Assessment of heavy metals mobilization in road-deposited sediments induced by COVID-19 disinfection.

Road-deposited sediments (RDS) on urban impervious surfaces are important carriers of heavy metals (HMs), and can contribute to urban runoff pollution. With the outbreak of COVID-19, chlorinated disinfectants (CDs) have been extensively sprayed on these surfaces. This practice may have a superposed or priming effect on HMs contaminants in RDS, yet this remains unknown. This study examined the effects of seven CDs concentration gradients (0, 250, 500, 1000, 2000, 5000, 60,000 mg/L) on the leaching and chemical forms of HMs (Cd, Cr, Ni, Pb, and Zn) in seven particle size fractions (<44, 44-63, 63-105, 105-149, 149-250, 250-450, 450-1000 μm). The results showed that CDs can promote the leaching of HMs in RDS, at the recommended CDs dose (2000 mg/L), except for Pb, the leaching amounts increased by 21.8%-237.2% compared with the untreated RDS. The alteration in the leaching were primarily attributed to the redistribution of chemical forms of HMs in RDS, specifically, the acid-extractable fractions percentage increased by 0.23%-24.39%, and the reducible fractions percentages decreased by 3.21%-38.35%. The lower oxidation-reduction potential (ORP) and alkalinity of CDs as strong oxidants were responsible for the redistribution of forms. The leaching and chemical forms of HMs vary among different particle sizes, but in any case, finer particle sizes (< 105 μm) still dominate their contribution. The current control measure of street sweeping is ineffective in removing these particles. These findings will facilitate the development of strategies for controlling urban diffuse pollution from RDS during the pandemic. Finally, this study suggests potential directions for future research.