Bioavailability of heavy metals in urban particles

Urban particles, as one of the toxic air pollutants, are important issues concerning air quality and public health, especially in large cities like Guangzhou （China）. Toxicological studies implicated heavy metals （particularly water-soluble metals） as a health hazard of particles. Once absorbed into human lung tissues, heavy metals are likely released from the particles and do harm to human body even in low concentrations. Thus, evaluating the bioavailability of heavy metals in urban particles is quite necessary. The particle samples used in this study were collected from a building roof in Guangzhou. Three different methods, sequential extraction procedure and two leaching tests, were employed to investigate the bioavailability of heavy metals in the particles. The sequential extraction scheme is specific for analyzing the chemical speciation of metals in particles, which consists of four fractions： F1： soluble and exchangeable metals; F2： carbonates, oxides and reducible metals; F3： bound to organic matter, oxidisable and sulphidic metals; and F4： residual metals. Leaching tests, GB 5086.2-1997 and TCLP, are standard methods developed by China-EPA and US-EPA and widely used in evaluating the toxicity of solid wastes. They were applied to gain additional information about more easily mobilized form of metal. Heavy metals in extraction solution, including Cu, Zn, Pb, Cd, Cr, and Ni, were analyzed by ICP-MS. According to the data from the total concentration analysis, the relative contents of 6 heavy metals in particles follow the order of Pb〉Zn〉Cu〉Cr〉Ni〉Cd. The results of sequential extraction showed that more than 50% of Cu, Zn and Cd were distributed in the F1, F2, and F3. This indicated that the bioavailability of Cu, Zn and Cd in the particles is much higher than that of Pb, Cr, and Ni. Leaching tests revealed that the concentrations of heavy metals in leachate are relatively lower than the regulatory level. The results of TCLP are much higher than those of GB 5086.2-1997, mainly due to the low pH value of the extraction fluid.

Bioavailability of heavy metals in urban particles