M.A. ALI*, H.F. MOHAMED**, W.M. AMER***

*Department of Biophysics, Faculty of Science, Cairo University, Giza 12613, Egypt
**Department of Physics, Faculty of Science, El-Minia University, El-Minia 61519, Egypt
***Department of Botany, Faculty of Science, Cairo University, Giza 12613, Egypt

Heavy metal (lead) concentrations in two marsh plants (Phragmites australis and Cyperus rotundus) and one free floating hydrophyte (Eichhornia crassipes) growing near metal smelters (lead pollutant area) were investigated. The shoots of the investigated plants were analyzed for lead content by flame atomic absorption spectrometry. The data indicated high lead levels due to the influence of urban and industrial effluents. This showed that the target plants could be considered as lead pollution biosensors. Scanning electron microscopy (SEM) and positron annihilation lifetimes (PAL) technique were used to ascertain the localization of lead in the living tissues. Cross-sections of plant organs were examined using SEM attached with an Energy Dispersed X-ray (EDX) unit for elemental analysis of the formed crystals that appeared abundant in the aerenchyma tissues of the polluted plants. PAL data reflected the correlation between the fraction of free volume hole and lead concentration; higher lead accumulation gives lower fraction of free volume hole. The results demonstrate the extreme sensitivity of the PAL technique towards structural changes occurring in polluted plants.

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