Impact of turbidity and hydrophobicity on PAH release from sediment assessed by passive sampling

Sediments can act as reservoirs for hydrophobic contaminants, such as polycyclic aromatic hydrocarbons (PAHs), but can also release these pollutants into the water, posing risks to aquatic life. Conventional risk assessments typically focus on total sediment concentrations, even though the bioavailable fraction provides a more accurate measure of ecological risk. This study aimed to explore how sediment resuspension and contaminant hydrophobicity influence contaminant release into the water. We conducted an experiment where the release of four PAHs (acenaphthene, fluorene, phenanthrene, and fluoranthene) from an artificial sediment was studied at different resuspension treatments. Polyethylene passive samplers were used to sample PAHs released from sediment and water turbidity was used as a proxy for sediment resuspension. We identified a turbidity threshold at 2.7 NTU, below which PAH release was primarily driven by diffusion from sediment pore water, whereas at higher turbidity, resuspension and desorption processes played a more dominant role. Hydrophobicity was a critical factor for contaminant release: contaminants with a log K OW below 4.3 were more likely to be released at low turbidity, whereas those with a log K OW above 4.5 were released more at higher turbidity. Taken together, the results show that the release of contaminants from sediment into the water column is influenced by contaminant hydrophobicity and turbidity. • Hydrophobicity and turbidity jointly influence contaminant sediment release. • Release of contaminants with log K OW >4.5 increases under high turbidity. • Chemical activity allows extrapolation of lab results to field conditions. • Polymer passive samplers improve sediment risk assessments in turbid conditions.