The influence of tree species composition on the storage and mobility of semivolatile organic compounds in forest soils Klára Komprdová a, ⁎, Jiří Komprda a , Ladislav Menšík b , Lenka Vaňková a , Jiří Kulhavý b , Luca Nizzetto a,c a RECETOX (Research Centre for Toxic Compounds in the Environment), Kamenice 753/5, CZ-625 00 Brno, Czech Republic b Mendel University in Brno, Faculty of Forestry and Wood Technology, Zemědělská 3, Brno 613 00, Czech Republic c Norwegian Institute for Water Research, Gaustadalleen 21, NO-0349 Oslo, Norway HIGHLIGHTS • Tree species composition influences vertical distribution of PCBs and PAHs in soils. • PCBs and PAHs were more mobile in the soil of the broadleaved plot. • Low molecular weight PCBs displayed higher mobility in all forest types. • Humic substances were important de- scriptors of contaminant concentration. GRAPHICAL ABSTRACT abstract article info Article history: Received 5 October 2015 Received in revised form 16 February 2016 Accepted 18 February 2016 Available online 22 March 2016 Editor: F.M. Tack Soil contamination with PCBs and PAHs in adjacent forest plots, characterized by a distinct composition in tree species (spruce only, mixed and beech only), was analyzed to investigate the influence of ecosystem type on con- taminant mobility in soil under very similar climate and exposure conditions. Physical-chemical properties and contaminant concentrations in litter (L), organic (F, H) and mineral (A, B) soil horizons were analyzed. Contam- inant distribution in the soil core varied both in relation to forest type and contaminant group/properties. Con- taminant mobility in soil was assessed by examining the ratios of total organic carbon (TOC)-standardized concentrations across soil horizons (Enrichment factors, EF TOC ) and the relationship between EF TOC and the octanol-water equilibrium partitioning coefficient (K OW ). Contaminant distribution appeared to be highly un- steady, with pedogenic/biogeochemical drivers controlling contaminant mobility in organic layers and leaching controlling accumulation in mineral layers. Lighter PCBs displayed higher mobility in all forest types primarily controlled by leaching and, to a minor extent, diffusion. Pedogenic processes controlling the formation of soil ho- rizons were found to be crucial drivers of PAHs and heavier PCBs distribution. All contaminants appeared to be more mobile in the soil of the broadleaved plot, followed by mixed canopy and spruce forest. Increasing propor- tion of deciduous broadleaf species in the forest can thus lead to faster degradation or the faster leaching of PAHs and PCBs. The composition of humic substances was found to be a better descriptor of contaminant concentration than TOC. © 2016 Elsevier B.V. All rights reserved. Keywords: Forest horizon Mobilization Soil profile PAHs PCBs Humic substances Enrichment factors Tree composition Global change Science of the Total Environment 553 (2016) 532–540 ⁎ Corresponding author. E-mail address: komprdova@recetox.muni.cz (K. Komprdová). http://dx.doi.org/10.1016/j.scitotenv.2016.02.132 0048-9697/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv