Size-Dependent Distribution And Inhalation Exposure Of Particle-Bound Semivolatile Organic Contaminants

Size distribution of particles in part dictates the environmental behavior of particlebound organic pollutants in the atmosphere. Inhalation of pollutants is an important exposure route for causing human health hazards, and inhalation exposure assessment must take into account particle size distribution because particle-bound pollutants are size-dependent. Atmospheric size-fractionated particle samples were collected using a 10-stage Micro-Orifice Uniform Deposit Impactor from an e-waste recycling zone and urban Guangzhou in South China for analyzing semivolatile organic contaminants(SVOCs), including halogenated flame retardants(HFRs; including polybrominated diphenyl ethers(PBDEs), alternative brominated flame retardants, and Dechlorane Plus(DP)), organophosphate flame retardants(OPFRs), and polycyclic aromatic hydrocarbons(PAHs). The present study was conducted to examine the potential mechanisms responsible for the distribution of the SVOCs in sizefractionated particles and their environmental implications, and inhalation exposure risk.The concentrations of particle-bound ΣPBDE(sum of 18 PBDE congeners) were significantly greater at 5 and 20 m than those at 1.5 m. The size-fractionated distributions of airborne ΣPBDE displayed trimodal peaks in 0.10-0.18, 1.8-3.2 and 10-18 μm at 1.5 m, but only an unimodal peak in 1.0-1.8 μm at 20 m height. Emission sources, resuspension of dust and soil and volatility of PBDEs were important factors influencing the size distribution of particle-bound PBDEs. The dry deposition fluxes of particle-bound PBDE estimated from the measured data in the present study were approximately twice the estimated wet deposition fluxes, with a total deposition flux of 3000 ng m-2 d-1. The relative contributions of particles to dry and wet deposition fluxes were also size-dependent, e.g., coarse(particle aerodynamic diameters(Dp) > 1.8 μm) and fine(Dp < 1.8 μm) particles dominated the dry and wet deposition fluxes of PBDEs, respectively.The overall concentrations of particle-bound alternative halogenated flame retardants(AHFRs) in the e-waste recycling zone were at high levels in the world, suggesting that ewaste recycling activities may be a significant emission source of AHFRs in the atmosphere. Concentrations and size distributions of AHFRs at different heights above the ground had no significantly difference. The AHFRs were uniformly associated with coarse and fine particels. Distribution of DP isomers in the atmospheric particles was size-dependent, indirectly confirming the transformation of DP isomers in the long distance atmospheric transport process. The estimated average dry and wet deposition fluxes of total AHFRs were 141 and 71 ng m-2 d-1, repectively. Dry and wet deposition fluxes of particle-bound AHFRs were dominant contributed by the coarse particles.The deposition efficiencies and fluxes of size-fractionated HFRs in the human respiratory tract were estimated using the International Commission on Radiological Protection deposition model. The majority of HFRs was found to deposit in the head airways, with coarse particles contributed the most(69-91%). Conversely, fine particles were dominant in the alveolar region(62-80%). The inhalation intake of PBDEs within the ewaste recycling zone was 44 ng d-1(95% confidence interval(CI): 30–65 ng d-1), close to those through food consumption in non-e-waste recycling regions. The estimated total hazard quotient of particle-bound HFRs was 5.6×10-4(95% CI: 3.8×10-4-8.8×10-4). In addition, incremental lifetime cancer risk induced by BDE-209 was 1.36×10-10(95% CI: 7.3×10-11-2.3×10-10), much lower than the Safe Acceptable Range(1.0×10-6-1.0×10-4) established by the United States Environmental Protection Agency. These results indicate that the potential health risk from inhalation exposure to particle-bound HFRs for residents dwelling in the e-waste recycling zone was low.The mean total air concentrations of eight OPFRs were 130 and 127 ng m-3 in the ewaste recycling zone and in urban Guangzhou, respectively. Nonchlorinated tributoxyethyl phosphate(TBEP) was the most abundant OPFR and may be attributed to the widespread use of TBEP-containing products. Compositional profiles of chlorinated OPFRs were different between the e-waste recycling zone and in urban Guangzhou, but the size distribution patterns were not significantly different at different heights at both sites, i.e., coarse and fine particles contributed almost equally to the concentrations of OPFRs. Estimated atmospheric deposition fluxes of particle-bound OPFRs were 51 and 55 μg m-2 d-1 in the e-waste recycling zone and in urban Guangzhou, respectively, and the coarse particles dominated both the dry and wet deposition fluxes. In addition, not all particle-bound OPFRs were inhalable and deposited in the human respiratory tract. The calculated inhalation doses of OPFRs were much lower than the reported reference doses, suggesting that potential health risk due to inhalation exposure to particle-bound OPFRs in the e-waste recycling zone and urban site was low.Atmospheric particle size distribution of PAHs in the e-waste recycling zone and urban Guangzhou featured a unimodal peak in 0.56–1.8 μm for 4–6 ring PAHs but no obvious peak for 2–3 ring PAHs. The atmospheric deposition fluxes of PAHs were estimated at 5.4±2.3 μg m-2 d-1 in the e-waste recycling zone and 3.1±0.6 μg m-2 d-1 in urban Guangzhou. In addition, dry and wet deposition fluxes of PAHs were dominated by coarse and fine particles, respectively. Fine particles predominated the deposition of PAHs in the lung. The results estimated by incremental inhalation cancer risk suggested that particle-bound PAHs posed serious threat to human health within the e-waste recycling zone and urban Guangzhou.