Particle-phase chemistry of secondary organic material: modeled compared to measured O:C and H:C elemental ratios provide constraints

Chemical mechanisms for the production of secondary organic material (SOM) are developed in focused laboratory studies but widely used in the complex modeling context of the atmosphere. Given this extrapolation, a stringent testing of the mechanisms is important. In addition to particle mass yield as a typical standard for model-measurement comparison, particle composition expressed as O:C and H:C elemental ratios can serve as a higher dimensional constraint. A paradigm for doing so is developed herein for SOM production from a C(5)-C(10)-C(15) terpene sequence, namely isoprene, α-pinene, and β-caryopyhllene. The model MCM-SIMPOL is introduced based on the Master Chemical Mechanism (MCM v3.2) and a group contribution method for vapor pressures (SIMPOL). The O:C and H:C ratios of the SOM are measured using an Aerosol Mass Spectrometer (AMS). Detailed SOM-specific AMS calibrations for the organic contribution to the H(2)O(+) and CO(+) ions indicate that published O:C and H:C ratios for SOM are systematically too low. Overall, the measurement-model gap was small for particle mass yield but significant for particle-average elemental composition. The implication is that a key chemical pathway is missing from the chemical mechanism. The data can be explained by the particle-phase homolytic decomposition of organic hydroperoxides and subsequent alkyl-radical-promoted oligomerization.     

The nature of soil organic matter affects sorption of pesticides. 1. Relationships with carbon chemistry as determined by 13C CPMAS NMR spectroscopy

The structural composition of soil organic matter (SOM) was determined in twenty-seven soils with different vegetation from several ecological zones of Australia and Pakistan using solid-state CPMAS 13C NMR. The SOM was characterized using carbon types derived from the NMR spectra. Relationships were determined between Koc (sorption per unit organic C) of carbaryl(1-naphthylmethylcarbamate) and phosalone (S-6-chloro-2,3-dihydro-2-oxobenzoxazol-3-ylmethyl O,O-diethyl phosphorodithioate) and the nature of organic matter in the soils. Substantial variations were revealed in the structural composition of organic matter in the soils studied. The variations in Koc values of the pesticides observed for the soils could be explained only when variations in the aromatic components of SOM were taken into consideration. The highly significant positive correlations of aromaticity of SOM and Koc values of carbaryl and phosalone revealed that the aromatic component of SOM is a good predictor of a soil's ability to bind such nonionic pesticides.     

Black carbon and kerogen in soils and sediments. 1. Quantification and characterization

A comprehensive wet chemical procedure was developed by combining acid demineralization, base extraction, and dichromate oxidation for fractionation and quantitative isolation of soil/sediment organic matter (SOM) into four fractions: (1) humic acids + kerogen + BC (HKB); (2) kerogen + BC (KB); (3) humic acid (HA); and (4) BC. The soil/sediment samples tested were collected from the suburban areas of Guangzhou, a rapidly developing city of China. The results show that BC and kerogen constitute 57.8-80.6% of the total organic carbon (TOC) and that the relative content of BC ranges from 18.3% to 41.0% of the TOC, indicating that both BC and kerogen are major organic components in soils and sediments from this industrialized region. Systematic characterization of the isolated SOMs shows that both BC and kerogen have sizes ranging from a few microns to above 100 microm, relatively low O/C and H/C atomic ratios, and low contents of oxygen-containing functional groups. The isolated BC has unique fusinite and semifusinite macerals, highly porous nature, and structures indicative of its possible origins. The study indicates that SOM is highly heterogeneous and that humin, the nonextractable humus fraction, consists mainly of kerogen and BC materials in the tested soil/sediment samples. The presence of these materials in soils and sediments may have significant impacts on pollutant mass transfer and transformation processes such as desorption and bioavailability of less polar organic chemicals in surface aquatic and groundwater environments.     

Secondary organic aerosol formation by irradiation of 1,3,5-trimethylbenzene-NOx-H2O in a new reaction chamber for atmospheric chemistry and physics

A new environmental reaction smog chamber was built to simulate particle formation and growth similar to that expected in the atmosphere. The organic material is formed from nucleation of photooxidized organic compounds. The chamber is a 27 m3 fluorinated ethylene propylene (FEP) bag suspended in a temperature-controlled enclosure. Four xenon arc lamps (16 kW total) are used to irradiate primary gas components for experiments lasting up to 24 h. Experiments using irradiations of 1,3,5-trimethylbenzene-NOx-H2O at similar input concentrations without seed particles were used to determine particle number and volume concentration wall loss rates of 0.209+/-0.018 and 0.139+/-0.070 h(-1), respectively. The particle formation was compared with and without propene.     

基于机器学习的植烟区土壤有机质和全氮含量预测

为揭示植烟土壤有机质（SOM）和土壤全氮（STN）含量的空间分布规律,以重庆市巫山县笃坪乡为研究区,以成土母质和地形因子为预测因子,采用随机森林（RF）、梯度提升决策树（GBDT）和极端梯度提升（XGBoost）3种机器学习方法进行模型构建和评价,同时选择最优模型进行数字土壤制图并分析了环境变量的重要性。结果表明:①成土母质为二叠系梁山组灰岩发育的土壤SOM和STN含量显著高于成土母质为三叠系大冶组灰岩发育土壤。②GBDT模型的预测精度最佳,对于SOM和STN含量的预测, 其决定系数（R2）分别为0.616 7和0.746 8,平均绝对误差（MAE）分别为4.81 g/kg和0.25 g/kg,均方根误差（RMSE）分别为5.94 g/kg和0.34 g/kg。③主要环境因子对SOM含量影响的排序依次为母质 > 海拔 > 地形湿度指数 > 山谷深度,对STN含量影响排序依次为母质 > 坡高 > 海拔。      

Transfer, attachment, and formation of biofilms by Escherichia coli O157:H7 on meat-contact surface materials

Studies examined the effects of meat-contact material types, inoculation substrate, presence of air at the liquid-solid surface interface during incubation, and incubation substrate on the attachment/transfer and subsequent biofilm formation by Escherichia coli O157:H7 on beef carcass fabrication surface materials. Materials studied as 2 × 5 cm coupons included stainless steel, acetal, polypropylene, and high-density polyethylene. A 6-strain rifampicin-resistant E. coli O157:H7 composite was used to inoculate (6 log CFU/mL, g, or cm(2)) tryptic soy broth (TSB), beef fat/lean tissue homogenate (FLH), conveyor belt-runoff fluids, ground beef, or beef fat. Coupons of each material were submerged (4 °C, 30 min) in the inoculated fluids or ground beef, or placed between 2 pieces of inoculated beef fat with pressure (20 kg) applied. Attachment/transfer of the pathogen was surface material and substrate dependent, although beef fat appeared to negate differences among surface materials. Beef fat was the most effective (P < 0.05) inoculation substrate, followed by ground beef, FLH, and TSB. Incubation (15 °C, 16 d) of beef fat-inoculated coupons in a beef fat homogenate (pH 4.21) allowed the pathogen to survive and grow on coupon surfaces, with maximal biofilm formation observed between 2 and 8 d of storage and when air was present at the liquid-solid interface. The results indicated that the process of fabricating beef carcasses may be conducive to the attachment of E. coli O157:H7 onto meat-contact surfaces and subsequent biofilm formation. Furthermore, it is recommended that substrates found in beef fabrication settings, rather than laboratory culture media, be used in studies designed to investigate E. coli O157:H7 biofilm development and control in these environments. PRACTICAL APPLICATION: Findings of this study provide knowledge on the effect of type of beef carcass fabrication surface material, fabrication-floor fluids and residues, and incubation conditions on attachment/transfer and subsequent biofilm formation by E. coli O157:H7. The results highlight the importance of thoroughly cleaning soiled surfaces to remove all remnants of beef fat or other organic material that may harbor or protect microbial contaminants during otherwise lethal antimicrobial interventions.     

重庆典型烟区土壤有机质及其活性组分的分布特征

为了解重庆典型烟区土壤有机质数量和质量状况,采用现场调查与室内分析相结合的方法,对重庆彭水、丰都和巫山3个典型烟区土壤有机质及其活性组分的分布特征及相互关系进行了研究。结果表明,3个典型烟区土壤有机质(SOM)含量为3.35～53.94 g/kg,在适宜植烟范围(15～30 g/kg)内的比例呈现出丰都>巫山>彭水的趋势,变异系数为巫山烟区大于丰都和彭水烟区。用33、167和333 mmol/L KMnO₄测得的高活性有机质(HLOM)、中活性有机质(MLOM)、活性有机质(LOM)占SOM的比例分别表现为巫山>丰都>彭水、丰都>巫山>彭水、丰都>彭水>巫山,与各烟区的SOM含量均呈极显著正相关,说明土壤活性组分不仅可以很好的反映土壤碳素动态变化,还可用作评价重庆植烟土壤肥力和土壤质量的指标之一。     

低温加热状态下烤烟气溶胶释放量及其影响因素

为考察烟草在低温加热状态下气溶胶释放特性,采用自制稳态热解装置和烟密度计联用测试系统(SSTF-SDG)建立了可定量表征气溶胶释放量的烟草质量光密度(D_m)测试方法,考察了全国不同产区、品种、部位共34种烤烟样品在低温加热状态下的D_m,并对D_m与烤烟主要元素及常规化学成分的关系进行了统计分析。结果表明:①基于SSTF-SDG,该方法可分析低温加热状态下烟草D_m。②D_m与烟草中碳、氢、氮、烟碱均在0.01水平显著正相关,与钾硫比、钾氮比、(碳+氢)/氧以及糖碱比均在0.01水平显著负相关。③D_m各影响因素重要性排序依次为:碳 > 烟碱 > 钾硫比 > 氮 > 钾氮比 > 氢 > (碳+氢)/氧 > 糖碱比 > 硫 > 钾 > 总糖 > 氧 > 还原糖 > 氯 > 钾氯比。④由碳、氮和钾硫比为自变量的回归方程可较好地评价烤烟烟叶低温加热状态下气溶胶释放量。      

Survival of Escherichia coli O157:H7 in Galotyri cheese stored at 4 and 12 degrees C

Post-process contamination of fresh acid-curd cheeses with Escherichia coli O157:H7 may pose a risk considering the low infectious dose and the ability of the pathogen to survive in acidic foods. To evaluate its survival in Galotyri, a traditional Greek acid-curd cheese, portions (0.5 kg) of two commercial fresh products, one artisan (pH 3.9+/-0.1) and the other industrial (pH 3.7+/-0.1), were inoculated with approximately 3.0 or 6.5 log cfu g(-1) of a five-strain cocktail of E. coli O157:H7, including rifampicin-resistant derivatives of the strains ATCC 43895 and ATCC 51657, and stored aerobically at 4 and 12 degrees C. Survival was monitored for 28 days by plating cheese samples on tryptic soy agar with 100 mg l(-1) rifampicin (TSA+Rif), SMAC and Fluorocult E. coli O157:H7 agar media. The pathogen declined much faster (P<0.05) in the industrial as compared to the artisan cheeses at both temperatures. Thus, while E. coli O157:H7 became undetectable by culture enrichment after 14 days at 4 degrees C in industrial samples, irrespective of the inoculation level, populations of 1.4-1.9 and 4.2-5.1 log cfu g(-1) survived after 28 days in the corresponding artisan cheeses with the low and high inocula, respectively. Survival was longer and greater (P<0.05) on TSA+Rif than on SMAC and Fluorocult, indicating the presence of acid-injured cells. Interestingly, survival of E. coli O157:H7 after 14-28 days in cheeses was better at 12 degrees C than at 4 degrees C, probably due to yeasts which grew on the surface of temperature-abused cheeses. The large difference in the pathogen's inactivation between the industrial and artisan cheeses at 4 degrees C could not be associated with major differences in pH or type/concentration of organic acids, suggesting another anti-E. coli O157:H7 activity by the industrial starter. The high survival of the pathogen in artisan Galotyri under conditions simulating commercial storage should be of concern.     

Peroxidase-catalyzed oxidative coupling of phenols in the presence of geosorbents: rates of non-extractable product formation

Oxidative coupling processes in subsurface systems comprise a form of natural contaminant attenuation in which hydroxylated aromatic compounds (HACs) are incorporated into soil/sediment organic matter matrices. Here we describe the oxidative coupling of phenol catalyzed by horseradish peroxidase (HRP) in systems containing two geosorbents having organic matter of different composition; specifically Chelsea soil, a near-surface geologically young soil having a predominantly humic-type soil/sediment organic matter (SOM) matrix, and Lachine shale, a diagenetically older natural material having a predominantly kerogen-type SOM matrix. It was found that each of these two different types of natural geosorbents increased the formation of non-extractable coupling products (NEPs) over that which occurred in solids-free systems. The extent of coupling was higher in the systems containing humic-type Chelsea SOM than in those containing kerogen-type Lachine SOM. It was observed that HRP inactivation by free radical attack was significantly reduced in the presence of each geosorbent. A rate model was developed to facilitate quantitative evaluation and mechanistic interpretation of such coupling processes. Experimental rate measurements revealed thatthe greater extent of reaction observed in the presence of Chelsea soil than in the presence of Lachine shale can be attributed to two factors: (i) more effective protection of HRP from inactivation by the Chelsea SOM and (ii) the greater reactivity of Chelsea SOM with respect to cross-coupling. Interrelationships among enzyme protection, cross-coupling reactivity, and SOM chemistry are discussed.     

Influence of metallic chlorides on the formation of PCDD/Fs during low-temperature oxidation of carbon

Experimental study was conducted to clarify the formation behavior of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) from carbonaceous materials through a de novo synthesis route. Samples were prepared by changing mixing method and composite state of metallic chloride in graphite powder in order to simulate the texture of "unburned carbonaceous particles", i.e., soot, formed in thermal processes. Reagents of KCl, CaCl2. 2H2O, FeCl3 x 6H2O, and CuCl2 x 2H2O were used as chlorine sources and were added to graphite powder with different methods. The composite state of metallic chloride was varied by preliminary treatments: hand-mixing, mixed-grinding using a high-intensity ball mill, and preheating at different temperatures between 500 and 1100 degrees C. In the de novo experiment, reaction temperature and oxygen concentration of flowed gas were set at 300 degrees C and 2.5 mol %, respectively. During the experiment, formation rates of CO and CO2 and the formed amounts of organic chlorine and PCDD/Fs were measured. The results show a reasonable relation between the amount of formed organic chlorine and oxidation rate of carbon, and the order of the activity of metallic chlorines was obtained as KCl < CaCl2 < FeCl3 < CuCl2. Furthermore, it was found that the effect of the composite state of metallic chloride on the formation of PCDD/Fs significantly depends on the kind of metal. The results will give useful information to examine the formation mechanism of PCDD/Fs from unburned carbon particles in thermal processes.     

Chloride and organic chlorine in forest soils: storage, residence times, and influence of ecological conditions

Recent studies have shown that extensive chlorination of natural organic matter significantly affects chlorine (Cl) residence time in soils. This natural biogeochemical process must be considered when developing the conceptual models used as the basis for safety assessments regarding the potential health impacts of 36-chlorine released from present and planned radioactive waste disposal facilities. In this study, we surveyed 51 French forested areas to determine the variability in chlorine speciation and storage in soils. Concentrations of total chlorine (Cl(tot)) and organic chlorine (Cl(org)) were determined in litterfall, forest floor and mineral soil samples. Cl(org) constituted 11-100% of Cl(tot), with the highest concentrations being found in the humus layer (34-689 mg Cl(org) kg(-1)). In terms of areal storage (53 - 400 kg Cl(org) ha(-1)) the mineral soil dominated due to its greater thickness (40 cm). Cl(org) concentrations and estimated retention of organochlorine in the humus layer were correlated with Cl input, total Cl concentration, organic carbon content, soil pH and the dominant tree species. Cl(org) concentration in mineral soil was not significantly influenced by the studied environmental factors, however increasing Cl:C ratios with depth could indicate selective preservation of chlorinated organic molecules. Litterfall contributions of Cl were significant but generally minor compared to other fluxes and stocks. Assuming steady-state conditions, known annual wet deposition and measured inventories in soil, the theoretical average residence time calculated for total chlorine (inorganic (Cl(in)) and organic) was 5-fold higher than that estimated for Cl(in) alone. Consideration of the Cl(org) pool is therefore clearly important in studies of overall Cl cycling in terrestrial ecosystems.     

Quantifying the availability of clay surfaces in soils for adsorption of nitrocyanobenzene and diuron

Coverage of clay surfaces by soil organic matter (SOM) may limitthe efficacy of the soil mineral fractions for adsorption of organic contaminants and pesticides. Two methods were scrutinized for quantitatively assessing the availability of clay surfaces in a smectitic Webster A-horizon soil for sorption of p-nitrocyanobenzene (p-NCB) and diuron. One method, described previously, involves the summation of independent contributions of SOM and swelling clays to sorption of organic solutes. For this method, several assumptions must be made and/or procedural difficulties overcome in the determination of certain terms in the equation proposed for calculating the fractional availability of mineral surfaces (fa). To alleviate the methodological limitations, we developed an alternative approach for determining fa. Good agreement between fa values was obtained from both methods for p-NCB but not diuron. For p-NCB sorption, fa values varied between 0.55 and 0.71. For diuron sorption, our alternative equation estimated fa values varied between 0.41 and 0.61; the other approach yielded negative values. The results demonstrate that SOM does reduce the availability of clay surfaces, hence, suppressing sorption by the Webster A-horizon soil. Our newly developed method provides more reasonable estimates of the availability of soil-clay surfaces for sorption than an earlier published approach.     

香肠中红色2G的HPLC法及UPLC-MS/MS检测

建立香肠中红色2G色素的高效液相色谱法(HPLC)测定和确证的超高压液相色谱-质谱/质谱法(UPLC-MS/MS)。以0.662mol/L氨水为提取液,样品均质提取两次,离心后用C18柱净化,采用高效液相色谱-二极管阵列检测器(HPLC-DAD)检测,流动相为乙酸-乙酸铵缓冲液-甲醇(55:45,V/V),等度洗脱,流速为1mL/min,检测波长为530nm,阳性结果用UPLC-MS/MS确证。HPLC-DAD法在0.0212～1.06mg/L范围内,红色2G的峰面积与其相应浓度呈现良好相关性,r＞0.999,方法测定限为0.106mg/kg,在空白样品中添加已知浓度的红色2G色素,平均回收率在79.0%～86.5%之间,相对标准偏差(RSD)在3.19%～5.06%之间。UPLC-MS/MS法的测定限为0.005mg/kg,平均回收率在75.5%～80.2%之间,RSD在3.62%～9.97%之间。该方法可用于香肠中红色2G的检测及确证。     

An FTIR-DRIFT study on river sediment particle structure: implications for biofilm dynamics and pollutant binding

Diffuse reflectance infrared Fourier transform (DRIFT) spectrometry was applied to a set of sediment samples collected by traps over one and a half years in a mid-mountainous river. Dynamic changes in hydrological and life-cycle conditions generated sediment particles of different C(org) content and organic composition. Periods in the midst of or shortly after flood events left particles poor in C(org) content with spectral features that were enriched in carboxylic and aromatic signals. These are characteristic of terrestrial oxidized vascular plant debris. Low-flow conditions saw the consequent build-up of amide, aliphatic, and polysaccharide moieties as expected for autochthonous biofilm derived material. A peak ratio of two bands representing the alternation of these two types of organic matter showed that flood particle C(org) had a higher affinity for metals than the high C(org) of mature biofilms, probably owing to higher COO- contents in the first. The relative dietary bioavailability of the metals from sediment C(org), which is related to the nutritional value of the substrate, is therefore probably lower in the aftermath of a flood than in prolonged low-flow situations. This needs to be accounted for in future metal speciation and bioavailability modeling approaches.     

Survival of Escherichia coli O157:H7 in bovine feces over time under various temperature conditions

Although Escherichia coli O157:H7 prevalence estimates in cattle have increased over time due to improvements in detection methods, fecal sample transport conditions from farm to microbiological laboratories for further analysis may be a factor for prevalence underestimation. The objective of this study was to compare and determine the survival characteristics of E. coli O157:H7 in bovine feces under various storage conditions that could be encountered during transport. Fecal pats were inoculated with a four-strain cocktail of antibiotic-resistant E. coli O157:H7 to contain approximately 1 x 10(5) CFU/g. Inoculated and control samples were taken after 0, 24, 48, 120, and 168 h at each storage temperature and examined for presence and numbers of E. coli O157:H7. Each sample was subdivided and placed at each of the four following temperatures: 37, 23, 4.4 degrees C, and in a plastic cooler with refrigerant packs (0, 4, 4, 21, and 23 degrees C at five sampling times, respectively) to simulate transportation conditions. A statistically significant decrease in the population of the pathogen was observed after 48 h in samples held at 37 degrees C (P < 0.01) and after 168 h at 4.4 degrees C (P = 0.02). At 37 degrees C, E. coli O157:H7 was not detected after 48 h, either by direct plating (P < 0.01) or by immunomagnetic separation. Overall, the results of this study showed that E. coli O157:H7 survived without significant detriment in bovine fecal material inside the cooler for up to 168 h. These results indicate that shipment and storage under these conditions before microbiological analysis would be acceptable and should not affect pathogen detection.     

Soil CO2 emissions from Northern Andean páramo ecosystems: effects of fallow agriculture

The effects of fallow agriculture on soil organic matter (SOM) dynamics and CO2 emissions were assessed in the tropical Andean páramo ecosystem. Possible changes during the cultivation-fallow cycle were monitored in four areas of the Quebrada Pi?uelas valley (Venezuela). Uncultivated soils and plots at different stages of a complete cultivation--fallow cycle were incubated, and SOM mineralization kinetics was determined. Soils exhibited a low SOM mineralization activity, total CO2 evolved never reaching 3% of soil carbon, pointing to a stabilized SOM. Potential soil CO2 effluxes differed significantly according to their plot aspect: northeast (NE)-aspect soils presented higher CO2 effluxes than southwest (SW)-aspect soils. Soil CO2 emissions decreased after ploughing as compared to virgin páramo; low CO2 effluxes were still observed during cropping periods, increasing progressively to reach the highest values after 4-5 y of fallow. In all cases, experimental C mineralization data was fitted to a double exponential kinetic model. High soil labile C pool variability was observed, and two different trends were identified: NE-oriented soils showed more labile C and a wider range of values than SW-facing soils. Labile C positively correlated with CO2 effluxes and negatively with its instantaneous mineralization rate. The instantaneous mineralization rate of the recalcitrant C pool positively correlated with %C evolved as CO2 and negatively with soil C and Al2O3 contents, suggesting the importance of aluminum on SOM stability. The CO2 effluxes from these ecosystems, as well as the proportion of soil C released to the atmosphere, seem to depend not only on the size of the labile C pool but also on the accessibility of the more stabilized SOM. Therefore, fallow agriculture produces moderate changes in SOM quality and temporarily alters the CO2 emission capacity of these soils.     

Gas-phase chemistry of (alpha-terpineol with ozone and OH radical: rate constants and products

A bimolecular rate constant, kOH+alpha-terpineol, of (1.9 +/- 0.5) x 10(-10) cm3 molecule(-1) s(-1) was measured using gas chromatography/mass spectrometry and the relative rate technique for the reaction of the hydroxyl radical (OH) with alpha-terpineol (1-methyl-4-isopropyl-1-cyclohexen-8-ol) at (297 +/- 3) K and 1 atm total pressure. Additionally, a bimolecular rate constant, kO3+alpha-terpineol, of (3.0 +/- 0.2) x 10(-16) cm3 molecule(-1) s(-1) was measured by monitoring the first order decrease in ozone concentration as a function of excess alpha-terpineol. To better understand alpha-terpineol's gas-phase transformation in the indoor environment, the products of the alpha-terpineol + OH and alpha-terpineol + 03 reactions were also investigated. The positively identified alpha-terpineol/OH reaction products were acetone, ethanedial (glyoxal, HC(=O)C(=O)H), and 2-oxopropanal (methyl glyoxal, CH3C(=O)C(=O)H). The positively identified alpha-terpineol/O3 reaction product was 2-oxopropanal (methyl glyoxal, CH3C(=O)C(=O)H). The use of derivatizing agents O-(2,3,4,5,6-pentalfluorobenzyl)hydroxylamine (PFBHA) and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) clearly indicated that several other reaction products were formed. The elucidation of these other reaction products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible alpha-terpineol/OH and alpha-terpineol/O3 reaction mechanisms based on previously published volatile organic compound/ OH and volatile organic compound/O3 gas-phase reaction mechanisms.     

Thermal resistance of Listeria monocytogenes, Salmonella Heidelberg, and Escherichia coli O157:H7 at elevated temperatures

A continuous-flow apparatus was developed to measure thermal resistance (D- and z-values) of microorganisms at temperatures above 65 degrees C. This apparatus was designed to test whether vegetative microorganisms exhibited unusually high thermal resistance that prevented them from being completely eliminated at temperatures applicable to vacuum-steam-vacuum processes (116 to 157 degrees C). The apparatus was composed of a high-pressure liquid chromatography pump, a heating unit, and a cooling unit. It was designed to measure small D-values (<1 s). Three randomly selected organisms, Listeria monocytogenes, Salmonella Heidelberg, and Escherichia coli O157:H7 suspended in deionized water were tested in the continuous-flow apparatus at temperatures ranging from 60 to 80 degrees C. Studies showed that the D-values of these organisms ranged from 0.05 to 20 s. Heating at 80 degrees C was found to be basically the physical limit of the system. Experimental results showed that L. monocytogenes, Salmonella Heidelberg, and E. coli O157:H7 did not exhibit unusual heat resistance. The conditions used in the vacuum-steam-vacuum processes should have completely inactivated organisms such as L. monocytogenes, Salmonella Heidelberg, and E. coli O157:H7 if present on food surfaces. The complete destruction of bacteria during vacuum-steam-vacuum processes might not occur because the surface temperatures never reached those of the steam temperatures and because bacteria might be hidden beneath the surface and was thus never exposed to the destructive effects of the steam.     

Distribution and reactivity of O2-reducing components in sediments from a layered aquifer

The redox status of subsurface aqueous systems is controlled by the reactivity of solid redox-sensitive species and by the inflow of such species dissolved in groundwater. The reactivity toward molecular oxygen (O2) of solid reductants present in three particle size fractions of sediments from a pristine aquifer was characterized during 54 days. The stoichiometric relationships between carbon dioxide (CO2) production and O2 consumption was used in combination with sulfate production to discriminate between the contributions of sedimentary organic matter (0-87%), pyrite (6-100%), and siderite (0-43%) as the dominant reductants. The observed simultaneous oxidation of these reductants indicates that they are reactive on the same time scales. The measured reduction capacity 18-84 micromol O2/g) ranged from 8 to 42% of the total reduction capacity present as pyrite and organic carbon in the total sediment fraction (<2 mm). Fine fractions (<63 microm) were 10-250 times more reactive than their corresponding total fractions. Oxygen consumption rates decreased continuously during carbonate buffered conditions, due to a decreasing reactivity of reductants. Acidification accelerated pyrite oxidation but impeded SOM respiration. Our findings indicate that the geological history of aquifer sediments affects the amounts of organic matter, pyrite and siderite present, while environmental conditions, such as pH and microbial activity, are important in controlling the reactivity of these reductants. These controls should be considered when assessing the natural reduction activity of aquifer sediments in either natural or polluted systems.