Food chains environmental fate

It is also important to develop an understanding of the movement of chemicals through the environment by investigating their fate and behaviour. Based on a chemical s inherent physicochemical properties, it is possible to predict with some degree of certainty which environmental compartment it is likely to reside in and to what extent it is likely to be bioavailable and accumulate through the food chain. 

In Chapter 3, the distribution of enviromnental chemicals through compartments of the gross environment was related to the chemical factors and processes involved, and models for describing or predicting environmental fate were considered. In the early sections of the present chapter, the discnssion moves on to the more complex question of movement and distribntion in the living environment— within individuals, communities, and ecosystems—where biological as well as physical and chemical factors come into play. The movement of chemicals along food chains and the fate of chemicals in the complex communities of sediments and soils are basic issues here. 

Dispersion modelling of the emissions concerns how air pollutants disperse in the ambient atmosphere. This step is also called environmental fate analysis, especially when it involves more complex pathways that pass through the food chain. The pollutants dispersed to the atmosphere are in general modelled using dispersion models. 

The US EPA characterizes As, Be, Sb, Cd, Cr, Cu, Pb, Hg, Ni, Se, Ag, Tl, and Zn as priority metals because of their potential hazardousness to human health. However, the environmental fate and effect of only a few metals (As, B, Cd, Cr, Cu, Mo, Ni, Pb, and Zn) have been studied extensively (Rechcigl 1995). For a given metal the potential to cause harm depends on the identifiable risk pathway, which is different for different metals. One pathway usually provides the highest probability of adverse affects to some receptor and is, therefore, the limiting pathway (Ryan Bryndzia 1997). The most toxic elements to humans are Hg, Pb, Cd, Ni, and Co. Some of the principal limiting pathways for various metals are the direct ingestion of Pb-contaminated soil by children plant phytotoxicity from Cu, Zn, Ni food-chain concentration and transfer of Cd and Hg to humans and food-chain transfer of Se and Mo to livestock (Ryan Bryndzia 1997). 

An understanding of the environmental fate of these elements is necessary in the total assessment of associated health risks. Mercury is known to cycle between the geosphere and biosphere (35). Once in the hydrosphere, it can be converted by sediment flora into highly toxic methylmercury whereupon it is incorporated into aquatic life and ultimately accumulates in human food chains (31). Limited bacterial conversion of inorganic to organic mercury has been shown to occur in soil humus (36) and in animal tissue as well (37). There is no evidence that alkylated mercury is generated from coal combustion directly if it did it would probably be dissociated to the elemental form (14). 

Vegetation plays an important role in the fate of many chemicals. Plants are the first link in terrestrial food chains, and hence the accumulation of chemicals in plants is a crucial step determining exposure of higher terrestrial organisms, including humans, to environmental chemicals. Plants affect the atmospheric transport of chemicals by scavenging them from the air, and they also serve as a medium for transfering chemicals between the soil and the... 

The Division of Chemistry and the Environment of the International Union of Pure and Applied Chemistry (IUPAC) has recently approved the creation of an IUPAC-sponsored book series entitled Biophysico-Chemical Processes in Environmental Systems to be published by John Wiley Sons, Hoboken, NJ. This series addresses the fundamentals of physical-chemical-biological interfacial interactions in the environment and the impacts on (1) the transformation, transport and fate of nutrients and pollutants, (2) food chain contamination and food quality and safety, and (3) ecosystem health, including human health. In contrast to classical books that focus largely on separate physical, chemical, and biological processes, this book series is unique in integrating the frontiers of knowledge on both fundamentals and impacts on interfacial interactions of these processes in the global environment. 

Food Chain Bioaccumulation. There is information that barium bioconcentrates in certain plants and aquatic organisms (Bowen 1966 Schroeder 1970). However, the extent to which plants bioconcentrate barium from soil or to which uptake occurs in terrestrial animals is not well characterized. Further studies on the bioconcentration of barium by plants and terrestrial animals and on the biomagnification of barium in terrestrial and aquatic food chains would be useful to better characterize the environmental fate of barium and define the importance of food chain accumulation as a source of human exposure. 

No on-going studies regarding the environmental fate, environmental levels, food chain bioaccumulation, or exposure levels in humans for either 2-nitrophenol or 4-nitrophenol were found in the literature. 

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 evaluation of the results from the environmental fate leads to a predicted environmental concentration (PEC) of the pesticide representing the exposure level. The accumulation in the food chain of fish is expressed as BAF ( bioaccumulation factor in aquatic environment), that of mammals and birds as BCF (bioconcentration factor in terrestrial environment). Accumulation increases the exposure. The NOAEL (no observed adverse effect level) represents the hazard level. It is the result... 

Again, it is important to emphasise that the environmental fate of a chemical substance is a choice variable for the chemical producer. All chemical substances couldbe made to decay instantaneously, andthusnot accumulate, but this would imply zero effectiveness. The problem is that the cost of in-built persistence is implied accumulation. The studies on affinity indicate the route of accumulation that such persistence will take. The organochlorines (such as D D T) are fat soluble and hence accumulated within the food chain. Substances such as atrazine are more water soluble and hence are more problematic with respect to groundwater. 

Exposure to amines and related compounds has large impact on human health workers exposed to benzidine and naphthylaanine have developed cancer of the bladder [12,13] the Food and Drug Administration (F.O.A.) has found that aromatic amines [14] and nitroaromatics [15] can enter the food chain. In addition, many degradation products from nitroaromatics are easily polymerized, in presence of oxygen, to persistent macromolecules [16]. The wide distribution of these compounds in the environment, coupled with their toxicity, has given rise to concern about their environmental fate. 

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