Hydrophobic organic contaminants, uptake

Skoglund RS, Swackhamer DL (1994) Environmental chemistry of lakes and reservoirs. In Baker LA (Ed) Processes affecting the uptake and fate of hydrophobic organic contaminants by phytoplankton. American Chemical Society, Washington, DC, p 559... 

Black, M.C. and J.F. McCarthy. 1988. Dissolved organic macromolecules reduce the uptake of hydrophobic organic contaminants by the gills of rainbow trout (Salmo gairdneri). Environ. Toxicol. Chem. 7 593-600. 

The ability of humic substances to bind hydrophobic organics can affect not only their mobility, by decreasing the sorption to sediments, but also the rate of chemical degradation, photolysis, volatilization, and biological uptake of these organics. This interaction can serve to lengthen the lifetimes and transport distances of these contaminants in the environment. 

This review provides insight on several important processes that control bioaccumulation of PAHs in marine organisms. Some of the more important points covered concern the role of organic carbon and lipid in the control of PAH partitioning, the observed anomalous sediment-water partitioning behavior, the routes by which PAHs are taken up, the rates of uptake and elimination, the role of biotransformation in bioaccumulation, the variation of bioaccumulation over a range of hydrophobic PAHs, the temporal nature of exposure and its impact on persistence, the time to reach steady-state tissue burdens, the efficiency of uptake, and the relationships between environmental concentrations and tissue accumulations. An examination of the literature related to these points will help explain the complexities and subtleties of bioaccumulation of PAHs and other organic contaminants. The abbreviations and formulas that are used here are defined in the Appendix. 

Unlike organic contaminants, nutrient and metal ions are generally actively transported into roots since the rate of passive transport of charged compounds across hydrophobic root membranes is limited. Plants take up most nonnutrient metals incidentally while acquiring nutrients for growth (Pulford and Watson, 2003 Saison et al., 2004). We do not address uptake of metals and nutrients in this chapter. The reader is referred to the above references and to phytoremediation reviews by Salt et al. (1995), Raskin and Ensley (2000), and Weis and Weis (2004). 

Although the simple bioconcentration model assumes relatively unhindered movement of a contaminant across the barriers between water and lipid tissue, such is often not the case. The uptake of an organic species can be a relatively complex process in which the chemical must traverse membranes in the gills and skin to reach a final lipid sink. A physiological component of the process by which a chemical species moves across membranes tends to cause bioconcentration to deviate from predictions based on hydrophobicity alone. 

Physiologically based toxicokinetic (PB-TK) models are used to describe the kinetics of uptake and depuration of hydrophobic contaminants by an organism. The great promise of PB-TK models lies in their potential to link contaminant concentrations in specific tissues with toxic effects in those tissues. We will discuss these models only in relation to the premise that lipid class significantly affects the kinetics of lipophilic chemical uptake and release. For in-depth descriptions of PB-TK models in fish, several excellent reviews and recent articles are available36,75,84,85. 

The studies which have focussed on the uptake and bioaccumulation from food, sediment or soil show that many factors significantly influence bioaccumulation, such as food composition, feeding rate, developmental stage or age, the hydrophobicity of the contaminant, the contact time between contaminant and soil/sediment, the nature and amount of organic carbon and other soil/se-diment characteristics, the behavior of soil/sediment organisms, etc. 

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