EDXRS STUDY OF LICHENS AS BIOMONITORS AND EFFECT OF WASHING PROCEDURE ON ELEMENT CONCENTRATIONS

A monitoring survey was carried out in North Italy using Pseudevernia furfuracea as a monitor of air pollution. The experiment was carried out on lichen thalli exposed for different periods varying from 3 to 10 months at urban and rural sites, to examine and compare the bioaccumulation of several elements. Every 2 months a fraction of exposed lichens was collected to analyse the thallus, Each fraction was divided into two parts, one of which was washed in deionized water, in order to quantify the element loss due to the washing procedure. The samples were anlaysed by energy-dispersive x-ray fluorescence spectrometry in the secondary excitation mode; quantitative analysis was performed by the fundamental parameter method with NIST standard reference materials. The targets for the fluorescence spectrometer were obtained by digestion under pressure with microwave heating. At the end of the exposure period (10 months), nearly all elements, showed higher concentrations at the urban than at the rural site.