EGS Seminar – Tuesday 6th March 2012

Tuesday 06^th March, *E0.05, John Dalton East Building, from 1.00-2.00pm. Sandwiches, coffee and tea are available from 12.30 pm in room *E402.

Geochemical Mapping of Urban Soils and Road Dusts: Towards Improved Risk Assessments

Raquel Cardoso, MMU

Urban soil quality is of concern under current UK contaminated land legislation in terms of potential impacts on human health and the need for sustainable development. Another environmental media that is a likely source of potentially harmful substances (PHS), with possible deleterious human health effects due to close proximity to the receptors, is road dust sediment (RDS). Studies of PHS in RDS and soils of urban areas have been published; yet little is known about the spatial, geochemical and mineralogical linkages between these two different media - urban agglomerations tend to grow exponentially and so does the importance of RDS and soil characterization and monitoring. The aim of this research is to characterize PHS presence in these media, explore the spatial, geochemical and mineralogical linkages, and produce novel mineralogical data on the PHE/particulate relationships within and between soils and RDS.

Geochemical datasets are composed of 144 RDS and 300 soil samples, collected across 75 Km2 of Manchester urban centre. PHE maximum and average concentrations, determined by XRF, are generally higher in soils than in RDS. Geographic information systems (GIS) allowed the spatial detection of contamination hotspots for these media, where PHE concentrations (namely for Cr, Ni, Cu, Zn, Pb, As and Cd) were in excess of the regional 90th percentile. Spatial analysis pointed to localised contamination sources as main influences on RDS composition, which vary considerably over short distances. However, spatial distribution of PHE in soil highlighted broader areas with systematically high concentrations. Principal component analysis (PCA) has evidenced important PHE associations both for soils and RDS. PCA of grain size data obtained by laser diffractometry revealed that, in RDS, the 63-125µm fraction might act as hosts for PHE. SEM-EDS analysis supported this observation, but the source(s) of these grains still needs further investigation.

This detailed geochemical and mineralogical characterization of both soil and RDS, as well as their spatial associations, will allow a better understanding of PHE dynamics in urban systems and add vital knowledge on the risks posed to human populations by PHE exposure.