Environmental pathway

Once the particle-reactive species have been scavenged, subsequent packaging and/or aggregation can result in the flux of particles and particle-reactive species from the water column. Thorium provides a unique way to study the environmental pathways and the biogeochemical processes that affect particle-reactive species. The four useful thorium isotopes are Th = A x yx), °Th... 

EPA. 1978c. Environmental pathways of selected chemicals in Ifeshwater systems Part II. Laboratory studies. Athens, GA U.S. Environmental Protection Agency, Office of Research and Development, Environmental Research Laboratory. EPA-600/7-78/074. 

Envlroiunental testing Is a critical element In this process since It enables the qualitative and quantitative determination of toxic chemicals In the environment and the definition of environmental pathways which may lead to human exposure This paper briefly reviews the overall process of health risk assessments and the particular role which environmental testing plays Recent efforts to assess environmental health risks In relation to Love Canal Illustrate both the usefulness and the limitations of environmental testing In risk assessment ... 

Measurement of exposure can be made by determining levels of toxic chemicals in human serum or tissue if the chemicals of concern persist in tissue or if the exposure is recent. For most situations, neither of these conditions is met. As a result, most assessments of exposure depend primarily on chemical measurements in environmental media coupled with semi-quantitative assessments of environmental pathways. However, when measurements in human tissue are possible, valuable exposure information can be obtained, subject to the same limitations cited above for environmental measurement methodology. Interpretation of tissue concentration data is dependent on knowledge of the absorption, excretion, metabolism, and tissue specificity characteristics for the chemical under study. The toxic hazard posed by a particular chemical will depend critically upon the concentration achieved at particular target organ sites. This, in turn, depends upon rates of absorption, transport, and metabolic alteration. Metabolic alterations can involve either partial inactivation of toxic material or conversion to chemicals with increased or differing toxic properties. 

Smith, J. H. "Environmental Pathways of Selected Chemicals in Freshwater Systems" Part I. EPA Report 600/7-77-113,1977. 

The studies involved determining appropriate environmental pathways that would result in exposure to humans, determining appropriate occupancy factors (number and distribution) within structures, characterizing the source term for each property, selecting an appropriate set of health risk coefficients, calculating health effects, and providing summary reports of potential health effects for each vicinity property. 

Because estimates of health risk are based on the levels of radionuclides in or near the vicinity properties, the quality of the potential health risk estimates depends upon the availability of appropriate measurement data. Hence, the first steps involved the determination of the appropriate environmental pathways of exposure and developing the source term for the exposure of persons potentially at risk. For our work, the radiological source-term data was based on measurements made principally by the Oak Ridge National Laboratory and the Mound Laboratory. 

Smith, J.H., Mabey, W.R., Bahonos, N., Holt, B.R., Lee, S.S., Chou, T.W., Venberger, D.C., Mill, T. (1978) Environmental Pathways of Selected Chemicals in Fresh Water Systems Part II. Laboratory Studies. Interagency Energy-Environment Research Program Report. EPA-600/7-78-074. Environmental Research Laboratory Office of Research and Development. US EPA, Athens, GA 30605, pp. 304. 

ENVIRONMENTAL PATHWAY EVALUTION (Evaluations increasingly related to adverse effects—emission, concentration, exposure dose, ecosystem response)... 

The environmental pathway evaluation considers various routes by which ecosystems could be exposed to acid deposition (Figure 2). 

The major environmental pathways of pesticides into streams and into the food chains are presented in Figure 2. 

Figure 2. Major environmental pathways for the distribution of pesticides in the biosphere.

In recent studies, pesticides such as atrazine have been found in precipitation. Therefore volatilization and subsequent transport in the gaseous phase is an important environmental pathway. Vaporization rates of pesticides deposited on surface of soil and plant leaves depend on the physical-chemical properties of the substance. A useful physicochemical criterion is Henry s constant, Ku, which is defined as the equilibrium air-to-water partial pressure ratio of the substance (see Chapter 7). 

In the Asian region with prevalent monsoon climate and heavy rain events during rain seasons, surface runoff plays the most important role in the environmental pathways of many pesticides. The major factors influencing the amount of pesticides carried away by runoff are as follows (Richter, 1999) ... 

Dudzinska, M.R., Kozak, Z., Polychlorinated dibenzo-p-dioxins and dibenzofurans -properties and environmental pathways (in Polish), Monographies of Polish Academy of Sciences, 2001, ISBN 83-915874-4-4. 

UNEP (1993) Organic Contaminants in the Environment, Environmental Pathways and Effects, (ed. K.C.Jones) Elsevier, London, pp. 275-289. 

Environmental Pathways of Selected Chemicals in Freshwater Systems Part 1 Background and Experimental Procedures 821R98008 Evaluating Field Techniques for Collecting Effluent Samples for Trace Metals Analysis... 

Hazard identification, consisting of the assessment of the potential environmental risk of a substance based on its physicochemical properties and expected environmental pathways. 

Isomorphous substitution of iron oxides is important for several reasons. In the electronics industry, trace amounts (dopants) of elements such as Nb and Ge are incorporated in hematite to improve its semiconductor properties. Dopants are also added to assist the reduction of iron ores. In nature, iron oxides can act as sinks for potentially toxic M", M and M heavy metals. Investigation of the phenomenon of isomorphous substitution has also helped to establish a better understanding of the geochemical and environmental pathways followed by Al and various trace elements. Empirical relationships (e. g. Fe and V) are often found between the Fe oxide content of a weathered soil profile and the levels of various trace elements. Such relationships may indicate similarities in the geochemical behaviour of the elements and, particularly for Al/Fe, reflect the environment in which the oxides have formed (see chap. 16). 

What are the most significant environmental pathways for exposure ... 

Congener patterns in humans may provide information on the nature or pathway of PBDE exposures (Hooper and McDonald 2000). Low- tetra deca congener ratios are suggestive of direct, recent, or occupational exposures to tire parent PBDE mixture, whereas higher ratios may indicate an environmental pathway where exposures result from PBDEs that have leached from the parent mixtures and have been degraded in the environment. 

This review focuses on the occurrence, sources, and environmental chemistry (physical-chemical properties, analysis, and environmental pathways) of PCNs and places observations from the Laurentian Great Lakes basin of North America in context with studies from other regions around the world. We summarize the significant body of research conducted since reviews published in the late 1990s [6,7,12] and finish by highlighting continuing areas of PCN occurrence, behavior, and effects which are in need of understand-... 

Biomonitoring data are more challenging to interpret than other exposure measures, such as personal air sampling or exposure diaries, in that they provide information on internal doses that are integrated across environmental pathways and routes of exposure and directly reflect the amount of chemicals that are absorbed into the blood and are distributed, stored, metabolized, and excreted. Therefore, not only must the complexities of the biologic system be considered, but also the properties of the chemicals or their metabolites. 

Fig. 7-2. Summary of environmental pathways by which terrestrial plants may become contaminated with radionuclides. In the case of an input from atmosphere, or as a result of the process of resuspension , any external radionuclide burden may be reduced by field loss mechanisms conversely, an initially external radionuclide deposit (Rat) may become internalised (i int) following foliar absorption and translocation. Radioactive contaminants of soils may be derived either from atmospheric inputs or from seepage in ground waters. Partitioning of radionuclides in soil—soil water systems controls their availability for root absorption, which normally occurs exclusively from the liquid phase. The chemical speciation of the nuclide in this phase, however, provides a further control on bioavailability which is highly radionuclide specific.

Herrera-Portugal C, Ochoa H, Franco-Sanchez G, Yanez L, Diaz-Barriga F (2005) Environmental pathways of exposure to DDT for children living in a malarious area of Chiapas, Mexico. Environ Res, 99(2) 158-163. 

As indicated in Figure 1, all environmental media where pollutants could lodge have been of interest, including air, surface water and sediment, soil, and groundwater. The environmental pathways of greatest concern obviously vary from site to site. Figure 2 summarizes the media of principal interest at nine "typical" sites selected from an EPA survey of 160 sites. 

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