Source attributions of heavy metals in rice plant along highwayin Eastern China

Air and soil pollution from traffic has been considered as a critical issue to crop production and food safety, however, few efforts havebeen paid on distinguish the source origin of traffic-related contaminants in rice plant along highway. Therefore, we investigated metals(Pb, Cd, Cr, Zn and Cu) concentrations and stable Pb isotope ratios in rice plants exposed and unexposed to highway traffic pollutionin Eastern China in 2008. Significant differences in metals concentrations between the exposed and unexposed plants existed in leaf forPb, Cd and Zn, in stem only for Zn, and in grain for Pb and Cd. About 46% of Pb and 41% of Cd in the grain were attributed to thefoliar uptake from atmosphere, and there were no obvious contribution of atmosphere to the accumulations of Cr, Zn and Cu in grain.Except for Zn, all of the heavy metals in stem were attributed to the root uptake from soil, although significant accumulations of Pb andCd from atmosphere existed in leaf. This indicated that different processes existed in the subsequent translocation of foliar-absorbedheavy metals between rice organs. The distinct separation of stable Pb isotope ratios among rice grain, leaf, stem, soil and vehicleexhaust further provided evidences on the different pathways of heavy metal accumulation in rice plant. These results suggested thatfurther more attentions should be paid to the atmospheric deposition of heavy metals from traffic emission when plan crop layout forfood safety along highway.