Conclusions
Fifteen MSWI fly ash samples covering almost all of China were analyzed to investigate the content and chemical speciation of Hg. The results showed that concentration of HgT in fly ash samples ranged from 1 to 24 mg kg1, and 10 mg kg1 on average. Hg in fly ashes existed mainly as F4, which accounted for 65–94% of
HgT. F5 accounted for 5–13% and F3 accounted for 0–4% of HgT.Exchangeable Hg accounting for 0–27% of HgT. The results above were well supported by the 6 months sequential inspection of samples in two typical MSWI plants. The concentration of HgT kept at 5–27 mg/kg for samples from MSWI 8, and 4–27 mg/kg for samples from MSWI 11. The main fraction of Hg in the samples was F4, which accounted for 26–79% and 30–82% of the HgT for MSWI 8 and MSWI 11, respectively. TCLP test indicated that leaching Hg contents were all lower than the USEPA TCLP regulatory level standard 0.2 mg L1. According to PCA, the HgT content was closely connected with that of F4 and the leaching content was preferentially associated with the exchangeable Hg content. Furthermore, HQtotal ranged from 0.02 to 0.75, lower than the ‘‘safe’’ threshold of 1. Inhalation of Hg vapor and re-suspended particles from fly ash was the main exposure pathway, and the HQinh ranged from 0.01 to 0.57, accounting for the major proportion of the total risk.
As a conclusion, exposure of Hg in fly ashes to workers on site did not exhibit potential health risk. Despite, Hg pollution is still an important environmental problem when reuse of MSWI fly ash, the pretreatment should be performed for the formation of strongly-complexed Hg fraction.