Release of Electron Donors during Thermal Treatment of Soils.

Thermal treatment of soil and groundwater may provide an in situ source of soluble organic compounds and hydrogen (H2) that could stimulate microbial reductive dechlorination (MRD) at sites impacted by chlorinated solvents. The objectives of this study were to identify and quantify the release of electron donors and fermentable precursors during soil heating and to estimate availability of these compounds following thermal treatment. Fourteen solid materials containing <0.01 to 63.81 wt % organic carbon (OC) were incubated at 30, 60, or 90 °C for up to 180 d, leading to the release of direct electron donors (i.e., H2 and acetate) and fermentable volatile fatty acids (VFAs). Total VFA release ranged from 5 ± 0 × 10-9 carbon per gram solid (mol C/gs) during 30 °C incubation of quartz sand to 820 ± 50 × 10-6 mol C/gs during 90 °C incubation of humic acid, and was positively impacted by incubation time, temperature, and solid-phase OC content. H2 gas was detected at a maximum of 180 ± 50 × 10-9 mol H2/gs, accounting for less than 0.3% of reducing equivalents associated with VFAs released under the same conditions. These findings will allow for more reliable prediction of substrate release during thermal treatment, supporting the implementation of coupled thermal and biological remediation strategies.

Changing agricultural practices: potential consequences to aquatic organisms.

Agricultural practices pose threats to biotic diversity in freshwater systems with increasing use of glyphosate-based herbicides for weed control and animal waste for soil amendment becoming common in many regions. Over the past two decades, these particular agricultural trends have corresponded with marked declines in populations of fish and mussel species in the Upper Conasauga River watershed in Georgia/Tennessee, USA. To investigate the potential role of agriculture in the population declines, surface waters and sediments throughout the basin were tested for toxicity and analyzed for glyphosate, metals, nutrients, and steroid hormones. Assessments of chronic toxicity with Ceriodaphnia dubia and Hyalella azteca indicated that few water or sediment samples were harmful and metal concentrations were generally below impairment levels. Glyphosate was not observed in surface waters, although its primary degradation product, aminomethyl phosphonic acid (AMPA), was detected in 77% of the samples (mean = 509 µg/L, n = 99) and one or both compounds were measured in most sediment samples. Waterborne AMPA concentrations supported an inference that surfactants associated with glyphosate may be present at levels sufficient to affect early life stages of mussels. Nutrient enrichment of surface waters was widespread with nitrate (mean = 0.7 mg NO3-N/L, n = 179) and phosphorus (mean = 275 µg/L, n = 179) exceeding levels associated with eutrophication. Hormone concentrations in sediments were often above those shown to cause endocrine disruption in fish and appear to reflect the widespread application of poultry litter and manure. Observed species declines may be at least partially due to hormones, although excess nutrients and herbicide surfactants may also be implicated.

Arsenic in soils and forages from poultry litter-amended pastures.

In regions of concentrated poultry production, poultry litter (PL) that contains significant quantities of trace elements is commonly surface-applied to pastures at high levels over multiple years. This study examined the effect of long-term applications of PL on soil concentrations of arsenic (As), copper (Cu), Zinc (Zn), and the uptake of these elements by bermuda grass grown on Cecil (well-drained) and Sedgefield (somewhat poorly-drained) soils. The results showed that concentrations of As, Cu, and Zn in soils that had received surface-applied PL over a 14-year period were significantly greater than untreated soil at 0-2.5 and 2.5-7.5 cm depths. However, the levels were well below the USEPA loading limits established for municipal biosolids. Arsenic fractionation showed that concentrations of all As fractions were significantly greater in PL-amended soils compared to untreated soils at 0-2.5 and 2.5-7.5 cm depths. The residual fraction was the predominant form of As in all soils. The water-soluble and NaHCO(3)-associated As were only 2% of the total As. Significant differences were found in concentrations of these trace elements and phosphorus (P) in forage from PL-amended soils compared to that in untreated plots. The concentrations of Cu, Zn, As, and P were significantly greater in forage from Sedgefield amended soil compared to Cecil soil, but were in all cases below levels of environmental concern.

Enrichment of elements in detritus from a constructed wetland and consequent toxicity to Hyalella azteca.

In a pilot constructed wetland treatment system specifically designed to treat constituents of flue gas desulfurization wastewater, detritus adsorbs significantly high concentrations of Hg, Se, and As. Results of this research indicate that Hg, Se, and As were enriched in detritus from Schoenoplectus californicus and Typha angustifolia collected from the constructed wetland by factors up to 4600, 26,300, and 15,600, respectively. As an important food source for many organisms, element enrichment makes the detritus an even greater source of contaminants to the food web. Results demonstrate that the natural decomposition of plants in this constructed wetland treatment system produces detritus enriched with Hg, Se, and As at levels potentially hazardous to aquatic organisms. To completely assess ecological risks associated with the use of constructed wetland treatment systems, contaminant enrichment, bioavailability, and toxicity in detritus must be considered.