Evaluation of Tree Bark as a Passive Atmospheric Sampler for Flame Retardants, PCBs, and Organochlorine Pesticides AMINA SALAMOVA AND RONALD A. HITES* School of Public and Environmental Affairs, Indiana University, Bloomington, Indiana 47405 Received May 11, 2010. Revised manuscript received June 23, 2010. Accepted June 30, 2010. To investigate the relationship between the levels of persistent organic pollutants in tree bark (a passive sampler) and those in air and precipitation, tree bark and air and precipitation samples were collected during the same time period at the five U.S. Integrated Atmospheric Deposition Network (IADN) sites located in Great Lakes basin. The concentrations of polybrominated diphenyl ethers, Dechlorane Plus, decabromo- diphenyl ethane, polychlorinated biphenyls, DDTs, and chlordanes were measured in these samples. Overall, the pollutant concentrations in tree bark are significantly related to the concentrations of these compounds in the air and precipitation collected where the tree was growing. Generally, the highest tree bark and air pollutant concentrations were observed at urban sites, and the lowest concentrations were observed at remote sites. The overall correlation between bark and atmospheric and precipitation concentrations for all the compounds measured in this study was highly significant ( P < 0.0001) over 3-4 orders of magnitude. In addition, bark-air partition coefficients, measured for all the chemical categories in this study, were about 10 6 , which was in good agreement with previously estimated bark-air partition coefficients for corresponding pollutant groups. Introduction The measurement of persistent organic pollutant concentra- tions in air is important to assess the atmospheric transport of these compounds. These measurements, however, are often limited by the high cost of conventional high-volume, active air sampling. Passive air sampling is a less expensive alternative to active air sampling; in fact, polyurethane foam (PUF) disk passive samplers are beginning to be widely used and have been shown to be effective (1, 2). One significant disadvantage of these PUF samplers is that they require deployment for several weeks to months. An alternate passive sampler is tree bark, which is always deployed and continu- ously collects pollutants from the surrounding air. Obtaining tree bark samples is easy, fast, and inexpensive. Tree bark passive sampling is especially advantageous in remote settings, where electrical power is not available to operate conventional high volume samplers. Contaminant screening by tree bark has been used to monitor various inorganic and organic pollutants, such as ammonia (3), heavy metals (3-8), polychlorinated biphenyls (9-11), polycyclic aromatic compounds (12), polychlorinated dibenzo-p-dioxins (13), organochlorine pesticides (14), and brominated and chlorinated flame retardants (15, 16). Tree bark works well as a passive sampler because of its high lipid content and its large surface area; thus, it is a good passive sampler for pollutants with high octanol-air partition coefficients. Tree bark seems to accumulate both vapor- and particle-phase pollutants from the surrounding air (17) and integrates pollutant levels over a period of several years, depending on the time the bark stays on the tree (18). The goal of this study is to examine the relationship between the levels of selected pollutants in tree bark and their levels in the vapor and particle phases in the surrounding air obtained using high-volume air sampling methods and to examine the relationship between the levels in tree bark and their levels in precipitation falling on the tree. Significant correlations between these concentrations on the one hand and in the tree bark on the other will demonstrate the ability of tree bark to passively sample these three atmospheric media and give some indication about how tree bark accumulates persistent organic pollutants from the atmo- sphere. The analytes of interest in this study are polybro- minated diphenyl ethers (PBDEs), Dechlorane Plus (DP), decabromodiphenyethane (DBDPE), polychlorinated biphe- nyls (PCBs), and selected organochlorine pesticides, such as DDT and chlordane. Tree bark, air, and precipitation samples were collected at the five U.S. Integrated Atmospheric Deposition Network (IADN) sites located in Great Lakes basin. Experimental Section Sampling Information. The locations of the U.S. IADN sampling sites are shown in the Supporting Information (Figure S1). There are five U.S. IADN sites: urban sites in Chicago, IL (41.8344°N, -87.6247°W) and Cleveland, OH (41.4921°N, -81.6785°W); rural sites at Sleeping Bear Dunes, MI (44.7611°N, -86.0586°W) and Sturgeon Point, NY (42.6931°N, -79.0550°W); and a remote site at Eagle Harbor, MI (47.4631°N, -88.1497°W). The IADN Web site provides more detailed information on air sampling procedures and site operations (www.msc.ec.gc.ca/iadn). The atmospheric samples discussed here were collected during the period January 1, 2003 to December 31, 2007. All tree bark samples were collected in the winter of 2008. Only white pine trees were used because of their occurrence at all sites. The average tree diameter at 1.5 m height was 89 cm. Although the exact age of the trees was unknown, based on their trunk diameter it was evident that these trees were fully grown. Given that pine bark has a residence time on the tree of about 5 years, bark samples collected in 2008 had been passively sampling the surrounding air during the 2003-2007 period corresponding to the air sampling. Bark samples were collected from four individual trees at each of the five IADN locations. Trees closest to the IADN active air sampler were chosen for bark sampling. A sample of bark (about 100 g) was collected from two different sides of each tree using a precleaned chisel at a height of 1.5 m. To avoid long-term damage to the tree, the cambium was not sampled. The bark sample was wrapped in aluminum foil, sealed in a plastic bag, and kept at ambient temperature until the samples were shipped to the laboratory, where they were kept at -20 °C until extraction. A modified Anderson high-volume air sampler (General Metal Works, model GS2310, modified) was used to collect air samples for 24 h every 12 days at a flow rate giving a total sample volume of about 820 m 3 . The vapor phase was collected on Amberlite XAD-2 resin (Supelco, Bellefonte, PA; * Corresponding author e-mail: hitesr@indiana.edu. Environ. Sci. Technol. 2010, 44, 6196–6201 6196 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 16, 2010 10.1021/es101599h  2010 American Chemical Society Published on Web 07/21/2010