Meteorological and pedological influence on the PCBs distribution in mountain soils Niccolò Guazzoni a,⇑ , Roberto Comolli b , Luigi Mariani c , Gabriele Cola c , Marco Parolini a , Andrea Binelli a , Paolo Tremolada a a Department of Biology, University of Milan, Via Celoria 26, 20133 Milan, Italy b Department of Environmental and Land Sciences (DISAT), University of Milan Bicocca, Piazza della Scienza 1, 20126 Milan, Italy c Department of Crop Science, University of Milan, Via Celoria 2, 20133 Milan, Italy article info Article history: Received 30 June 2010 Received in revised form 3 December 2010 Accepted 9 December 2010 Available online xxxx Keywords: PCBs Alpine soils Seasonal variation Layer effect Aspect effect Summer volatilisation abstract Polychlorinated biphenyls (PCBs) are a threat to environmental and human health due to their persis- tence and toxicological effects. In this paper, we analyse some meteorological and organic-matter-related effects on their distribution in the soils of an Alpine environment that is not subject to direct contamina- tion. We collected samples and measured the contamination of 12 selected congeners from three soil lay- ers (O, A1 and A2) and from North-, plain- and South-facing slopes on six different dates spanning the entire snowless portion of the year. We recorded the hourly air and soil temperatures, humidity and rain- fall in the study period. We found evidence that PCBs contamination in soils varies significantly, depend- ing on sampling date, layer and aspect. The observed seasonal trend shows an early summer peak and a rapid decrease during June. The layer effect demonstrates higher dry-weight-based concentrations in the O layer, whereas the differences are much smaller for SOM-based concentrations. Different factors caused significantly higher concentrations in northern soils, with a N/S enrichment factor ranging from 1.8 to 1.5 during the season. The southern site has significantly more rapid early-summer re-volatilisation kinetics (half-time of 16 d for South, 25 d for North). Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The continuing threat to human and environment health from PCBs (polychlorinated biphenyls) necessitates maintaining a high level of alert on these compounds (Helyar et al., 2009; Johnson et al., 2009). Mountains are useful and important areas for studying the environmental distribution of POPs (persistent organic pollu- tants), and many studies have been conducted worldwide (Grimalt et al., 2001; Barra et al., 2005; Nizzetto et al., 2008; Moeckel et al., 2008; Tremolada et al., 2009). It has been estimated that the soil contains the majority of the total environmental burden of POPs (Mackay, 2001; Meijer et al., 2003), and mountain soils in particu- lar have some characteristics that emphasise retention, such as high organic-matter content, efficient snow scavenging (Lei and Wania, 2004), low temperatures and particular wind conditions (anabatic winds) that move contaminants from point sources along the mountain slopes. The total pollutant burden of mountain soils depends on the physical and chemical properties of each pollutant, expressed by biphasic partition coefficients. These parameters are also correlated with temperature because a decrease in tempera- ture tends to lower the air–water partition coefficients (K AW ) of POPs (Daly et al., 2007) and raise their soil–air partition coeffi- cients (K SA )(Hippelein and McLachlan, 1998). This effect favours the accumulation of POPs in vegetation and soil at high altitudes. It is possible to identify an annual cycle of pollutant transfer in a mountain area. During the winter season, low temperature and the recurrence of snowy precipitation causes deposition of airborne pollutants and their retention in the snow mantle. The quantity of POPs deposited depends directly on the amount of pollutants in the air. The higher temperatures at lower altitudes (such as plains, in which the majority of pollutants are emitted) favour the volatilisation of compounds (Wania et al., 1998a), and anabatic winds (which blow during daytime) tend to carry polluted air masses up the slopes of mountains. During spring, the snow man- tle melts and releases pollutants into the atmosphere or the melt- ing water–soil system. This latter phenomenon drives a particular POP behaviour because hydrophobic pollutants will not flow away and tend to be deposited on soils (Meyer et al., 2006). When the thaw is complete, the soil surface is directly exposed to air, and soil temperatures increase, so PCBs can re-volatilise and deposit else- where by the well-known ‘‘Grasshopper Effect’’ (Calamari et al., 1991). Dalla Valle et al. (2005) theorised the concept of a maxi- mum reservoir capacity for soils, which is based on temperature, K sa and organic matter composition. Based on this model, great concentration differences are expected in mountainous areas, which have steep gradients of temperature and soil properties 0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2010.12.043 ⇑ Corresponding author. Tel.: +39 02 50314715; fax: +39 02 50314713. E-mail address: niccolo.guazzoni@unimi.it (N. Guazzoni). Chemosphere xxx (2011) xxx–xxx Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere Please cite this article in press as: Guazzoni, N., et al. Meteorological and pedological influence on the PCBs distribution in mountain soils. Chemosphere (2011), doi:10.1016/j.chemosphere.2010.12.043