Elsevier

Environmental Pollution

Volume 189, June 2014, Pages 152-160
Environmental Pollution

Combining measurements and modelling to quantify the contribution of atmospheric fallout, local industry and road traffic to PAH stocks in contrasting catchments

https://doi.org/10.1016/j.envpol.2014.02.029Get rights and content

Highlights

  • Contributions of several sources to PAH stocks in soils were investigated.

  • PAH stocks in soils varied between 13 and 735 mg m−2 depending on source vicinity.

  • Roadside areas concentrated 20% of the catchment contamination.

  • Local industry was found to be responsible for 30% of the stocks.

Abstract

Various sources supply PAHs that accumulate in soils. The methodology we developed provided an evaluation of the contribution of local sources (road traffic, local industries) versus remote sources (long range atmospheric transport, fallout and gaseous exchanges) to PAH stocks in two contrasting subcatchments (46–614 km²) of the Seine River basin (France). Soil samples (n = 336) were analysed to investigate the spatial pattern of soil contamination across the catchments and an original combination with radionuclide measurements provided new insights into the evolution of the contamination with depth. Relationships between PAH concentrations and the distance to the potential sources were modelled. Despite both subcatchments are mainly rural, roadside areas appeared to concentrate 20% of the contamination inside the catchment while a local industry was found to be responsible for up to 30% of the stocks. Those results have important implications for understanding and controlling PAH contamination in rural areas of early-industrialized regions.

Introduction

Polycyclic Aromatic Hydrocarbons (PAHs) are widespread organic contaminants that are well known for their mutagenic or carcinogenic properties, and therefore represent a risk to the ecosystems and the human health (Grimmer et al., 1991, Nielsen et al., 1996, Tsai et al., 1995). They are mainly emitted during the incomplete combustion of fossil fuels or biomass (Wild and Jones, 1995) and they can be disseminated across large regions from their initial source through long-range atmospheric transport (LRT) (Sehili and Lammel, 2007). They are ubiquitous in the environment, but their concentrations were reported to be much higher in soils located in the vicinity of urban or industrialized areas as well as in atmospheric fallout collected in those areas (Wilcke, 2000). As in most early industrialized countries, the PAH issue is particularly problematic in the Seine River basin, in France, where excessive concentrations in Polycyclic Aromatic Hydrocarbons (PAHs) are reported in rivers (AESN, 2010), thereby compromising the achievement of the good chemical status required by the European Union (Water Framework Directive 2000/60/EC). In their study modelling PAH long-range transportation at the worldwide scale, Sehili and Lammel (2007) concluded that 64–97% of some PAHs remained stored in the soils. Similarly, Wild and Jones (1995) estimated that in UK more than 90% of PAHs accumulated in soils. This highlights the role of this compartment as a buffer of PAH contamination in the environment. As atmospheric PAH emissions have decreased during the last decades in Western Europe (Fernández et al., 2000, Pacyna et al., 2003), the soils represent secondary sources, and are likely to play an important role in the current and future environmental persistence of those contaminants. Villanneau et al. (2013) reported the presence of higher PAH concentrations driven by historical mining and industrial activities in soils of Northeastern France. In the Seine River basin, certain studies identified Paris City as the main source delivering PAHs into the atmosphere (Garban et al., 2002), whereas other investigations showed that PAH concentrations in soils were mainly associated with the presence of urban or industrial areas in their vicinity (Motelay-Massei et al., 2004). Consequently, to move the debate forward and given the importance of legacy contamination in northwestern Europe, the respective contribution of regional atmospheric fallout and local sources supplying PAHs to the soils must be further investigated.

Interactions between soils and PAHs have been extensively studied for many years and appear to be very complex (Xing and Pignatello, 1997). Because of their high lipophilicity, PAHs tend to bind strongly to the particles (Yang et al., 2013). Numerous studies have also highlighted the role played by organic matter (OM) in the sorption of those substances and showed that soils enriched in OM generally contain higher PAH concentrations (Bogan and Sullivan, 2003). Once deposited onto the soil surface, some contaminants gradually migrate to deeper soil horizons. This transfer mainly depends on the solubility of the compounds, their affinity for soil components and the magnitude of water infiltration into the soil (Enell et al., 2004, Yang et al., 2013). PAHs are both poorly soluble in water and highly lipophilic, and leaching is therefore limited to the upper soil layers. This leads to an accumulation of PAHs in the uppermost layers of the substrate as observed in undisturbed forest soils by Krauss et al. (2000). Some laboratory experiments showed that a very small fraction of PAHs is recovered when injecting a large amount of water through a soil core (Enell et al., 2004). In this context, PAH leaching is often considered to be negligible. However, high PAH concentrations have also been observed in deep horizons of heavily contaminated soils (Liao et al., 2012). In conclusion, the entire distribution of PAH contamination in soil horizons must be considered to correctly quantify their inventory in the substrate.

Overall, to the best of our knowledge, there is little information in the literature combining PAH contamination in soils, its evolution with depth and the relationship with the distance to the sources at the entire catchment scale. In this study, the PAH distribution is investigated in soils of two agricultural catchments to verify the relevance of factors that need to be taken into account when estimating contaminant stocks. a) The concentrations of PAHs in 336 soil samples collected in 2 catchments are reported. b) The variation of PAH content with depth in soils is investigated. c) The relationships between soil contamination and the distance to potential local sources (charcoal factory or road traffic) are investigated. d) Finally, the relative contribution of local and regional sources within the two catchments are detailed and the corresponding PAH stocks are calculated. Overall, this study is representative of the contaminant concentrations and stocks that may be found in most rural and agricultural catchments of early industrialized countries. The results of this study provide original and novel information on PAH stock distribution at the catchment scale. They may be useful to design and implement large scale remediation programmes required to achieve the legislative environmental targets.

Section snippets

Study sites

In order to compare the importance and the relative contribution of several PAH sources in the environment, soils from two catchments located in upstream parts of the Seine River basin (Fig. 1) were sampled and analysed. Site 1 is the Avenelles catchment located 70 km eastward from Paris City and draining a 46-km² area. Site 2 is the Saulx catchment, located 210 km eastward from Paris City and constituted of 3 subcatchments covering a total area of 614 km². According to CORINE Land Cover

Migration of PAHs in depth

Depth profiles of PAH concentrations in soils under different land covers are given in Fig. 3. Three types of behaviour were found.

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    First, in undisturbed soils (i.e. woodland), concentrations in all measured parameters decreased with depth except for PAH in the two first centimetres. This trend may be explained either by higher PAH losses (biodegradation or volatilization) in the uppermost layer of the soil or by lower atmospheric inputs during the last decades. On the one hand, volatilization

Conclusions

This study conducted in two rural catchments located at varying distance from the main regional source of contamination provided original results on PAH contamination in soils. First, soil contamination level and depth was shown to strongly depend on land use. At the catchment scale, PAH concentrations in soils displayed large variations and were shown to be partly controlled by the distance to local sources (road network or a charcoal factory). In terms of stocks, our calculations demonstrated

Acknowledgements

Research in the Seine River basin was conducted in the framework of PIREN Seine and GIS ORACLE long term environmental monitoring and research programmes. David Gateuille received PhD funding from the R2DS programme (Ile-de-France Region). The authors are also very grateful to Polytech'UPMC students and to Yassine Raguig El Moussaoui for their help during sampling or chemical analyses. This is LSCE contribution No 5261.

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