DEVELOPMENT OF A CHRONIC TOXICITY STRUCTURE-ACTIVITY RELATIONSHIP FORALKYL SULFATES

Much of the historical data regarding the toxicity of alkyl sulfate (A S) surfactants to aquatic organisms have been compromised due to exces sive loss of the parent material via biodegradation and precipitation- processes especially important during chronic tests. To minimize these issues, a novel flow-through system for Ceriodaphnia dubia was develo ped and acute and chronic toxicity data were obtained for several AS s tructures. Acute toxicity increased linearly with increased alkyl chai n length (CL) from C12AS to C16AS. However, a parabolic response was o bserved for reproduction where toxicity increased with alkyl chainleng th from C12AS to C14AS, but decreased with increased chain length from C14AS to C18AS. Soluble vs precipitated forms of AS contribute to the parabolic relationship. A quadratic approach using the chronic end po ints no observed effect concentration, lowest observed effect concentr ation, maximum acceptable toxicant concentration, EC50, and EC20 yield ed the best fit for EC20 (R-2 = 0.99). Quantitative structure-activity relationships for AS, based on acute toxicity alone, overpredict chro nic toxicity at chainlengths greater than C14AS. Use of the quadratic model [EC20(M)= 5.12 x 10(-7)(CL)(2) - 1.49 x 10(-5)(CL) + 11.1 x 10(- 5)] is advocated for use in environmental risk assessment. (C) 1997 by John Wiley & Sons, Inc.