Istvan Devai

Evidence for phosphine production and emission from Louisiana and Florida marsh soils

Abstract A diffusion chamber and solid adsorbent preconcentration technique followed by thermal desorption and gas chromatography were developed for quantifying phosphine production and emission from wetland soils. The first quantifiable emissions of phosphine from wetlands to the atmosphere are reported measured in Louisiana brackish (0.42-3.03 ng pH3/m2/h) and salt (0.91-6.52 ng PH3/m2/h) marshes. Laboratory experiments have demonstrated that Florida Everglades marsh soil can also produce phosphine (1.57 ± 2.9 pg PH3/g wet sediment/h), and these values can be increased significantly, by adding additional phosphate and energy source (to 380 ± 70 pg PH3/g wet sediment/h).

Immobilization of aqueous Hg(II) by mackinawite (FeS).

As one of the major constituents of acid volatile sulfide (AVS) in anoxic sediments, mackinawite (FeS) is known for its ability to scavenge trace metals. The interaction between aqueous Hg(II) (added as HgCl(2)) and synthetic FeS was studied via batch sorption experiments conducted under anaerobic conditions. Due to the release of H(+) during formation of hydrolyzed Hg(II) species which is more reactive than Hg(2+) in surface adsorption, the equilibrium pH decreased with the increase in Hg(II)/FeS molar ratio. Counteracting the loss of FeS solids at lower pH, the maximum capacity for FeS to remove aqueous Hg(II) was approximately 0.75 mol Hg(II) (mol FeS)(-1). The comparison of X-ray power diffraction (XRPD) patterns of synthetic FeS sorbent before and after sorption showed that the major products formed from the interaction between FeS and the aqueous Hg(II) were metacinnabar, cinnabar, and mercury iron sulfides. With the addition of FeS at 0.4 g L(-1) to a 1 mM Hg(II) solution with an initial pH of 5.6, Fe(2+) release was approximately 0.77 mol Fe(2+) per mol Hg(II) removed, suggesting that 77% of Hg(II) was removed via precipitation reaction under these conditions, with 23% of Hg(II) removed by adsorption. Aeration does not cause significant release of Hg(II) into the water phase.

Formation of volatile sulfur compounds in salt marsh sediment as influenced by soil redox condition

Abstract The effect of soil redox condition on the production or formation of gaseous sulfur compounds in anaerobic salt marsh soil was studied. Marsh soil from a Louisiana Gulf Coast Spartina alterniflora salt marsh was incubated under controlled soil redox potentials ranging from +220 mV to −240 mV, which represent a range in anaerobic soil conditions. The gas phase production of hydrogen sulfide, methanethiol, dimethyl sulfide, carbonyl sulfide, and carbon disulfide as influenced by soil redox level was quantified. Total reduced sulfur gases increased with decreasing soil redox potential. Percentage composition of the individual sulfur gases varied depending on soil redox level. Methanethiol, dimethyl sulfide and carbon disulfide progressively increased with decrease in soil redox level. A major increase in hydrogen sulfide was measured at redox potential of −100 mV and below. Likewise a significant increase in carbonyl sulfide was observed between −70 and −100 mV. Results show that intensity of soil reduction or degree of anaerobiosis is important in the production of these gaseous sulfur compounds.

Emission of reduced malodorous sulfur gases from wastewater treatment plants

The emission of malodorous gaseous compounds from wastewater collection and treatment facilities is a growing maintenance and environmental problem. Numerous gaseous compounds with low odor detection thresholds are emitted from these facilities. Sulfur-bearing gases represent compounds with the lowest odor detection threshold. Using solid adsorbent preconcentration and gas chromatographic methods, the quantity and composition of reduced malodorous sulfur gases emitted from various steps of the treatment process were determined in wastewater treatment plants in Baton Rouge, Louisiana. Hydrogen sulfide, which is a malodorous, corrosive, and potentially toxic gas, was the most dominant volatile reduced sulfur (S) compound measured. Concentrations were not only more than the odor detection threshold of hydrogen sulfide, but above levels that may affect health during long-term exposure. The concentrations of methanethiol, dimethyl sulfide, carbon disulfide, and carbonyl sulfide were significantly less than hydrogen sulfide. However, even though emissions of reduced sulfur gases other than hydrogen sulfide were low, previous studies suggested that long-term exposure to such levels may cause respiratory problems and other symptoms.

The influence of soil redox conditions on atrazine degradation in wetlands

Abstract The biotransformation of atrazine as affected by soil redox conditions was investigated in soil collected from a Taxodium distichum/Nyssa aquatic (bald cypress/water tupelo) swamp-forest receiving run-off from sugarcane growing on adjacent natural levees of the Mississippi River Deltaic Plain, LA. The soil was incubated under controlled redox conditions over a range representing both reducing and oxidizing conditions (−164, +169, +392, and +584 mV). The atrazine biotransformation rate was extremely rapid in oxidized soil (+392 mV and +584 mV). The concentration of atrazine dropped from approximately 70 μg g −1 soil to non-detectable levels after only two weeks of incubation under both oxidized redox treatments. Biotransformation of atrazine was considerably slower in soils maintained under reducing or anaerobic redox conditions (−164 mV and +169 mV). From an initial atrazine concentration of 70 μg g −1 soil, 9 μg g −1 and 3 μg g −1 atrazine, respectively, remained after 99 d for soil incubated at −164 mV and +169 mV. This study shows that there is a very clear demarcation in atrazine biotransformation between soil redox levels representing aerobic and anaerobic conditions. There was no significant difference in biotransformation between the two anaerobic redox treatments and between the two aerobic redox treatments. Results shows that atrazine will be more persistent under anaerobic conditions such as found in wetlands or subsurface environments than in more oxidizing environments such as surface agricultural soils in which it is commonly applied as a herbicide.

Methyl Mercury and Heavy Metal Content in Soils of Rivers Saale and Elbe (Germany)

Abstract The rivers Saale and Elbe, including their catchment areas (Germany), have been heavily polluted by ore mining and other anthropogenic emission sources during the last centuries. Heavy metal contamination along the Elbe River floodplains can vary depending on location. In this study data on methyl mercury, mercury, and other heavy metal contents in three soil profiles from a representative site under the influence of the rivers Elbe and Saale are presented. The relationship of metal distribution to chemical and physical characteristics in the soil profiles is outlined. Methyl and total mercury were detected in extremely high concentrations in the soil profiles. Results showed that Zn, Cu, and Pb were elevated, above the reported levels considered as excessive in soils. Concentrations of Ni, Cd, and Se were not elevated, while other elements (Al, Na, K, Ca, Mg, Mn, and Fe) were at geological or background levels. The research was supported by National Science Foundation (Grant # INT 9901301).

Relationship of Sediment Redox Conditions to Methyl Mercury in Surface Sediment of Louisiana Lakes

Abstract Surface sediment from three Louisiana Lakes containing overlying water layer spiked with 2 µg/g (2 ppm) mercury were incubated under oxygenated (air) and nonoxygenated (N2) conditions for determining the impact of oxygen status of overlying water on methylation of Hg in surface sediment from these lakes. The added mercury resulted in a greater than ten fold increase in methyl mercury (MeHg) as compared to native concentration of MeHg. The increase in methyl Hg production was less in sediment in which overlying water was exposed to oxygen rather than nitrogen. Results suggest that methyl Hg production would be less in lakes containing an oxygenated water column. In parallel microcosm studies without added mercury, MeHg decreased in sediment when redox potential of sediment suspension was increased from −200 mV to + 50 mV. Results of these studies demonstrate the importance of oxygenation or redox condition of surface sediment on mercury methylation and demethylation. Sediment conditions, which either reduce methylation or enhance demethylation in surface sediment, will limit the bioavailability of MeHg to the aquatic environment.

Changes in methylmercury concentration during storage : effect of temperature

Abstract The widespread presence of methylmercury (MeHg) in the environment and the potential toxicity and bioaccumulation in the food chain has stimulated a demand for accurate and sensitive methods for the determination of mercury compounds in water, sediments, fish and other biological samples. A capillary gas chromatographic method followed by atomic fluorescence spectrometry (GC–AFS) was used to determine changes in MeHg concentration with time during storage in methylene chloride and as affected by storage temperature. Results of our laboratory experiments showed that significant changes in MeHg concentrations occurred during a 15-day storage period. Decreases in the MeHg concentration with time were uniform and at the end of the 15-day storage period only about half the initial concentration (recoveries were between 40.2 and 51.2%) remained in samples stored at various temperature. These results draw attention to the need for immediate analysis of MeHg samples following extraction. Temperature of storage was not a significant factor in the change in MeHg concentration.

Phosphine Production Potential of Various Wastewater and Sewage Sludge Sources

A laboratory incubation procedure followed by gas chromatographic detection was used to measure phosphine production potential in representative wastewater and sewage sludge sources. Phosphine production potential was determined by measuring the rate of phosphine formation in samples incubated under laboratory conditions over a seven day period when both electron donors and the targeted electron acceptor were not limiting factors. Results of our experiments showed that except the primary effluent and secondary effluent wastewater samples all other samples studied (influent wastewater, various type of sludge and sediment sources) produced phosphine. The minimum phosphine production potential value (0.39 pg/ml wastewater/day) was measured in composite influent wastewater samples while the maximum (268 pg/g wet sludge/day) was measured in sediment samples collected from an open-air sewage treatment plant.

Evaluation of various solid adsorbents for sampling trace levels of methanethiol

Abstract The efficiency of fourteen solid adsorbent sampling tubes in trapping trace levels of methanethiol was evaluated. A thermal desorption-gas chromatographic method for the accurate separation of methanethiol from other simultaneously collected reduced volatile sulfur gases was developed. Trapping experiments demonstrated that silica gel (96.4% recovery) and molecular sieves (86.2% recovery) were the best solid adsorbent materials for collecting methanethiol when the sweep gas is dry. Using a calcium chloride drying tube, silica gel provided similar results (i.e., better than 95% recovery values) when the sweep gas contained moisture (i.e., normal field sampling conditions). Molecular sieves also were shown to be acceptable adsorbent materials for trapping methanethiol under moist conditions (73.9% recovery). Recovery values showed no significant changes during 36 h storage or using different flow rates (between 10–80 ml/min).