When Ash Meets Lead: Changing Rules for Lichens and Mosses

Lichens and mosses are great thermometers for tracking atmospheric deposits, especially the isotope 210 Pb. Scientists often use a method called gamma spectrometric analysis to measure this. But sometimes they need to boost the sensitivity by concentrating 210 Pb. One common way to do this is through a process called dry ashing. This involves burning off everything except the minerals, hopefully without losing any 210 Pb. Researchers wanted to find out if dry ashing really kisses away 210 Pb from our lichens and mosses. They tried different temperatures, focusing on 450°C, and looked at samples with varying ash contents—from less than 8% in mosses and lichens to more in things like litter. When the ash content was low, about 40% of 210 Pb was lost. With higher ash content, the loss was only 3-4%. It turns out, the higher the ash content, the less 210 Pb gets lost. These findings let scientists calculate the corrections needed for low and high ash samples. Then they ran some tests to check the accuracy. They found that measurements from unashed samples were pretty close to those corrected for ashing losses.