Lead concentrations and isotope ratios in urban tree leaves

Variation in stable lead isotopic composition has been recognized as a suitable indicator for source identification of Pb contamination in the environment. Some deciduous tree leaves have been reported as useful biomonitors of trace elements atmospheric pollution including lead. The focus of this work was to examine a relationship between the Pb concentration and the stable isotopic ratios (206Pb/207Pb and 208Pb/207Pb) in leaves of common urban deciduous trees Aesculus hippocastanum and Tilia spp. in the biomonitoring approach for source identification within the Pb atmospheric contamination studies. The study took place over a period of several years (2002–2006, 2009) when leaded gasoline was still in use in the Belgrade urban area, but an increasing number of vehicles using non-leaded gasoline was evident during the investigated time span. This status of decreasing atmospheric Pb contamination also reflected the leaf Pb content of the studied trees. However, while the Pb content in the leaves decreased during the studied period, the isotopic ratio of 206Pb/207Pb concomitantly increased throughout the years. The obtained Pb isotopic ratios in the leaves indicated the major contribution of leaded gasoline to the leaf Pb content. The leaf Pb isotope ratios also followed the switch (from Australian – 2002/2003/2004 to Chinese origin – 2005/2006) of the Pb ore used as the gasoline lead additive through the investigated years. The results of this study indicated A. hippocastanum as more appropriate than Tilia spp. in biomonitoring the Pb source identification, showing more consistency of data obtained on leaf Pb isotopic composition and the isotopic ratios of gasoline used throughout all studied years.