Cyclic exchanges and level of coupling between environmental media: intermedia feedback in multimedia fate models

The importance of cyclic transport of chemicals between media in the environment can be expressed in terms of the Feedback correction factor--a multiplier that accounts for the fraction of an emission that returns to the medium of release after transfer to other media. This factor is calculated analytically by explicitly solving the appropriate system of mass balance equations or using matrix techniques. It generalizes the concept of stickiness, the ratio between the net and the overall deposition rate constants, to multipathway feedback, while providing a clearer view of the level of coupling between media and analyzing the importance of coupling. This paper first shows the usefulness of the total removal rate coefficient in each media (sum of degradation rate and all intermedia transfer rates) as a baseline to determine the chemical mass in different media, the characteristic travel distance and to understand the cyclic behavior, rather than starting from the degradation lifetimes or the overall persistence in the environment. Starting from this baseline, the importance of feedback is limited for most organic chemicals. The predicted media concentrations are influenced by less than 10% due to the cyclic nature of the intermedia transport for more than 90% of the 317 tested chemicals in a 4-compartment, steady-state, closed-system multimedia model. The Feedback correction factor is always less than a factor of 5 with the greatest values when transfer fractions are important in both directions for adjacent media. This corresponds to a restricted range in the K(AW) and K(OA) space with long chemical lifetimes in both adjacent media. This analysis of the importance of the Feedback correction factor, in conjunction with resultant criteria for when cyclic exchanges between media are likely to be significant, facilitates a more transparent understanding of how substance masses are distributed in the modeled system. It is one of the important criteria to determine to what extent media can be independently modeled.     

Application of the multimedia urban model to compare the fate of SOCs in an urban and forested watershed

A multimedia model has been developed to estimate the dynamics of semivolatile organic compounds (SOCs) in urban areas. The model is based on a Level III fugacity model of Mackay and consists of six compartments: air, surface water, sediment, soil, vegetation, and an organic film that coats impervious surfaces. The model was used to illustrate the effect of impervious surfaces in urban areas by parametrization for downtown, Toronto, Canada, and modification of the same area to simulate forested conditions. With illustrative emissions of PCB homologues to air, the model indicates that most chemicals are lost by advection, with the remainder undergoing air-to-surface (organic film or vegetation) transfer. Under urban conditions chemicals with Log[K(OA)] < 7.5 volatilize from the film into air where they are susceptible to advection and photolytic degradation. Chemicals with Log[K(OA)] > 7.5 are washed off the film to surface waters where they may undergo volatilization, advection, sedimentation, and degradation. Both loss mechanisms from the film increase the overall mobility of SOCs in the urban relative to the forested environment. In forested areas, vegetation more efficiently accumulates gas- and particle-phase SOCs and subsequently transfers them to surface soils, the greatest chemical reservoir, where they are relatively immobile.     

提高环境监测数据可靠性的途径

环境监测工作在我国环境保护工作当中扮演着越来越重要的角色.在环境监测工作当中可以通过可靠性比较高的环境监测数据来对我国目前的环境现状进行真实反馈.环保部门可以根据反馈的情况制定行之有效的环境保护措施对目前存在的环境问题进行及时防治,大大提高了环保部门的工作效率和工作质量.本文首先针对提高环境监测数据可靠性的积极意义进行...     

Sorption of lipophilic organic compounds to wood and implications for their environmental fate

The sorption from water to wood (KWood) of 10 organic chemicals (log KOW, 1.48-6.20) was experimentally determined for oak (Quercus robur) and basket willow (Salix viminalis). Linear regression yielded log KWood = -0.27 (+/- 0.25) + 0.632 (+/- 0.063) log KOW for oak (r = 0.90, n = 27) and log KWood = -0.28 (+/- 0.40) + 0.668 (+/- 0.103) log KOW for willow (r = 0.79, n = 27). According to an equilibrium-partitioning model, wood should be an important storage compartment for lipophilic environmental chemicals, but this is contrary to analytical results. Diffusive uptake from air into wood was estimated to be a relevant transport process only for chemicals with a high KAW. Uptake of chemicals from soil via xylem into stem was simulated with a dynamic one-compartment model. This pathway seems to be important for chemicals with low and intermediate lipophilicity. In large trees, the chemicals are retained for a long time. If metabolism inside the stem occurs, wood can serve as a "safe sink" for environmental chemicals. This might be of use in phytoremediation.     

Black carbon-inclusive modeling approaches for estimating the aquatic fate of dibenzo-p-dioxins and dibenzofurans

A novel black carbon (BC) inclusive modeling tool is applied to estimate the distribution and long-term fate of dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the Norwegian Grenland Fjords. Three versions of the model were developed in which sediment-water partitioning was described using (i) an amorphous organic carbon (AOC) partitioning sorption model without BC sorption, (ii) a combined AOC and BC sorption model based on the Freundlich isotherm, and (iii) a combined BC-AOC model based on the Langmuir isotherm. The predictive ability of the three different models was evaluated for 17 PCDD/Fs by comparison of model predictions with observed organic carbon normalized sediment-water partition coefficients (K(TOC)) and with measured concentrations. All three versions of the model were able to predict concentrations that were in reasonable agreement with measured particulate concentrations (i.e., within a factor of 4 of median values). Estimated particulate concentrations were less sensitive to the model choice because the majority of the mass of these hydrophobic chemicals is associated with particulates regardless. However, for estimation of K(TOC) or dissolved water concentrations, both versions of the combined AOC and BC sorption models provided greatly improved estimates compared to the AOC-only model.     

Food-grade nanoemulsions: formulation, fabrication, properties, performance, biological fate, and potential toxicity

Nanoemulsions fabricated from food-grade ingredients are being increasingly utilized in the food industry to encapsulate, protect, and deliver lipophilic functional components, such as biologically-active lipids (e.g., ω-3 fatty acids, conjugated linoleic acid) and oil-soluble flavors, vitamins, preservatives, and nutraceuticals. The small size of the particles in nanoemulsions (r<100 nm) means that they have a number of potential advantages over conventional emulsions-higher stability to droplet aggregation and gravitational separation, high optical clarity, ability to modulate product texture, and, increased bioavailability of lipophilic components. On the other hand, there may also be some risks associated with the oral ingestion of nanoemulsions, such as their ability to change the biological fate of bioactive components within the gastrointestinal tract and the potential toxicity of some of the components used in their fabrication. This review article provides an overview of the current status of nanoemulsion formulation, fabrication, properties, applications, biological fate, and potential toxicity with emphasis on systems suitable for utilization within the food and beverage industry.     

Parametric correlation functions to model the structure of permanent environmental (co)variances in milk yield random regression models

The objective of the present study was to estimate milk yield genetic parameters applying random regression models and parametric correlation functions combined with a variance function to model animal permanent environmental effects. A total of 152,145 test-day milk yields from 7,317 first lactations of Holstein cows belonging to herds located in the southeastern region of Brazil were analyzed. Test-day milk yields were divided into 44 weekly classes of days in milk. Contemporary groups were defined by herd-test-day comprising a total of 2,539 classes. The model included direct additive genetic, permanent environmental, and residual random effects. The following fixed effects were considered: contemporary group, age of cow at calving (linear and quadratic regressions), and the population average lactation curve modeled by fourth-order orthogonal Legendre polynomial. Additive genetic effects were modeled by random regression on 1/6/2010orthogonal Legendre polynomials of days in milk, whereas permanent environmental effects were estimated using a stationary or nonstationary parametric correlation function combined with a variance function of different orders. The structure of residual variances was modeled using a step function containing 6 variance classes. The genetic parameter estimates obtained with the model using a stationary correlation function associated with a variance function to model permanent environmental effects were similar to those obtained with models employing orthogonal Legendre polynomials for the same effect. A model using a sixth-order polynomial for additive effects and a stationary parametric correlation function associated with a seventh-order variance function to model permanent environmental effects would be sufficient for data fitting.     

Investigating the global fate of DDT: model evaluation and estimation of future trends

The global environmental fate model CliMoChem has been used to calculate concentrations of dichlorodiphenyltrichloroethane (DDT) and its degradation products in the environment. To this end, best available physicochemical properties of DDT have been assembled, and a realistic DDT emission scenario covering the period from 1940 to 2005 has been generated. Results from the model are temporally and geographically resolved concentrations of DDT, dichlorodiphenyldichloroethylene (DDE), and dichlorodiphenyldichloroethane (DDD) in various environmental media. To confirm model results with measurements, we have developed a method for a qualitative and quantitative comparison of model and measurements. The agreement between the model and measurements is good, especially in the temporal dimension, and in the soil and air compartments. Using estimated DDT emissions for the future, we predict environmental concentrations in the next 50 years. The results show that, if emissions continue at a low level, concentrations will decrease by a factor of 30 in temperate regions and by a factor of 100 in the Arctic, as compared to the concentrations in the 1960s and 1970s. In the tropics, levels decrease by a factor of 5 to 10, only. Whereas environmental concentrations and estimated future emissions are at steady state after about 10 years in temperate and tropical regions, this takes over 50 years in the Arctic.     

Hexabromocyclododecane: current understanding of chemistry, environmental fate and toxicology and implications for global management

Hexabromocyclododecane (HBCD) is a globally produced brominated flame retardant (BFR) used primarily as an additive FR in polystyrene and textile products and has been the subject of intensified research, monitoring and regulatory interest over the past decade. HBCD is currently being evaluated under the Stockholm Convention on Persistent Organic Pollutants. HBCD is hydrophobic (i.e., has low water solubility) and thus partitions to organic phases in the aquatic environment (e.g., lipids, suspended solids). It is ubiquitous in the global environment with monitoring data generally exhibiting the expected relationship between proximity to known sources and levels; however, temporal trends are not consistent. Estimated degradation half-lives, together with data in abiotic compartments and long-range transport potential indicate HBCD may be sufficiently persistent and distributed to be of global concern. The detection of HBCD in biota in the Arctic and in source regions and available bioaccumulation data also support the case for regulatory scrutiny. Toxicity testing has detected reproductive, developmental and behavioral effects in animals where exposures are sufficient. Recent toxicological advances include a better mechanistic understanding of how HBCD can interfere with the hypothalamic-pituitary-thyroid axis, affect normal development, and impact the central nervous system; however, levels in biota in remote locations are below known effects thresholds. For many regulatory criteria, there are substantial uncertainties that reduce confidence in evaluations and thereby confound management decision-making based on currently available information.     

Identifying features, performance, and limitations of dairy ration formulation software: a comparison of three ration formulation programs

A method for evaluating and selecting dairy ration formulation software for microcomputers is presented. Information obtained from a survey of practicing nutritionists and from interviews with computer programmers was used to identify users' needs, desired features, and patterns of use. A benchmark problem consisting of 15 activities frequently required in designing dairy rations was developed to evaluate ease of use, ease of learning, and software performance. Ease of use was measured by counting keystrokes and recording time required by a user familiar with these ration formulation programs to complete the benchmark problem. Ease of learning was measured as the amount of help and time needed by users unfamiliar with this software to complete the benchmark problem. Software performance was measured by speed of formulation, ration costs, ingredients and amounts selected, and nutrient content of rations. Evaluation of three commercially available software applications was made using the method developed.     

试论环境监测仪器设备的管理

环境监测仪器设备是环境监测工作的重要组成部分,环境监测仪器设备的管理水平会影响设备的正常运行,并与环境监测数据收集的准确性有关.随着人们对生态和环境保护意识的增强,人们对环境监测的要求也越来越高,环境监测仪器设备管理水平的提高有助于确保环境监测的质量并促进国家的可持续发展.     

Application of enterobacterial repetitive intergenic consensus-polymerase chain reaction to trace the fate of generic Escherichia coli within a high capacity pork slaughter line

The dissemination of enteric contaminants (generic Escherichia coli and Salmonella) associated with pork carcasses and contact surfaces within a high capacity (6,000 carcasses per day) pork slaughter line was evaluated. Sponge samples were taken periodically from the holding area floor and carcasses at different points in the line throughout an 8.75 h production period. E. coli levels within the holding area were high (ca. 6 log cfu 100 cm(-2)) during the initial phase of processing and did not significantly increase throughout the activity period. In the course of dehairing carcasses, the levels of E. coli were significantly (p<0.05) reduced by scalding but increased during the scraping process. A combination of polishing and triple singeing reduced E. coli populations and the bacterium was only recovered sporadically on eviscerated carcasses. The E. coli populations associated with the slaughter line had a low diversity considering the large number of carcasses processed. In Visit I, the 665 E. coli isolates typed using ERIC-PCR could be grouped into 41 genotypes. In Visit II, 141 genotypes were identified among the 855 E. coli isolates tested. This would suggest that contamination on incoming pigs was of only minor significance compared to that present within the slaughterhouse environment. The holding area was shown to act as a reservoir for endemic E. coli genotypes that could be systematically transferred throughout the dressing line on carcasses. Indeed, the majority of genotypes could be re-isolated throughout the 8.75-h processing period. E. coli isolated from carcasses within the evisceration area could be traced to up-stream operations. The holding area and scraper operation were found to be the most important sites of cross-contamination. Fourteen genotypes recovered (primarily within the holding area) on Visit I were re-isolated on Visit II. Despite the presence of endemic E. coli populations, Salmonella was recovered from only two sites (holding area floor and a carcass within the cooler) on a single occasion. The two Salmonella recovered were genetically distinct (similarity index=22%) suggesting that they originated from different sources and were not part of an endemic population. The study has further illustrated the utility of molecular typing of generic E. coli isolates to establish the dynamics of enteric contamination within pork slaughter lines. However, the extent to which the distribution of E. coli can be extrapolated to that of Salmonella remains uncertain.     

Influence of the large grid size used in a multimedia mass balance model (POPsME) on the exposure assessment of polychlorinated dibenzo-p-dioxins and dibenzofurans

A multimedia mass balance model (MMM), POPsME, was evaluated for its performance to assess the fate and transport of 2,3,7,8-substituted PCDD/Fs in Seoul and a neighboring area (150 km x 150 km) in Korea. As part of the evaluation, the effects of the grid size with the homogeneous mixing assumption were estimated on the sign and magnitude of the prediction bias. The prediction compared with the monitoring data generally within 1 order of magnitude. In the presence of a concentration gradient within individual cells of 30 km x 30 km,the prediction bias for air and soil tended to increase with the distance from the sources. It was observed that the ratio of the predicted to the measured values could vary more than 4 times with the location of the monitoring site. Use of the large grid size in POPsME (and perhaps other MMMs) resulted in overpredictions for a major portion of the model domain at the cost of underprediction for limited areas nearthe sources. Beyond the source areas, a substantial contribution of the total prediction bias originated from the congeners with a large atmospheric loss rate and small TEF value. On a TEQ basis, therefore, the magnitude of the overpredictions could be significantly reduced as compared to that of the underprediction for the source areas.     

Towards sustainable Cleaning-in-Place (CIP) in dairy processing: Exploring enzyme-based approaches to cleaning in the Cheese industry

Cleaning-in-place (CIP) is the most commonly used cleaning and sanitation system for processing lines, equipment, and storage facilities such as milk silos in the global dairy processing industry. CIP employs thermal treatments and nonbiodegradable chemicals (acids and alkalis), requiring appropriate neutralization before disposal, resulting in sustainability challenges. In addition, biofilms are a major source of contamination and spoilage in dairy industries, and it is believed that current chemical CIP protocols do not entirely destroy biofilms. Use of enzymes as effective agents for CIP and as a more sustainable alternative to chemicals and thermal treatments is gaining interest. Enzymes offer several advantages when used for CIP, such as reduced water usage (less rinsing), lower operating temperatures resulting in energy savings, shorter cleaning times, and lower costs for wastewater treatment. Additionally, they are typically derived from natural sources, are easy to neutralize, and do not produce hazardous waste products. However, even with such advantages, enzymes for CIP within the dairy processing industry remain focused mainly on membrane cleaning. Greater adoption of enzyme-based CIP for cheese industries is projected pending a greater knowledge relating to cost, control of the process (inactivation kinetics), reusability of enzyme solutions, and the potential for residual activity, including possible effects on the subsequent product batches. Such studies are essential for the cheese industry to move toward more energy-efficient and sustainable cleaning solutions.     

Detection and fate of Bacillus anthracis (Sterne) vegetative cells and spores added to bulk tank milk

A preparation of Bacillus anthracis (Sterne strain) spores was used to evaluate commercially available reagents and portable equipment for detecting anthrax contamination by using real-time PCR and was used to assess the fate of spores added directly to bulk tank milk. The Ruggedized Advanced Pathogen Identification Device (RAPID) was employed to detect spores in raw milk down to a concentration of 2,500 spores per ml. Commercially available primers and probes developed to detect either the protective antigen gene or the lethal factor gene both provided easily read positive signals with the RAPID following extraction from milk with a commercially available DNA extraction kit. Nucleotide sequence analysis of the vrrA gene with the use of DNA extracted from spiked milk provided molecular data that readily identified the spores as B. anthracis with a 100% BLAST match to the Sterne and Ames strains and easily distinguished them from B. cereus. Physical-fate and thermal-stability studies demonstrated that spores and vegetative cells have a strong affinity for the cream fraction of whole milk. A single treatment at standard pasteurization temperatures, while 100% lethal to vegetative cells, had no effect on spore viability even 14 days after the treatment. Twenty-four hours after the first treatment, a second treatment at 72 degrees C for 15 s reduced the viability of the population by ca. 99% but still did not kill all of the spores. From these studies, we conclude that standard pasteurization techniques for milk would have little effect on the viability of B. anthracis spores and that raw or pasteurized milk poses no obstacles to the rapid detection of the spores by molecular techniques.