Development of a chronic toxicity structure-activity relationship for alkyl sulfates

Much of the historical data regarding the toxicity of alkyl sulfate (AS) surfactants to aquatic organisms have been compromised due to excessive 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 developed and acute and chronic toxicity data were obtained for several AS structures. Acute toxicity increased linearly with increased alkyl chain length (CL) from C12AS to C16AS. However, a parabolic response was observed for reproduction where toxicity increased with alkyl chainlength 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 points no observed effect concentration, lowest observed effect concentration, maximum acceptable toxicant concentration, EC50, and EC20 yielded the best fit for EC20 (R2=0.99). Quantitative structure–activity relationships for AS, based on acute toxicity alone, overpredict chronic toxicity at chainlengths greater than C14AS. Use of the quadratic model [EC20(M)=5.12×10−7(CL)2−1.49×10−5(CL)+11.1×10−5] is advocated for use in environmental risk assessment.