The distribution of automobile catalysts-cast platinum, palladium and rhodium in soils adjacent to roads and their uptake by grass

Hooda, P.S., Miller, A. and Edwards, A.C. (2007) The distribution of automobile catalysts-cast platinum, palladium and rhodium in soils adjacent to roads and their uptake by grass. Science of the Total Environment, 384(1-3), pp. 384-392. ISSN (print) 0048-9697

Official URL: http://dx.doi.org/10.1016/j.scitotenv.2007.05.040

Abstract

The introduction of automobile catalysts has raised environmental concern, as this pollution control technology is also an emission source for the platinum group elements (PGE). The main aim of this study was to assess the concentrations of Pt, Pd, Rh and Au in soil and grass herbage collected adjacent to 5 roads. Soil and grass samples were collected from 4 fixed distances (0, 1, 2 and 5 m) from the road edge at each site. PGE and Au were determined by ICP-MS in all samples after acid digestion. The maximum soil Pt, Rh and Pd concentrations were measured at the road perimeters. Averaged across the sites, the Pt and Rh concentrations of 15.9+/-7.5 microg Pt kg(-1) and 22.40+/-4.73 microg Rh kg(-1) at 0-m distance decreased to 2.04+/-1.7 microg Pt kg(-1) and 3.51+/-1.96 microg Rh kg(-1), respectively at 5-m away from the roads. Pd concentrations were much higher than Pt or Rh, ranging from 120.8+/-12.0 microg Pd kg(-1) (0-m) to 84.2+/-10.9 microg Pd kg(-1) (5-m), possibly due to differences in its use, emission and/or soil chemistry. Au showed little or no change with distance from the roads. However, the average Au concentration of 18.98+/-0.98 microg Au kg(-1) provides clear evidence of some input possibly due to attrition of automobile electronics. No straightforward influence of traffic flow rates on PGE distribution was found. A combination of dispersal impeding local features and slow moving and stop-and-start traffic conditions or fast moving traffic with flat open spaces may have offset the expected impacts. Rh and Pt soil concentration accounted for 66% and 34% (P<0.01) of the variability observed, respectively in their plant concentrations. Grass Pd and Au concentrations had no relationship with their respective soil concentrations.

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