Living organisms bioaccumulate trace elements due to direct exposure to contaminated water, air, and soil or indirectly through contaminated food. The relative contribution of each of these sources to the total body burden of the organism varies depending upon the specific environmental conditions, the organism, and the interaction between them. It is possible that, in a particular environmental setting, direct exposure due to contaminated water, air, and soil individually or collectively may contribute more to the trace element burden of a living organism than exposure through food or vice versa. For example, the potential human health risk associated with inorganic arsenic exposure is predominantly due to intake of As-contaminated water; however, in the case of methyl mercury exposure, health risk is associated with the consumption of contaminated food like fish and shell fish [11,12].
Bioaccumulation of trace elements in receptor biota and humans through food is essentially related to trophic transfer of trace elements in terrestrial and aquatic ecosystems. Increasingly, sophisticated analytical methods such as stable isotope analysis are being used to resolve food chain structure and define trophic position of biota in the food web [13,14]. Trophic transfer of trace elements within the food web has been demonstrated by relating the metal levels in the dietary components with those assimilated by animals ; indices such as bioaccumulation, bioconcentration, and biomagnification factors have been routinely used to estimate trophic transfer in the food chains .
Exposure resulting from terrestrial and aquatic food chains to humans and biota must be analyzed separately due to the fundamental differences between them. The number of trophic levels in the terrestrial food chain is greatly reduced compared to the aquatic food chain. Moreover, the terrestrial herbivores demonstrate low efficiency of converting plant biomass into protein due to a large percentage of indigestible structural material containing high levels of cellulose and lignin in terrestrial plants. However, the low energy efficiency causes higher consumption rates of food stuffs in herbivores, which can effectively intensify metal uptake in food webs within contaminated areas .
This chapter focuses on trophic transfer of trace elements as an exposure pathway for biota and humans. Trophic transfer of trace elements chronically exposes humans to sublethal concentration of elements, which can build overtime to reach toxic levels. The most important trace elements in terms of their trophic transfer potential through the food chain are Cd, Hg, Pb, As, and Se . Trophic transfer of trace elements and their bioaccumulation in biota have associated ecological and human health effects.
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