Polycyclic aromatic hydrocarbon contents and distributions in soils of the northern French Alps

Polycyclic aromatic hydrocarbons (PAHs) are toxic and persistent organic pollutants that are ubiquitous in the environment. In particular, their presence and persistence in soils represent public health and environmental problems. However, no regulation of the levels of these pollutants in soils has been introduced in France. Despite a few nationwide monitoring studies of PAHs, little is known about the contamination by these pollutants in ecosystems such as mountainous areas. The aim of this study was therefore to assess PAH soil contamination in the northern French Alps and to improve our understanding of (i) their spatial distribution and (ii) their dynamic on sites submitted to very local past and present contamination. To this end, PAH levels were measured in the topsoil (0-10 cm) along eight elevational gradients (220-2700 m), the latter allowing us to study a wide range of climatic and ecological conditions and different levels of PAH exposure over a limited spatial area. The results revealed that the distance from sources played a major role in determining the PAH distribution. In addition, sites subject to major past and present PAH-emitting industrial activities were studied. At the site subject to current high emissions, PAH levels were extremely high, with a specific signature. In contrast, at site that was no longer subject to any particular source, the PAH levels were close to the regional background. The complementary study of these different types of sites allowed us to improve our knowledge of the spatial and temporal dynamics of PAHs in mountainous areas.