Detection of air quality improvement within a suburban district (southern Italy) by means of lichen biomonitoring

The present work compared both the bioaccumulation of trace elements and the values of ecophysiological parameters measured in thalli of the lichen Pseudevernia furfuracea (L.) Zopf in two monitoring campaigns performed before and after improvement measures put in place by a 15 MW biomass power plant (BPP): the activation of a concentrated solar thermodynamic plant and the increasing percentage of exhausted olive pomace used as fuel. The cases of no enrichment and moderate enrichment change from 49 and 17% in 2013 to 68 and 4.2% in 2019, respectively. Several metals in 2019, show a Delta (difference between exposed and not exposed lichen thalli concentration) that is significantly lower than in 2013. The spatial pattern of contamination is comparable between the two years. However, the BPP affects the spatial variation of Ti, Al, V and Co in both 2019 and 2013, but only in the latter year also that of Cu, Cr and As which, in some monitoring sites, developed extremely high levels of enrichment. Traffic, whose rate increased over time, constantly influences the bio-accumulation of Cu, Sb and Mo. In 2019, the lichen oxidative stress is significantly reduced as well as the number of correlations between malondialdehyde levels and those of trace elements. Pigment values never differ (p > 0.05) from pre-exposure levels. Our results suggest that the development of hybrid plants, as well as a better fuel selection can reduce the environmental impact due to the combustion of biomass contributing to make this type of energy source more sustainable.