Vol. 7, No. 1, April 2002
Something Old, Something New
This issue of The CLER Review highlights the scientific progress on LAS by considering an “old” and a “new” topic. The old topic is an area of environmental research that was first considered over ten years ago – the question of the terrestrial safety of linear alkylbenzene sulfonate (LAS), the major cleaning agent or surfactant used in laundry detergents and cleaning products worldwide.
A terrestrial safety assessment is an important component of an overall safety assessment of laundry detergent ingredients because wash water is typically disposed of into sewers, which in developed countries are connected to sewage treatment plants. These use microorganisms to breakdown (or biodegrade) the organic compounds present in sewage, producing carbon dioxide, water, salts and additional microorganisms. Excess microorganisms, called biosolids or sewage sludge, are continually removed during the sewage treatment process and either placed in landfills, incinerated, or spread on soil as a fertilizer. Use as fertilizer is generally considered to be the best option for the environment because the nutrients are recycled in the soil. Since a portion of the LAS present in sewage ends up in the biosolids, a terrestrial risk assessment considers the safety of the LAS in biosolids applied to soil.
Although a terrestrial risk assessment of LAS was published in 1990,1 the seven papers in this edition of The CLER Review illustrate the new depth and breadth of the scientific under-standing of the terrestrial environment and the safety of LAS.
Gejlsbjerg and others (“Mineralization of Organic Contaminants in Sludge-Soil Mixtures”) studied the biodegradation of LAS and several other materials in biosolids-soil mixtures. The results demonstrate that LAS undergoes complete biodegradation (mineralization) and the rate of mineralization is rapid (over 75% in two months) provided the mixtures are not water saturated, which reduces the rate of biodegradation by reducing the exposure to air.
Prats and others (“Elimination of Xenobiotics During Composting”) report that the LAS present in sewage sludge can be nearly 100% eliminated by using the sludge to make compost. The rate of LAS biodegradation observed was quite rapid, with half the LAS biodegraded within 7 to 9 days (LAS half life = 7-9 d).
The remaining five papers are a comprehensive assessment of the environmental safety of LAS in biosolids used as fertilizer (“Effects and Risk Assessment of Linear Alkylbenzene Sulfonates in Agricultural Soil”).
Elsgaard and others (“1. Short-term Effects on Soil Microbiology”) determined the lowest concentration of LAS that had a measurable effect on soil microorganisms. These lowest effect concentrations ranged from less than 8 to 22 milligrams LAS per kilogram dry weight of biosolids, or <8-22 parts per million.
In a second study (“2. Effects on Soil Microbiology as Influenced by Sewage Sludge and Incubation Time”), Elsgaard and others found that the application of LAS in biosolids to soil had reduced effects compared to tests in which LAS was added directly to soil (an unrealistic scenario since the LAS is in the biosolids).
Holmstrup and Krogh (“3. Sublethal Effects on Soil Invertebrates”) reported that LAS had less effect on earthworms and other soil organisms than on soil microorganisms (higher LAS concentrations were required to produce effects).
Holmstrup and others (“4. The influence of Salt Speciation, Soil Type and Sewage Sludge on Toxicity using the Collembolan Folsomia fimetaria and the Earthworm Aporrectodea caliginosa as Test Organisms”) found that the type of soil (sand, loam or clay) had little influence on the level of LAS required to produce effects in earthworms or soil insects (springtails).
Jensen and others (“5. Probabilistic Risk Assessment of Linear Alkylbenzene Sulfonates in Sludge-amended Soils”) conducted a safety assessment of LAS using the results of the proceding studies plus data on maximal levels of LAS in biosolids and maximal application rates of biosolids to soil in Denmark. The assessment concludes that “LAS does not pose a significant risk to fauna, plants and essential functions of agricultural soils as a result of normal sewage sludge amendment.”
The new topic is a safety assessment of LAS in the oceans, an important part of the environment that can now be examined because of the extensive database of scientific information available on LAS. Numerous studies have documented the safety of LAS in rivers, streams and lakes,2 but consideration of LAS safety in estuaries and coastal areas is a new topic.
Temara and others (“Marine Risk Assessment: Linear Alkylbenzene Sulfonates (LAS) in the North Sea”) used environmental modeling and real world monitoring data to predict maximal LAS levels in the North Sea. These levels are then compared to the levels of LAS that produce no effects (predicted no-effect concentrations or PNEC) on oceanic fish and other organisms that live in the open sea (pelagic species). The assessment concludes, “Given that the maximal expected estuarine and marine concentrations are 3 to >30 times lower than the PNEC, the risk of LAS to pelagic organisms in these environments is judged to be low.”
These studies on LAS illustrate the nature of scientific progress – topics that have been explored previously, such as terrestrial safety assessment, have been expanded to include additional soil organisms and different soil properties. The results confirm what has been known from many years of practical experience in the US and Europe – the use of biosolids as fertilizer is beneficial to the soil and the presence of residual levels of LAS in the biosolids from sewage treatment does not pose a risk to the terrestrial environment.
Existing research on the environmental safety of LAS in rivers, streams and lakes has enabled research to be extended to an important part of the environment, the oceans. Again, the conclusion is that LAS does not pose a risk to the seawater environment. Nonetheless, environmental research is continuing, and will continue for the foreseeable future, including new studies on LAS environmental safety. This is the nature of scientific research – better answers can be provided to old questions and new questions can now be considered.
John E. Heinze, Ph.D.
1. Mieure, J.P., J. Waters, M.S. Holt and E. Matthjis, Terrestrial Safety Assessment of Linear Alkylbenzene Sulfonate, Chemosphere 21:251-262 (1990).
2. See The CLER Review, vols. 1-6.