Transport and Exposure

The transport and exposnre of meteorite specimens by the ice sheet adjacent to the Transantarctic Mountains was elegantly explained by Whillans and Cassidy (1983) in a paper entitled Catch a falling star Meteorites and old ice. Their model assumes that meteorite specimens are deposited on the surface of the ice at a constant rate and that the rate of flow of the ice sheet is also constant These assumptions lead to the conclusion that the meteorite specimens are uniformly distributed within the ice sheet When the ice encounters the Transantarctic Mountains in Fig. 18.5, it is deflected upward causing the meteorite specimens to emerge at the surface as the ice sublimates. As time passes, meteorites accumulate on the stranding surface because they are released by the ice, because of direct infaU to the ablation zones, and because of compression of the ice in the ablation zone which increases the concentration of meteorite specimens entrained in the ice sheet. 

The WhiUans-Cassidy model is based on an idealized conception of the interaction of the East Antarctic ice sheet with a mountain barrier. It assumes that the ice sheet is 3 km thick and that the bedrock surface over which it flows is relatively smooth. Actually, we know that the bedrock topography under the ice adjacent to the East Antarctic ice sheet consists of flat-topped mesas that are separated in some cases by deep valleys (Sections 17.3 and 17.4). The rugged subglacial bedrock topography causes meteorite stranding surfaces to form 

The model of Whillans and Cassidy (1983) in Fig. 18.5 assumes that meteorites that fall in the accumulation area of the East Antarctic ice sheet west of the Transantarctic Mountains, are buried and are then transported by the flow of the ice sheet until they emerge in the ablation zone adjacent to the Transantarctic Mountains. The flow lines of the Whillans-Cassidy model in Eig. 18.5 predict that the age of the ice in the ablation area decreases with increasing distance west of the Transantarctic Mountains. Therefore, the terrestrial ages of meteorite specimens (i.e., the time that has elapsed since the fall of a meteorite) should also decrease with increasing distance from the western slope of the mountains. 

The West Antarctic ice sheet undoubtedly also contains meteorites that landed on its surface. However, the glaciological, climatic, and topographic conditions do not permit them to accumulate on blue-ice stranding surfaces. 

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Analyst to conduct multipathway human health risk assessments and food-web based ecological risk assessment modeling. BREEZE risk analyst combines databases, GIS functionality, fate, transport, and exposure modeling equations into one software application... 

Morawska and co-workers have produced a number of review articles on this topic. For example, Holmes and Morawska [20] reviewed several simple and complex models covering a wide range of urban scales for the dispersion of particulate matter. Morawska et al. [21] focused on vehicle produced ultrafine particles and discussed limitations of measurement methods, sources, characteristics, transport and exposure of these particles in urban environments. Their further review focused on indoor and outdoor monitoring of airborne nanoparticles [3]. Morawska [22] discussed the importance of airborne ENPs from the health perspective. Regulations and policy measures related to the reduction of ambient particulate matter were discussed in their follow-up article [23], Their recent review article discussed the commuters exposure to ultrafine particles and associated health effects [24]. 

A key component in the initial site assessment is the identification of human and environmental receptors potentially impacted by the site. An exposure pathway analysis relies on transport information to identify receptor or exposure points. For example, potentially significant transport and exposure pathways may include groundwater transport, vapor migration into buildings or utilities, etc. Current and potential future land use is identified as well as the potential for future installation of groundwater drinking water wells. If surface water has been impacted by the release, then appropriate surface-water exposure pathways will be identified. 

Pacific Northwest Laboratory has developed health impact assessment systems, the Remedial Action Priority System (RAPS) and the Multimedia Environmental Pollutant Assessment System (MEPAS), for the U.S. Department of Energy (DOE) to evaluate the relative importance of environmental problems. RAPS, which was developed first, applies to releases from inactive waste sites. MEPAS, the most recent version of the system, allows consideration of releases from both active and inactive sites. MEPAS differs from RAPS mainly in terms of the types of emission options. Although MEPAS retains the documented framework of RAPS (1), several enhancements have been added to the transport and exposure components (2). 

Although MEPAS applications are often data intensive, the MEPAS documentation provides both application guidance (5) and definitions and sources of information for all input parameters (6). When available, site-specific data are used. Alternative procedures are provided for estimating emission, transport, and exposure parameter values for sites using local, regional, state, and federal information sources. 

The MEPAS methodology is composed of the computer models and the supporting documentation. The computer components are completely integrated in a single user-friendly system referred to as the MEPAS shell (15). The application documentation has been structured to directly correspond to the operation of the MEPAS shell (5, 6). The transport and exposure components have been individually tested using monitored values at DOE sites (9, 10). 

The SCENARIO selection activates screens for definition of the transport and exposure scenario to be used in evaluation of the environmental problems. The user can select from a list of scenarios already set up for the current ranking unit or choose to add one. To add a scenario, the user must choose the pathway that most closely represents the actual problem and then select those waste unit constituents that are transported by this particular pathway add or select receptors and match the receptors with exposure routes, such as ingestion, bathing, and direct contact. 

Transport and Exposure Analysis. When the Run/Print Reports/ Worksheets option is chosen at the main menu, a submenu is displayed with selection options that enable the user to execute the MEPAS transport and exposure codes and print results from the model run. 

The MEPAS shell has elements of a knowledge-based system. The source term, environmental. transport, and exposure assessment data entries build a database of information that can be used to define additional environmental problems. This feature, which was added to simplify evaluation of similar or related problems, will also be useful in the evaluation of remedial action alternatives for site cleanup using a baseline case. Also the knowledge base in the constituent database grows as MEPAS is applied to new constituents. 

Exposure to pesticides may occur in a variety of different ways including worker exposure during manufacture, during transport, and exposure to residues in edible crops, soil and water. Adverse effects on man may result from the compound itself, its mammalian metabolites, plant and soil metabolites or, possibly, from breakdown products in the environment. Pesticides are often dispersed widely in the environment as stable materials, such as DDT, which may remain as virtually permanent contaminants, though at detectable concentrations. This, together with the fact that pesticides are highly biologically-active molecules, requires a fine balance to be set between the benefits of pesticides and their possible hazard to man or the environment. 

The use of nuclear power has been a topic of debate for many years. Nuclear fuel represents a resource for generating energy weU into the future, whereas economically recoverable fossil fuel reserves may become depleted. Worker exposure, injuries, and fataHties in nuclear fuel mining are reportedly far less compared to those associated with recovery and handling of fossil fuels. Potential hazards associated with transporting and storing radioactive wastes do exist, however. 

Fig. 4. Comparison of the three types of tetracycline resistance where T represents the tetracycline molecule O, a tetracycline transporter and aaa/, the ribosome A shows the effect of tetracycline exposure on a sensitive cell B, the efflux of resistance where a cytoplasmic membrane protein ( D) pumps tetracycline out of the cell as fast as the tetracycline transporter takes it up C, the ribosomal protection type of resistance where the ribosome is modified by ( ) to block productive binding and D, the tetracycline modification type of resistance where t is an inactive form of tetracycline. Reproduced with...

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials No reactions Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization Polymerization is accelerated by heat and exposure to oxygen, as well as the presence of contamination such as iron rust. Iron surfaces should be treated with an appropriate reducing agent such as sodium nitrate, before being placed into isoprene service Inhibitor of Polymerization Tertiary butyl catechol (0.06 %). Di-n-butylamine, phenyl-beta-naphthylamine andphenyl-alpha-naphthylamine are also recommended. 

Polycyclic aromatic hydrocarbons have been classified as human carcinogens because they induce cancers in experimental animals and because smoking and exposure to mixtures of chemicals containing polycyclic aromatic hydrocarbons in the workplace increase the risk of lung cancer in exposed individuals. In experimental animals, benzo(a)pyrene induces cancer in different organs depending on the route of administration.Furthermore, exposure to polycyclic aromatic hydrocarbons commonly occurs in occupations related to traffic (use of diesel engines in transportation and railways). 

In this step, the assessor qiuuitifies tlie magnitude, frequency and duration of exposure for each patliway identified in Step 2. Tliis step is most often conducted in two stages estimation of exposure concentrations and calculation of intakes. The later estimation is considered in Step 4. In tliis part of step 3. the exposure assessor determines the concentration of chemicals tliat will be contacted over the exposure period. E.xposure concentrations are estimated using monitoring data and/or chemical transport and environmental fate models. Modeling may be used to estimate future chemical concentrations in media tliat are currently contaminated or tliat may become contaminated, and current concentrations in media and/or at locations for which tliere are no monitoring data. The bulk of the material in tliis chapter is concerned witli tliis step. 

The second case (Table 2) illustrates a hypothetic urban stream receiving both metals and nutrients mainly via urban runoff. Since urban runoff is directly linked with rainfall episodes, metal inputs and exposure will be variable under base-flow during a rainy period and very low under a situation of water scarcity (low rain and low-flow). In this case, a sudden flow increase after strong rains may cause contrasting effects on water metal transport depending on the previous situation. If previous rains have already washed the metals retained in land and sediments, the... 

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