Pollutant fate models

Bonazountas, M. J. Fiksel (1982). ENVIRO Environmental Mathematical Pollutant Fate Modeling Handbook/Catalogue, EPA Contract No. 68-01-5146, Arthur D. Little, Inc., Cambridge, MA 02140. 

Bonazountas M. 1988. Mathematical pollutant fate modeling of petroleum products in soil systems. In Calabrese EJ, Kostecki, eds. Soils contaminated by petroleum Environmental and public health effects. New York, NY John Wiley and Sons, 31-97. 

The primary means of obtaining an environmental concentration profile involve the use of monitoring data in combination with pollutant-fate modeling. At... 

Soil compartment chemical fate modeling has been traditionally performed for three distinct subcompartments the land surface (or watershed) the unsaturated soil (or soil) zone and the saturated (or groundwater) zone of a region. In general, the mathematical simulation is structured around two major cycles the hydrologic cycle and the pollutant cycle, each cycle being associated with a number of physicochemical processes. Watershed models account for a third cycle sedimentation. 

Fortunately — and not unfortunately — no one model exists as yet which simulates all of the physical, chemical, and biological processes associated with pollutant fate in soils. We say fortunately, because such a package would be very data intensive and difficult to use. Intensive research is required to accomplish the above objective and the value of the overall product may be questioned by users. Section 7.0 presents selected models. 

PATHS (30) is mainly an analytical groundwater model, that provides a rough evaluation of the spatial and temporal status of a pollutant fate. 

Analytic Easy model use limited calibration possibilities limited input data requirements desk computer use Rough averaged predictions of pollutant fate, limited application capabilities To be used as an overall fate (screening) tools... 

Because the significance of exposure has only been considered over the past few years, there is not as wide a selection of exposure models available as that for fate models. The latter have been applied for several decades to the calculation of ambient exposure levels compared with some standard values. Papers illustrative of human exposure assessments in this symposium include one on airborne pollutant exposure assessments by Anderson (2), a generic approach to estimating exposure in risk studies by Fiksel (5), and a derivation of pollutant limit values in soil or water based on acceptable doses to humans by Rosenblatt, Small and Kainz (6). 

Rosenblatt, D.H. Dacre, J.C. Cogley, D.R. "An Environmental Fate Model Leading to Preliminary Pollutant Limit Values for Human Health Effects," Technical Report 8005, U.S. Army Medical Bioengineering Research and Development Laboratory, Fort Detrick, Frederick, MD, 1980, AD B049917L. 

The purpose of an Exposure Route and Receptor Analysis is to provide methods for estimating individual and population exposure. The results of this step combined with the output of the fate models serve as primary input to the exposure estimation step. Unlike the other analytic steps, the data prepared in this step are not necessarily pollutant-specific. The two discrete components of this analysis are (1) selection of algorithms for estimating individual intake levels of pollutants for each exposure pathway and (2) determination of the regional distribution of study area receptor populations and the temporal factors and behavioral patterns influencing this distribution. 

For a limited number of exposure pathways (primarily inhalation of air in the vicinity of sources), pollutant fate and distribution models have been adapted to estimate population exposure. Examples of such models include the SAI and SRI methodologies developed for EPA s Office of Air Quality Planning and Standards (1,2), the NAAQS Exposure Model (3), and the GEMS approach developed for EPA s Office of Toxic Substances (4). In most cases, however, fate model output will serve as an independent input to an exposure estimate. 

MacLeod M, Woodfine DG, Mackay D, Mckone T, Bennett D, Randy M (2001) BERTNorth America a regionally segmented multimedia contaminant fate model for North America. Environ Sci Pollut Res 8(3) 156-163... 

During pollutants and/or SWM leachate transport through the surface/subsurface environments, physical and chemical processes can result in the accumulation of pollutants on the solid phase constituents. The degree to which this accumulation renders the trapped pollutants immobile is of vital interest in considerations for modeling the proposed pollutant fate and transport. 

When the rates of sorption or desorption processes are known, environmental fate modeling can provide an educated estimate and prediction on the accessibility and bioavailability of a target pollutant to a specific transport mechanism in the environment. Hence, the present chapter is an attempt to assess fate (i.e., in terms of pollutant mobility using predictive sorption or desorption coefficients) as well as effects (i. e., in terms of bioavailability) of various pollutants and to correlate these observations for development of predictive relationships. 

Exposure factors are also included in many of the more recently developed characterization factors for human toxicity. These characterization factors are obtained through more complex models that incorporate factors such as persistence, pollutant fate, and exposure pathways. Although involving greater complexity in development, end-users may simply employ the more complex characterization factors already calculated by existing impact assessment models such as TRACI. 

A second limitation resides in the fact that we have confined pollutant losses to those that occur by evaporation to the atmosphere. This ignores the role played by bottom sediments as well as solids suspended in the water of the basin in removing solute by adsorption, and of possible biodegradation of the solute by bacterial action. These are important mechanisms that add to the loss incurred by evaporation and have to be taken into account in comprehensive models of pollutant fate. By ignoring these processes, we have in effect set an upper limit to the pollutant concentration in the water. In other words, things will not be as bad as our model predicts, at least as far as the aqueous phase is concerned, because a good deal of the pollutant may disappear as a result of adsorption and biodegradation. 

MacLeod, M. Woodfme, D. G. Mackay, D. McKone, T. Bennett, D. Maddalena, R. 2001. BETR North America A regionally segmented multimedia contaminant fate model for North America, Environmental Science and Pollution Research 8 156-163. 

Wania, R and Mackay, D. 1999. The evolution of mass balance models of persistent organic pollutant fate in tlie environment. Environmental Pollution 100, 223-240. 

Aerosol Dynamics. Inclusion of a description of aerosol dynamics within air quaUty models is of primary importance because of the health effects associated with fine particles in the atmosphere, visibiUty deterioration, and the acid deposition problem. Aerosol dynamics differ markedly from gaseous pollutant dynamics in that particles come in a continuous distribution of sizes and can coagulate, evaporate, grow in size by condensation, be formed by nucleation, or be deposited by sedimentation. Furthermore, the species mass concentration alone does not fliUy characterize the aerosol. The particle size distribution, which changes as a function of time, and size-dependent composition determine the fate of particulate air pollutants and their... 

PLATE 7 Chemical engineers develop models to understand the formation, transport, and environmental fate of airhorne pollutants such as ozone. This photograph shows a graphic display of a chemical engineering model for ozone concentrations in the Los Angeles hasin. Courtesy, John Seinfeld, California Institute of Technology. 

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