Equilibrium sampling devices.
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Environmental Monitoring↗
Biomedical subjects
Donald Mackay
Publications and source records attributed to Donald Mackay.
Temperature dependence of the characteristic travel distance.
The effect of temperature variation on the environmental fate of organic chemicals can be evaluated in steady-state multimedia box models by expressing chemical partitioning data and reaction rate coefficients as functions of temperature. Using such a modelthetemperature dependence of the characteristic travel distance in air L(A), which is a measure for the atmospheric long-range transport potential of organic chemicals, is calculated. Simulations are reported for a set of 40 chemicals of environmental interest. Increasing temperature is shown to have two opposing effects on L(A). Rates of chemical transformations in the atmosphere (k(air)) and surface media are increased, which reduces L(A). Rates of atmospheric deposition (k(dep)) are reduced leading to increased mobility and L(A). Accordingly, L(A) can monotonically increase or decrease with increasing temperature, or it can have a maximum in the modeled temperature range, but it cannot have a minimum. For chemicals with a strong temperature dependence of k(air) relative to k(dep), L(A) will increase with increasing temperature. Results for selected polychlorinated biphenyls are compared to monitoring data yielding qualitative agreement when chemical properties are adjusted to mean temperatures for the measurement period. The results demonstrate that the temperature dependence of the characteristic travel distance is highly dependent on chemical characteristics and can be counterintuitive. The use of mass balance models is thus essential. The difference between the L(A) values at 5 degrees C and 30 degrees C can be up to a factor of 6. Accordingly, chemical ranking with respect to L(A) can change significantly if performed at different temperatures. Implications of the different temperature dependencies on long-range transport to polar regions are discussed.
Air Movements↗
A high-resolution model for estimating the environmental fate of multi-species chemicals: application to malathion and pentachlorophenol.
A high-resolution multi-species (HR-MS) model is presented that assesses the fate of up to four inter-converting chemical species. The current model has a more detailed environmental description than previous multi-species models in order to give a more accurate description of environmental fate. Improvements to the model environment include stratified air, soil and sediment compartments, the inclusion of a vegetation compartment, and the separation of the aerosol phase from the gas phase of the atmosphere. Such detailed environmental descriptions are particularly valuable when chemical heterogeneity is expected within environmental media as occurs with more reactive chemicals or local-scale simulations. The HR-MS model is illustratively applied to two situations for which a detailed environmental description is needed to describe the chemical fate accurately. The first example is the estimation of the atmospheric concentrations of malathion and its degradation product malaoxon following a local-scale application. The second example is a regional simulation of pentachlorophenol, which benefits from the more detailed treatment of ionizing chemical in the atmosphere. In both these cases, the HR-MS model is shown to be in good agreement with observed field data and provides a more accurate description of environmental fate than simpler multi-species models.
Environment↗
Routine drainage is not required in reduction mammaplasty.
To date, there have been no randomized trials documenting the efficacy of closed suction drainage when applied to reduction mammaplasty. Despite this, it has become the standard of care. A recent retrospective review suggests that closed suction drainage is not necessary. This study attempts to resolve this issue in a prospective, randomized fashion. The Institutional Review Board of the College of Medicine of The Pennsylvania State University approved the study. Forty-nine consecutive patients who underwent reduction mammaplasty by the inferior pedicled techniques were enrolled. Each patient was randomized to having a drain in either the right or left breast. The other breast was undrained. Patients were followed up for rate of complications and for patient satisfaction. Their ages ranged from 17 to 62 years, with a mean of 33 years. Weight of reduction from the drained breasts ranged from 360 to 1090 g, with a mean reduction of 675 g. Weight of reduction from the undrained group ranged from 380 to 1011 g, with a mean of 620 g. There were a total of 11 complications in the study. In the drained group, there were six complications out of 49 breasts (partial nipple loss in one, minor wound breakdown in two, fat necrosis in two, and hematoma in one). In the undrained group, there were five complications out of 49 breasts (partial nipple loss in none, minor wound breakdown in three, fat necrosis in one, and hematoma in one). Statistical analysis using the McNemar test revealed no significant difference between the two groups. A questionnaire revealed that the patients preferred the increased early postoperative comfort afforded by the absence of a drain. Performing reduction mammaplasty without the use of closed suction drainage is safe and is preferred by the patients.
Adolescent↗
Development and application of a generalized physiologically based pharmacokinetic model for multiple environmental contaminants.
The pharmacological disposition of four environmental contaminants resulting from acute and chronic exposure regimes is simulated using a general physiologically based pharmacological (PBPK) model. The model, which is detailed in supporting materials, is mechanistic in structure and relies on available physical-chemical partitioning and reactivity data, but experimental partitioning and absorption efficiency data can be used to refine the parameters. It is designed to complement environmental fate models, thus linking chemical emission rates with environmental and physiological behavior as part of the larger environmental risk assessment process. The model is illustratively applied to inhaled styrene and trichloroethene as well as ingested dibutyl phthalate and di(2-ethylhexyl) phthalate. The phthalate simulations include the corresponding monoester and conjugated monoester as metabolites. Tissue concentrations for each of the chemicals and metabolites are simulated for acute, occupational, and environmental exposure regimes. The same model is used for all chemicals and exposure regimes with only the physical-chemical properties, reaction rates, and exposure estimates being changed.
Animals↗
General fugacity-based model to predict the environmental fate of multiple chemical species.
A general multimedia environmental fate model is presented that is capable of simulating the fate of up to four interconverting chemical species. It is an extension of the existing equilibrium criterion (EQC) fugacity model, which is limited to single-species assessments. It is suggested that multispecies chemical assessments are warranted when a degradation product of a released chemical is either more toxic or more persistent than the parent chemical or where there is cycling between species, as occurs with association, disassociation, or ionization. The model is illustratively applied to three chemicals, namely chlorpyrifos, pentachlorophenol, and perfluorooctane sulfonate, for which multispecies assessments are advisable. The model results compare favorably with field data for chlorpyrifos and pentachlorophenol, while the perfluorooctane sulfonate simulation is more speculative due to uncertainty in input parameters and the paucity of field data to validate the predictions. The model thus provides a tool for assessing the environmental fate and behavior of a group of chemicals that hitherto have not been addressed by evaluative models such as EQC.
Alkanesulfonic Acids↗
Complexity in multimedia mass balance models: when are simple models adequate and when are more complex models necessary?
Three environmental multimedia models of varying degrees of complexity are compared to assess when simple models are adequate and when more complex models are advantageous. The simplest model, the level II (L-II) model, assumes all environmental media are at chemical equilibrium, whereas the more complex models treat chemical disequilibrium between well-mixed media (standard level IV [L-IV] model) or the major media are subdivided into separate layers to simulate heterogeneity (high-resolution level IV [HR-IV] model). The three models are compared for their performance in predicting steady-state, regional concentrations; dynamic, local-scale concentrations; and chemical persistence in the environment. The results indicate that the L-IV model often provides adequate regional simulations when chemical emission occurs to air or water. This model also is useful for assessing chemical persistence in both steady-state and dynamic scenarios. More complex models, such as the HR-IV model, are suggested for local-scale, dynamic simulations or when the chemical emission occurs to soil because they better characterize rates of intramedia transport, which can greatly affect the model predictions. The simplest L-II model predicts environmental concentrations that can differ significantly from those of more complex models, but it is useful for establishing partitioning tendencies and for ranking chemicals for their relative persistence in steady-state situations.
Air Movements↗
A suite of multi-segment fugacity models describing the fate of organic contaminants in aquatic systems: application to the Rihand Reservoir, India.
The fugacity-based quantitative water-air-sediment interaction (QWASI) model is described which can be used to establish a mass balance for an organic or metallic contaminant in a lake ecosystem consisting of water, suspended matter, bottom sediments and the atmosphere. A suite of such models is described and discussed with various degrees of complexity including versions treating equilibrium and non-equilibrium situations, steady-state and dynamic conditions with either single or multiple segments. It is suggested that when seeking to apply a mass balance model to a specific lake and contaminant situation, it is desirable to start with a simple model and increase the complexity as circumstances dictate. This approach is illustrated by application of QWASI models to the Rihand Reservoir in India for lindane and benzo(a)pyrene. The roles are discussed by which such models can contribute to improved management of chemicals that may adversely affect aquatic systems, especially in developing regions.
Diffusion↗
Assessing the environmental fate of chemicals of emerging concern: a case study of the polybrominated diphenyl ethers.
It is suggested that assessments of chemicals of emerging concern can be rationally structured around a multistage process in which fate and risk are evaluated with increasing accuracy as new data become available. An initial tentative and approximate assessment of fate and risk can identify key data gaps and justify and direct further investigations, which progressively improve the reliability of the assessment. This approach is demonstrated for a class of chemicals, the polybrominated diphenyl ethers (PBDEs), which is of increasing concern, but about which there is presently a lack of comprehensive data on properties, sources, fate and effects. Specifically, 20 PBDE congeners are investigated using the suggested approach and research needs are identified.
Environmental Monitoring↗
A dynamic level IV multimedia environmental model: application to the fate of polychlorinated biphenyls in the United Kingdom over a 60-year period.
A dynamic or level IV multimedia model is described and illustrated by application to the fate of three polychlorinated biphenyl (PCB) congeners in the United Kingdom over a 60-year period from their introduction into commerce until the present. Models of this type are shown to be valuable for elucidating the time response of environmental systems to increasing, decreasing, or pulse inputs. The suggestion is made that in addition to the outputs of time-dependent concentrations (which can be compared with monitoring data for validation purposes), it is useful to examine masses, fugacities, and fugacity ratios between media? The relative importance of processes is best evaluated by compiling cumulative intermedia fluxes and quantities lost by reaction and advection and examining the corresponding process rate constants or their reciprocals, the characteristic times. The suggestion is made that uncertainty and sensitivity analyses are desirable, but it must be appreciated that relative sensitivities of input parameters may change during the simulation period, so a single sensitivity analysis conducted at one point in time can be misleading. The use of the model for forecasting future trends in concentration is illustrated. Given the uncertainties in emission and advective inflow rates, the simulation of PCB fate in the United Kingdom is regarded as showing time trends that are in satisfactory agreement with monitoring data.
Environmental Monitoring↗
Selecting internally consistent physicochemical properties of organic compounds.
Methods are presented for selecting values of chemical properties of vapor pressure, water solubility, Henry's law constant, and octanol-water and octanol-air partition coefficients, which are subject to thermodynamic constraints, while taking advantage of all measurements. The aim of the mathematical procedures is to find the one set of internally consistent partitioning parameters that is minimally divergent from the experimental values. Information about the reliability or uncertainty of reported values can be accounted for by weighing factors. A similar approach is applied to the temperature dependence of these properties. The influence of partial miscibility of the octanol-water system is discussed and a correction is suggested for this effect. The selection method is applied to 50 mostly aromatic chemicals for which multiple measured partitioning data are available. The resulting sets of consistent property data are presented and discussed.
Environmental Pollutants↗