Conjugation of organic pollutants in aquatic species

Aquatic organisms can take up organic pollutants from their environment and subsequently excrete the pollutant or its biotransformation products (metabolites). Phase II (conjugation) biotransformation products are almost always less toxic than the unmetabolized organic pollutant. For many organic pollutants, the extent to which conjugates are formed is extremely important in determining the rate of excretion of the pollutant. This is because most conjugates (glycosides, sulfates, amino acid conjugates, mercapturic acids) are organic anions which are readily water-soluble and are rapidly excreted by fish (and probably higher invertebrates) by a combination of glomerular filtration and tubular transport. In this paper, each major conjugation pathway is discussed with respect to what is known about its occurrence in fish and aquatic invertebrates, both from in vivo and in vitro data. Although limited data are available, this paper also considers what is known about how each conjugation reaction affects the toxicity and potential for renal and biliary excretion of organic xenobiotic substrates.