Abstract
Urban surface contamination, by atmospheric deposits as well as human activities, is a major concern for urban pollution management. Besides coarse street deposits which are clearly perceived and easily removed, suspended solid (SS) surface loads and contamination by heavy metals and hydrocarbons are rarely assessed although they could be of major importance with regards to combined or separate server overflow (CSO and SSO) impacts. Both dry and wet vacuum sampling procedures have been first compared, in the laboratory, using dry and sieved clay or street deposits. Then the wet vacuum sampling procedure has been refined, coupling the injection of water and the hand-brushing of the surface prior to its vacuum cleaning, and evaluated on a car parking area close to the University. Finally this procedure has been assessed in Béarn Street within the ‘Le Marais’ district in Paris centre, and 34 samples have been analysed for metal and eight for aromatic hydrocarbon contamination. Heavy metal concentrations (0.1–1.7 g kg −1 dry wt. Cu, 0.9–6.1 g kg −1 dry wt. Pb and 1.5–4.6 g kg −1dry wt. Zn) within street deposit samples collected in Paris centre, indicate a high contamination, especially for copper and zinc, as compared to reported data. Total polyaromatic hydrocarbons (PAHs) are in the 3–11 mg kg −1 dry wt. range, thus approximately 10 times less contaminated than dry atmospheric deposits. This paper presents data obtained and discusses the difficulties encountered when sampling street deposits in busy areas of a city like Paris. The water jet street cleaning procedure used by Paris city workers was tested for its efficiency, by comparison of surface loads before and after the cleaning procedure. Although solids cleaning efficiency is highly variable (20–65%) and somewhat higher for particles larger than 100 μm, particulate metal cleaning efficiency is even more variable (0–75%) and particulate PAHs appear not to be significantly removed.
Highlights
Urban surfaces receive deposits issued from more or less remote sources Žcar traffic, industries, waste incineration, domestic heating., through atmospheric transport as well as from local human activities
The wet vacuum sampling allowed a collection of 12.2 g dry wt. my2 for the first assay and 1.5, 1.1 and 1.0 g dry wt. my2 for three successive assays on the same area: the sum of these four samples represent a surface load of 15.9 g dry wt. my2, which means that the first assay yielded only 80% of this sum
One should note that a 4-l injection, even coupled with hand brushing, is insufficient for a total urban deposit sampling on an asphalt surface
Summary
Urban surfaces receive deposits issued from more or less remote sources Žcar traffic, industries, waste incineration, domestic heating., through atmospheric transport as well as from local human activities. The sampling of dry and wet atmospheric deposits can be achieved either directly or through a roof outlet. Soils are generally much more polluted in the immediate vicinity of major roads ŽHarrison and Johnston, 1985; Hewitt and Rashed, 1991., which suggests that a significant part of pollution due to traffic has a very short residence time in the atmosphere, and cannot be measured by atmospheric deposition sampling techniques. Both remote and locally produced deposits contribute to urban run-off pollution. Their quantity, their composition, and their physical characteristics Žat least their grain size. should be characterised in order to determine their transport under wet or dry conditions, related both to urban wash-off as well as to the efficiency of usual street cleaning procedures
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