CHAPTER ONE

1.0 INTRODUCTION 1.1 Background to the study

Since the middle of the 20th century there has been an increasing concern about the exposure ofhumans and wildlife to certain xenobiotic that were released into the environment due to diverse anthropogenic activities. One group of environmental toxicants that is of particular interest with regard to potential environmental health effects are polychlorinated aromatic compounds (PACs). These ubiquitous compounds are hydrophobic, lipophilic and resistant to biological and chemical degradation, properties that impart persistency and a propensity to bio-accumulate and biomagnify to concentrations that can cause harmful effects (Eichbaum et al., 2014; Giesy et al., 1994; Larsson et al., 2013; Poland et al., 1982; Song et al., 2006; Vries et al., 2006). Polychlorinated aromatic compounds are a group of compounds comprising polycyclic aromatic hydrocarbons with two or more aromatic rings and one or more chlorine atoms attached to the ring system. Polychlorinated aromatic compounds can be divided into two groups: chloro-substituted Polycyclic Aromatic Hydrocarbons(PAHs), which have one or more hydrogen atoms substituted by a chlorine atom, and chloro-addedChlorinated Polycyclic Aromatic Hydrocarbons(ClPAHs), which have two or more chlorine atoms added to the molecule(Nilssonetal., 1993).They are products of incomplete combustion of organic materials. They have many congeners, and the occurrences and toxicities of the congeners differ (Kitazawaet al., 2016). ClPAHs are hydrophobic compounds and their persistence within ecosystems is due to their low water solubility (Cernigliaetal., 1992). They are structurally 2 similar to other halogenated hydrocarbons such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). ClPAHs in the environment are strongly susceptible to the effects of gas/particle partitioning, seasonal sources, and climatic conditions (Ohuraet al., 2008). Polychlorinated aromatic compounds such as polychlorinated dibenzo–p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs), as well as other related halogenated aromatic compounds are trace amounts of undesired impurities (by products) in the manufacture of other chemicals such as chlorinated phenols and their derivatives, chlorinated biphenyl ethers, and polychlorinated biphenyls (PCBs), and combustion of chlorine containing materials under some conditions. These compounds are also referred to as unintentionally produced Persistent Organic Pollutants (UPOP) (WHO, 1988).

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