Pollution level and chemical speciation of heavy metals in PM_2.5 during autumn in Guangzhou city

PM_2.5 samples were collected in Guangzhou city during autumn. Total concentration and chemical speciation of 10 heavy metals in PM_2.5 were quantified by acid digestion method and sequential extraction procedure. The pollution level and bioavailability of these metals were also evaluated. Results showed that PM_2.5 and heavy metal concentration were significantly high in Guangzhou city. Ranged from 0.083 3 to 0.1900 mg·m^-3, PM_2.5 levels in the region were much higher than outdoor PM_2.5 standard recommended by US-EPA. High enrichment factor values (K > 10) were obtained for Cd, Pb, Zn, Cu and Mo, reflecting the importance of anthropogenic inputs. In contrast, K values of Ni, Mn, Co and Fe were among 1 to 10, suggested that they were mainly from natural sources except for human activities. According to the results of chemical speciation analysis, more than 80% of Al and Fe were found bound to organic matter, oxidisable and sulphidic fraction, and residual fraction. Meanwhile, most of Zn, Pb, Cd and Cu were distributed in soluble and exchangeable fraction and carbonate, oxide and reducible fraction. Bioavailable coefficients (k) revealed that the order of comparative mobility and bioavailability of heavy metals is: Cd > Zn > Pb > Cu > Mn > Mo > Co > Ni > Fe > Al. With k > 0.8, Cd, Zn and Pb were classified as bioavailable elements, while Cu, Mn, Mo, Co and Ni (k ≈ 0.5) were remarked as potential bioavailable elements, and Fe and Al (k <0.2) as non-available elements.