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Understanding how individual pollution sources contribute to ambient sulfate pollution is critical for assessing past and future air quality regulations. Since attribution to specific sources is typically not encoded in spatial air pollution data, we develop a mechanistic model which we use to estimate, with uncertainty, the contribution of ambient sulfate concentrations attributable specifically to sulfur dioxide (SO2) emissions from individual coal-fired power plants in the central United States. We propose a multivariate Ornstein–Uhlenbeck (OU) process approximation to the dynamics of the underlying space-time chemical transport process, and its distributional properties are leveraged to specify novel probability models for spatial data that are viewed as either a snapshot or time-averaged observation of the OU process. Using US EPA SO2 emissions data from 193 power plants and state-of-the-art estimates of ground-level annual mean sulfate concentrations, we estimate that in 2011—a time of active power plant regulatory action—existing flue-gas desulfurization (FGD) technologies at 66 power plants reduced population-weighted exposure to ambient sulfate by 1.97 μg/m3 (95% CI: 1.80–2.15). Furthermore, we anticipate future regulatory benefits by estimating that installing FGD technologies at the five largest SO2-emitting facilities would reduce human exposure to ambient sulfate by an additional 0.45 μg/m3 (95% CI: 0.33–0.54). for this article are available online. [ABSTRACT FROM AUTHOR]

In this study, we present the associations of fine particle nitrate, sulfate, and four organic carbon fractions with ambient temperature in urban and background monitoring sites in the United States for the 2011–2012 period. Nitrate concentrations increased for decreasing temperatures, while sulfate levels increased for temperatures higher than 14 °C. The profiles of organic carbon fractions for different temperatures were comparable to that observed for elemental carbon, a thermally stable and non-reactive component emitted from combustion-related sources. The trends for all parameters were comparable for the nine regions and independent to emission estimates of fine particles and their precursors. These patterns demonstrated that ambient temperature may manipulate fine particulate composition. These differences may be augmented by rising temperatures due to changing climate. Considering the causal associations between particulate pollution and pulmonary and cardiovascular diseases, changes in the composition of particulate pollution may imply adjustments on the human health impacts. [ABSTRACT FROM PUBLISHER]

Permeable bioreactors have gained both research and management attention as viable methods for treating mine runoff waters. We examined the operation of a field-scale bioreactor (containing mixed compost, straw and gravel) for treatment of runoff from the Mother Load (ML) mine in northern Idaho, U.S. and compared it to an experimental laboratory-scale reactor, containing a similar matrix and treating similar mine runoff water. In general both reactors were efficient in removing most of the metals assayed, Al, As, Cd, Fe, Ni, Pb and Zn, with the exception of Mn. Both systems showed evidence of bacterial-mediated sulphate reduction and concomitant metal sulphide complexes. However, the experimental laboratory bioreactor showed greater proportions of immobile metals reductions than did the ML bioreactor, presumably due to the greater action of sulphate-reducing bacteria. The major metal removal mechanism in the ML bioreactor was surmised to be adsorption. Differences in metal removal mechanisms between the reactors were hypothesized to be due to fluctuating hydraulic residence times at the ML site, in turn, due to unregulated runoff flow. [ABSTRACT FROM AUTHOR]

Environmental assessments of metals are often simplified by referring to metals in terms of their elemental names without further consideration of specific metal compounds. Such simplifications can obscure important information on the fate and effects of the particular metal compounds. Barium sulfate (barite) provides a good example of the importance of knowing the specific compound when evaluating exposure, effects, and risks. We illustrate this by comparing the solubility and toxicity of barite to the soluble barium salts used to derive the U.S. Environmental Protection Agency barium ecological soil screening levels (Eco-SSLs). For ecologically relevant exposure pathways, the toxicity of barium compounds is largely controlled by their solubility. In contrast to soluble barium salts (e.g., barium acetate, barium chloride, and barium nitrate), barite is sparingly soluble and practically nontoxic to invertebrates, plants, or wildlife. No-effect levels for soil invertebrates (17,000 to 1,000,000 mg/kg) are several orders of magnitude higher than the barium Eco-SSL for soil invertebrates (330 mg/kg). And, low solubility likely limits the bioaccumulation of barium associated with barite and potential for effects on wildlife species. The importance of knowing the form of a metal compound is underscored by the fact that barite is one of the most commonly occurring barium compounds in soils and is widely used in commerce. The large differences between barite and the soluble barium compounds used to derive the Eco-SSL indicate that this screening tool cannot be usefully applied to soils containing the most commonly found barium compound, barite. The value of considering the specific metal compounds present in exposure media applies to other metals and indicates a need to go beyond simplified characterizations of metals expressed solely in terms of their elemental names. [ABSTRACT FROM AUTHOR]

Potential sulfate reduction and in situ hydrogen sulfide emission rates for three Louisiana marsh soils of varying salinities (salt, brackish, and freshwater) were used to evaluate the influence of soil physicochemical parameters on sulfur transformations in different seasons (summer, winter, and spring). Solid adsorbent preconcentration and emission flux chambers were used in field experiments to measure hydrogen sulfide emissions. Soil redox potential (Eh) was measured at depths between 5 and 50cm. Duplicate soil cores were obtained and sectioned for laboratory analysis. The fresh and brackish marsh soils were composed predominantly of organic matter, while the salt marsh soils were composed of predominantly minerals. Fresh marsh soils were generally the most oxidized and salt marsh soils the most reduced. In situ hydrogen sulfide emissions, but not potential sulfate reduction rates, were highest for the brackish marsh. Potential sulfate reduction assays may have overestimated in-situ rates, particularly for the more oxidized fresh marsh. Sulfate turnover times were longer in the salt marsh (approximately 40 days) than in either the fresh or the brackish marshes (3-8 days). Tidal action replenishes sulfate less frequently in the fresh and brackish marshes, thus sulfate depletions are more likely. The lowest potential sulfate reduction rates for all marshes occurred in winter. This was attributed to lower temperature and decreased soil sulfate content. [ABSTRACT FROM AUTHOR]

Current levels of air pollution particles in American cities can increase human mortality. Both the mechanism of injury and the responsible components are not known. We have postulated that injury following air pollution particle exposure is produced through a generation of oxygen-based free radicals catalyzed by metals present in the particles. As a result of its abundance in the atmosphere, sulfate appears to potentially be the most successful ligand to complex metal cations. We tested the hypothesis that (1) some portion of iron in ambient air pollution particles is present as sulfate and (2) this relationship between iron and sulfate results from the capacity of the latter to function as a ligand to mobilize the metal from the oxide. Concentrations of sulfate and iron in acid extracts of 20 filters (total suspended particles) from Utah were measured using inductively coupled plasma emission spectroscopy. In vitro oxidant generation was also measured using thiobarbituric acid-reactive products of deoxyribose. There were significant correlations between sulfate content, iron concentrations, and oxidant generation. Agitation of calcium sulfate with iron(III) oxide produced concentrations of water-soluble, catalytically active iron. We conclude that some portion of iron in the atmosphere is present as a sulfate. This relationship between sulfate and iron concentrations is likely the product of SO42- functioning as a ligand for the meal after its mobilization from an oxide by photoreduction. There were also associations between sulfate content, iron concentrations, and oxidant generation. However, sulfates had no capacity to support electron transport unless they were present with iron. [ABSTRACT FROM AUTHOR]

Discusses a study by researchers at the U.S. National Aeronautics & Space Administration and the Open University in Great Britain, which revealed that acid rain inhibits wetland bacteria from producing methane, a greenhouse gas linked to global warming. Annual production of methane gas in wetlands; Percentage of methane emissions suppressed by sulfate similar to that found in acid rain; Effect of acid rain on the ecosystem.

Sulfate status in soil solution at various depths in the vadose zoneand in surficial groundwater were evaluated in sandy soils under intensive citrus production in central Florida. Sulfate in the vadose zone was evaluated using soil solution sampled from suction lysimeters at 60, 120, and 240 cm depths. Sulfate distribution and movement in the soil profile were closely monitored following the fertilizer application by weekly profile soil sampling up to the depth of soil groundwater interface. Sulfate status was evaluated by sampling the surficial aquifer either using a monitor well at the top 150 cm depth or using a multi-level sampler at 60 cm intervals at the top 600 cm depth. The sulfate concentrations in the soil solution occasionally exceededthe maximum contaminant level (MCL), i.e., 500 mg SO42- L-1. Soil profile sulfate distribution data indicated rapid downward movement of sulfate following the application offertilizer mixture containing sulfate as sulfate of potash magnesia.However, sulfate concentrations in the surficial groundwater collected from depth-specific monitoring wells and multi-level sampling wells ranged from 60 to 240 and 6 to 325 mg SO42- L-1, respectively. Therefore, the sulfate loading from the vadose zone was diluted in the surficial groundwater. [ABSTRACT FROM AUTHOR]