Contribution of settling measurements to the study of polycyclic aromatic hydrocarbons' (PAHs) mobilisation during resuspension of PAHs-associated sediment

This paper aims to investigate the effect of the settling behaviour of sediment particles during resuspension on the mobilisation of pollutants such as polycyclic aromatic hydrocarbons (PAHs). Sediments were collected in different areas (basin, channel, beach) of a Mediterranean harbour, located in the south of France (the Grau du Roi harbour), and then separated into different size fractions: large (80-1000 μm), intermediate (40-80 μm), and fine (< 40 μm). Total PAHs concentrations in the initial sediment ranged from 320 to 1043 μg kg^-1. Study of the settling behaviour of the PAH-contaminated sediment revealed two sedimentation regimes: sedimentation by mass, which exhibits a sharp interface between the supernatant and the deposit, and sedimentation by clarification with no interface. It appears that sediment particles settle either by the clarification regime or by a combination of the two sedimentation regimes, depending on the size fraction. Particle size distribution monitoring during the settling process allowed the identification of sediment particles less than 20 μm which remain in the water column up to 20 min after resuspension and appear to be the ones that can potentially mobilise PAHs.