Characterisation of road sediments near Bordeaux with emphasis on phosphorus

Abstract

Road sediments from the region of Bordeaux (France) were analysed for trace metals, hydrocarbons (including Polycyclic Aromatic Hydrocarbons, PAHs) and phosphorus. The aim of the study was to assess their potential risk for the environment. The sediments were collected by means of a sweeper. The particles are mostly sandy clay loam and silty clay loam with 5.6–8.3% CaO. Heavy metal concentrations are generally below the French and Dutch standards for polluted soils, but a few samples have higher concentrations, e.g., 547 mg kg⁻¹ for Zn, and 222 mg kg⁻¹ for Pb. PAH concentrations are above the Dutch target value for polluted soils, and could be a threat to the environment: pyrene (2600 µg kg⁻¹) and fluoranthene (1400 µg kg⁻¹) have the highest concentrations, whereas chrysene (340 µg kg⁻¹) has the lowest. Consequently, these sediments must be considered as waste according to the French circular n° 2001-39 from 18 June 2001 and cannot be disposed of anywhere. The Standards Measurements and Testing (SMT) protocol for sequential extraction of phosphorus in sediments was used to determine the forms of phosphorus in the samples. Total phosphorus concentration is 620 mg kg⁻¹ on average, with a maximum of 933 mg kg⁻¹; organic phosphorus content is low (36 mg kg⁻¹ on average). The protocol could be slightly amended, especially with regards to organic phosphorus at low concentrations and could then be used for the determination of phosphorus in other materials such as sludge from detention ponds.