Environmental fate of amine oxide: Using measured and predicted values to determine aquatic exposure.

Amine oxide (AO) surfactants are used widely in North American household detergents resulting in >44,000mtons disposed down the drain annually. Due to AOs substantial down the drain disposal volume, wide dispersive use, and high aquatic toxicity, there is a need to evaluate ecological exposure and corresponding risk. This study refined the current knowledge regarding the fate of AO disposed down the drain through laboratory simulation studies to evaluate biodegradation in the sewer and during activated sludge wastewater treatment. A monitoring program which measured effluent AO concentrations for the dominant carbon chain lengths, C12 and C14, at 44 wastewater treatment plants (WWTP) across the continental US was also conducted. The study results were then used as input into probabilistic exposure models to predict US receiving stream concentrations. In three separate OECD 314A Sewer Water Die-Away studies AO was rapidly biodegraded with >76% mineralized by study completion and the geometric mean of the primary biodegradation rates being 0.184h-1. Two OECD 303A Activated Sludge WWTP Simulation studies showed rapid and complete biodegradation of AO with ≤0.09% of parent AO remaining in the effluent, ≤0.03% of parent AO sorbed to sludge solids, and >97% complete mineralization of AO. Monitoring at US WWPTs confirmed low levels of AO in effluents with mean C12 and C14AO concentrations of 52.8 and 20.1ng/L respectively. Based on the monitoring data, the 90th percentile concentrations of C12 and C14AO for 7Q10 low flow stream conditions were >2 orders of magnitude lower than the predicted no effect concentrations indicating negligible aquatic risk from AO in US receiving streams. This study verifies that AO is safe for the aquatic environment even at the currently high usage volumes due to rapid biodegradation during transit through the sewer and wastewater treatment.

Assessing the biodegradability of microparticles disposed down the drain.

Microparticles made from naturally occurring materials or biodegradable plastics such as poly(3-hydroxy butyrate)-co-(3-hydroxy valerate), PHBV, are being evaluated as alternatives to microplastics in personal care product applications but limited data is available on their ultimate biodegradability (mineralization) in down the drain environmental compartments. An OECD 301B Ready Biodegradation Test was used to quantify ultimate biodegradability of microparticles made of PHBV foam, jojoba wax, beeswax, rice bran wax, stearyl stearate, blueberry seeds and walnut shells. PHBV polymer was ready biodegradable reaching 65.4 ± 4.1% evolved CO2 in 5 d and 90.5 ± 3.1% evolved CO2 in 80 d. PHBV foam microparticles (125-500 µm) were mineralized extensively with >66% CO2 evolution in 28 d and >82% CO2 evolution in 80 d. PHBV foam microparticles were mineralized at a similar rate and extent as microparticles made of jojoba wax, beeswax, rice bran wax, and stearyl stearate which reached 84.8  ± 4.8, 84.9  ± 2.2, 82.7  ± 4.7, and 86.4 ± 3.2% CO2 evolution respectively in 80 d. Blueberry seeds and walnut shells mineralized more slowly only reaching 39.3  ± 6.9 and 5.1 ± 2.8% CO2 evolution in 80 d respectively.

Evaluation of anionic surfactant concentrations in US effluents and probabilistic determination of their combined ecological risk in mixing zones.

Alcohol sulfates (AS), alcohol ethoxysulfates (AES), linear alkyl benzenesulfonates (LAS) and methyl ester sulfonates (MES) are anionic surfactants that are widely used in household detergents and consumer products resulting in over 1 million tons being disposed of down the drain annually in the US. A monitoring campaign was conducted which collected grab effluent samples from 44 wastewater treatment plants (WWTPs) across the US to generate statistical distributions of effluent concentrations for anionic surfactants. The mean concentrations for AS, AES, LAS and MES were 5.03±4.5, 1.95±0.7, 15.3±19, and 0.35±0.13µg/L respectively. Since each of these surfactants consist of multiple homologues that differ in their toxicity, the concentration of each homologue measured in an effluent sample was converted into a toxic unit (TU) by normalizing to the predicted no effect concentration (PNEC) derived from high tier effects data (mesocosm studies). The statistical distributions of the combined TUs in the effluents were used in combination with distributions of dilution factors for WWTP mixing zones to conduct a US-wide probabilistic risk assessment for the aquatic environment for each of the surfactants. The 90th percentile level of TUs for AS, AES, LAS and MES in mixing zones were 1.89×10-2, 2.73×10-3, 2.72×10-2, and 3.65×10-5 under 7Q10 (lowest river flow occurring over a 7day period every 10years) low flow conditions. Because these surfactants have the same toxicological mode of action, the TUs were summed and the aquatic safety for anionic surfactants as a whole was assessed. At the 90th percentile level under the conservative 7Q10 low flow conditions the forecasted TUs were 4.21×10-2 which indicates that there is a significant margin of safety for the class of anionic surfactants in US aquatic environments.

Determination of biodegradation rates for surfactants and a fatty alcohol in aerobic sediment using a simplified test system.

The development of specific regulatory persistence criteria and a growing need to conduct risk assessments in sediment have increased the need to better understand fate in this compartment. A simplified test approach was developed to assess the fate of chemicals in aerobic sediments and used to evaluate the biodegradation of (14) C-labeled representative analogs of alcohol sulfate, alcohol ethoxylate, alcohol ethoxy sulfate, linear alkylbenzene sulfonate, and tetradecanol in 2 different sediments. The method provides kinetic data on primary and ultimate biodegradation in sediments as well as information on biodegradation pathways and metabolites. All test materials exhibited extensive biodegradation in both sediments; disappearance of parent exhibited biphasic kinetics, described by a 2-compartment model, and mineralization was coupled to parent disappearance with little accumulation of metabolites. The first-compartment decay rates ranged from 10.8 d(-1) to 17.1 d(-1) for tetradecanol, 2.54 d(-1) to 24.8 d(-1) for alcohol sulfate, 0.17 d(-1) to 0.75 d(-1) for alcohol ethoxylate, 0.41 d(-1) to 0.71 d(-1) for alcohol ethoxy sulfate, and 0.26 d(-1) to 1.25 d(-1) for linear alkylbenzene sulfonate. These rates corresponded to half-lives ranging from 0.041 d to 4.08 d. This method's simplicity and focus on only sediment-associated processes offer potential benefits over the current Organisation for Economic Co-operation and Development 308 aerobic sediment-water test. Environ Toxicol Chem 2016;35:2199-2208. © 2016 SETAC.

Widespread Microbial Adaptation to l-Glutamate-N,N-diacetate (L-GLDA) Following Its Market Introduction in a Consumer Cleaning Product.

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.

Fate of free and linear alcohol-ethoxylate-derived fatty alcohols in activated sludge.

Pure homologues of [1-14C] C12, C14, and C16 alcohols and the linear alcohol ethoxylates, AE [1-14C alkyl] C13E9 and C16E9 were tested in a batch-activated sludge die-away system to assess their biodegradation kinetics and to predict levels of free alcohol derived from AE biodegradation in treated effluent. First-order rates for primary biodegradation were similar for all alcohols (86-113 h(-1)) and were used to predict removal under typical treatment conditions. Predicted removals of fatty alcohols ranged from 99.76% to 99.85%, consistent with published field data. During the biodegradation of the AE homologues, lower than expected levels of fatty alcohol based upon the assumption that biodegradation occurs through central fission were observed. Rather than fatty alcohols, the major metabolites were polar materials resulting from omega oxidation of the alkyl chain prior to or concurrent with central cleavage. The amounts of free fatty alcohols that were formed from AEs in influent and escape into effluent were negligible due both to their rapid degradation and to the finding that formation of free alcohol through central cleavage is only a minor degradation pathway in activated sludge.

Effect of ethoxylate number and alkyl chain length on the pathway and kinetics of linear alcohol ethoxylate biodegradation in activated sludge.

Batch activated-sludge die-away studies were conducted with various pure homologs to determine the effect of ethoxylate number and alkyl chain length on the kinetics of primary and ultimate biodegradation of linear alcohol ethoxylates. The 14C-(ethoxylate) homologs C14E1, C14E3, C14E6, and C14E9 were used to investigate the effect of ethoxylate number, and 14C-(ethoxylate) homologs C12E6, C14E6, and C16E6 were used to examine the effect of chain length. Activated sludge was dosed with a trace concentration (0.2 microM) of each homolog, and the disappearance of parent, formation of metabolites, production of 14CO2, and uptake into solids were monitored with time. Ethoxylate number had little effect on the first-order decay rates for primary biodegradation, which ranged from 61 to 78 h(-1). However, alkyl chain length had a larger effect, with the C16 chain-length homolog exhibiting a slower rate of parent decay (18 h(-1)) compared to its corresponding C12 and C14 homologs (61-69 h(-1)). Ethoxylate number affected the mechanism of biodegradation, with fission of the central ether bond to yield the corresponding fatty alcohol and (poly)ethylene glycol group increasing in dominance with increasing ethoxylate number. Based upon the measured rates of primary biodegradation, removal of parent during activated-sludge treatment was predicted to range between 99.7 and 99.8% for all homologs except C16E6, which had a predicted removal of 98.9%. Based upon the measured rates of ultimate biodegradation, removal of ethoxylate-containing metabolites was predicted to exceed 83% for all homologs. These predictions corresponded closely with previously published removal measurements in laboratory continuous activated-sludge systems and actual treatment plants.