Biomonitoring of airborne trace elements using transplanted lichens around a paper industry (Morelia, Mexico)

The deposition of trace elements around a pulp and paper industry in Morelia, Mexico, was evaluated using two lichen species as biomonitors. Samples of the foliose lichen Flavopunctelia praesignis and the fruticose lichen Usnea ceratina were collected in two remote areas and transplanted at different distances and directions from the pollution source. Lichen samples were exposed for 4 months (1) around the industrial area and (2) in their native habitats (control sites). We investigated the bioaccumulation of 11 trace elements in lichen thalli, and we compared the response of the two lichen species. To identify possible common sources, we evaluated the relationships between trace elements by correlations and cluster analyses. Our results showed that Cd was a good tracer for air pollution from the pulp and paper mills. In samples of Usnea ceratina exposed around the industrial area, Cd was significantly higher than in the remote area. Within the study area, trace element contents increase with the distance from the source, and they showed high depositions in the direction of prevailing winds. Moreover, we were able to detect groups of elements with similar behavior and common origins. Our results indicated that Flavopunctelia praesignis showed a higher capacity to accumulate trace elements than Usnea ceratina.