Assessment of Heavy Metal Sources and Microplastics in Drainage Deposited Sediments from Highways and Rest Areas

Highways are considered sites of nonpoint-source pollution. Pollutants such as heavy metals, from vehicles contaminate adjacent soils and water bodies by passing through the drainage systems during rainfall. We measured the concentrations of heavy metals (Zn, Cu, Cr, Pb, Ni, As, Cd) in drainage deposited sediments at four sampling sites along the Yeongdong Expressway: the highway upline drainage (HU), highway downline drainage (HD), rest area drainage (RA), and nearby stream (ST), assessed the levels of contamination, and identified the sources. Pollution indices, Spearman correlation analysis, and principal component analysis were used. Analysis was also conducted to identify microplastics (MPs) released from vehicles. Linear regression analysis was performed to examine relationships between microplastics and heavy metals. The average concentrations of Zn and Cu in highways exceeded 8 and 10 times, respectively, their natural background values. The Single Pollution Index (PI) and the Geo-accumulation Index (Igeo) values for Zn, Cu indicated very highly polluted level in the HU and HD, while the Nemerow Pollution Index (PINemerow) values indicated heavy pollution. The Spearman correlation analysis revealed strong positive correlations between the heavy metals, and the principal component analysis identified anthropogenic sources of heavy metal contamination. Vehicle-released MPs, such as polystyrene and acrylonitrile butadiene styrene, were found in the highway sediments. A linear relationship between microplastics and Zn and Pb was identified. Therefore, the sediments in highway drainage reflect the severity of heavy metal contamination attributable to vehicle releases, and proactive measures are required to address heavy metal pollution from highways. High PI and Igeo values of Zn and Cu indicate severe heavy metal accumulation.Nemerow Pollution Index showed heavy pollution levels in the study areas.Acrylonitrile butadiene styrene and polyamide used in vehicles and roads were identified.High correlations between various heavy metals was found.Anthropogenic sources of heavy metals were identified.