| Fly ashes were sampled from15municipal solid waste incineration plants inChina to survey distribution and characteristics of dioxins content. Fly asheswere also sampled from2municipal solid waste incineration plants in Shanghai.A five-step sequential selective extraction procedure was used to study thespeciation of Hg in all fly ashes. Total mercury analysis and TCLP leaching testwere also conducted to investigate the pollution status and distributioncharacteristics of Hg in fly ashes. Research results are as follows:(1) The concentrations of PCDD/PCDFs and dl-PCBs in fly ash ranged from2.8to190ng/g, and59.6ng/g on average. TEQ in the fly ash samples ranged from0.034to2.5ng-TEQ/g, and0.79ng-TEQ/g on average. For PCDDs, thedominant homologue was hexa-chlorinated homologue. For PCDFs,tetra-chlorinated homologue was dominant. The ratio of PCDDs/PCDFs rangedfrom0.32to2.44(average0.97). The contribution of dl-PCBs to the totalconcentrations and TEQ of dioxins was relatively low. The main contribution tothe dl-PCBs TEQ came from3,3’,4,4’,5-PeCB, and3,3’,4,4’-TeCB had thehighest concentration among12dl-PCBs congeners. Concentration of1,2,3,4,7,8-HxCDF+1,2,3,4,7,9-HxCDF,1,2,3,7,8-PeCDD, and2,3,4,7,8-PeCDF showed strongest correlation to the TEQ of15fly ash samples.The main contribution to the TEQ was from1,2,3,7,8,-PeCDD and2,3,4,7,8-PeCDF.(2) Total mercury contents of15fly ash samples ranged from0.55to24.48mg/kg, and9.67mg/kg on average. Mercury in fly ashes existed mainly aselement Hg, which accounted for65.34%-93.73%of HgT. Hg-s, accounted for4.64%-13.11%and Hg-o accounted for0%-3.70%of HgT. The percentage ofexchangeable Hg (defined as water soluble Hg plus ‘human stomach acid’ soluble Hg) was0.08%–26.59%. Leaching contents of Hg were all belowenvironment leaching standard (0.2mg L-1) except FA4(0.21mg L-1).According to principal components analysis, the concentrations of HgT wereclosely connected with that of fraction4since the percentage of this fraction ofHg was relatively high. Leaching content was preferentially associated with theconcentration of fraction1for this fraction was water-soluble.(3) Total mercury contents of40Yuqiao fly ash samples ranged from5.36to26.80mg/kg, and13.80mg/kg on average. The concentration of Jiangqiao flyash samples ranged from3.75to44.81mg/kg, and15.83mg/kg on average.Total mercury contents in fly ash samples did not change greatly, but slightlydecreased after November. Mercury in fly ash samples from two municipal solidwaste incineration plants all existed mainly as element Hg, which accounted for26.44%-79.02%and30.21%-82.08%of HgT. Leaching contents of Hg in all flyash samples were all below environment leaching standard.(4) Health risk assessment was conducted for workers working in municipalsolid waste incineration plants or fly ash landfill as they expose to fly ashescontaining Hg and dioxins. According to calculation of hazard quotient andexposure dose, exposure of fly ash containing Hg did not exhibit potential healthrisk to workers in site. But dioxins existing in the fly ash exhibit health rish.Exposure of fly ash containing Hg to children exhibited high potential healthrisk. Inhalation of Hg vapor was the main exposure pathway to fly ash. |
