Food-chain exposure pathway

Children can be exposed to biological as well as chemical contaminants through the food-chain. For example, approximately 1.5 billion episodes of diarrhoea occur globally each year, resulting in the deaths of three million children under five years of age (mainly in developing countries) (WHO, 1999). It is estimated that 70% of these annual cases of diarrhoea worldwide have been caused by biologically contaminated food (WHO, 1999). Foodbome parasitic diseases also present a major public health problem. For example, foodbome trematodes affect 40 million people, with more than 10% of the world s population at risk of infection (WHO, 1999). 

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Generally, the main pathways of exposure considered in tliis step are atmospheric surface and groundwater transport, ingestion of toxic materials that luu c passed tlu-ough the aquatic and tcncstrial food chain, and dermal absorption. Once an exposure assessment determines the quantity of a chemical with which human populations nniy come in contact, the information can be combined with toxicity data (from the hazard identification process) to estimate potential health risks." The primary purpose of an exposure assessment is to... 

Biotic Transport Biotic transport can be defined as the actions of plants and animals that result in the transport of a radioactive material or other substance from a waste site to locations where it can enter pathways that may result in exposure to humans. Small mammals are ubiquitous and inhabit areas containing radioactive contamination or radioactive waste sites. Mammals inhabiting these areas may become contaminated with americium by consuming contaminated soil or plants and disturb americium-contaminated soil through their burrowing and excavating activities. These animals may therefore affect the distribution of americium within the waste site or transport americium to previously uncontaminated areas. In addition, small mammals may be consumed by animals higher in the food chain such as hawks and coyotes, which would add to the dispersal of americium from disposal areas. However, results of... 

Although the sequestration by plants immobilizes As, it may also facilitate its entry into the food chain and provide an exposure pathway to animals. 

Results show that for Cd (i) birds of prey are always more sensitive that beasts of prey and (ii) bioaccumulation is lowest in the food chain Soil —> worm —> bird/mammal. The latter food chain to birds of prey is by far the most critical pathway for Cd exposure, leading to very low critical limits for soils (approximately 0.1 ppm,... 

Importantly, past and present human exposure to PCDD/PCDFs and PCBs results primarily from their transfer along the pathway atmospheric emissions air deposition -> terrestrial/aquatic food chains - human diet. Information from food surveys in industrialized countries indicates a daily intake of PCDD/PCDFs on the order of 50-200 pg I-TEQ/person per day for a 60 kg adult, or 1-3 pg I-TEQ/kg bw per day. If dioxin-like PCBs are also included, the daily total TEQ intake can be higher by a factor of 2-3. Recent studies from countries that started to implement measures to reduce dioxin emissions in the late 1980s clearly show decreasing PCDD/PCDF and PCB levels in food and, consequently, a lower dietary intake of these compounds by almost a factor of 2 within the past 7 years. 

Human Health At present, studies on the impact of POPs on human health are very limited in China. Most of the existing literature is focused on dietary studies, as the food chain is considered a major pathway for POPs to effect human health. Information on human health effects such as body burden and metabolism is insufficient and generally extrapolated from modeling data because few doctors have been involved in research on POPs exposures in China. Other exposures through respiration and skin as well as air and soil are seldom studied. 

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. 

Food Chain Bioaccumulation. The data available indicate that silver can bioconcentrate to a limited extent in algae, mussels, clams, and other aquatic organisms. However, many of the studies that were performed do not conform to the current state of the art in terms of sample size, duration, and analysis of contaminant levels in aquaria. Reliable data would be useful in determining the possibility of biomagnification and in defining pathways for general population exposure, as well as in estimating exposures from NPL site contamination. 

Food Chain Bioaccumulation. The existing information indicates that radium may be transferred through the food chain from lower trophic levels to humans. Additional monitoring studies in areas where radium occurs naturally at high concentrations in soil would be helpful to determine if this pathway is a significant route of exposure. The transfer of radium-228 from soils through the food chain has not been assessed. 

Ingestion of contaminants is the primary exposure pathway for drinking-water. Dermal absorption and inhalation of contaminants during bathing are other common pathways. When contaminated surface waters serve as recreational areas for children, accidental ingestion (water or sediment) and dermal contact become additional pathways for exposure. Finally, aquatic organisms can bioaccumulate contaminants in surface waters, which can lead to dietary exposure through the food-chain. 

PTMs-contaminated soils pose a human health risk on the basis of the potential of the contaminant to leave the soil and enter the human bloodstream. In order to assess human health risk, several pathways of transfer of metals from soil to humans have to be taken into account. The most important metal intake takes place via the food chain in which plants or meat of animal play a key role. The direct ingestion of soil can be a major route of exposure for humans to many low mobile soil contaminants, particularly for small children through putting hands into the mouth (Gupta et al., 1996). The contribution from the inhalation of particles smaller than 10 pm and from dermal contact with soil have little meaning compared with oral ingestion and are found to be less than 1% and 0.1% of the total intake, respectively (Paustenbach, 2000). 

The food chain has been shown to be the primary pathway of human exposure to PCDDs and PCDFs (Table 5).34 39 We will examine the accumulation of dioxin in those foods found in the average American diet fruits and vegetables, beef, milk and dairy products, and fish. 

For risk assessment purposes, an important objective in evaluating the environmental fate of PCDD/Fs is predicting the major pathways of human exposure. It is well established that the food chain, especially meat and dairy products, accounts for more than 90% of human exposure to PCDD/Fs and perhaps as much as 99% of human exposure to 2,3,7,8-TCDD.34 In industrialized countries, the average daily intake via food (the major route of exposure to dioxins and furans) ranges from 1.5 to 2.5 pg TEQ kg-1 body weight. 

The food chain is the primary pathway of human exposure to dioxin, with meat (38%) and dairy products (28%) dominating. Fish ingestion can be a significant contributor in countries with high fish consumption (26% of total intake in the Netherlands), but is not an important factor in the US. The exact contribution of fruits and vegetables is unclear, but vegetable oil does appear to play a role in human dioxin exposure. Inhalation and consumption of contaminated water and soil are not major sources of human exposure to TCDD. 

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 wide dispersal of the dioxin-like chemicals throughout the environment is primarily the result of atmospheric transport and deposition. Eventually the dioxin-Uke chemicals become adsorbed to dust particles and surfaces and are deposited in sediments. The two primary pathways for dioxin-like chemicals to enter the food chain are from the air-to-plant-to-animal and from water-and sediment-to-fish. A third route for dioxin-Uke chemicals to enter the food chain is through the accidental contamination incidents resulting from inappropriate handling and processing of feed and food substances. It has been estimated that more than 90% of human exposure to dioxin and dioxin-like chemicals is through the ingestion of contaminated food substances. ... 

Diet provides the major pathway for lead exposure, and amounts in bone are indicative of estimated lead exposure and metabolism. Amounts of whole body lead and feeding habits of roadside rodents were correlated body burdens were highest in insectivores such as shrews intermediate in herbivores, and lowest in granivores. Food chain biomagnification of lead, although uncommon in terrestrial communities, may be important for carnivorous marine mammals, such as the California sea lion accumulations were highest in hard tissues, such as bone and teeth, and lowest in soft tissues, such as fat and muscle. A similar pattern was observed in the harbor seal. 

Finally, man may also be indirectly exposed to PAH, the air being an agent of transfer to soil, water and plants from which different food chain contaminations are possible, including contaminations of meat, milk or egg. The same pathways must also be considered for the polluted waters and sediments. We must consider the global exposure to PAH from different types of exposure. 

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