Accumulation of Persistent Organic Pollutants in Canopies of Different Forest Types: Role of Species Composition and Altitudinal-Temperature Gradient LUCA NIZZETTO, †,§ KEVIN C. JONES, ‡ PAOLA GRAMATICA, † ESTER PAPA, † BRUNO CERABOLINI, † AND ANTONIO DI GUARDO* ,§ Department of Structural and Functional Biology, University of Insubria, Via J. H. Dunant 3, 21100 Varese VA, Italy, Centre for Chemicals Management and Environmental Science Department, Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK, and Department of Chemical and Environmental Sciences, University of Insubria, Via Valleggio, 11, 22100 Como CO, Italy Leaves from the dominant tree species in three different alpine forests were sampled along an altitudinal gradient and analyzed for HCB, R- and γ-HCH, and PCBs. The mean canopy concentration was calculated, considering the relative abundance of each species in the respective forest. Compound fractionation occurred in the vegetation along the altitudinal/temperature gradient. Results were compared with air concentrations and in-field plant/air partition coefficients (K PA ) were calculated for each species; this showed differences between broadleaves and needles. The mean canopy/air partition coefficient (K CA ) was also calculated by averaging results from single species. The variability of persistent organic pollutants distribution in canopies is discussed considering two main factors, the altitudinal/temperature gradient and the species composition. The latter is responsible for most of the concentration variability of the more volatile compounds. A model to calculate dry gaseous deposition to different forest canopies is presented. Introduction Important advances in our knowledge of the global distribu- tion of organic pollutants have been made by studying vegetation (1). Persistent organic pollutants (POPs) have been measured in the vegetal biomass across latitudes and with altitude, reflecting the accumulation of organic pollutants from the atmosphere (2, 3) and supplying terrestrial food webs (4, 5). Exposure of forest ecosystems to semivolatile organic pollutants has also been investigated (6-10). Forest canopies can influence air concentrations temporally (11, 12) and spatially (13). Given the proportion of the earth’s surface covered by forests, their role in influencing pollutant fate on a regional or global scale merits consideration (14- 17). POPs were recently studied in vegetation in the Canadian Rocky Mountains (18). Concentrations of some organochlo- rine pesticides increased along the altitudinal gradient. Alpine systems provide the opportunity to compare different forest types which change in specific composition with the in- creasing elevation over relatively small distances (compared to latitudinal gradients) and where air concentrations may be more uniform. Mountain environments were therefore recently pinpointed as ideal sites to comparatively investigate some of the transport phenomena (such as role of temper- ature or species composition) associated with the global distribution of pollutants (19). In this study, concentrations of PCBs, R- and γ-HCH, and HCB were determined in leaves and needles from three different forest sites in the Italian Alps. Previously, these sampling sites were used to compare air concentrations within and outside the forest (13, 20) and the deposition fluxes to the canopies. The main aims of this investigation were to evaluate the distribution of POPs in vegetation in three different ecosystems and assess the contribution of dominant species to the overall load of POPs in forest canopies. Experimental Section Sampling Sites. Leaves were sampled from three sites in the Lys Valley, Aosta, Italy, located at 1100, 1420, and 1790 m above sea level (asl), respectively (Figure 1). Each site is characterized by a different forest type, according to the altitude, as described in Table 1. Sampling. Leaf samples were collected from the dominant tree species. Table 1 summarizes the species sampled and their abundance at each site. Samples were collected in October 2002, at the end of the growth season. For spruce (Picea abies) new needles (year 0) were collected, to normalize exposure time to deciduous species. Leaves were collected from 21 transects using latex gloves at least 1.5 m from the soil. At each location g3 trees of the same species were sampled in an area of 400 m 2 at least 100 m from the forest edge. Samples therefore reflected the most abundant foliar biomass in the inner canopy. Samples were kept in solvent- rinsed glass jars and frozen at -20 °C, until extraction. Analysis. Samples were freeze-dried, homogenized, and spiked with PCB 40 and PCB 128 as recovery standards. Extraction (typically of 5 g) was performed in precleaned cellulose thimbles (Schleicher & Schuell, Dassel, Germany) using an all glass Soxtech-type automatic extractor (Velp Scientifica, Usmate, Italy) with n-hexane/acetone 6:1 for 6 h. Solvents were pesticide residue grade from Sigma-Aldrich, Seelze, Germany. Gel permeation cleanup was then per- formed in accordance with method USEPA 3640A (1998) (21), using a 600 mm length, 26 mm i.d. glass column filled with SX-3 beads (200-400 mesh, Bio-Rad, Hercules, CA) and coupled to an Agilent 1100 series HPLC system (flow rate 3.5 mL/min, run time 72 min). Fractions were collected using retention times of chemical markers according to the USEPA procedure (21). Calibration standards were injected every 6 samples. Samples were subsequently fractionated in 15 cm × 5 mm i.d. glass columns packed with activated Florisil for residue analysis (60-100 mesh) purchased from Merck, Darmstadt, Germany. Samples were eventually concentrated to 50 μL and PCB 30 and PCB 141 were added as internal standards. Analyses were performed using a Hewlett-Packard 5890 series 2 gas chromatograph (GC) equipped with dual ECD. Injection was split via a Y connector into two parallel * Corresponding author phone: +39 031 2386480; fax: +39 031 2386449; e-mail: antonio.diguardo@uninsubria.it. † Department of Structural and Functional Biology, University of Insubria. ‡ Lancaster University. § Department of Chemical and Environmental Sciences, University of Insubria. Environ. Sci. Technol. 2006, 40, 6580-6586 6580 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 21, 2006 10.1021/es0605523 CCC: $33.50  2006 American Chemical Society Published on Web 09/28/2006