Evaluation of the interactions between hydrophobic organic pollutants and suspended particles in estuarine waters

Hydrophobic organic pollutants have a low aqueous solubility and tend to be adsorbed by suspended particulates, leading eventually to their storage in bed sediments. However, studies on the adsorption behaviour of extremely hydrophobic organic contaminants are scarce, and require more in-depth investigations. In this work, partition of two classes of hydrophobic contaminants was studied first in well-defined mineral particles covered with well-characterised humic substances, moving on to mixed end-member samples from the Tees, Tamar and Humber estuaries along a salinity gradient. Such chemicals partitioned more strongly to humic coatings than to estuarine particles, and the organic carbon normalised partition coefficient (Koc) values were well correlated with the aromaticity of organic coatings, suggesting that organic matter on estuarine particles consists of very complex mixtures with varying affinity for pollutant molecules. The partition coefficient (Kp) for permethrin and bis(2-ethylhexyl) phthalate decreased with pH but increased with salinity, due to increased chemical hydrolysis in higher pH waters and decreased solubility in saline waters. The organic coatings on particles induced a more negative charge, due to the presence of uncomplexed carboxylic and phenolic hydroxyl groups. Estuarine suspended particles showed invariant electrophoretic mobility above 3 PSU salinity.