Vol. 6, No. 1 – Preface (October 2000)
Important News from CESIO 2000 – LAS Biodegrades Even in the Absence of Air
A major scientific breakthrough was reported at the CESIO 2000 Congress – evidence was presented from several independent research groups using several lines of evidence that LAS undergoes biodegradation even in the absence of air, i.e. under anaerobic conditions. This special issue of The CLER Review focuses on this and the other key scientific findings on LAS presented at CESIO 2000, the 5th World Surfactants Congress held earlier this year in Florence, Italy.
Anaerobic biodegradation is used as a pass/fail criterion for the White Swan environmentally friendly labeling, or eco-labeling, program in Scandinavia. In this program, if a cleaning agent (surfactant) or other ingredient in a detergent product did not biodegrade under oxygen-free conditions in a laboratory test, the laundry detergent could not receive the White Swan seal. However, as pointed out in two papers from CESIO 2000 (AISE-CESIO Task Force, “Assessment of the Environmental Relevance of Anaerobic Biodegradation of Surfactants,” and
J.L. Berna, “The Misuse of Anaerobic Biodegradation Criteria in Regulatory Affairs of Surfactants”), use of anaerobic biodegradation as a pass/fail criterion is not justified by the environmental data on surfactants. Real world monitoring data demonstrate that lack of anaerobic biodegradation has little environmental consequence for detergent ingredients like LAS that rapidly and completely biodegrade in the presence of air (aerobically).
Furthermore, the White Swan program’s exclusive reliance on a single test method, the ECETOC-28 test, to measure anaerobic biodegradation is a major limitation of the pass/fail criterion. Failure of previous researchers to demonstrate anaerobic biodegradation of LAS using this standard anaerobic biodegradation test method is apparently due to reliance of the test on an indirect measure of biodegradation, production of biogas. Direct measurement of LAS reveals substantial losses during the test, even under conditions rigorously designed to exclude any possible leakage into or out of test vessels. Consequently, the findings of LAS anaerobic biodegradation reported below demonstrate that the pass/fail criterion on anaerobic biodegradation is simply wrong for LAS and likely wrong for other materials as well.
Although partial anaerobic biodegradation (removal of the sulfate group, or desulfonation) of LAS had been reported last year by Denger and Cook (The CLER Review, vol. 5, pages 62-66, 1999), the demonstration was limited to sulfate depleted conditions, situations that may occur in soil but perhaps not widely in other parts of the environment. The new results suggest that anaerobic biodegradation of LAS can occur under a variety of conditions:
- D. Prats and others at the University of Alicante, Spain (“The Use of Specific Analytical Methods to Assess the Anaerobic Biodegradation of LAS”) report that LAS undergoes anaerobic biodegradation using modifications of the ECETOC-28 test. The results demonstrate substantial biodegradation of LAS under anaerobic conditions such as those that might be found in an anaerobic digester of a wastewater treatment plant. The finding of no significant biogas production suggests that the anaerobic biodegradation of LAS may be partial or incomplete under these test conditions.
- J.L. Sanz and others at the Autonomous University of Madrid (“Evaluation of the Inhibition Potential of LAS to the Methanogenic Process”) conducted tests designed to measure the potential of high concentrations of LAS to inhibit anaerobic biodegradation. As part of these tests, they included specific analytical measurements to confirm that the amount of LAS added was still present at the end of the 14-day test period. Substantial losses of LAS occurred during this brief test period even at the highest concentrations of LAS added to the test, concentrations much higher than occur in digesters of sewage treatment plants. Consequently, the results not only confirm anaerobic biodegradation of LAS but indicate that anaerobic biodegradation can take place at the highest LAS levels observed in sewage treatment plants.
- I. Angelidaki and others of the Denmark Technical University (“Anaerobic Transformation of LAS in Continuous Stirred Tank Reactors Treating Sewage Sludge”) report loss of 14 to 25% of the LAS in a laboratory anaerobic biosolids digester. According to the authors, only the reversibly bound (bioavailable) portion of the LAS was anaerobicly biodegraded, providing an explanation for partial transformation of LAS in sediment or biosolids systems. The further implication is that the fraction that is not bioavailable would not be expected to inhibit biosolids or sediment organisms and thus is unlikely to pose a risk to organisms that may be present.
- V.M. León and others of Cadiz University in Spain (“Identification of LAS Biodegradation Intermediates in Anoxic Marine Coastal Sediments”) found low LAS concentrations, and relatively high LAS biodegradation intermediates (sulfophenycarboxylates or SPCs), in anaerobic marine sediments below a treatment plant discharging primary treated (settled, but not biologically treated) sewage. This finding suggests that anaerobic biodegradation of LAS occurs in real world sediments.
Other key findings from the CESIO 2000 conference include:
- Cook and Hrsak (“The Complete Degradation of LAS is Becoming Better Understood with Pure Cultures of Bacteria”) report that individual steps in the biodegradation pathway of LAS are being identified with the help of isolated microorganisms (pure cultures of various bacteria) that are capable of degrading specific steps in the LAS biodegradation process. The result of such study is that the detailed biodegradation pathway for LAS is becoming completely understood.
- M.T. Garcia and others (“Bioavailability of LAS from Activated Sludge”) report that LAS binding to sewage biosolids (activated sludge) from treatment plants consists of two types, a reversible binding fraction that consists of LAS that is available for biodegradation (bioavailable) and a fraction that is irreversibly bound, likely consisting of insoluble LAS calcium and magnesium salts, that are not bioavailable. This fraction is likely not available to be biodegraded or to cause toxicity to earthworms or other terrestrial organisms which may be exposed to it from the application of biosolids as a soil fertilizer and conditioner.
- D. Prats and others (“Elimination of LAS in Sewage Biosolids by Composting”) report that residual levels of LAS and other organics in sewage biosolids can be efficiently reduced by composting, an important consideration for Denmark, where restrictions have been placed on the use of sewage biosolids as soil fertilizer based on the content of LAS and other organics. Although these restrictions, at least for LAS, are not based on sound science (The CLER Review, vol. 5, pages 2-60, 1999), and have been strenuously opposed by the detergent industry on that basis, this research provides a treatment option that allows sewage biosolids to continue to be used as a soil fertilizer, the environmental preferred method of biosolids disposal.
- M.S. Holt and others (“Monitoring Studies in the UK Designed for the Validation of the Geo-referenced Exposure Assessment Tool for European Rivers (GREAT-ER)”) report the results of an environmental monitoring study focused on the removal of LAS in various sewage treatment plants and in rivers and streams receiving residual levels of LAS in treated sewage from the outflow of treatment plants. The results demonstrate high removal efficiencies (90 to 97%) of LAS even in the less efficient “trickling filter” plants and rapid rates of biodegradation in receiving waters.
- C. Gandolfi and others (“Validation of the GREAT-ER Model in the River Lambro Catchment”) conducted an environmental monitoring study on a major river in Italy. Despite discharges of treated and partially treated sewage from numerous towns and cities in the area, the study documents low, harmless levels of LAS in the Lambro due to the rapid biodegradation of LAS in river water.
- S.W. Morrall and others (“Use of Isomer Distributions to Characterize the Environmental Fate of LAS”) describe detailed studies on the various structural isomers of the C12 homologue of LAS. While the results document differences between the isomers as would be expected based on their difference structures, the study also documents the rapid biodegradation of LAS in a US river, with LAS concentrations return to background levels within 24 hours of receiving a 100-fold higher than background load of LAS and other materials from a trickling filter sewage treatment plant discharging to the river.
- L. Cavalli and others (“Surfactants in Sediments”) reviewed the available scientific literature on LAS and other surfactants in river and ocean sediments. The presence of trace levels of surfactants is to be expected because of their widespread use in laundry detergents and other cleaning products, the disposal of these products after use to sewers and the presence of residual levels of these materials in treated wastewater discharged to rivers and the oceans. The review concludes that levels of LAS on sediments are generally below levels that might pose a risk to sediment organisms but more data is needed, particularly on other surfactants.
The findings presented at CESIO 2000 illustrate not only the unsurpassed breadth of the research on LAS, but also the continuing commitment of CLER, the detergent industry and environmental scientists to better understanding the safety of even very well studied materials such as LAS. The demonstration of LAS anaerobic biodegradation under modifications of the ECETOC-28 test should not only enable detergent products containing LAS to receive the White Swan eco-label but to major revisions in the anaerobic biodegradation criteria used by the White Swan and other environmental labeling programs.
John E. Heinze, Ph.D.