Pollutants exposure pathways

Multiple chemical agent exposure assessment (EARC, 2005) 

Characterization of the Composition of Personal, Indoor, and Outdoor Particulate Exposure 

This is a temporal study of personal exposures to particulate matter in a panel of patients with chronic obstructive pulmonary disease. Fifteen subjects will be monitored 

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Biogeochemical cycling of elements and pollutants exposure pathways in the tropical ecosystems, which occur between 30°N and 30°S, are both intensive and at high probability of risk for human and ecosystem health. The tropical belt receives about 60% of solar radiation inputting on the Earth s surface. The total area of tropical ecosystems is about 40 x 106 km2, with exception of the High Mountain and Extra-Dry Sandy Deserts with strongly depressed life processes. 

States have made substantial recent progress in the adoption, and EPA approval, of toxic pollutant water-quahty standards. Furthermore, virtually all states have at least proposed new toxics criteria for priority toxic pollutants since Section 303 (c) (2) (B) was added to the CWA in February of 1987. Unfortunately, not all such state proposals address, in a comprehensive manner, the requirements or Section 303 (c) (2) (B). For example, some states have proposed to adopt criteria to protect aquatic hfe, but not human health other states have proposed human health criteria that do not address major exposure pathways (such as the combination of both fish consumption and drinking water). In addition, in some cases final adoption or proposed state toxics criteria that would be approved by EPA has been substantially delayed due to controversial and difficult issues associated with the toxic pollutant criteria adoption process. 

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. 

Estimation of Intake. For each exposure pathway, the general equation for estimation of the individual pollutant intake is ... 

Population Characterization. An important part of any exposure assessment is the development of a detailed and up-to-date human demographic data base for the area being studied. These data can provide the basis for estimates of subpopulations associated with different exposure pathways. In national exposure assessments it is common to use an average population density for the total U.S. or to simply distinguish between rural and urban densitites. In a geographic exposure assessment in which site-specific data on pollutant releases, environmental fate and ambient levels are measured or estimated, it is important to have equally detailed population data. Population breakdowns by age, sex, housing and... 

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. 

Exposure assessment is one of the most important steps in risk assessment. It is the process that predicts or estimates the amount of the substance under study that reaches the human body. To assess the exposure, it is necessary to define in detail the exposure pathway, the route of exposure, the concentration of the pollutant in the particular media, the contact rate, the frequency of exposure, and the population exposed (age, gender, and vulnerable population, among others). A general equation (Eq. 1) to determine the exposure dose is as follows ... 

Thus, from the viewpoint of environmental risk assessment (critical loads) the most important exposure pathways are nitrate leaching and denitrification, which are both very sensitive to anthropogenic pollution. These links of biogeochemical nitrogen cycle should be firstly quantitatively parameterized to assessing environmental risk. 

In the southern direction the Podzols are transferred into Podzoluvisols and Distric Phaerozems. These soils have less acidity and less pronounced migration of various elements. Accordingly, this determines the exposure pathways of pollutants, like heavy metals, in soil compartments of forest ecosystems. 

We can see that the Tropical Rain Green Forest ecosystems occupy about 1/5 of the African equatorial belt, whereas about 1/2 of this area is Woody and Tall Grass Savanna ecosystems. The rest of the area are occupied by various Dry Steppe and Dry and even Extra-Dry Desert ecosystems, like the Sahara, with annual rainfall less than 200 mm. As it has been mentioned above, the amount of precipitation is of high significance for exposure pathways of pollutants. 

The main specificity of biogeochemical cycling and exposure pathways in Tropical Rain Forest ecosystems is related to its almost closed character. This means that almost the total number of nutrients and/or pollutants is re-circulating in biogeochemical cycles (Figure 1). 

Many quantitative aspects of exposure pathways and their relevant application during environmental risk assessment depend on regional biogeochemical peculiarities and should be undoubtedly considered on the regional scale. Accordingly this part includes some characteristic examples and case studies from local up to regional and continental dimensions. We discuss the importance of the trans-boundary of pollutant exposure as well as the application of critical load methodology for risk estimates. 

Such pollutants as PAHs and PCBs also tend to be accumulated in the terrestrial environment but HCB and y-HCH in the marine ones. Thus, this information gives us an idea of the POPs exposure pathways to human beings. 

Thus, in according to the concept of equilibrium distribution, the relation of an organic pollutant concentration in the soil solid and liquid phase is constant at any moment (Vasilyeva and Shatalov, 2004). The example of such an approach application for assessing exposure pathways of POPs to living biota is shown in Box 1. 

Exposure pathways were estimated using the modified soil module of the MSCE-POP model (http //www.msceast.org). At present the scheme is complemented with the fraction of dissolved organic matter (/doc) and with the fraction of the chemical non-equilibrium adsorbed by solid phase (/n0n-equii) or low available with individual degradation rate. The scheme of a pollutant distribution between different soil components is shown in Figure 16. 

The committee recommends the inclusion of a detailed and accurate exposure analysis for a subset of the biomonitored population in large-scale biomonitoring studies that includes analyses of environmental media in the residence and uses a survey instrument to obtain information on diet, consumer product use, occupational exposures, and other factors relevant to the chemical exposure pathways that are being examined. The exposure assessment can be patterned on protocols used in other exposure analyses, such as the National Human Exposure Assessment Survey (NHEXAS), the Minnesota Children s Pesticide Exposure Study, and Children s Total Exposure to Pesticides and Other Persistent Organic Pollutants. 

An example of a concentration limit is a cleanup level, which is a type of an action level used in remediation projects. Pollutant concentrations in an environmental medium that are greater than the cleanup levels warrant a remedial action. Cleanup levels are often developed based on site conditions, such as future land use exposure pathways the presence of groundwater and the likelihood of its beneficial use the presence of specific ecological receptors background concentrations. 

Soils are the main and ultimate culprit of many different human exposure pathways to pollutants through the food chain, partly because lipophilic compounds that reside mainly in soils dissolve pesticides, herbicides, and the like. 

The series of steps starting with a release of toxicants and concluding in their contact with and/or entrance into a human body is referred to as the exposure pathway. Gaining entry into the body is the exposure route. There are three exposure routes through which environmental pollutants may enter the body ... 

Exposure pathway The physical course a chemical or pollutant takes Pom the source to the organism exposed (USEPA, 1992a,b, 1997b,c REAP, 1995 AlHA, 2000). Some examples of exposure pathways are drinking water ingestion, dietary consumption, pesticide handling, contact with an exposure media, or an activity that brings an individual into contact with an exposure media (Sielken, Ch. 8). 

An ecotoxicological process requires three primary elements (1) a source (what is the pollutant and where is it coming from ), (2) a receptor (which organism is likely to be affected by the pollutant ), and (3) an exposure pathway (how does the pollutant get from the source to the receptor ). The exposure pathway element also involves quantifying how much pollutant (if any) reaches a receptor. If one of these elements is missing, it is unlikely that a pollutant will be able to affect an organism. If all three are present, an ecotoxicologist can assess the potential for adverse responses in individuals, populations, or communities. 

Small mammals (e.g., moles, mice, and voles) and certain bird species that live or nest in subsurface burrows may inhale volatile pollutants that are evaporated out of the soil as a vapor. This pathway is likely to be significant only in those cases where poor ventilation allows vapors to collect and concentrate and where the receptor spends a lot of time (e.g., when nesting) in such a poorly ventilated space. There is, however, little information available about how to quantify this exposure pathway. Small mammals are more likely to be significantly exposed to pollutants that have been taken up in their food items (e.g., plants, soil invertebrates) or through incidental ingestion of polluted soil particles. 

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. 

The Remedial Action Priority System (RAPS) and Multimedia Environmental Pollutant Assessment System (MEPAS) are different names for an objective exposure pathway evaluation system developed by Pacific Northwest Laboratory to rank chemical and radioactive releases according to their potential human health impacts. Constituent migration and impact are simulated using air, groundwater, overland, surface water, and exposure components based on standard assessment principles and techniques. A shell allows interactive description of the environmental problem to be evaluated, defines required data in the form of problem-specific worksheets, and allows data input. The assessment methodology uses an extensive constituent database as a consistent source of chemical, physical, and health-related parameters. 

Ground Water Pathway. The ground water pathway ranks the potential for pollutant exposure to occur from contaminated ground water. If actual ground water contamination has not been detected, but there is contamination in soil or surface water, there is a potential for ground water contamination to occur in the future. The following factors are scored to obtain a ground water pathway score ... 

When air and water become polluted, it is relatively easy to identify the most important exposure pathways (i.e. for water it would typically be consumption). However, humans may be exposed to soil contaminants through several potential exposure routes and the significance of each of these routes will vary depending on the contaminant involved, the geological characteristics of the soil, the type of receptor, the site location and the proposed end use of the site. It is important to ensure that all potentially viable exposure pathways are properly evaluated. Fundamentally, soil contaminants can enter the body by three main pathways ... 

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