Declining trends of PCDD/Fs in lichens over a decade in a Mediterranean area with multiple pollution sources

Lichens are one of the most useful environmental biomonitors, due to their ability to clearly reflect atmospheric deposition of pollutants. Dioxin and furan (PCDD/F) emissions have been reported to be decreasing in North European countries as a consequence of European regulations. This reduction has been perceptible across several environmental matrices, but it hasn't yet been shown in lichens as typical biomonitors of atmospheric pollution. In this work we compared concentrations of PCDD/Fs in two lichen species collected in a Mediterranean area with mixed land-uses, encompassing urban, industrial and natural areas, in 2009 and 2011 with the ones obtained in the same species collected in the same region in 2000. We found that PCDD/F concentrations in both lichen species have decreased approximately 70% since 2000 whereas industrial emissions have only decreased 25% for the same period. This substantial greater reduction observed in lichens may be due to several causes; after excluding fires as a possible explanation, we point out that possible causes could not only be the overall decrease in industrial emissions but also other causes such as traffic reduction and/or increase efficiency in the use of fuels. Capsule: PCDD/F concentrations in lichens have decreased 70% over the last decade, whereas industrial emissions have only decreased 25%.