IMPACT OF SEDIMENT PARTITIONING METHODS ON ENVIRONMENTAL SAFETY ASSESSMENT OF SURFACTANTS

Selection of laboratory methods for partitioning and toxicity tests of sediments has a significant impact on interpretation of aquatic safet y of surfactants. This is the case for the assessment of the sediment toxicity of C12 linear alkylbenzene sulfonates, LAS. In this study, th e batch-equilibrium partition coefficient (K(d)) was measured as a fun ction of organic carbon, cation exchange capacity, and quantity of sed iments. The quantity of sediment was varied from a low of 5 g per 1,00 0 ml of water to a level of 500 g to 500 ml of water. The measured K(d ) decreased by an order of magnitude when the ratio of water to sedime nts increased to 1:1, and as a consequence of this observation, LAS on suspended solids was included in the quantitaton of LAS in the water phase. When measured K(d) values were then used to predict the toxicit y (based on known aquatic toxicity concentrations of LAS using Cerioda phnia dubia), LAS was calculated to be an order of magnitude less toxi c by the low-solids test compared to the high-solids test system. This work reaffirms that selection of a laboratory test to assess environm ental safety must be made on the basis of its correlation to the real- world behavior of the surfactant.