Ultimate and primary biodegradation of a range of non-polymeric and polymeric surfactants in seawater.

Abstract

Surfactants are a major class of chemicals commonly used in a wide range of domestic and industrial products. In this study, ultimate biodegradation of 18 surfactants representing different classes (including several polymeric alcohol ethoxylates), was determined in seawater (SW) at 20°C by the OECD306 Closed Bottle test method. After 28 days of incubation, 12 surfactants reached 60% biodegradation and were considered to be readily biodegradable in SW. The results for the 6 additional surfactants indicated that the 60% threshold level may be reached by extended incubation time, or that reduced biodegradation could be associated with toxicity of the chemicals. All these 6 surfactants were biodegraded >20% after 28 days, indicative of primary biodegradation in SW. Polymeric ethoxylates with high numbers of ethylene oxide (EO) groups (40-50 EO groups) were more slowly biodegraded than polyethoxylates with 4 to 23 EO groups. A primary biodegradation experiments of the alcohol ethoxylate (AE) C12-EO9 (3 to 18 EO groups) in a carousel system at 20°C with natural SW and a surfactant concentration of 500 µg/L, showed rapid primary biodegradation by targeted analyses of the AE, with >99% primary biodegradation after 2 days of incubation. The surfactant depletion coincided with temporary formation of polyethylene glycols, suggesting that central fission is an important degradation step in SW. A primary biodegradation experiment in the carousel system with C12-EO9 was conducted in the presence of suspended particulate materials (SPMs; marine phytoplankton and clay particles), showing that the presence of SPMs did not hamper the primary biodegradation of the surfactant. Separation of fractions in 20 µm steel filters indicated some particle association of the surfactant. This article is protected by copyright. All rights reserved. Environ Toxicol Chem 2023;00:0-0. © 2023 SETAC.