Ultimate and Primary Biodegradation of a Range of Nonpolymeric and Polymeric Surfactants in Seawater

Surfactants are chemicals commonly used in a wide range of domestic and industrial products. In the present study, ultimate biodegradation of 18 surfactants representing different classes (including several polymeric alcohol ethoxylates [AEs]) was determined in seawater at 20 °C by a Closed Bottle test method. After 28 days of incubation, 12 surfactants reached 60% biodegradation and were considered to be readily biodegradable in seawater. The results for the six additional surfactants indicated that the 60% pass level may be reached by extended incubation time, or that reduced biodegradation could be associated with toxicity of the chemicals. All these six surfactants were biodegraded >20% after 28 days, indicative of primary biodegradation in seawater. 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. Biodegradation experiments of the AE C12 EO9 (3 to 18 EO groups) in a carousel system at 20 °C with natural seawater 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 seawater. 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. Environ Toxicol Chem 2023;42:1472-1484. © 2023 SETAC.