The fate and transport of RDX, HMX, TNT and DNT in the volcanic soils of Hawaii: a laboratory and modeling study

The adsorption and degradation behavior of RDX, HMX, TNT and DNT and the impact of pH, ionic strength and dissolved organic matter on sorption were examined for two volcanic soils of a former military training area on Hawaii Island, Hawaii, USA. The transport of these chemicals in the soil was also studied in small packed columns and simulated using a water-flow and solute-transport model, HYDRUS_1D. The results show that HMX and RDX are both significantly more mobile than TNT and DNT. The adsorbability of the four chemicals was ranked as: RDXRDX>DNT>TNT. No significant trend was observed for the effect of ionic strength, pH and dissolved organic carbon (DOC) on the adsorption of explosive compounds within the concentrations and pH ranges evaluated. The simulation results show that TNT and DNT would not leach beyond a depth of 30cm soil profile whereas a significant amount of HMX and RDX would pass the 30cm depth. It seems that the risk for contamination of groundwater is much higher for both HMX and RDX than for DNT and TNT as the substratum in this area consists of highly permeable lavas.     

Antimicrobial Activity of Natural Agents against Saccharomyces cerevisiae

The antimicrobial (AM) activity of starch‐based films coated with linalool, carvacrol or thymol against Saccharomyces cerevisiae in vitro and/or inoculated on the surface of Cheddar cheese was investigated. In solid medium using the agar diffusion method and in experiments involving the inoculation of the microorganism on the surface of Cheddar cheese, all the films containing these AM agents in coatings demonstrated an inhibitory effect against S. cerevisiae. The results suggest that the overall inhibitory effect of linalool, carvacrol or thymol increased significantly (p ≤ 0.05) with the concentration of each of the AM agents in the film coating and that the response is linear in the concentration range of 1 to 5% (w/w) of the AM agent. Thymol had the highest AM efficacy followed by carvacrol, whereas linalool had the lowest efficacy amongst the three systems. The zones of inhibition in the agar diffusion test method at 25°C for S. cerevisiae were found to be 7.6, 7.1 and 6.1 mm for thymol, carvacrol and linalool at 1% (w/w) loading and 13.2, 12.2 and 11.2 mm at 5% (w/w) loading of the AM agents, respectively. The death rates of S. cerevisiae on Cheddar cheese wrapped in films coated with thymol, carvacrol and linalool and stored for up to 28 days at 15°C were found to be 0.044, 0.043 and 0.038 per day at 1% (w/w) loading and 0.077, 0.073 and 0.063 per day at 5% (w/w) loading of the AM agents, respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Adsorption of aromatic carboxylate ions to black carbon (biochar) is accompanied by proton exchange with water

We examined the adsorption of the allelopathic aromatic acids (AA), cinnamic and coumaric, to different charcoals (biochars) as part of a study on bioavailability of natural signaling chemicals in soil. Sorption isotherms in pH 7 buffer, where the AAs are >99% dissociated, are highly nonlinear, give distribution ratios as high as 10(4.8) L/kg, and are insensitive to Ca(2+) or Mg(2+). In unbuffered media, sorption becomes progressively suppressed with loading and is accompanied by release of OH(-) with a stoichiometry approaching 1 at low concentrations, declining to about 0.4-0.5 as the pH rises. Sorption of cinnamate on graphite as a model for charcoal was roughly comparable on a surface area basis, but released negligible OH(-). A novel scheme is proposed that explains the pH dependence of adsorption and OH(-) stoichiometry and the graphite results. In a key step, AA(-) undergoes proton exchange with water. To overcome the unfavorable proton exchange free energy, we suggest AA engages in a type of hydrogen bond recognized to be of unusual strength with a surface carboxylate or phenolate group having a comparable pK(a). This bond is depicted as [RCO(2)···H···O-surf](-). The same is possible for AA(-), but results in increased surface charge. The proton exchange pathway appears open to other weak acid adsorbates, including humic substances, on carbonaceous materials.     

Carbon and sulfur cycling by microbial communities in a gypsum-treated oil sands tailings pond

Oil sands tailings ponds receive and store the solid and liquid waste from bitumen extraction and are managed to promote solids densification and water recycling. The ponds are highly stratified due to increasing solids content as a function of depth but can be impacted by tailings addition and removal and by convection due to microbial gas production. We characterized the microbial communities in relation to microbial activities as a function of depth in an active tailings pond routinely treated with gypsum (CaSO(4)·2H(2)O) to accelerate densification. Pyrosequencing of 16S rDNA gene sequences indicated that the aerobic surface layer, where the highest level of sulfate (6 mM) but no sulfide was detected, had a very different community profile than the rest of the pond. Deeper anaerobic layers were dominated by syntrophs (Pelotomaculum, Syntrophus, and Smithella spp.), sulfate- and sulfur-reducing bacteria (SRB, Desulfocapsa and Desulfurivibrio spp.), acetate- and H(2)-using methanogens, and a variety of other anaerobes that have been implicated in hydrocarbon utilization or iron and sulfur cycling. The SRB were most abundant from 10 to 14 mbs, bracketing the zone where the sulfate reduction rate was highest. Similarly, the most abundant methanogens and syntrophs identified as a function of depth closely mirrored the fluctuating methanogenesis rates. Methanogenesis was inhibited in laboratory incubations by nearly 50% when sulfate was supplied at pond-level concentrations suggesting that in situ sulfate reduction can substantially minimize methane emissions. Based on our data, we hypothesize that the emission of sulfide due to SRB activity in the gypsum treated pond is also limited due to its high solubility and oxidation in surface waters.     

Scanning electron microanalysis and analytical challenges of mapping elements in urban atmospheric particles

Elemental mapping with energy-dispersive X-ray spectroscopy (EDX) associated with scanning electron microscopy is highly useful for studying internally mixed atmospheric particles. Presented is a study of individual particles from urban airsheds and the analytical challenges in qualitatively determining the composition and origin of heterogeneous urban-air particles from high-resolution elemental maps. Coarse-mode particles were taken from samples collected in three U.S. cities: Atlanta, Los Angeles, and Seattle. Elemental maps distinguished particles with heterogeneously mixed phases from those with homogeneously mixed phases that also contained inclusions or surface adducts. Elemental mapping at low and high beam energies, along with imaging at an oblique angle helped to classify particles by origin. The impact of particle shape on X-ray microanalysis was demonstrated by having the beam enter the particle at ≥ 52° from normal. Potential misinterpretations of particle composition due to artifacts in the elemental maps were minimized by tilt imaging to reveal particle surface roughness and depth, mapping at low beam energies, noting the position of the EDX detector in the map field, and assessing differences in the mass absorption coefficients of the particle's major elements to anticipate X-ray self-absorption.     

Effect of extrusion on the antioxidant capacity and color attributes of expanded extrudates prepared from purple potato and yellow pea flour mixes

Abstract: Foods with antioxidant capacity provide protection against cardio‐vascular, certain forms of cancers, and Alzheimer's diseases caused by oxidative damages and contribute health benefits. The effect of extrusion cooking on the antioxidant capacity and color attributes of extruded products prepared from 3 selected formulations of purple potato and yellow pea flours using a co‐rotating twin screw extruder were studied. Expansion ratios of the extruded products varied from 3.93 to 4.75. The total antioxidant capacities (TAC) of the extruded products, using DPPH assay, were 3769 to 4116 μg trolox equivalent/g dry weight sample and not significantly different (P > 0.05) from their respective raw formulations. The total phenolic contents (TP) of the extruded products varied from 2088 to 3766 μg of gallic acid equivalent/g dry weight sample and retained 73% to 83% of the TP from the raw formulations after extrusion. The total anthocyanins contents (TA) in the extrudates were 0.116 to 0.228 mg of malvidin‐3‐glucosides/g dry weight sample. Compared with their raw formulations, significant losses (60% to 70%) of the TA in the extruded products occurred due to extrusion cooking. Browning indices and color attributes such as brightness, chroma, and hue angle agreed with degradation of anthocyanins in the extruded products. However, extrusion cooking retained antioxidant capacities of the raw formulations in the extruded products either in their natural forms or degraded products with radical scavenging activity. This study demonstrated the potential for the production of puffed extruded food products with the improved antioxidant content from colored potatoes and pulse formulations.