Dynamic behaviour of polycyclic aromatic hydrocarbons in Brighton marina, UK

https://doi.org/10.1016/S0025-326X(03)00393-XGet rights and content

Abstract

The distribution of polycyclic aromatic hydrocarbons (PAHs) between various phases is fundamental in the control of their movement and impact in the marine environment. In this study samples of water and sediments were regularly collected from Brighton marina, UK, to quantify the intensity, spatial and temporal variations of PAH contamination. The results show clearly that PAH behaviour in marine systems is highly complex, and controlled by the interplay of PAH sources, compound physicochemical properties, water and sediment movement, and field conditions. Levels of total PAHs (16 compounds) in the dissolved phase were found to vary between <2 and 11,400 ng/l, with higher values observed in the winter months. Total PAH concentration in sediment samples varied between 24 and 4710 ng/g dry weight. PAHs in water were dominated by low molecular mass compounds (2-ring), while PAHs in sediments were mainly derived from 2–4 ring compounds. In addition, dissolved concentrations were increased during sediment dredging and after a period of severe rainfall. PAHs in Brighton marina are likely to be from both pyrolytic and petrogenic sources; as a result, field-derived distribution coefficients for individual PAHs between sediment and water tend to follow the equilibrium partition models, although slight exceedance is apparent. The extended partition model incorporating soot carbon has achieved limited success in better predicting PAH behaviour.

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic pollutants comprised of two or more fused benzene rings that have been found to be ubiquitous contaminants in the natural environment. They are an important class of marine contaminants since di- and tri-aromatic compounds have been shown to be narcotic to marine organisms such as the mussel, Mytilus edulis (Widdows et al., 1995), while many high molecular mass PAHs are known to be carcinogenic and mutagenic (Simpson et al., 1996). The PAH naphthalene and its methyl-substituted derivatives 1- and 2-methylnaphthalene have been described as some of the most acutely toxic and water soluble components of crude oils (Heitkamp and Cerniglia, 1987).

There are three well-defined sources of PAHs in the marine environment: combustion of fossil fuels (pyrolytic origin), slow maturation of organic matter (petrogenic origin) and degradation of biogenic precursors (diagenic origin) (Baumard et al., 1998). Upon entering the aquatic system PAHs distribute between different phases including truly dissolved, colloids, suspended particulate matter, surface sediments and biota (Readman et al., 1987; Zhou et al., 1998). The way in which PAHs are distributed between these different phases is controlled by their intrinsic physicochemical properties including solubility, vapour pressure and lipophilicity (Zhou et al., 1998). In addition, it has been observed that environmental behaviour and bioavailability of PAHs are source dependent. Gschwend and Hites (1981) suggested that oil-associated PAHs might be more available for microbial degradation than PAHs associated with combustion particles. Farrington et al. (1983) found that petroleum-derived PAHs were more available for uptake by mussels than pyrogenic PAHs.

The distribution of PAHs between various phases is frequently described with the use of the distribution coefficient (Kd):Kd=CsCaqwhere Cs is the PAH concentration in the solid phase, and Caq is the PAH concentration in the dissolved phase. Sediment organic matter and in particular organic carbon content have long been known to play an important role in the partition behaviour of PAHs since they can bind particularly strongly to these fractions (Karickhoff et al., 1979; Means et al., 1980). Hence the organic carbon normalised distribution coefficient, Koc, can be calculated:Koc=Kdfocwhere foc is the sediment fraction organic carbon. It is also possible to predict Koc from the octanol/water distribution coefficient (Kow), using linear free energy relationships (e.g. Means et al., 1980):logKoc=logKow−0.317

However, field results obtained tend to deviate from these relationships. Broman et al. (1991) found no correlation between particle associated PAHs and particulate organic carbon content and Zhou et al. (1999) found there was no linear relationship between Kd and foc as is predicted by Eq. (2) in a study of the PAHs in the Humber estuary, UK. It has been observed that values of Kd measured in situ can differ from those predicted by equilibrium partition models, Zhou et al. (1999) measured values between 1 and 3 orders of magnitude higher in the field than those predicted by laboratory partitioning experiments. Readman et al. (1987) also found PAH concentrations in sediments collected from the Tamar Estuary, UK, to be 2–5 orders of magnitude greater than those predicted. These results indicate enrichment of PAHs in sediments, which is widely attributed to the presence of soot particles in sediment that may occlude PAHs making them unavailable for partitioning.

Brighton marina is located on the southeast coast of England (Fig. 1). It is one of the largest marinas in the UK, berthing up to 1300 boats. Pontoons radiate from two floating jetties, there is a 24-h fuelling pontoon on the eastern side of the marina and a mean tide level of 3.5 m; the site is protected by two breakwaters. The marina is subject to potential PAH sources from both point and non-point sources, these may include both pyrolytic and petrogenic PAHs from activities of boats berthed in the marina, atmospheric deposition and run-off from the surrounding area. To our knowledge, no previous study has been performed on PAHs in Brighton marina; in addition, marina environments have not been widely studied due to their high spatial and temporal variability. This project therefore aims to fill such a gap in knowledge, by quantifying the intensity, temporal and spatial variations of PAH contamination in Brighton marina, assessing the effects of dredging and extreme weather (e.g. heavy rainfall) on PAHs levels, and determining the distribution of PAHs between sediment and water and its controlling factors.

Section snippets

Chemical standards

Two standard solutions from Supelco were used. The first was a deuterated internal standard (IS) mixture (EPA 525/525.1) containing acenaphthene-d10, phenanthrene-d10 and chrysene-d12, from which a stock solution containing 50 ng/μl each in hexane was prepared. Samples of both sediment and water were spiked with this IS mixture at concentrations of 100 ng/g and 80 ng/l, respectively in order to quantify compound losses through the extraction procedure. The second solution (TCL PAH mix)

PAH concentrations in water

Total PAH concentration (16 compounds) in water samples was found to vary between <2 ng/l (e.g. station 3 in November 1999 and January 2001) and 11,400 ng/l (station 15 in November 2000) (Table 1). It can be seen in Fig. 2 that total PAH concentrations in the dissolved phase were higher in the winter than in the summer months, especially between November 2000 and January 2001. The day before the samples were collected in November 2000 there were severe gales and heavy rain. It was observed at

Conclusions

This research shows the need to use a holistic approach to contaminant assessment in field situations. Moderate PAH contamination was observed in water and surface sediment from Brighton marina, UK. External factors can have a powerful influence on contaminant behaviour and even compounds bound to sediment and theoretically removed from the water column can become remobilised and reassert their influence on marine pollution. These factors make the modelling of PAH behaviour very difficult. PAH

Acknowledgements

The research was funded by a studentship from the Engineering and Physical Sciences Research Council in the UK (Award reference 99309975) and a Royal Society Research Grant (grant code RSRG/21162) to J.L. Zhou.

References (31)

Cited by (64)

  • State of the art and future challenges for polycyclic aromatic hydrocarbons is sediments: sources, fate, bioavailability and remediation techniques

    2019, Journal of Hazardous Materials
    Citation Excerpt :

    A list of the more relevant research articles and detected concentrations in sediments is given in Table 1. This coefficient is defined as the ratio of Kd and foc (sediment fraction organic carbon), and can be calculated from the octanol/water distribution coefficient (Kow), using linear free energy relationships [56,62]. Kow describes the distribution of an organic compound between the organic compound in the solid phase (Cs) and concentration in water (Cw).

  • The effects of dredging and environmental conditions on concentrations of polycyclic aromatic hydrocarbons in the water column

    2018, Marine Pollution Bulletin
    Citation Excerpt :

    Therefore, PAH diagnostic ratios, combined with forensic analysis, allow to apportion the sources of PAH contaminated sediment (MacAskill et al., 2016; Walker et al., 2017) and to have useful information about source control for remediation decision making and environmental protection (Walker et al., 2017). On the basis of physicochemical properties of PAHs, such as solubility, it is possible to find them in different forms in water (e.g. in the dissolved or colloidal phase) associated with suspended particulate matter in the surface sediments or in organisms (King et al., 2004). The PAH solubility in water is generally very low and tends to decrease with an increase in the number of the molecular rings (Nikolaou et al., 2009; Pane et al., 2005).

View all citing articles on Scopus
View full text