Natural and pre-treatments induced variability in the chemical composition and morphology of lichens and mosses selected from active monitoring of airborne elements for active monitoring of airborne elements

Abstract To enhance the reliability of the moss and lichen transplant technique for active biomonitoring of trace metals in urban environments, we evaluated the natural variability in the chemical composition of the (epilithic and epiphytic) moss Hypnum cupressiforme and the epiphytic lichen Pseudevernia furfuracea from two reference areas in NE Italy. Green shoots of epilithic mosses and lobes of epiphytic lichens from larch branches showed rather homogenous composition and were selected for the exposure in nylon bags. As different physico-chemical pretreatments are usually applied to selected cryptogamic material before its exposure, we also evaluated the effects of oven-drying at 120 _C for 24 h, washing in 1 N HNO3 solution, and in 0.5% NH4 oxalate solution at 85 _C for 15 h on the chemical composition and morphology of water-washed moss shoots and lichen lobes. Pre-treatments remarkably changed the chemical composition of selected materials but not their surface morphology. In conclusion, the above results show that properly selected and treated H. cupressiforme shoots and P. furfuracea lobes have adequate chemical and morphological homogeneity to be used as active biomonitors of atmospheric deposition of trace elements. The overall evaluation of accumulation efficiency and reproducibility during the exposure in nets, and therefore the effective usefulness of different pre-treatment procedures has been discussed elsewhere. Anyhow, water-washed and oven-dried moss shoots resulted the most suitable material for monitoring trace element deposition in two urban environments.