Problems related to lichen transplants to monitor trace element deposition in repeated surveys: a case study from central Italy

The results of a transplant experiment with the fruticose lichen Evernia prunastri aimed at monitoring the trends of trace elements deposition in a repeated biomonitoring study are reported. Data comparability between the two surveys and interpretation of the results were addressed in this study. The ratio between the concentration of each element after the exposure and in control samples prior to exposure (exposed-to-control ratio, EC ratio), as well as an appropriate interpretative scale, were adopted as a means of determining the temporal trends of element accumulation by lichen transplants. The results showed that the method adopted is indeed a reliable tool, pinpointing a Zn smelting plant and an oil refinery as principal pollution sources in the area, which indicate that elements associated with the former were similarly accumulated in both 2002 and 2003, while elements associated with the latter tended to decrease in 2003.