ORIGIN AND PATTERNS OF DISTRIBUTION OF TRACE-ELEMENTS IN STREET DUST - UNLEADED PETROL AND URBAN LEAD

The elemental composition, patterns of distribution and possible sourc es of street dust are not common to all urban environments, but vary a ccording to the peculiarities of each city. The common features and di ssimilarities in the origin and nature of street dust were investigate d through a series of studies in two widely different cities, Madrid ( Spain) and Oslo (Norway), between 1990 and 1994. The most comprehensiv e sampling campaign was carried out in the Norwegian capital during th e summer of 1994. An area of 14 km(2), covering most of downtown Oslo and some residential districts to the north of the city, was divided i nto 1 km(2) mapping units, and 16 sampling increments of approximately 150 g were collected from streets and roads in each of them. The frac tion below 100 mu m was acid-digested and analysed by ICP-MS. Statisti cal analyses of the results suggest that chemical elements in street d ust can be classified into three groups: ''urban'' elements (Ba, Cd, C o, Cu, Mg, Pb, Sb, Ti, Zn), ''natural'' elements (Al, Ga, La, Mn, Na, Sr, Th, Y) and elements of a mixed origin or which have undergone geoc hemical changes from their original sources (Ca, Cs, Fe, Mo, Ni, Rb, S r, U). Soil resuspension and/or mobilisation appears to be the most im portant source of ''natural'' elements, while ''urban'' elements origi nate primarily from traffic and from the weathering and corrosion of b uilding materials. The data for Pb seem to prove that the gradual shif t from leaded to unleaded petrol as fuel for automobiles has resulted in an almost proportional reduction in the concentration of Pb in dust particles under 100 mu m. This fact and the spatial distribution of P b in the city strongly suggest that lead sources other than traffic (i .e. lead accumulated in urban soil over the years) may contribute as m uch lead, if not more, to urban street dust. (C) 1997 Elsevier Science Ltd.