An aquatic hazard assessment was conducted for branched and linear nonionic surfactants using toxicity and biodegradation measurements. Four nonionic alcohol ethoxylate surfactants with different degrees of branching (ranging from 0.1, essentially linear, to 4.0 internal methyl groups per hydrophobe) were evaluated for neat surfactant toxicity, degradation in laboratory sewage treatment units, and aquatic toxicity of treated effluents. Acute testing with neat surfactants showed ranges for EC50s of 1.3 to 11.6 mg/L for Daphnia, 1.6 to 6.1 mg/L for Pimephales promelas (fathead minnow), and 1.5 to 11.4 mg/L for Microtox®. Chronic testing of algae showed NOECs of 1 to 10 mg/L and maximum acceptable toxicant concentrations (MATCs) of 0.8 to 14.2 mg/L. Seven‐day chronic estimation tests showed MATCs of 0.6 to 41.4 mg/L for Pimephales promelas and 1 to 14 mg/L for Daphnia. Effluents collected from treatment units receiving a 50‐mg/L surfactant feed at 25°C showed no acute toxicity to either Daphnia or fathead minnows, with the exception of a unit containing nonylphenol ethoxylate. Chronic effluent toxicity was greatest in effluent from the nonyl‐phenol ethoxylate unit and least in the effluent from the linear alcohol ethoxylate unit. Chronic toxicity of the highly branched C13 alcohol ethoxylate effluent was greater than that for the linear alcohol ethoxylate unit effluent.

A number of ethoxylated nonionic surfactants differing in hydrophobe branching and chainlengths have been evaluated for environmental responses. Screening biodegradation tests show that those nonionics having more than one methyl group per hydrophobe degrade considerably slower than those having less extensive branching. Continuous flow-through activated sludge tests, simulating actual waste treatment, show that the more highly branched nonionics biodegrade more slowly and less extensively than those with less hydrophobe branching. In addition, treated effluents originating from influents containing the more highly branched nonionics tend to be more surface active and more toxic to aquatic species than those originating from influents containing surfactants with less hydrophobe branching. Under conditions simulating plant stress, such as high surfactant concentrations in the influent or low temperature, biodegradation of the highly branched nonionics was considerably less extensive, while biodegradation of the linear nonionics was not affected to any measurable degree compared to more normal operating conditions. KEY WORDS: Activated sludge, alcohol ethoxylates, aquatic toxicity, linear and branched hydrophobes, nonylphenol ethoxylates, primary and ultimate biodegradation.

A new thermospray liquid chromatography/mass spectrometry (LC/MS) method for quantitative determination of trace levels of alcohol ethoxylates (AE) in dilute aqueous environmental samples has been developed. This method has been validated for use in aquatic safety assessments to determine concentrations of total AE and individual AE species. This validation was accomplished by determination of recoveries of spiked AE samples from waste treatment plant effluents and receiving waters. The method distinguishes highly branched propylenebased AE from isomeric linear ethylene-based AE. Surfactants are used in large volumes in a broad variety of household and commercial detergents and cleaning products. After use, the surfactants are usually disposed into a wastewater treatment system and the effluents ultimately are released into surface waters. Biodegradation and other removal mechanisms greatly reduce the mass and concen-' Shell Development Co.

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This report describes a method for obtaining the concentrations of the total and individual alcohol ethoxylate (AE) species in sewage treatment plant (STP) effluents by using electrospray liquid chromatography/mass spectrometry (LC/MS). This is a more advantageous method for quantitative analysis of AE in environmental matrices as compared with a previous thermospray LC/MS method. This new method is more sensitive, uses less solvents, utilizes a deuterated internal standard blend [C 13 D 27 O(CH 2 CH 2 O) n H, where n varies from 0 to 21 with an average of n = 9], which corresponds more closely to the AE, and it is a more robust instrumental technique. In this report, we document the results for validation of the electrospray LC/MS method by spike recovery of AE from STP effluent and influent samples. JAOCS 74, 765-773 (1997).