Fate of heavy metals related to vehicular traffic emissions in Rome in the last 50 years.

In a city like Rome the principal source of pollution is vehicular traffic. In the last 10 years owing to the introduction of unleaded petrol, a decrease of Pb occurred in soils and air. In the meantime the introduction of cars equipped with catalytic converters originate the emission of pollutant like Pt, Pd, and Rh. This event represents a good occasion to evaluate the interaction between urban environment and traffic pollution. The aim of this study is to reconstruct the fate of time depended accumulation of some heavy metals mainly related to traffic emission during the last 50 years in the city of Rome. A good opportunity to do that is represented by sediment sampling and studying of two artificial ponds located inside two green areas in Rome. The first one was built in the 19th century inside Villa Doria Pamphilj Park, the second at the time of the Olympic games in 1960 located in a city area called EUR. The oldest is located in a natural valley flooded by constant water adduction; the second one is a cemented basin refuelled by an aqueduct. Common features characterize these lakes. Both are located near roads travelled by more than 70,000 cars/day and heavy sedimentation is acting. This last feature is very important, in fact it is possible to record time-pollution trends studying two core sediments from these ponds. Time resolution is related only to sampling frequency (EUR: 4 cm / Villa Pamphilj: 5 cm). A sedimentation model has been developed using 137Cs as stratigraphic marker and applying 210Pb activity method. In both cases radiocaesium activity related to Chernobyl accident is well recognized.The main difference between the two lakes is that in Villa Pamphilj pond the sediments result mainly from material released from soil erosion and, secondarily, from direct dust fallout. In EUR area the pond basin is physically isolated from surrounding soils and detritus result principally composed of diatoms, related to the algae activity and secondary, from dust fallout. Elemental analyses confirm these observations. Unfortunately Pb content doesn’t show a well recognizable trend during time. This is caused by the fact that soils in the study areas are mainly developed on volcanic rocks with a volcanism characterized by a high content of metals. It is therefore very important to calculate elemental ratios with elements strictly related to vehicular emissions for outlining the effective trend.