23. Method development for the determination of polycyclic aromatic hydrocarbons (PAHs) in environmental matrices

Abstract

Abstract Polycyclic aromatic hydrocarbons (PAHs) and some of their derivatives represent a class of important environmental pollutants possessing a high mutagenic and carcinogenic potential as proven by in vitro experiments with various animal species using different modes of application and in vitro experiments using tissue homogenates, cells in culture and subcellular fractions as well [1,2]. PAHs are ubiquitous in the environment, although their concentrations vary within a wide range in the various matrices that are relevant to man. They originate mainly from two sources. First, they are formed as natural side products during the coalification of biomass to fossil fuels such as peat, lignite, crude oil and hard coal. During this process preformed structures are converted into polycyclic aromatic compounds by a series of condensation, water elimination and dehydrogenation reactions [aromatization process]. Prominent examples for this process are (a) the formation of perylene from fungal and insect pigments as an early occurring PAH in peat [3]; (b) the formation of retene (1-methyl-7-isopropylphenanthrene) from abietic acid in pine-tree resins as found in soils and in lignite [4,5]; and (c) the formation of chrysene and picene derivatives from plant triterpenes as found in sediments [6]. Apart from this, PAHs are continuously formed by incomplete combustion processes as anthropogenic products. Main sources of emission are domestic coal heating, coke production, open fires such as refuse burnings, forest fires and after-crop burning, but also vehicle exhaust and oil combustion. By these processes PAHs contaminate the environment e.g. air, water and soil from which they may enter vegetables and various other foodstuffs. Accordingly, PAHs are widely distributed throughout the environment. It has been demonstrated by balancing the biological effect that for various emissions which permanently pollute the environment (such as vehicle exhaust, hard coal combustion, used motor oil) PAHs are the main contributors to the carcinogenic potential of these matrices compared to other classes of compounds present [7–12]. More recent investigations have also presented data on the ecotoxicity of some PAHs [for a review see ref. 13]. Due to their wide environmental distribution and to their carcinogenic potential, PAH require continuous analytical monitoring. As a further consequence, in some countries national recommendations and regulations have set limits for the emission and exposure to benzo[a]pyrene as typical representative of PAHs. There are presently well-justified tendencies to include some individual PAHs for the assessment of the carcinogenic potential of matrices and products as is the practice for polychlorinated furans and dioxins already. More recently, the interest of environmental toxicologists has been focused on some classes of heterocyclic compounds and various PAH derivatives since potent carcinogens have been found among the thiaarenes (sulfur-containing polycyclic aromatic compounds) [14] and the azaarenes (nitrogen-containing polycyclic aromatic compounds) [15]. On the other hand, aromatic amines have been found to be potent bladder carcinogens and nitro-PAHs which occur in considerable concentrations in vehicle exhaust possess high mutagenic activities [16]. PAHs are not carcinogenic by themselves but require enzymatical activation to display biological [mutagenic and/or carcinogenic] effects. Cytochrom P450- dependent monooxygenases and hydrases are responsible for the activation converting PAHs into phenols (via epoxides) and trans-dihydrodiols. The latter ones are considered to function as proximate carcinogens which may be further activated to trans-dihydrodiol epoxides -the ultimate carcinogens of PAHs. The determination of these metabolites is of essential interest in biological monitoring e.g. for the risk assessment of people occupationally exposed to PAHs.