The fate of detergent surfactants in the sewer can be studied both in laboratory tests and in field experiments. The laboratory studies can be used to determine the rate of disappearance of a test molecule as a function of residence time and estimate its half-life in a given habitat. In addition, important information can be obtained on the mechanism of degradation. Field studies can determine the actual environmental concentrations of surfactants in raw sewage which can then be compared with the expected concentration based on consumption volumes. The difference between the measured and predicted concentration provides an estimate for the disappearance of the test chemical during its travel in the sewer and confirms the results of the laboratory tests. This paper focuses on the fate of a number of important representative anionic, nonionic and cationic surfactants, in the sewer. The results of laboratory die-away studies showed that, in general, the half-life for disappearance in the sewer was in the order of hours for Fatty Alcohol Ethoxylate (AE), Fatty Alcohol Ethoxy Sulphate (AES) and Di-Ethyl-Ester Di-methyl-Ammonium Chloride (DEEDMAC). These laboratory findings for AES were confirmed by monitoring actual raw sewage reaching municipal sewage treatment plants. In addition, a field study demonstrated that the concentration of glucose amides (GA) is considerably reduced during its travel in the sewer. These complementary laboratory and field studies provide key information for the safety assessment of surfactants. They demonstrate that the concentration of surfactants can be significantly reduced in the sewer resulting in a rapid reduction of the environmental loading, which is particularly important in environmental situations where inadequate or no sewage treatment exists.

An approach has been devised for determining the kinetics of primary and ultimate biodegradation of chemicals under realistic conditions in activated sludge. A radiolabeled test chemical is dosed at an environmentally relevant concentration into biotic and abiotic activated sludge. Periodically, samples are removed, acidified, and analyzed by LSC to determine 14 CO 2 evolution. In addition, samples are flashfrozen, lyophilized, and extracted to recover the parent and metabolites, which are analyzed by Rad-TLC. The extracted residue is then sequentially extracted with cold TCA, ethanol/ether, hot TCA, and 10 N NaOH and combusted to determine incorporation into constituents of biomass. Loss of parent, 14 CO 2 evolution, and incorporation into biomass are fitted to a variety of decay or production functions using nonlinear regression to identify the best models and estimate rates. Linear alkylbenzene sulfonate ( 14 C-ring C 12 -LAS) was tested as model compounds in two sludges. Within 8 h, 41-44% was evolved as 14 CO 2 , 1-2% remained as parent, 24-33% was incorporated into biomass, and 10-15% was present as intermediates, primarily sulfophenylcarboxylates. Primary and complete biodegradation were best described by a first-order model. First-order rate constants for LAS were 0.96-1.10 h -1 for primary loss and 0.50-0.53 h -1 for complete degradation. This approach provides an accurate and comprehensive kinetic picture of biodegradation under realistic conditions as well as information on the mechanism of biodegradation.

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l-Glutamate-N,N-diacetate (L-GLDA) was recently introduced in the United States (U.S.) market as a phosphate replacement in automatic dishwashing detergents (ADW). Prior to introduction, L-GLDA exhibited poor biodegradation in OECD 301B Ready Biodegradation Tests inoculated with sludge from U.S. wastewater treatment plants (WWTPs). However, OECD 303A Activated Sludge WWTP Simulation studies showed that with a lag period to allow for growth (40-50 days) and a solids retention time (SRT) that allows establishment of L-GLDA degraders (>15 days), significant biodegradation (>80% dissolved organic carbon removal) would occur. Corresponding to the ADW market launch, a study was undertaken to monitor changes in the ready biodegradability of L-GLDA using activated sludge samples from various U.S. WWTPs. Initially all sludge inocula showed limited biodegradation ability, but as market introduction progressed, both the rate and extent of degradation increased significantly. Within 22 months, L-GLDA was ready biodegradable using inocula from 12 WWTPs. In an OECD 303A study repeated 18 months post launch, significant and sustained carbon removal (>94%) was observed after a 29-day acclimation period. This study systematically documented field adaptation of a new consumer product chemical across a large geographic region and confirmed the ability of laboratory simulation studies to predict field adaptation.

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