Human exposure pathways

One important purpose of monitoring is to provide data that permit the analysis and evaluation of human radiation exposure. For this purpose, programmes for monitoring radionuclides in the environment should focus on pathways of human exposure. An exposure pathway defines routes from a source of radionuclides and/or radiation to a target individual or a population through media in the environment. There are two main categories of exposure pathway external exposure pathways (the source of exposure remains outside the body) and internal exposure pathways (the source of exposure is incorporated into the body). 

The main external exposure pathways considered in this Safety Guide 

At different stages of an accident the exposure pathways may change and different monitoring data may be necessary to support decision making on protective actions. Thus, at an early stage of an accidental atmospheric release. 

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Davies K. 1990. Human exposure pathways to selected organochlorines and PCB s in Toronto and Southern Ontario. Advances in Environmental Science and Technology 23(Food Contam Environ Sources) 525- 540. 

Food Chain Bioaccumulation. Bioconcentration factors have been determined for algae, shellfish, and fish and exhibit a wide range (29-17,000) (ERA 1976 Oliver and Niimi 1983 Pearson and McConnell 1975). This wide range may be explained in part by species differences in metabolism or differences in concentrations tested. Studies also indicate that hexachlorobutadiene preferentially accumulates in the livers of fish. Further studies which might explain the wide range of BCF values would be helpful. No information was located regarding the bioaccumulation of hexachlorobutadiene in plants or aquatic organisms. More information is needed to determine the importance of terrestrial/aquatic food chain bioaccumulation as a potential human exposure pathway. 

Food Chain Bioaccumulation. Limited data indicate that carbon tetrachloride has a low tendency to bioconcentrate in the food chain, even though it is a lipophilic compound (Neeley et al. 1974 Pearson and McConnell 1975). The lack of bioconcentration is mainly due to the volatility of carbon tetrachloride, which facilities clearance from exposed organisms. Nevertheless, carbon tetrachloride does tend to become concentrated in fatty tissues, and further studies on the levels of carbon tetrachloride in the fat of fish would help evaluate the risk of carbon tetrachloride exposure by this pathway. No data are available on the bioconcentration in plants. Additional studies would be useful in assessing potential for human exposure from ingestion of plant foodstuff. Data are also needed on the biomagnification of the compound in the aquatic and terrestrial food chain. These data would be useful in assessing food chain bioaccumulation as a potential human exposure pathway. 

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. 

Currado, G. M., Harrad, S. (1998) A comparison of polychlorinated biphenyl concentrations in indoor and outdoor air and the potential significance of inhalation as a human exposure pathway. Environ. Sci. TechnoL, 32 3043-3047. 

Identifying and evaluating exposure pathways (environmental transport mechanisms and human exposure pathways). In this step, the health assessor evaluates exposure pathways at the site. There are five elements in an exposure pathway (1) source of contamination (source of contaminant release into the environment), (2) environmental media (this includes groundwater, surface water, air, surface soil, subsurface soil, sediment, and... 

Because the major human exposure pathway is food, human exposures to SCCPs as indirect exposures via food are evaluated. The risk of SCCPs to human health is estimated as MOE and MOE is compared with uncertainty factors. The MOE is defined by the following equation ... 

In Fig. 1, we present a diagram of om understanding of the human exposure pathways and potential factors that affect human asthma susceptibility between mban and rmal areas. In this model, different environmental mban-based exposures (e.g., particulate or gaseous air pollutants from vehicular traffic, and indusfiy), and similar ones in rmal areas (e.g., indoor pollution from biomass fuel combustion, and keeping or herding animals) are known to potentially affect susceptible adult hosts. Such exposmes may produce airway inflammation and obstruction. However, there... 

Fig. 1 A diagram of human exposure pathways and potential factors that aifect adult asthma susceptibility between urban and rural areas (PM j particulate matter less than 10 microm in diameter NO nitrogen dioxide ETS environmental tobacco smoke HDM house dust mite temp temperature)...

Haug LS, Huber S, Becher G et al (2011) Characterisation of human exposure pathways to perlluorinated compounds—Comparing exposure estimates with biomarkers of exposure. Environ Int 37(4) 687-693... 

Bismuth has similar human exposure pathways as lead. Its overall exposure opportunity to the human population is much less than lead since bismuth has seen many fewer uses in industry. The opportunity for exposure from ingestion is low, except in its use in medicines. The general population is not subject to bismuth exposure by direct contact. Bismuth is a byproduct of lead smelting and thus there is human exposure from airborne lead smelting emissions. 

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