Keywords: 
• PM_2.5 /
• heavy metal /
• chemical speciation /
• bioavailability /
• health risk assessment

Abstract: To study the bioavailability and the potential ecological risk of heavy metals to the environment and the human more accurately, PM_2.5 samples were collected in Guiyang City during the winter. The chemical speciation of Cu, Mn, Co, Cd, and Pb in PM_2.5 samples were investigated using the modified BCR sequential extraction procedure. The bioavailability and health risk of the five heavy metals were also estimated based on the results of chemical speciation analysis. The results showed that the different heavy metals in PM_2.5 display different chemical speciation distribution. The Cu was mainly distributed in the acid-soluble fraction, and then the oxidizable fraction. The Mn primarily existed in the acid-soluble fraction, then the residual fraction. The Co was evenly distributed in all the fractions except the reducible fraction. The Pb and Cd were almost presented in the acid-soluble fraction. The results of the bioavailability coefficient (K) revealed that the order of bioavailability of the heavy metals was: Cd > Pb > Mn > Cu > Co. The Pb and Cd were classified as bioavailable elements due to K > 0.8. While the Cu, Mn, and Co were remarked as potential bioavailable elements because the values of K ranged from 0.4 to 0.7. The results of health risk assessment indicated that those heavy metals may lead to higher level carcinogenic risk for adults compared with children. The health risk assessment result of Cd indicated potential carcinogenic risk for adult, especially for male adult. Mn may pose potential non-carcinogenic risk to human health, especially for children.