The influence of the dry ashing procedure on the correctness of Pb determination in lichens and mosses.

Mosses and lichens are often used to assess atmospheric deposition of Pb. The most widely used method for determining this isotope is gamma spectrometric analysis. There is often a need to enhance the sensitivity of the method, which can be achieved by pre-concentrating Pb. The simplest method in this case is direct dry ashing according to commonly accepted standardized procedures. However, the question of potential losses of Pb during the combustion of mosses and lichens remains unclear. The main objective of this study is to investigate the effect of the dry ashing procedure on the accuracy of determining Pb concentrations in the studied samples. The conducted experiment showed that ashing samples with low (< 8%) ash content, which includes all mosses and lichens, at a temperature of 450 °C leads to significant losses of Pb (up to 40%). For samples with an ash content > 14% (litter), the losses of this isotope do not exceed 3-4%. For both groups, the value of ashing losses has a nearly linear dependence, inversely proportional to the ash content in the studied material. The obtained relationships allowed us to calculate the corrections necessary to account for Pb losses during ashing of both low and high ash materials. The application of several statistical tests demonstrated good convergence and consistency of the results of Pb determination obtained by direct measurement in unashed samples and those calculated through the measured activity of this isotope in ashes, corrected for ashing losses.