The use of mosses as environmental metal pollution indicators

Naturally growing mosses have been extensively employed for surveying trace metal deposition from the atmosphere. Mosses represent suitable monitors for assessing the long-term accumulation of deposited airborne metals by virtue of their physicochemical properties. Indeed, they occur in almost all terrestrial ecosystems because, for their ability to tolerate long periods of drought, they may even colonize areas with extreme environmental conditions; they obtain most of their elemental supply from the atmosphere and efficiently retain many elements received from precipitation because they have a high surface:volume ratio, a simple anatomy and no cuticle. The monitoring technique using mosses has, therefore, led to reliable estimates of large-scale geographic patterns of trace metal deposition, in spite of possible flaws due to variabilities in local elemental concentrations and interferences with soil dust contamination. While in northern Europe from the late 1960s mosses have been used as passive or active bioindicators, the countries in southern Europe have initiated to participate to the European programme on heavy metal atmospheric deposition in Europe measured from mosses only since 1995. The objectives of the present chapter are therefore: i) to show the last developments of the biomonitoring technique by mosses in Europe; ii) to compare the surveys made in European southern countries, namely France, Spain and Italy; iii) to indicate the changes made to the recommendations of European protocol defined by Rühling in 1994 because of different environmental conditions in these geographic areas; iv) to provide information that can be useful for the next large-scale surveys. Finally, as moss biomonitoring example, a more detailed study is reported regarding the use of mosses as environmental bioindicators in order to evaluate the metal atmospheric deposition in different areas in Piedmont (Italy).