity is a key parameter used to estimate the plume volumetric flow required for controlling effluents from exothermic processes. Subsequent to developing the proposed equation, plume velocity data were collected with a thermal anemometer for a model exothermic process in the laboratory, and an actual exothermic process in the field. Laboratory and field results were then compared to solutions provided by the proposed, American Conference of Governmental Industrial Hygienists (ACGIH), and Hemeon mean velocity equations. To determine which equation most closely matched the laboratory and field data, either t-tests or Wilcoxon Signed Rank tests were conducted (based on examination of data normality) to determine the difference between collected data and solutions from the proposed, ACGIH, and Hemeon equations. Median differences and P-values from Wilcoxon Signed Rank tests (nonparametric) indicate that the ACGIH mean velocity equation provides significantly different estimates from the laboratory and the field mean velocity data. However, the proposed and Hemeon equation provided solutions that were not significantly different from the collected data. These results were unexpected due to the similar developmental backgrounds between the ACGIH and Hemeon equations. Findings indicate that radiant heat flux is an important consideration when using horizontal plate heat transfer equations to estimate plume mean velocity over the range of parameters investigated. Results indicate that the mean velocity equation currently recommended by ACGIH is not as accurate as either the proposed or Hemeon equations over the range of parameters investigated.

Ventilation equations for improved exothermic process control.

Exothermic or heated processes create potentially unsafe work environments for an estimated 5-10 million American workers each year. Excessive heat and process contaminants have the potential to cause acute health effects such as heat stroke, and chronic effects such as manganism in welders. Although millions of workers are exposed to exothermic processes, insufficient attention has been given to continuously improving engineering technologies for these processes to provide effective and efficient control. Currently there is no specific occupational standard established by OSHA regarding exposure to heat from exothermic processes, therefore it is important to investigate techniques that can mitigate known and potential adverse occupational health effects. The current understanding of engineering controls for exothermic processes is primarily based on a book chapter written by W. C. L. Hemeon in 1955. Improvements in heat transfer and meteorological theory necessary to design improved process controls have occurred since this time. The research presented involved a review of the physical properties, heat transfer and meteorological theories governing buoyant air flow created by exothermic processes. These properties and theories were used to identify parameters and develop equations required for the determination of buoyant volumetric flow to assist in improving ventilation controls. Goals of this research were to develop and describe a new (i.e. proposed) flow equation, and compare it to currently accepted ones by Hemeon and the American Conference of Governmental Industrial Hygienists (ACGIH). Numerical assessments were conducted to compare solutions from the proposed equations for plume area, mean velocity and flow to those from the ACGIH and Hemeon. Parameters were varied for the dependent variables and solutions from the proposed, ACGIH, and Hemeon equations for plume area, mean velocity and flow were analyzed using a randomized complete block statistical design (ANOVA). Results indicate that the proposed plume mean velocity equation provides significantly greater means than either the ACGIH or Hemeon equations throughout the range of parameters investigated. The proposed equations for plume area and flow also provide significantly greater means than either the ACGIH or Hemeon equations at distances >1 m above exothermic processes. With an accurate solution for the total volumetric flow, ventilation engineers and practicing industrial hygienists are equipped with the necessary information to design and size hoods, as well as place them at an optimal distance from the source to provide adequate control of the rising plume. The equations developed will allow researchers and practitioners to determine the critical control parameters for exothermic processes, such as the exhaust flow necessary to improve efficacy and efficiency, while ensuring adequate worker protection.