ABSTRACT
Organic pollutants, as combustion, industrial, agricultural and other chemicals, are continually entering the aquatic and terrestrial environments.1,2 A proportion of this potentially toxic material is readily taken up into the tissues of resident organisms. Uptake can take place from sediments, soils and particulate material, the water column, atmosphere and food sources.3,4 Such organic pollutants comprise a diverse and ever increasing range of compounds including polynuclear aromatic hydrocarbons (PAHs) and nitroaromatics; polychlorobiphenyls (PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans; other organochlorines such as hexachlorohexanes, hexachlorobenzenes and chlorophenols; organophosphate and organochlorine pesticides; organotin antifouling agents; phthalate ester plasticizers; and alkylbenzene sulphonate detergents.3,5 The extent of bioaccumulation of pollutants by biota depends on many factors, but mainly the lipophilicity of the compound, its external bioavailable concentration, and the capacity of the organism to metabolise and eliminate it.3 Thus, uptake increases with increasing lipophilicity and environmental concentration of the pollutant, and decreases with biotransformation and elimination. Poorly metabolised pollutants, such as many PCB congeners, accumulate to highest tissue concentrations in vertebrates at the top of food chains, whereas readily metabolised compounds, such as PAHs, reach highest tissue concentrations at the bottom of food chains in invertebrates where rates of biotransformation are low.3 Movement of organisms and movement of pollutants along food chains can result in the dispersal of chemicals far from their point of origin and from areas of significant human activity, eg PCBs in whales and seals in oceanic waters, deep-sea fish and arctic polar bears and birds.3,6
The need to detect and assess the impact of pollution, particularly low concentrations of increasingly complex mixtures of chemicals, on environmental quality has lead to the development of molecular markers of biological effect of pollutants on organisms-most recently called biomarkers.7,9 Such diagnostic and prognostic early-warning tests offer the potential of specificity, sensitivity and application to a wide range of organisms. Thus, induction (increased synthesis) of the biotransformation enzyme cytochrome P-450 1A1 (CYP1A1) is used as biomarker of exposure to organic pollution (NB the nomenclature of CYP1A1 is based on knowledge of its gene sequence (see section 8.3.1) but unless this is known, it has been recommended that the more general term of CYP1A be used, eg for fish10).
