Can washing-pretreatment eliminate the health risk of municipal solid waste incineration fly ash reuse?

• Using Monte Carlo and bioaccessibility to assess the risk of washed fly ash reuse.
• Washing process resulted in concentrated content and decreased bioaccessibility.
• Effects of water-washing and acid-washing process on cancer risk are different.
• The difference of washing process's influence on actual hazard index is uncertain.
• Washing process cannot reduce the actual risk to acceptable level.

Although the reuse of washing-pretreated MSWI fly ash bas been a hot topic, the associated risk is still an issue of great concern. The present study investigated the influence of washing-pretreatment on the total contents and bioaccessibility of heavy metals in MSWI fly ash. Furthermore, the study incorporated bioaccessibility adjustment into probabilistic risk assessment, to quantify the health risk from multi-pathway exposure to the concerned chemicals as a result of reusing washed MSWI fly ash. The results revealed that both water-washing and acid-washing process have resulted in the concentrated heavy metal content, and have reduced the bioaccessibility of heavy metals. Besides, the acid-washing process increased the cancer risk in most cases, while the effect of water-washing process was uncertain. However, both water-washing and acid-washing pretreatment could decrease the hazard index based on bioaccesilbility. Despite the uncertainties accompanying these procedures, the results indicated that, in this application scenario, only water-washing or acid-washing process cannot reduce the actual risk from all samples to acceptable level, especially for cancer risk.