A contribution of nanoscale particles of road-deposited sediments to the pollution of urban runoff by heavy metals.

Road-deposited sediments (RDS) present a sink for traffic-related pollutants including heavy metals (HMs). HMs associated with RDS particles enter the urban aquatic environment during rainfall events and have adverse effects for biota. RDS nanoscale particles (NSPs) require special consideration due to their specific properties, extremely high mobility in the environment, and ability to penetrate into living organisms. In the present work, the contribution of NSPs of RDS to the pollution of urban runoff by HMs has been evaluated for the first time. It has been shown that bulk RDS samples are polluted by HMs as compared to background urban soils (geo-accumulation indexes of Cu and Zn may attain 2-3). Meanwhile, NSPs of RDS are enriched by HMs as compared to bulk samples; concentration factor for Ni, Cu, Zn, Cd, Sn, and Pb in NSPs being varied from 2 to 10. The water-soluble fractions of RDS samples were also analyzed. Results have shown that the content of water-soluble HMs in RDS is insignificant and rarely exceeds 0.5% of the total contents of HMs in the bulk samples; the highest contents are identified for Cu and Pb. It should be noted that the water-soluble fraction is nearly free from Zn and this element is almost entirely present as particulate matter (NSPs). In general, the overall contribution of NSPs and water-soluble fraction of HMs to the pollution of urban runoff is comparable.