Lipid Content of the Organisms

The bio concentration of chemicals is generally considered to be a partitioning process of the chemicals between the lipids of aquatic organisms, such as fish, mussels, oysters etc., and the water. This process is controlled by the relative solubilities or activities of the chemical in the lipids of the aquatic organisms and 

In an international ring test with lindane it was found that the relative standard deviation (S.D.) of the bioconcentration factor on a wet weight basis (BCFw) was 38%, whereas the S.D. was 23% if the BCF was related to the lipid 

Source Taken with permission from Geyer et al. [38], BCFw Bioconcentration factor on a wet weight basis. 

BCFl Bioconcentration factor on a lipid weight basis  

Outlier (R-Test by Nahmov) not included in statistical analysis. SD X 100, ,  

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Often we are interested in apolar or weakly monopolar pollutants (PCBs, chlorinated solvents, PAHs) and in organisms/tissues that contain significant lipid content (>5% on a dry weight basis). Also, investigators sometimes specially sample the fatty tissues (e.g., in some animals or humans). In such cases, the terms/iipC p or f ipKnipmei dominate in Eqs. 10-3 and 10-4 (see Illustrative Examples 10.1 to 10.3). Consequently it is reasonable to assume that the measured concentrations chiefly reflect the compounds present in the lipid phase and the concentrations can be normalized to the lipid content of the organism. Thus, the lipid normalized, K, bl0 hp, is simply given by ... 

It was shown by Geyer et al. [17] and others [18] that the BCF value oflipo-philic organic chemicals is dependent on the lipid content of the organism (see Sect. 5.5). Therefore, for the sake of comparison, the most important BCF value of a lipophilic chemical in an organism is that on the lipid basis (BCFg). The BCFl values can easily be calculated from BCF values, if the lipid content (L in % on a wet weight basis (%)) of the organism is known ... 

Sometimes the lipid content of the organisms is given on a dry weight basis (Ld in %). In this case the water content (%) of the organisms must also be measured. But more important is the lipid content on a wet weight basis (Lw in %) of the organisms. 

In case that the kg is not known, this adjustment can be eliminated by multiplying the chemical concentration by the total weight of the organism. Estimation of ty2 based on body burden provides a better basis for comparisons of ti/2 of a chemical among studies with the same organism [25 a] (see also Sect. 8.2.3). However, recently it was shown that the half-Ufe of a chemical in different aquatic organisms is dependent on its lipid content [29 a, b, 40]. For persistent lipophilic chemicals ty2 increases with the lipid content of the organism (Fig. 1). 

It was also found that the bio concentration potential is dependent on the age, sex, and species of the aquatic organisms. Many of these factors can be eliminated if the test is performed under identical conditions with the organisms of the same species, strain, sex, age, etc. or if the bio concentration factor is related to the lipid content of the organism (see Sect. 5.4). Some other important factors which may affect the bio concentration potential of chemicals in fish and other aquatic organisms are the toxic effects, bio availability, concentration of the chemicals in water, pH of the water, and especially the lipid content of the organisms. These factors will be discussed in more detail in the following sections. 

Biotic factors which can influence the lipid content of the organisms are numbers A. (1) to... 

The lipid content of the organism is a critical controlling factor of body residues of organic chemicals. Bio concentration studies often provide lipid-corrected results to compensate for this. Therefore, the lipid content of organisms used in bioassays should be reported routinely in all aquatic bioassays, such as bio concentration, bio accumulation, biomagnification, and toxicity studies with organic chemicals. 

With regard to altering the plasma cholesterol level, 3 main points of attack may be considered decrease of intestinal absorption of cholesterol, inhibition of synthesis and acceleration of catabolism and excretion. When changes in the plasma levels of cholesterol and other lipids are produced under the influence of different agents, it is also important to consider the total cholesterol and lipid content of the organism, and the possibility of shifts from plasma into tissues. 

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