Heavy metal accumulation from Diesel engine combustion by moss and lichen in bags in controlled conditions

Heavy metal (HM) deposition from atmosphere can be assessed by environmental biomonitors such as moss and lichen used as transplants (bags). Mosses and lichens accumulate large amounts of HMs directly over their whole surface showing a chemical composition that reflects atmospheric inputs. The bioaccumulation efficiency of mosses and lichens is essentially due to passive processes of interception and scarcely related to their vitality; it mainly depends on the ability to entrap particulate matter, on the high surface to mass ratio (especially in mosses) and on the cation exchange capacity of their cell walls, due to negative-charged constituents. Anyhow it is quite difficult to establish the relative contribution of natural (i.e. soil, mineral dust, volcanic emissions, sea salts, etc.) and anthropogenic sources (mainly vehicular traffic, together with industrial and domestic combustion processes) to the concentration of bioaccumulated trace elements. In urban area where both sources occur this distinction would be fundamental in order to define appropriate actions of pollutant prevention. This work focuses on the reliability of active biomonitoring by moss and lichen transplanted in "bags" in the evaluation of trace metals emitted in controlled conditions. The analysis was carried out at the exhaust of a Unijet Common Rail (CR) diesel engine equipped with a Catalyzed Diesel Particulate Filter (CDPF). It was considered. engine operating conditions reproducing the typical driving states in urban area, especially in high road traffic, In addition, a submicroscopical and microanalytical characterisation of PM directly collected from engine exhausts was performed by SEM/EDS.