Clearly explain eliminated pathways. For example, groundwater is contaminated, but it is not used as a drinking water source. Or, if community members expressed concern about private wells, but they happen to be located upgradient of a site, explain why no pathway exists i. You may also want to include local water resources and contact information so the community can get more specific information on their water quality and well locations. Discussion of environmental fate and transport should provide only the information necessary for the reader to understand how contaminants migrate. You need not include all known geologic, topographic, hydrogeologic, climatic, and other environmental information.
Likewise, discussion of physical and chemical properties of contaminants and environmental media should be limited to supporting general conclusions about the ultimate fate of site contaminants or to support a recommendation that further sampling is needed. For example, if trichloroethylene TCE were detected in very high concentrations i. Discussions of any quantitative transport analysis e. However, you also need to be sure not to bury critical information or bottom line conclusions in appendices.
See Section 5.
Lastly, any data gaps and how they affect the assessment should be clearly described. Refer to Section 5. In addition to text discussions, summarize the results of the exposure pathway evaluation in tabular format such as the example provided in Table , based on the Figure scenario indicating the contaminated media involved, points of exposure, routes of exposure, and potentially exposed populations. Such a table can serve as a tool for documenting exposure pathway information. Some version of this table should be included in all PHAs.
Estimated numbers of people exposed via each pathway should be specified as well, but this is often times done in demographic maps. Alexander M. Aging, bioavailability, and overestimation of risk from environmental pollutants. Environ Sci Technol 34 Estimating Populations at Hazardous Waste Sites.
October 15, Directions for completing the exposure and demographic structure file EDS file. July revision. June , Atlanta, Georgia.
Chapter 6: Exposure Evaluation: Evaluating Exposure Pathways
March 20, Summary report for the ATSDR expert panel meeting on tribal exposures to environmental contaminants in plants. March 23, Case Studies in Environmental Medicine. Environmental Triggers of Asthma. April Handbook of chemical property estimation methods. Cadmium and lead uptake by edible crops grown in a silt loam soil.
Bull Environ Contam Toxicol Partition coefficient to measure bioconcentration potential of organic chemicals in fish. Environ Sci Technol Health effects of particulate air pollution: time for reassessment? Environ Health Perspect 5 Fine particulate air pollution and mortality in 20 U. N Engl J Med 24 Census Bureau. Summary File 1. Acute effects of urban air pollution on respiratory health of children with and without chronic respiratory symptoms. Occup Environ Med 56 12 Washington: National Environmental Policy Institute.
Committee on Bioavailability of Contaminants in Soils and Sediments. National Research Council of the National Academies. National Academies Press. Washington, DC. Superfund exposure assessment manual. Washington: Office of Emergency and Remedial Response. Publication No.
Handbook: ground water. Protection of public water supplies from ground-water contamination. Seminar publication. Cincinnati: Center for Environmental Research Information. UXO annual report to Congress. March 25, Office of the Secretary of Defense division not listed. August 16, Unexploded ordnance UXO : an overview. October Wilcox RG. Institutional controls for ordnance response. May 30, If an exposure investigation protocol is expanded to provide more than basic service, IRB clearance may be required. Next Section Table of Contents. Skip directly to site content Skip directly to page options Skip directly to A-Z link.
Section Navigation. Can it be eliminated from analysis altogether? Exposure Pathway Top of Page.
Top of Page. Examples of contamination sources include, but are not limited to, the following: Drums Tanks Buried waste Emission stacks and vents Landfills. Lagoons Impoundments Open burning areas Detonation areas Airfield and fire training areas. Affected media may include: Groundwater Surface and subsurface soils Sediment Surface water.
Air Soil gas Food chain biota Sludge, leachate, waste materials. How should it be evaluated?
UXO is often defined as ordnance that meet the following three criteria: It has been armed or prepared for action. It has been fired, dropped, launched, buried, or placed in a manner that can cause hazard. It remains unexploded, either by design or by malfunction. The following categories of information may be useful for some site-specific evaluations: Possible transport processes that may carry a substance away from its source see Section 6.
- Radiation hazards.
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- Assessment of Risk from Low-Level Exposure to Radiation and Chemicals!
- Drift Smoke: Loss And Renewal In A Land Of Fire (Environmental Arts and Humanities).
Physical, chemical, and biologic factors that influence the persistence and movement of a substance within and across environmental media, which can be important in determining whether opportunities for human exposure may exist see Section 6. Site-specific environmental conditions such as climate and topography that determine how contaminants move through the environment at a given location see Section 6. Fate and Transport and Exposure Pathways: What exactly needs to be done?
The following questions are useful considerations for understanding how fate and transport mechanisms might influence the likelihood of exposures: How fast are contaminants moving?
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Groundwater flow rates, for example, determine when a groundwater contamination plume may have reached downgradient private wells or may migrate to other downgradient wells in the future. How fast are contaminants dispersing along the flow path? In some cases, residents living far from sources of contamination express concern about potential exposures. Insights from fate and transport models can provide context for these concerns. For instance, air models see Chapter 5 can estimate how ambient air concentrations of pollutants are expected to decrease with downwind distance from a particular emissions source.
The rate of this decrease ultimately will depend on the type of source e. Where are contaminants moving in a particular medium? Grasping the anticipated spatial variations in contamination will help you determine whether exposure points might be impacted. For instance, when evaluating a site with contaminated groundwater, you should consider the likelihood that contaminants might migrate laterally perhaps to drinking water supply wells or vertically into different aquifers which may or may not be used for drinking water supply.
To what extent might natural attenuation be occurring?
- Copp on Fire (Joe Copp, Book 2).
- Kyrie 2 - No. 5 from Short Service.
- A Critical Overview;
Natural attenuation refers to any natural process that is known to degrade or dissipate environmental contamination. Natural attenuation processes, therefore, include biologic degradation, volatilization, and adsorption. As a site-specific example, for chemicals found at elevated concentrations in soil, you might decide that migration to exposure points is unlikely for those chemicals both with a high propensity for adsorbing to soil and with a relatively short half-life for biologic degradation.
Note that some biodegration products can be equally or more toxic than their parent compounds e. Are contaminants entering the food chain? Even though contaminants are essentially never released directly to fish, animals, or plants, fate and transport processes sometimes can make food chain contamination the most important public health issue for your site.
For instance, though the source of contamination at a facility might be limited to its wastewater discharge of PCBs to surface water, these contaminants can biomagnify resulting in relatively high concentrations in fish at the highest level of the food chain. Water solubility refers to the maximum concentration of a chemical that dissolves in a given amount of pure water. For liquids that are insoluble in water or immiscible with water , liquid density plays a critical role. In groundwater, liquids with a higher density than water called dense non-aqueous phase liquids or DNAPL may penetrate and preferentially settle to the base of an aquifer, while less dense liquids called light non-aqueous phase liquids or LNAPL will float.
Vapor pressure is a measure of the volatility of a chemical in its pure state. Thus, the vapor pressure largely determines how quickly contaminants will evaporate from surface soils or water bodies into the air.
Contaminants with higher vapor pressures will evaporate more readily. It is a function of molecular weight, solubility, and vapor pressure. The organic carbon partition coefficient K oc describes the sorption affinity a chemical has for organic carbon and consequently the tendency for compounds to be adsorbed to soil and sediment based on the organic carbon content of the soil or sediment.
This coefficient is often referred to as the adsorption coefficient. A high K oc indicates that organic chemicals bond tightly to organic matter in the soil so less of the chemical is available to move into groundwater or surface water.