Polyethoxylated alkyl phenols: Relationship of structure to biodegradation mechanism

Using various isolation procedures and measurement by infrared spectroscopy, the mechanism of biodegradation of the polyethoxylated alkyl phenols (ABE) in the river water die‐away test has been ascertained. Degradation is shown to proceed by carboxylation of the alkyl chain and, in certain cases, by degradation of the ethylene oxide chain. Degradation of the ether chain has been found to take place only when the chain contains ten or less units of ethylene oxide. The analytical evidence points to the degradation of the ether chain by a hydrolysis mechanism. The effect of ether chain degradation on the measurement of residual surfactant by ultraviolet spectroscopy and the cobalt thiocyanate procedures has been demonstrated. Ether chain degradation causes the ABE results to be high by ultraviolet measurement and low by the cobalt thiocyanate procedures. Results of this investigation emphasize the necessity of understanding the mechanism by which degradation takes place, and the significant importance of that degradation, in the various biodegradability tests, before the applicability and reliability of any test for measurement of the residual surfactant can be evaluated.