The use of moss transplants for monitoring heavy metals deposition is briefly reviewed. The methodological study concerns the effects of different types of pre-treatment on data variability. Epiphytic samples of Hypnum cupressiforme were collected from an unpolluted area, treated in different ways, and the resulting bags were exposed in two sites in the province of Trieste (NE ltaly) with widely different pollution: a natural woodland far from urban and indust,ial centers, and a site near an iron smelting industry in the industriai area of Trieste. The content of eight heavy metals (Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb) was measured in 80 moss samples by atomic absorption spectrophotometry. The results, which represent a contribution to the standardization of the moss bags technique, concem: a) variability of metal conteni in mosses from natural areas: this is influenced by soil contamination; it is advisable to collect epiphytic samples, avoiding those growing near the base of the trunks; b) effects of different washing treatments on metal contents: compared to distilled water, washing with an acid solution is particularly efficient in removing metal ions associateci with the cell wall, but produces more variable data; c) uptake capacity of exposed moss bags: this is not influenced by the type of washing, and even short periods of exposure were sufficient to reveal differences in metal depositions between the two sites.
