A Comparison of Polycyclic Aromatic Hydrocarbon Mobilization from Environmental Matrices

Lorenzi, Damien (2011) A Comparison of Polycyclic Aromatic Hydrocarbon Mobilization from Environmental Matrices. Doctoral thesis, Northumbria University.

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Abstract

A method has been developed to analyse PAHs in solid environmental matrices using an in-situ PFE-GC-MS method. The method involves the use of 2 g of alumina as the in-situ clean-up sorbent, in order to remove interferences and impurities in the soils that could contaminate the instrument. By using this method, samples from two sites have been analysed for PAHs content, specifically (i) soils from a contaminated former Tar Works site, and (ii) urban road dust from Newcastle upon Tyne, UK. It was found that particle size was a significant parameter in both cases, showing a higher concentration (from 9 to 1404 mg/kg in the Tar Works, and 0.5 to 95 mg/kg in the road dust site) in the smaller grain size (< 250 μm); this is important when considering the ingestion exposure pathway as smaller particles are more likely to be ingested by children via hand-to-mouth behaviour. In addition, the source of the PAHs was investigated in the anthropogenically contaminated areas; it was found that pyrogenic sources (higher molecular weight PAHs, 4-5-6 rings) of PAHs were significantly more abundant compared to petrogenic sources (lower molecular weight PAHs: 2-3 rings). Generally the lower molecular weight such as naphthalene, acenaphthene, acenaphthylene and fluorene were found in lower concentration than fluoranthene, pyrene and other higher molecular weight PAH. In the case of the Tar Works lower molecular weights PAH were showing individual PAH concentration below 50 mg/kg whereas higher molecular weights were showing individual concentrations up to 270 mg/kg. The same trend was observed in the road dust samples, and was clearly identified by using ratios of PAH concentration to demonstrate dominance of pyrogenic sources. In this latter case, the pyrogenic sources were clearly identified as vehicle exhaust. However, other sources were identified such as the road pavement and the tire debris as potential sources of PAHs in urban areas. In the former case the PAH distribution was attributed to the locations of the chemicals productions areas in the former industrial site. The mean daily oral intake was used as an estimate of the environmental health risk from the sites; values of PAH intake were determined based on the PAH individual concentration and compared against known values. Risk was often present for pyrogenic PAHs in road dust and soil samples. Further investigation of the environmental health risk was realized using a physiologically-based extraction test on soil samples from the former Tar works; the results, using a fed-version of the test, showed elevated bioaccessibilities of PAHs, mainly due to the presence of food and the lipophilicity of PAHs, however other PAH properties could influence their individual mobilizations such as the molecular weight, the ring number and the liquid-to-soil ratio.

It was noticed that the risk can be evaluated differently and can show different conclusions depending on the risk assessment chosen. Overall, the determination of PAHs in environmental soil and urban dust samples has highlighted the necessity to assess the potential impact on human health of their presence. The use of the fed-version of the physiologically-based extraction test is one tool that could be used to assess the environmental health risk to humans. This tool was shown to be robust using an inter-laboratory study, as values for total PAH content and bioaccessible fractions were within the same acceptable range.

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