Critical body residue to fish of organic pollutants

Abstract

The internal concentration represented by critical body residue(CBR) is an ideal indicator of the intrinsic toxicity of a chemical that can be used to assess toxicity to aquatic organisms. In this study, we systematically summarized the method for calculation of CBR in fish, CBR values with different modes of toxic action, the relationship between CBR and BCF, and the factors influencing the CBR based on the progress in this field as a result of studies conducted worldwide and our own investigations. The CBRs could be calculated by the LC50 and BCF based on the toxicokinetic model. The modes of toxic action of fish are usually recognized based on classification of organic compounds as acting by non-polar narcosis(baseline compounds), polar narcosis(less inert compounds), or reactive and specific acting mechanisms. Baseline toxicity is associated with chemicals acting narcosis mechanism, which is the reversible suppression of physiological function brought about by hydrophobic binding of chemicals to cell membranes and proteins. The CBRs to fish for narcotic chemicals vary in a narrow range and are close to constant. The CBRs for non-polar narcotic chemicals are higher than those for polar narcotic chemicals. Moreover, non-polar and polar narcotic compounds have different underlying mechanisms. Polar compounds intercalate less deeply into membranes, leading to lower CBR values than non-polar narcotic compounds. Reactive compounds interact and/or react with biological molecules, leading to enhanced toxicity relative to that associated with narcosis, and their CBRs are lower than those of narcotic compounds. Because the CBRs of narcotic compounds are close to constant, their toxicities are mainly affected by bioconcentration and linearly related to hydrophobicity. Conversely, the CBRs of reactive compounds are closely related to the reactivity of chemicals with biomolecules at the target site, with different values being observed for different reactive compounds. Their toxicities are not only related to the bioconcentration factor, but also to the descriptors used to describe the reactivity of chemicals with biomolecules(CBRs). Many factors can affect the CBRs of chemicals. For example, linear models of the relationship between log BCF and log Kow can underestimate the log BCF for compounds with log Kow 0.5 and overestimate the log BCF for compounds with log Kow 7, resulting in larger errors for CBRs calculated from the BCF and LC50 of highly hydrophilic and hydrophobic compounds. Organism size, lipid content, exposure time, metabolism and transformation, and uncertainty of toxic data can also affect the calculation or determination of CBRs.