Evaluation of various mercury forms in the urban road runoff sediments

Mercury (Hg) contamination urban areas is a very important issue in environmental research studies. Current study was aimed to determine the Hg content and its distribution characteristics, and to ascertain the speciation of Hg in urban surface sediment. This study also discussed the driving factors of Hg content and its speciation. Road runoff and surface sediment samples collected from different districts in Nanjing, China were analyzed for different forms of Hg. These samples were analyzed using a Cold Vapor Atomic Absorption Spectroscopy (CVAAS). The results indicated that the total mercury (THg) content in the soil of study districts in Nanjing was in range of 35.2-4.99 x 10(3) mu g/kg and the mean value (323 mu g/kg) was much higher than the normal values. The THg content shows clear differences for various functional zones, e.g. Electronic business district (1.15 x 10(3) mu g/kg) > Comprehensive business district (274 mu g/kg) > Residential district (266 mu g/kg) > Cultural and educational district (119 mu g/kg) > Traffic district (105 mu g/kg) > Natural district (60.8 mu g/kg) > Industrial district (53.5 mu g/kg). The speciation of Hg in surface sediment was as follows: F1-soluble mercury (Hg-sol) (2.21%), F2-exchangeable mercury (Hg-ex) (2.21%), F3-reactive mercury (Hg-re) (3.53%), F4-mercury oxide (Hg-oxide) (47.9%), and F5-residual mercury (Hg-resid) (44.2%). The correlation analysis shows that THg significantly correlated with F4 and F5. Furthermore, results reveal that the surface sediments in Nanjing are alkaline, therefore THg and Hg-resid were higher in lower pH. Overall, the rainfall events have various effects on THg content on the surface sediment from different districts in Nanjing. The characteristics of rainfall event may alter the speciation of Hg in surface sediment.