| Recently, due to the advantages of high-temperature detoxification, significant volume and mass reduction of municipal solid waste, the incineration technology has been booming and applied in developed regions in mainland China. However, the construction and operation of municipal solid waste (MSW) incineration plant has stirred public concerns due to the potential secondary pollution from the facility, especially the environmental toxics and associated adverse health effects of the emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs). In order to establish effective countermeasures to control the emissions of PCDD/Fs, it is urgent to understand the pollution status of PCDD/Fs around the MSW incineration plant. In this study, by combination of the modeling procedures, i.e., Industrial Source Complex Short Term Version 3 (ISCST3) model and Reservoir Mixing (RM) model, environmental monitoring and statistical analysis (Factor Analysis and Chemical Mass Balance Analysis), we investigated the levels and profiles of PCDD/Fs in soil, air and potential sources around an MSW incineration plant in Hangzhou, the gas/particle partitioning of PCDD/Fs in ambient air, the source identification of PCDD/Fs in environmental media and the environmental exposure risk of PCDD/Fs for residents living around the facility.The total concentration (I-TEQ value) of soils in 2006 and 2007 ranged from 54.1 to 285 ng kg-1 (0.39 to 5.04 ng I-TEQ kg-1) and from 73.6 to 377 ng kg-1 (0.60 to 6.38 ng I-TEQ kg-1), respectively. On the other hand, the temporal variations (2006-2007) of the total concentration and I-TEQ value in soils increased by 30% and 31%(median value), respectively, with three sampling sites exceeding 1 ng I-TEQ kg-1. Similar homologue, congener concentration and congener I-TEQ profiles were found among the soils. As for homologues, OCDD was the dominant contributor and the concentrations of PCDF homologues decreased with increasing level of chlorination. With respect to congener concentration profile,1,2,3,4,6,7,8-HpCDD,1,2,3,4,6,7,8-HpCDF and OCDF were the main contributor besides OCDD. With regard to congener I-TEQ fingerprint,2,3,4,7,8-PeCDF was the dominant contributor, accounting for 31% and 30%(mean value) in 2006 and 2007, respectively.The atmospheric PCDD/F concentration ranged from 3.96 to 164 pg m-3 (0.059 to 3.03 pg I-TEQ m-3). The spatial distribution of atmospheric PCDD/F levels was in line with those observed in soils (temporal variations). Almost all ambient air samples showed a TCDF-dominant (20-41%) homologue pattern, characterized by decreasing concentrations with increasing levels of chlorination (except for OCDD). Similar to soils,2,3,4,7,8-PeCDF (30-53%) was the dominant contributor of I-TEQs to ambient air. By contrast, the dominant congener in terms of concentration profiles showed temporal and spatial variations among OCDD, OCDF and 1,2,3,4,6,7,8-HpCDF.The PCDD/F emission levels of the MSW incineration plant in 2007 were relatively low (0.083-0.795 ng I-TEQ Nm"3). By contrast, the diffuse emission sources showed high dioxin levels. For instance, the concentrations of flue gas from wood-fueled hot water boiler (HWB-W) and the ambient air leeward of open burning of cloth (OB-C) were 1.95 ng I-TEQ Nm-3 and 6.14 pg I-TEQ m-3, respectively. The homologue profiles of emission sources were similar, with PCDDs/PCDFs ratio less than 1. In comparison, the congener concentration patterns were distinct from each other, e.g., the HWB-W was dominated by 2,3,4,7,8-PeCDF whereas OB-C was dominated by OCDD,1,2,3,4,6,7,8-HpCDF and OCDF. Nevertheless,2,3,4,7,8-PeCDF was the dominant contributor to I-TEQ (49-75%) for most emission sources.The fraction of particle-bound PCDD/Fs (φ) increases as the chlorination level increases and/or the ambient temperature decrease, and the annual averaged values were as follows:C14DD/Fs (37-56%), Cl5-6DD/Fs (58-86%) and Cl7-8DD/Fs (86-98%). Generally, good agreements were obtained (except for winter) between measuredφand theoretical estimates of both the Junge-Pankow (PLo) adsorption model and the Harner-Bidleman (Koa) absorption model. Models utilizing PLo estimates, derived from gas chromatographic retention indices (GC-RIs), were more accurate than that of entropy-based. Moreover, the Koa-based model using the GC-RIs approach performed better than that of PLo-based. The disagreement found between the modeled and observed values during winter under high concentration of total suspend particles was more attributed to the non-equilibrium partitioning of PCDD/Fs that had slowed down the exchange between gaseous and particulate fractions than the gas adsorption artifact of filter.The results from a congener-specific factor analysis revealed that the emissions from the open burning of wastes, hot water boilers and motor vehicles were the major sources that accounted for the temporal variations of PCDD/Fs in soils and atmospheric PCDD/F pollution. By contrast, the impact of emissions from the MSW incineration plant was limited. The average contributories to atmospheric I-TEQ values from the above mentioned four emission sources (based on CMB model) were 63%,18%,12%and 7%, respectively. On the other hand, the results from ISCST3 and RM modeling indicated that the average contribution of emissions from the MSW incineration plant to atmospheric levels and soil temporal variations (I-TEQ) in three sub-regions, i.e., within a radius of 250,500-750 and 1500-3000 m from the stack were 2%,64%,8.5% and 1.1%, respectively. For a modern MSW incineration plant that meets the national PCDD/F emission standard, i.e.,1 ng I-TEQ Nm-3, the impact of a long-term operation of the facility on surrounding soils, especially those far away(d>1km) from the facility, is limited.The environmental exposure to PCDD/Fs ranged from 3.45×10-5 to 1.77×10-4 ng I-TEQ kg-1 day-1 and 2.61×10-5 to 1.35×10-4 ng I-TEQ kg-1 day-1 for children and adults living in the vicinity of the MSW incineration plant. Inhalation is the dominant pathway, accounting for 87-99% and 88-99% of environmental exposure for children and adults, respectively. The non-carcinogenic and carcinogenic risk of environmental exposure was 8.66-44.3×10-3 and 5.17-26.5×10-6 for children and 65.3-33.8×10-3 and 3.91-20.2×10-6 for adults, respectively, among which only 7% was from the emissions of the MSW incineration plant.
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