Factors affecting the release of hydrophobic organic contaminants from natural sediments

Numerous physical and chemical changes in aquatic systems can affect the sorption and desorption of organic contaminants. In this study, the effects of competitive sorption, caustic treatment, and temperature on the release of sorbed chlorinated hydrocarbons and naphthalene from natural sediments were studied. The experiments were specially designed so that the results would reflect the nature of the irreversible compartment. The effect of competitive sorption fell into two categories. The release of chlorinated benzenes and hexachlorobutadiene from the reversible fraction in Lake Charles, Louisiana, USA, sediment was increased with the competitive sorption of naphthalene, while the release of naphthalene and 1,4-dichlorobenzene from the irreversible compartments in Dickinson, Texas, USA, sediment was unaffected by the sorption of trans-cinnamic acid at 100 mg/L. Similarly, preliminary experiments showed that caustic treatment of sediments did not enhance the desorption from the irreversible fraction. Also, the enthalpy of sorption associated with the irreversible compartment was -21.60 +/- 0.76 kJ/mol, indicating that sorption was via simple van der Waal's forces. Experimental results in this study support a previously proposed irreversible sorption mechanism in which irreversible sorption is attributed to the physical entrapment of organic molecules in sediment matrices after the hydrophobic partitioning.