Deposition of platinum group elements and polycyclic aromatic hydrocarbons on ryegrass exposed to vehicular traffic

Abstract - Along highways, platinum group elements (PGE: Pt, Pd and Rh) and polycyclic aromatic hydrocarbons (PAHs) produced by the vehicle traffic can be deposited on grass and soil, leading to a risk of contamination through the food chain via farm animals. We studied the deposition of platinum group elements and polycyclic aromatic hydrocarbons on ryegrass pots exposed along a highway with 65 000 vehicles per day for 90 days in summer and autumn. After this exposure period, the ryegrass pots were transferred to a remote area for 5 weeks. The Pt, Pd and Rh concentrations were determined in ryegrass samples using inductively coupled plasma mass spectrometry (ICP-MS) and PAHs were quantified by high-pressure liquid chromatography (HPLC). Our results show that Pd and Rh concentrations increased with time of exposure. Pd concentrations ranged from 1.5 to 6.8 ng/g dry weight (d.w.), Rh from 1.5 to 3 ng/g d.w. and Pt from 0.3 to 1.4 ng/g d.w. The total PAH concentrations varied from 6 to 175 ng/g d.w. PGE and PAH deposition on ryegrass near the highway occurred mainly for the first weeks of exposure. During the 5 weeks following the exposure, the levels and profiles of PAHs and PGE (except Rh) in highway grasses transferred to a remote area did not significantly decrease, suggesting a potential risk of contamination for dairy ruminants.