Thesis Abstract

Abstract
Polycyclic aromatic hydrocarbons (PAHs) are widely distributed environmental contaminants that can accumulate in aquatic organisms such as fish. This study aimed to investigate the levels of PAHs in fresh water fish dried under different drying regimes. The fish samples were subjected to three drying methods sun drying, oven drying, and freeze-drying. Gas chromatography-mass spectrometry (GC-MS) was used to analyze the PAH levels in the dried fish samples. The results showed that the levels of PAHs varied among the different drying methods. The highest levels of PAHs were found in fish samples dried using the sun drying method, followed by oven drying and freeze-drying. This suggests that the drying method can significantly influence the PAH levels in dried fish. The differences in PAH levels could be attributed to factors such as temperature, duration of drying, and exposure to contaminants during the drying process. Furthermore, the study found that certain PAH compounds, such as benzo(a)pyrene, were present in higher concentrations compared to other PAHs in the dried fish samples. Benzo(a)pyrene is a known carcinogen and its presence in dried fish raises concerns about the potential health risks associated with consuming contaminated fish products. The levels of PAHs detected in the dried fish samples were within the limits set by regulatory authorities, but continued monitoring and control measures are necessary to ensure food safety. Overall, this study highlights the importance of considering the drying method in controlling PAH levels in dried fish products. Proper drying techniques and monitoring of PAH levels are essential to minimize health risks associated with PAH exposure through fish consumption. Future research could focus on optimizing drying processes to reduce PAH contamination in dried fish and exploring potential mitigation strategies to ensure the safety of fish products for consumers.

Thesis Overview

1.1 INTRODUCTION

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic compounds consisting of two or more fused benzene rings (linear, cluster or angular arrangement), or compounds made up of carbon and hydrogen atoms grouped into rings containing five or six carbon atoms. They are called ?PAH derivatives? when an alkyl or other radical is introduced to the ring, and heterocyclic aromatic compounds (HACs) when one carbon atom in a ring is replaced by a nitrogen, oxygen or sulphur atoms. PAHs originate mainly from anthropogenic processes particularly from incomplete combustion of organic fuels. PAHs are distributed widely in the atmosphere. Natural processes, such as volcanic eruptions and forest fires, also contribute to an ambient existence of PAHs (Suchanova et al., 2008). PAHs can be present in both particulate and gaseous phases, depending on their volatility. Low molecular weight PAHs (LMW PAHs) that have two or three aromatic rings (molecular weight from 152 to 178g/mol) are emitted in the gaseous phase, while high molecular weight PAHs (HMW PAHs), molecular weight ranging from 228 to 278g/mol, with five or more rings, are emitted in the particulate phase, (ATSDR, 1995) . In the atmosphere, PAHs can undergo photo-degradation and react with other pollutants, such as sulfur dioxide, nitrogen oxides, and ozone. Due to widespread sources and persistent characteristics, PAHs disperse through atmospheric transport and exist almost everywhere. There are hundreds of PAH compounds in the environment but in practice PAH analysis is restricted to the determination of six (6) to sixteen (16) compounds. Human beings are exposed to PAH mixtures in gaseous or particulate phases in ambient air. Long term exposure to high concentration of PAHs is associated with adverse health problems. Since some PAHs are

16

considered carcinogens, inhalation of PAHs in particulates is a potentially serious health risk linked to lung cancer (Philips, 1999).

1.2. Physical and Chemical Characteristics of PAHs.

PAHs are a group of several hundred individual organic compounds which contain two or more aromatic rings and generally occur as complex mixtures rather than single compounds. PAHs are classified by their melting and boiling points, vapour pressure, and water solubility, depending on their structure. Pure PAHs are usually coloured, crystalline solids at ambient temperature. The physical properties of PAHs vary with their molecular weight and structure (Table1). Except for naphthalene, they have very low to low water solubilities, and low to moderately high vapour pressures. Their octanol-water partition coefficients (Kow) are relatively high, indicating a relatively high potential for adsorption to suspended particles in the air and in water, and for bioconcentration in organisms (Sloof et al., 1989). Table 1 shows physical and chemical characteristics of few selected PAHs from the sixteen (16) priority PAHs, listed by the US EPA. (see appendix). Most PAHs, especially as molecular weight increases, are soluble in non-polar organic solvents and are barely soluble in water (ATSDR, 1995).

Most PAHs are persistent organic pollutants (POPs) in the environment. Many of them are chemically inert. However, PAHs can be photochemically decomposed under strong ultraviolet light or sunlight, and thus some PAHs can be lost during atmospheric sampling. Also, PAHs can react with ozone, hydroxyl radicals, nitrogen and sulfur oxides, and nitric and sulfuric acids which affect the environmental fate or conditions of PAHs (Dennis et al., 1984; Simko, 1991).

PAHs possess very characteristic UV absorbance spectra. Each ring structure has a unique UV spectrum, thus each isomer has a different UV absorbance spectrum. This is especially useful in

17

the identification of PAHs. Most PAHs are also fluorescent, emitting characteristic wavelengths of light when they are excited (when the molecules absorb light). Generally, PAHs only weakly absorb light of infrared wavelengths between 7 and 14‘m, the wavelength usually absorbed by chemical involved in global warning (Ramanathan, 1985).

Polycyclic aromatic hydrocarbons are present in the environment as complex mixtures that are difficult to characterize and measure. They are generally analyzed using gas chromatography coupled with mass spectrometry (GC-MS) or by using high pressure liquid chromatography (HPLC) with ultraviolet (UV) and fluorescence dectetors (Slooff et al., 1989)