Physicochemical properties and toxic elements in bus stop dusts from Qingyang, NW China

To appraise the content and pollution level of cadmium (Cd), arsenic (As), mercury (Hg), nickel (Ni) and lead (Pb) in bus stop dusts, representative samples (n = 53) were collected from the city of Qingyang in Gansu province, NW China. The Cd, As, Hg, Ni, and Pb contents and physicochemical properties (particle size, organic matter, pH and magnetic properties) of the bus stop dusts were investigated. Pollution levels were evaluated by the Nemero synthesis pollution index (NSPI) and geoaccumulation index (I_geo). The results indicate that the magnetic susceptibilities of the bus stop dusts were higher than those in the local soils. Cd, As, Ni, and Pb contents ranged from 0.4 to 3.1, 7.1 to 16.3, 12.7 to 151.3, and 20.1 to 96.2 mg kg^-1, with average values of 1.2, 10.1, 22.2, and 44.9 mg kg^-1, while Hg content ranged from 4.5 to 1357.7 µg kg^-1 with an average of 214.0 µg kg^-1. The mean contents of Cd, As, Hg, Ni, and Pb were 12.0, 0.8, 10.0, 0.6, and 2.4 times the local soil background value, respectively. Cd, Hg and Pb in approximately 96%, 62% and 19% of the bus stop dusts were above the "moderately polluted" level in terms of I_geo. As and Ni were defined as "practically unpolluted" in all of the bus stop dusts. The NSPI values of all of the bus stop dust samples exceeded 3, which reveals overall serious contamination of harmful elements.