Study On Distribution And Health Risk Assessment Of PCDD/F Emissions From Municipal Solid Waste Incinerations (MSWIs)

With rapid economic growth, massive urbanization and increasing population, treatment and management of municipal solid waste (MSW) are one of the major contents of urban management and environmental protection, and are an important hallmark of a civilized progressive society. They relates to the very interests of the people and urban stability and sustainable development. Recently, MSW incineration (MSWI) is one of important methods for MSW treatment. MSWI has remarkable advantages of reducing mass/volume and recovering energy; however, development of MSWI industry in China faces several major challenges, including secondary pollution and location problems. Especially, impact of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) emissions from MSWIs on surrounding environment and health risk has been a topic of wide concern. In order to determine the environmental impact of PCDD/F emissions from two types of MSWIs (named M and L) on surrounding environment and health risk assessment, this dissertation launched a series of fundamental experimental and theoretical studies. The objectives of the current research involved as follows:1) The PCDD/F baseline concentrations in the soil samples, which collected near16MSWIs prior to construction in5different areas, range from0.32-11.40ng I-TEQ/kg (dry matter). The PCDD/F concentration in soil samples surround M and L MSWI is in range of0.39-5.54ng I-TEQ/kg and0.972-1.46ng I-TEQ/kg, respectively. Comparison with worldwide PCDD/F levels, the concentrations of PCDD/Fs in most soil samples are at the lower levels for rural areas (1-5ng I-TEQ/kg), indicating low contamination of baseline soils prior to the construction of16new MSWIs and soils surrounding established two types of MWSIs.Based on the combination of the environmental monitoring data, including PCDD/F levels in air atmosphere, surface and core soils, and modeling procedures, i.e., source apportionment (including statistical analysis and fingerprint profiles) and atmospheric deposition flux model, the results indicate that PCDD/F concentration in surrounding air atmosphere and deposition flux of M MSWI are at relative high end of the world. Preliminary study also shows that the PCDD/F contamination in this area should attribute to current waste incineration, such as open burning, MSWI etc. however; the PCDD/F contamination from historical activities is very small. 2) Air distribution models are used to determine the behavior and transport of dioxin emissions both from M and L MSWIs, indicating that airborne dioxin concentration is proportional to emission levels, and meteorological data is one of the major influencing factors of dioxin airborne dispersion. Potentially severe pollution from dioxins occurs at a wind speed of1.5m/s with atmospheric stability class F, where the mixing height is only100m and height of plume rise is only116, resulting higher ground level concentration. Based on actual dioxin emission parameters and meteorological conditions, local residents in the study area of M MSWI are exposed to severe weather conditions most of time, while the study area of L MSWI is favorable to dioxin airborne dispersion. Those results are agreed with the dioxin monitoring concentration in environmental media surrounding two MSWIs.3) The temporal and long dioxin exposure distributions in soils and vegetables surrounding the M MSWI were investigated, indicating that the dioxin fingerprint profiles both in soil and vegetable samples are similar with that in air atmospheric samples. A soil and a plant equilibrium dioxin models were carried out to determine the dioxin transfer in air-soil-vegetable system. These results show that the background concentration is the most important pathway contributing to dioxin concentrations in soil, followed by dry and wet deposition. However, the soil contamination from pathways of dry and wet deposition increases with the time, especially for higher chlorinated PCDD/Fs as well as PCDFs higher than that for PCDDs. In addition, the vapor-phase absorption and air (including dry and wet) deposition pathways are major pathways contribution to dioxin concentrations in vegetation. In both models, the uptake by roots was not obvious. Compared with dioxin monitoring concentrations in soil and vegetables, the soil model is better to predict the levels of17dioxin congeners in soils.4) The health risks of dioxin exposure in the vicinity of MSWI were evaluated for children and adults using the VLIER-HUMAAN model recommended by Nouwen. The results indicate that the food ingestion is the major exposure pathway. Experimental formula for dioxin exposures via inhalation and food ingestion of children and adults, respectively, were derived. Based on experimental formula, it shows a good linear correlation between inhalation and food ingestion. Comparison of dioxin concentrations in air atmosphere, the dioxin concentration in air in M area is approximately10times higher than that in L area. Dioxin contaminations in parts of M area have been exceeded the Japanese Air Quality Standard (0.6pg I-TEQ/m3). According to the health risk assessment by experimental formula, risk exposure for the residents located in M area is higher than that in L area, and risk exposure for the residents in L area is agreed with the tolerable daily intake of dioxin recommended by the World Health Organization (WHO) of1-4pg TEQ/kg·day even under severe weather conditions. High risk exposure in M area attributes to higher dioxin emission concentrations and unfavorable weather to airborne.Overall, food ingestion is major dioxin risk exposure for local residents surrounding the MSWIs, where the food ingestion is strongly related to dioxin levels in air atmosphere. Further, combination of air dispersion and atmospheric deposition, statistic analysis, air-soil-vegetable transfer models, it also indicates that dioxin emission parameters and meteorological conditions are the major influencing factors of airborne dioxin dispersion and transfer in environment surround the MSWIs. When dioxin emission concentration of the MSWI is equal to or more than1.0ng I-TEQ/Nm3, the study of site-specific exposure scenario (M MSWI) indicates that dioxin emissions from the MSWI have certain impact on surround environment and health risk. However, according to the study of site-specific exposure scenario (L MSWI), the effect of dioxin emission from the MSWI on surrounding environmental could be ignored as the dioxin emission concentration is less than0.01ng I-TEQ/Nm3. Finally, the results in this study are consistent with a new emission guideline composed by the MEP of China, and also agreed with the aim of973programme (No.2011CB201500).