Quantifying unfrozen water in frozen soil by high-field 2H NMR

To understand wintertime controls of biogeochemical processes in high latitude soils it is essential to distinguish between direct temperature effects and the effects of changes in water availability mediated by freezing. Efforts to separate these controls are hampered by a lack of adequate methods to determine the proportion of unfrozen water. In this study we present a high-field 2H2O NMR method for quantifying unfrozen water content in frozen soil. The experimental material consisted of the humic layer of a boreal spruce forest soil mixed with varying proportions of quartz sand and humidified with deuterium-enriched water. The relative standard deviation of unfrozen water content (measured as NMR signal integral) was less than 2% for repeated measurements on a given sample and 3.5% among all samples, based on a total of 16 measurements. As compared to 1H NMR, this 2H NMR method was found to be superior for several reasons: it is less sensitive to field inhomogeneity and paramagnetic impurities, it gives a bigger line shape difference between the ice and liquid signal, it shows a sharper response to water fusion, and it excludes the possibility of hydrogen in the organic material interfering with the measurement.     

Applications of contaminant fate and bioaccumulation models in assessing ecological risks of chemicals: a case study for gasoline hydrocarbons

Mass balance models of chemical fate and transport can be applied in ecological risk assessments for quantitative estimation of concentrations in air, water, soil, and sediment. These concentrations can, in turn, be used to estimate organism exposures and ultimately internal tissue concentrations that can be compared to mode-of-action-based critical body residues that induce toxic effects. From this comparison, risks to the exposed organism can be evaluated. To demonstrate the use of fate models in ecological risk assessment, we combine the EQuilibrium Criterion (EQC) environmental fate model with a simple screening level biouptake model for three representative organisms: a bird, a mammal, and a fish. This effort yields estimates of internal body concentrations that can be compared with levels known to elicit toxic effects. As an illustration, we present an analysis of 24 hydrocarbon components of gasoline that differ in properties but are assumed to elicit toxicity by a common narcotic mode of action. Results demonstrate that differences in chemical properties and mode of entry into the environment lead to profound differences in the efficiency of transport from emission to target biota. We discussthe implications of these results and draw attention to the insights gained about regional fate and ecological risks associated with gasoline. This approach is suitable for assessing single chemicals or mixtures that have similar modes of action. We conclude that the model-based methodologies presented are widely applicable for screening level ecological risk assessments that support effective chemicals management.     

Studies on the contents of water-soluble chlorides and water-soluble sulfates in food color aluminum lakes

Japan's Specifications and Standards for Food Additives, 7th Edition (JSFA-VII) does not set limits for total contents of water-soluble chlorides and water-soluble sulfates (water-soluble inorganic salts) in food color aluminum lakes (FC-Als). However, the regulatory limit is 2% in JECFA and CFR. We used column switching suppressor-type ion chromatography (CSS-IC) for determination of anions. The total contents of water-soluble inorganic salts in FC-Als (112 qualified samples) were determined using the modified CSS-IC from fiscal year 1998 to fiscal year 2003. Total contents of water-soluble inorganic salts in four samples exceeded 2%. From an international point of view, it is desirable that the total content of water-soluble inorganic salts in FC-Al should again be regulated in Japan.     

Mathematical model of Listeria monocytogenes cross-contamination in a fish processing plant

Listeriosis is a foodborne disease caused by the bacterium Listeria monocytogenes. The food industry and government agencies devote considerable resources to reducing contamination of ready-to-eat foods with L. monocytogenes. Because inactivation treatments can effectively eliminate L. monocytogenes present on raw materials, postprocessing cross-contamination from the processing plant environment appears to be responsible for most L. monocytogenes food contamination events. An improved understanding of cross-contamination pathways is critical to preventing L. monocytogenes contamination. Therefore, a plant-specific mathematical model of L. monocytogenes cross-contamination was developed, which described the transmission of L. monocytogenes contamination among food, food contact surfaces, employees' gloves, and the environment. A smoked fish processing plant was used as a model system. The model estimated that 10.7% (5th and 95th percentile, 0.05% and 22.3%, respectively) of food products in a lot are likely to be contaminated with L. monocytogenes. Sensitivity analysis identified the most significant input parameters as the frequency with which employees' gloves contact food and food contact surfaces, and the frequency of changing gloves. Scenario analysis indicated that the greatest reduction of the within-lot prevalence of contaminated food products can be achieved if the raw material entering the plant is free of contamination. Zero contamination of food products in a lot was possible but rare. This model could be used in a risk assessment to quantify the potential public health benefits of in-plant control strategies to reduce cross-contamination.     

Ady2p is essential for the acetate permease activity in the yeast Saccharomyces cerevisiae

To identify new genes involved in acetate uptake in Saccharomyces cerevisiae, an analysis of the gene expression profiles of cells shifted from glucose to acetic acid was performed. The gene expression reprogramming of yeast adapting to a poor non-fermentable carbon source was observed, including dramatic metabolic changes, global activation of translation machinery, mitochondria biogenesis and the induction of known or putative transporters. Among them, the gene ADY2/YCR010c was identified as a new key element for acetate transport, being homologous to the Yarrowia lipolytica GPR1 gene, which has a role in acetic acid sensitivity. Disruption of ADY2 in S. cerevisiae abolished the active transport of acetate. Microarray analyses of ady2Delta strains showed that this gene is not a critical regulator of acetate response and that its role is directly connected to acetate transport. Ady2p is predicted to be a membrane protein and is a valuable acetate transporter candidate.     

Metabolic disturbance of tryptophan-nicotinamide conversion pathway by putative endocrine disruptors, bisphenol A and styrene monomer

Bisphenol A, a monomer of polycarbonate plastics, disturbed the conversion pathway of the amino acid tryptophan to the vitamin nicotinamide. The conversion ratio of tryptophan to nicotinamide was reduced to 1/15 by feeding a diet containing 1% bisphenol A. A putative disturbing reaction is kynurenine-->3-hydroxykynurenine, which is catalyzed by kynurenine monohydroxylase. This is an FAD-enzyme and requires NADPH as a coenzyme. Styrene monomer (1% addition to a normal diet) did not affect the food intake or the body weight, but slightly reduced the conversion ratio of tryptophan-nicotinamide.     

Biomagnification of alpha- and gamma-hexabromocyclododecane isomers in a Lake Ontario food web

The extent of bioaccumulation of hexabromocyclododecane (HBCD) isomers (alpha, beta, and gamma) was determined in the Lake Ontario pelagic food web using liquid chromatography tandem mass spectrometry (LC/MS/MS). Concentrations of the alpha-isomer were consistently higher than that of the gamma-isomer. The beta-isomer was below method detection limits in all samples. Whole body concentrations (ng/g, wet wt) of alpha- and gamma-HBCD were highest in the top predator lake trout samples ranging from 0.4 to 3.8 ng/g for the alpha-isomer and 0.1 to 0.8 ng/g for the gamma-isomer. For the prey fish species, the trends in alpha- and gamma-HBCD levels were slimy sculpin > smelt > alewife. Mean concentrations of total (sigma) HBCD (sum of alpha- and gamma-isomers) in the macrozooplankter Mysis relicta (0.14 +/- 0.02 ng/g wet wt) and in the benthic invertebrate Diporeia hoyi (0.16 +/- 0.02 ng/g, wet wt) were similar and approximately twice as high as in plankton (0.06 +/- 0.02 ng/g, wet wt). A strong positive linear relationship was found between sigmaHBCD concentrations (wet wt) and trophic level based on delta15N suggesting that HBCD biomagnifies in the Lake Ontario food web. The trophic magnification factor (TMF = 6.3) derived from the slope of the sigmaHBCD - trophic level relationship was slightly higher than TMFs for p,p'-DDE (6.1) and sigmaPCBs (5.7) found previously. Biomagnification factors (BMF, calculated as the ratio of lipid corrected concentration in predator/lipid corrected concentration in prey) were variable between feeding relationships and ranged from 0.4 to 10.8 for the alpha-isomer and from 0.2 to 10 for gamma-isomers.     

Characterization of O157:H7 and other Escherichia coli isolates recovered from cattle hides, feces, and carcasses

In a previous study, the seasonal prevalence was reported for stx+ Escherichia coli O157:H7 in feces and on hides and carcasses of cattle at processing. Overall, 1,697 O157:H7 isolates have now been characterized for the incidence of (i) eae(O157), hlyA, stx1, and stx2 in the recovered isolates and (ii) presumptive rough and presumptive nonmotile isolates. Seven O157:H7 isolates (0.4%) lacked stx genes, although they carried eae and hlyA. All but one of the isolates carried both eae and hlyA. Approximately two-thirds of the isolates (64% when one isolate per sample was considered) carried both stx1 and stx2. E. coli O157:H7 cells that harbored both stx1 and stx2 were more often recovered from hides in the fall (79% of the fall hide isolates) and winter (84% of the winter hide isolates) than in the spring (53%) and summer (59%). Isolates recovered from preevisceration carcasses showed a similar but not statistically significant trend. Twenty-three of the 25 O157:H7 isolates carrying stx1 but not stx2 were recovered during summer. Fifteen presumptive rough and 117 presumptive nonmotile stx+ O157:H7 isolates were recovered. Ten (67%) of the presumptive rough isolates were recovered during summer. Ninety-five of the presumptive nonmotile isolates (81%) were recovered during fall. Forty-eight percent of the false-positive isolates (175 of 363) tentatively identified as O157:H7 were O157+ H7- and lacked eae(O157), hlyA, and stx. These data suggest that in beef processing samples (i) there are minor seasonal variations in the prevalence of stx genes among E. coli O157:H7 isolates, (ii) presumptive rough and presumptive nonmotile stx+ O157:H7 isolates are present, (iii) E. coli O157:H7 isolates lacking stx genes may be rare, and (iv) O157+ H7- isolates lacking stx genes can result in many false-positive results.