Environ. Sci. Technol. 2008, 42, 6514–6518
Analysis of Polychlorinated Biphenyls in Concurrently Sampled Chinese Air and Surface Soil Z H I Z H A N G , †,‡ L I Y A N L I U , † Y I - F A N L I , †,§ DEGAO WANG,| HONGLIANG JIA,| T O M H A R N E R , § E D S V E R K O , §,∇ XINNAN WAN,⊥ DIANDOU XU,# N A N Q I R E N , * ,† J I A N M I N M A , § A N D KARLA POZO§ International Joint Research Center for Persistent Toxic Substances (IJRC-PTS), State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, China, College of Agricultural Resource and Environment, Heilongjiang University, Harbin, China, Science and Technology Branch, Environment Canada, IJRC-PTS, Dalian Maritime University, China, IJRC-PTS, Chengdu University of Technology, China, IJRC-PTS, Institute of High Energy Physics, Chinese Academy of Sciences, China, and IJRC-PTS, McMaster University, Canada
Received February 9, 2008. Revised manuscript received June 1, 2008. Accepted June 12, 2008.
Polychlorinated biphenyl (PCB) concentrations were measured in a concurrent air and surface soil sampling program acrossChina.Passiveairsampleswerecollectedforapproximately 3 months from mid-July to mid-October, 2005 using polyurethane foam (PUF) disk type samplers at 97 sites and surface soil samples were collected in a subset of 51 sites in the same year. As expected, the air concentrations (pg m-3) were highest at urban sites (mean of 350 ( 218) followed by rural (230 ( 180) and background sites (77 ( 50). The PCB homologue composition was similar across China, with no distinction among site types, and reflected the profile of Chinese transformer oil with a greater proportion of lower molecular weight (LMW) congeners, particularly the tri-PCBs. This differs from the profile in Chinese soil that was shifted toward the higher molecular weight (HMW) congeners and likely attributed to numerous years of deposition and accumulation in this reservoir. The PCB profile in surface soil also reflects an “urban fractionation effect” with preferential deposition of HMW congeners near sources. The profile of PCBs in Chinese air was shown to be different than reported for Europe and for the Great Lakes Area (GLA) in North America. European and GLA air samples show a distinction between urban and rural/ background sites, with urban sites dominated by tetra- and penta-PCBs, whereas rural and background sites are shifted toward LMW congeners. European and GLA samples also exhibit much higher PCB concentrations at urban sites. This may be * Corresponding author phone: 86-451-8628-2008; e-mail:
[email protected]. † Harbin Institute of Technology. ‡ Heilongjiang University. § Environment Canada. | Dalian Maritime University. ∇ McMaster University. ⊥ Chengdu University of Technology. # Chinese Academy of Sciences. 6514
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attributed to the use of PCBs in building materials in European and North American cities. In China, the difference between urban and rural/background sites is less pronounced. Strong soil-air correlations were found for the LMW PCBs at the background and rural sites, and for the HMW PCBs at the urban sites, a strong evidence of the urban fractionation effect. To our knowledge, this is the first national-scale study in China investigating PCBs in both air and surface soil samples.
Introduction Polychlorinated biphenyls (PCBs) are one of the 12 persistent organic pollutants (POPs) targeted by the Stockholm Convention on POPs (1). PCBs are stable in the environment, undergo long-range atmospheric transport (LRAT) and possess the ability to bioaccumulate through the food chain with the potential of toxic effects to humans and biota. The cumulative global production of commercial PCBs is approximately 1.3 × 106 t (2). Of this amount, 440 to 92 000 t is estimated to have been emitted into the environment (3) and is now dispersed through LRAT to global media such as soil, water sediments and air. PCBs were manufactured in China from 1965 until they were banned in 1974. Over this period, approximately 10 000 t of PCBs were produced, of which 9000 t was produced as trichlorobiphenyl, known as no. 1 PCB, and 1000 t as pentachlorobiphenyl, no. 2 PCB (4). Trichlorobiphenyl was used primarily in power capacitors, while pentachlorobiphenyl was used mainly as a paint additive (5). Due to the rapid response of air concentrations to changes in primary emissions, the atmosphere is expected to be particularly useful as an indicator of the “effectiveness” of the Stockholm Convention. Indeed, in the revised guidance document for a POPs monitoring program prepared by UNEP (6), air is one of only two target media (human tissues being the other) recommended for initially assessing POPs trends on a global scale. The Chinese POPs Soil and Air Monitoring Program (SAMP) started in 2005. The objective of this national-scale program is to study and relate both temporal and spatial trends of POPs in air and surface soil. The program had run on a seasonal basis for 2 years. The focus is on Chinese agricultural regions although several urban and background sites are included for comparison purposes. Results can be used to assess the effectiveness of regulatory measures implemented in China to control POPs. Comparison of coupled soil and air concentrations will also provide insight into soil-air interactions and fate processes. The results for PCBs in surface soil across China have been previously reported (7). The mean soil concentration of total PCBs (pg g-1 dw (dry weight)) was 488, and ranged from 138 to 1840. PCBs in background and rural soils were generally uniform and varied by less than 1 order of magnitude. Compared to a global survey of background soils from 1998 (8), the Chinese background/rural soil in 2005 had approximately one-tenth the PCB content and a profile that was shifted toward the low molecular weight (LMW) congeners. This paper reports PCB air concentrations across China at 97 sites. PCB levels and patterns in air are related to sources and compared to other regions of the world. Results are also related to previously reported soil residues (7) that were collected at most of the same sites.
Material and Methods Sampling. Passive air samplers (PASs) comprised of polyurethane foam (PUF) disks (9, 10) were deployed at 97 sites 10.1021/es8004078 CCC: $40.75
2008 American Chemical Society
Published on Web 07/23/2008
(4 background, 69 rural, and 24 urban, see Table S1 of the Supporting Information (SI) for detail) across China in 2005 for 3 months (from mid-July to mid-October). Background sites were situated in remote areas, far from human activities; rural sites were in agricultural regions; and urban samples were typically from urban residential areas. Site coordinates are given in SI Table S1. The PUF disks (15 cm diameter; 1.45 cm thick; surface area, 420 cm2; mass, 5.12 g; volume, 256 cm3; density, 0.02 g cm-3) were housed inside a stainless steel chamber, which protects the sampler from precipitation, UV sunlight, and particle deposition. The chamber also dampens the windeffect on sampling rates, resulting in a sample that is more equally weighted with time over the sampling period (9). PASs at the background and rural sites were installed 1.5-2 m above the ground, whereas at urban sites, this varied from 2 to 30 m (when mounted on roof tops). Sampling chambers were prewashed and solvent-rinsed with acetone prior to installation of the PUF disks which was carried out using clean gloves. Sample installation and removal was performed outside to avoid the risk of contamination in the laboratory. Disks were precleaned by Soxhlet extracted for 24 h using acetone and hexane (1:1 v/v) at the laboratories at International Joint Research Center for Persistent Toxic Pollutants (IJRC-PTS), Harbin Institute of Technology and Dalian Maritime University, China, and then transferred to the sampling locations in sealed, solvent-cleaned brown glass jars with Teflon-lined caps. At the end of the deployment period, the PUF disks were retrieved, resealed in their original jars at the sampling locations, and returned to the IJRC-PTS laboratories, where they were stored cold (
