Quantification of Polycyclic Aromatic Hydrocarbons in Sediment Samples from the Trondheimsfjord by Accelerated Solvent Extraction and GC-MS

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are a group of hundreds of different chemical com- pounds that are formed mainly by incomplete combustion of organic matter. PAHs are also found as complex mixtures in fossil fuels and petroleum products. They are toxic, persistent and characterised as environmental pollutants. Several are also carcinogenic when metabolised. Benzo[a]pyrene is a well-known example of this. Many PAHs also bioaccumulate in mussels and invertebrates, while for other organisms, like fish, some are more easily excreted. Due to the physico-chemical properties of PAHs, they tend to accumulate in sediments where they are stabilised by the environmental conditions. Analyses of sediments are therefore important in mapping the amount of environmental pollutants that can give toxic effects in organisms. They can also be used to evaluate clean-up or other measures to prevent spreading. In this thesis, sediment samples from the Trondheimsfjord were collected from 11 different locations outside Trondheim in Norway. Each of the main samples were divided into three layers: an upper layer (0-2.5 cm), a middle layer below (about 2.5-5 cm depth into the sediment) and a bottom layer (below about 5 cm depth). The different samples were analysed for the presence of 16 PAHs. The samples were extracted using accelerated solvent extraction with acetone-dichloromethane (1:1, v/v) as the solvent. The samples were analysed by coupled gas chromatography-mass spectrometry. Validation of the method was done by comparing to a standard reference material with known concentrations of different PAHs. It was found that the method needs further optimisation to improve accuracy as the analyses show underestimation of all the PAHs. The recovery values were also low for a few internal standards. The status of the sediments were classified according to the classification system by the Norwegian Environment Agency. It was found that most of the sampling locations were mildly contaminated by PAHs as most samples were classified as Class II "Good" or Class III "Moderate". Three sampling locations were found to have very low concentrations of PAHs as almost all samples from those locations were classified into Class II "Good". Two samples showed PAH concentrations in Class V "Very Bad" and were the two most contaminated samples. The ratio between two specific PAHs was used to determine the origin of the pollution. It was found that the PAH contamination for all the samples came from combustion rather than oil spills or petroleum products.