Organic xenobiotics Concentration

Studies on the bioaccumulation of xenobiotics should parallel the chemical qualification of the environmental compartment surrounding the organism. The concentration technique (natural and physicochemical) plays a crucial role. 

A comprehensive review about the effect of DOM on the bioavailabilty of organic xenobiotics is given by Haitzer et al. (1998). Most studies show that DOM concentration of up to 10 mg liter-1 decreases the bioavailability of organic chemicals. It is also obvious that the difference in the character of the DOM due to its origin is of vital importance on the results. 

Fig. 5. Relationship between rate of in vivo metabolism and tissue xenobiotic concentration for the pooled data of a variety of organic xenobiotic (excluding hydrocarbons and DDT) and crustacean species. Data are from Table 21. The equation of the log-log regression is given by log,o (rate of metabolism in pmol min g ) = -0.4571.014[log,o(tissue cone, in nmol g )] correlation coefficient = 0.974 (n = 24) 95% confidence limits for the regression line shown on the graph...

Consistent with the preceding comments on the metabolism of xenobiotics in the presence of additional carbon substrates, the result of deliberate addition of organic carbon may be quite complex and will not be addressed in detail. Two examples on rates of mineralization are given as illustration in which addition of glucose apparently elicited two different responses. It should, however, be emphasized that since the concentration of readily degradable substrates in natural aquatic systems will generally be extremely low, the environmental relevance of such observations will inevitably be restricted ... 

The formation of polar metabolites from nonpolar materials may actually facilitate monitoring programs—in many cases the polar chemicals are highly concentrated in certain body fluids such as bile and urine. On the other hand, materials such as certain cyclodienes and polychlorinated biphenyls, which are very lipid soluble and resistant to metabolism, may accumulate and these chemicals may persist in the environment and may be transferred via the food chain to man. There is also interest in these biotransformation processes in lower organisms since the simplicity of these systems may lead to a better understanding of the phylogenetic development of xenobiotic metabolism. 

Organ blood flow and organ concentration - organ blood flow is an important factor which determines the distribution of a xenobiotic once it has been absorbed. This flow is related to blood pressure and while mammalian pressures are around 100 mm Hg, fish species usually are about one-fifth or less of this value. 

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