Total, degradable, labile, percolable, colloidal, soluble fractions of hydrophobic organic contaminants in five sediments before and after aerobic and anaerobic maturation

Abstract : This study aimed to quantify the potential for degradation and emission of hydrophobic organic contaminants (HOC: PAHs, PCBs and TPH) from different sediment in oxic and anoxic storage conditions. Degradable fractions were measured by monitoring concentrations for 1.5 year under drained condition and one year under waterlogged condition. Fractions of hydrophobic contaminants with fast, slow and very slow desorption rate were measured by adsorption on Tenax TA. The concentrations of HOC emitted during a standard percolation column tests were measured and the dissolved organic matter was speciated following standardized protocols. The free dissolved concentrations fractions were determined by passive sampler LDPE. These levels were compared with concentrations calculated by the classical equations of solubility in water according to various parameters based mainly on the hydrophobicity of the contaminants. Total concentrations change very little during maturation. The majority of HOC is desorbable only at a slow or very slow rate. The concentrations of the percolates are controlled by colloidal organic material, and are therefore much higher than the dissolved one, and are on the other hand not well estimated by the current equations of solubility. It is clear from this work that the emission of sediment contaminants should be measured by percolation tests and not calculated by equations that don’t take into account the colloidal organic matter fraction.