INFLUENCE OF SALINITY UPON SEDIMENT-WATER PARTITIONING OF AROMATIC-HYDROCARBONS

Concern over the potential acute and long-term effects of oil pollution on marine environments has lead to a resurgence of investigations of the fate, transport and chemical transformations of aromatic hydrocarbons associated with spilled oil, exploration and operational discharges and produced water discharges in coastal marine and estuarine environmental systems. The nature of the particle reactivity or sorption/desorption equilibria which control the fate, transport and chemical transformations of hydrocarbons has been investigated on various sediment types (a range of organic carbon and particle sizes) over a range of salinities. No significant differences were observed between sorption and desorption equilibrium constants (K-d). Significant increases in sorption/desorption constants were observed with increasing salinity. A thermodynamically-based model is presented which allows the estimation of both the Setchenow constant as well as the chemical activity coefficient of the compound in the sediment organic phase from experimental data. The results of the application of this model suggest that the increase in sorption with salinity is the result of two phenomena: salting out as the result of electrolyte effects on the aqueous activity coefficient of the solute and the salting out of the sediment-organic matter resulting in changes in the charge and conformation with increasing ionic strength.