Vol. 13, No.1 (May 2013) – Preface
In this Issue – A Snapshot of the Breadth of the Environmental Research on LAS
Readers,
Think of this issue of The CLER Review as a snapshot of the breadth of the continuing environmental research on linear alkylbenzene sulfonate (LAS), the leading cleaning agent (surfactant) in laundry detergents and cleaning products worldwide. The studies represent practically every aspect of environmental science: 1. Test methods (demonstrating both test material evaluation and method validation), 2. Biodegradation testing, 3. Environmental monitoring (with implications for public policy), and 4. Risk assessment (three papers).
The test methods study is the paper by Serrano et al., “Ultimate Biodegradation of Commercial Linear Alkylbenzene Sulphonates (LAS) under ISO 14593 Headspace CO2 Test: Compliance with EU Detergent Regulation 648/2004.” The Headspace CO2 Test is listed as the reference method for biodegradability testing under the 2004 European Union (EU) Detergent Regulation. Despite the listing of ISO 14593 as the reference method in the regulation, there are few data available for commercial surfactants. Various commercial LAS products were among the first surfactants to be reported tested with the test method. As Serrano et al. report, all of the LAS commercial products passed the test. And since LAS’ rapid and complete biodegradability in laboratory tests has been repeatedly demonstrated, the LAS results also serve as a further validation of the Headspace CO2 Test method.
Real world biodegradability testing on LAS was demonstrated in the paper by Mauffret et al., who studied LAS biodegradation in seawater. The authors conclude that microbial communities present in seawater have the ubiquitous capability to biodegrade LAS. These findings provide assurance that any residual levels of LAS that may be discharged into the marine environment will be biodegraded.
The environmental monitoring study by Cantarero et al. reported on the actual levels of LAS and soap in sewage sludge applied to soil in Spain as fertilizer. A draft working paper in the EU has proposed restriction on the levels of certain organic compounds, including LAS in sewage sludge. Based on the results on the monitoring study, more than 55% of anaerobic sewage sludge in Spain would exceed the proposed cut-off limit for LAS; thus, the sewage sludge could not be applied to soil in the preferred disposal method.
Previous studies have demonstrated that LAS levels in sewage sludge in Spain do not pose a risk to the terrestrial environment.1
The reason cited in the EU working paper for restricting LAS levels is that in standard tests for anaerobic biodegradation (this is distinct from aerobic biodegradation discussed above), LAS does not undergo anaerobic biodegradation while soap does. Based on laboratory test methods, levels of LAS in sewage sludge (which is primarily treated in anaerobic digesters) are predicted to be high while levels of soap are predicted to be low. Contradicting this prediction, the monitoring study found levels of soap in sewage sludge to be consistently higher than levels of LAS, suggesting that the rationale in the EU working paper for the cut-off limit on LAS is not factually based. In short, the monitoring study found that the EU working paper would exclude more than 55% of anaerobic sewage sludge in Spain from land application, the preferred disposal method. Furthermore, the sludge contained higher levels of soap than LAS, contrary to the key assumption for the cut-off limit on LAS.
There are three papers on the important topic of risk assessment. The first paper is by Rasmussen et al. and focuses on LAS and two other widely used surfactants in household detergents, alcohol ethoxylates and alcohol ethoxysulphates. The risk assessment is unique in that it is an aquatic (marine and freshwater) risk assessment that considers both the broader European environmental scenario and the more specific Danish environmental scenario. The study concludes that, based on the methods used in the study, use of LAS, alcohol ethoxylates, and alcohol ethoxysulphates in household detergents does not appear to present a risk to the aquatic environment. The final two papers in this issue are companion papers in that they were originally published together as part of a single large study. The papers were actually published several years ago, but we have decided to publish them in The CLER Review at this time because we often refer to them2 and have noticed that, despite their importance to the literature on LAS, they are not as renowned as they should be.
The two studies focus on developing a risk assessment for untreated wastewater discharged to the Balatuin River in The Philippines. Untreated wastewater discharge is a common occurrence in many parts of the world, and yet there is very little data to form an environmental risk assessment. The first paper, by Dyer et al., focuses on the influence of physical and chemical factors — including levels of LAS — on aquatic communities in the river, including algae, invertebrates, and fish. The study found that the critical factors impacting aquatic communities were low dissolved oxygen (DO) levels and high ammonia concentrations.
The second study, by McAvoy et al., developed a risk assessment model for untreated wastewater discharge. The model involves an impact zone concept in which the river can be thought of as a natural wastewater treatment system. After the river has recovered via “self-purification” (biodegradation of bulk organic compounds (BOD), conversion of ammonia to other compounds, etc.), it can be assessed by traditional risk assessment methods, focusing on DO and ammonia concentrations as critical parameters.
A key takeaway is that the data show that LAS biodegrades faster than BOD, the biodegradation of which is a key driver of low DO levels. Consequently, LAS concentrations are not critical factors which influence the risk assessment. LAS is certainly present in untreated wastewater. But this risk assessment shows that standard water quality parameters — DO, ammonia, and BOD — are in fact the critical factors for an aquatic risk assessment.
We think you will agree that the six studies in this issue indeed represent a remarkably complete snapshot of the breadth of the environmental research on LAS.
John Heinze, Ph.D.
Editor
1. Schowanek et al., The CLER Review, vol. 11, p. 42, 2007.
2. See for instance, J.E. Heinze, J. Surf. Deterg., vol. 15, p. 59, 2012