Updated HERA Report Provides Substantial Assurances on Linear Alkylbenzene Sulfonate (LAS) Safety
November 16, 2007
The environmental assessment section of the LAS HERA report has been extensively updated to include:
- New data on LAS concentrations in sewage sludge,
- Clarification of the LAS biodegradation rate in sludge-amended soil,
- Updating the Predicted No Effect Concentration (PNEC) value for LAS in the terrestrial environment, and
- Calculation of a PNEC value for LAS in sludge.
The new data and analysis strongly supports the conclusion of the environmental assessment that “the ecological risk of LAS is judged to be low.”
The HERA (Human and Environmental Risk Assessment) project is a European voluntary initiative launched in 1999 by AISE,1 representing the formulators and manufacturers of household cleaning products, and Cefic,2 representing the suppliers and manufacturers of the raw materials. The purpose of the HERA Project is to provide a common risk assessment framework for the household cleaning products industry, and show that this process will deliver evaluated safety information on the ingredients used in these products in an effective and transparent way.
Linear alkylbenzene sulfonate (LAS), as the major cleaning agent (surfactant) used in laundry and cleaning products worldwide, was one of the first cleaning product ingredients to be assessed by the HERA Project (full assessment completed May 2002) and one of the first to be updated based on the comments from the HERA External advisory Panel (May, 2004). Because of its importance to the LAS HERA report, it was published in its entirety inThe CLER Review (vol. 9, number 1, December 2004).
As the HERA project notes, no HERA document can be considered “final” because it is still open for additional public comment and updating on new research. Once again LAS is a leader in this field as one of the first HERA reports to be updated after an External Panel review based on the availability of extensive additional data. This updating of the LAS HERA (HERA Project, October 2007) provides a substantial increase in our understanding of the environmental properties of LAS, particularly those properties related to the terrestrial environment. The update considerably strengthens the database of studies supporting the already very strong assurances provided by the HERA report on LAS safety.
Because of the number and significance of these findings – and the research they report – this article reviews and summarizes the most important updates. The page numbers cited in the text refer to the LAS HERA report. Key supporting studies are also noted.
Updates to Risk Assessment and Environmental Effects
The LAS HERA report considers possible environmental effects, and conducts scientific safety assessments, called risk assessments, for all environmental compartments where LAS may be present. These include soil, sewage sludge, sediments and water.
The most extensive update is the calculation of the LAS Predicted No Effect Concentration (PNEC) for the soil environment (LAS HERA, pp. 30-1). The PNEC is a key value because it is compared to the Predicted Environmental Concentration (PEC) to determine a risk ratio. A PEC/PNEC ratio below 1.0 indicates low risk to the environment.
This updated PNEC value – 35 milligrams LAS per kilogram dry weight soil (35 mg/kg dw) – is based on an in-depth review and updating of the extensive LAS terrestrial ecotox data (Krogh et al., The CLER Review , p. 8; Jensen et al., The CLER Review , p. 20), including the results of over twenty toxicity studies on agricultural crops and plants, earthworms and other soil invertebrates, and microbial processes in the soil. The PNEC value also takes into consideration the fact that the primary route of LAS transport to soil is from use of sewage sludge as a soil fertilizer and takes into account the physical form of LAS in the sludge as well as variations in soil types.
Use of this PNEC value gives a PEC/PNEC ratio of 0.04, indicating low risk for the soil environment (p. 32).
The LAS PNEC value for sludge (sewage biosolids) have been calculated for the first time in the updated HERA report (p. 31). This value (49,000 mg/kg dw) is calculated from the soil PNEC value and the European Union Technical Guidance Document guidelines for the application of sewage sludge on agricultural soil (Schowanek et. al. The CLER Review , p. 42).
The PEC/PNEC ratio for sludge is also less than 1.0, indicating low risk (p. 32).
A new study on two sediment organisms ( Comber et al., The CLER Review , p. 68) is provided to support the sediment PNEC value of 8.1 mg/kg dw (pp. 31-2). Use of this PNEC value was previously shown to give a PEC/PNEC value of 0.65, indicating low risk to the sediment environment (p. 32).
Regarding the aquatic environment, data are reported (p. 25) for an additional chronic aquatic toxicity study on a fish and three other aquatic organisms (Versteeg & Rawlings, The CLER Review , p. 82 ). These data support the PNEC value (p. 30) of 0.27 mg per liter (L) from a well conducted mesocosm study (Belanger et al. 2002) and from single-species chronic studies (van de Plassche et al. 1999).
Use of this PNEC value was previously shown to give a PEC/PNEC value of 0.17, indicating low risk (p. 32).
The updating of the PNEC values based on the extensive new data available provides added confidence in the conclusion of the HERA assessment of low LAS risk to soil, sewage sludge, sediments and water.
Updates to the Exposure Assessment
The Exposure Assessment section of the LAS HERA has been significantly updated:
- The section on biodegradation (pp. 10-1) has been updated to included three recent studies conducted according to Good Laboratory Practices (GLP) guidelines. These studies demonstrate that LAS passes standard tests for ready biodegradability. While it has been known for years that LAS is rapidly and completely biodegradable under real world conditions, use of testing procedures and GLP guidelines set by the Organization for Economic Cooperation and Development (OECD) ensures that the testing results meet the highest international standards.
- The primary biodegradation half-life for LAS (3 hours) in the aquatic environment is provided, based on three real world studies (p. 11). Since the half-life is the period of time for half of the material to biodegrade, the biodegradation half life for LAS means that after 3 hours one-half the LAS will remain, after 6 hours one-quarter will remain, after 9 hours one-eight, etc. This is truly an impressive rate of biodegradation.
Biodegradation in the Absence of Air (Anaerobic Biodegradation)
- Additional data is provided (pp. 11-2) to confirm previous observations that LAS undergoes biodegradation under anaerobic conditions although this biodegradation appears to be limited in scope.
- The update also includes the opinion of the European Commission’s expert Scientific Committee on Health and Environment Risks (SCHER) that the requirement for full (ultimate) biodegradability under anaerobic conditions is not an effective method for ensuring environmental protection. The SCHER opinion points out that ready biodegradation (as demonstrated by LAS) is a much more important property for environmental acceptability and does not support proposals to restrict detergent ingredients (surfactants) that do not undergo full biodegradation under anaerobic conditions.
- Additional data are also presented on the LAS concentrations required to inhibit anaerobic processes in sewage treatment plants (p. 12). Comparison of inhibitory concentrations (14 mg/L) to those required to inhibit aerobic processes (PNEC = 3.5 mg/L) indicates that LAS concentrations that are protective of aerobic processes will also be protective of anaerobic processes.
- Extensive additional data are presented (pp. 12-3) to support the conclusion that LAS undergoes rapid biodegradation in the soil environment (maximum primary biodegradation half-life = 7 days). This half-life means that after 28 days – the usual minimal period between sludge application to soil and crop planting – LAS levels in soil will be only one-sixteenth of their initial level.
Environmental Monitoring and Modeling
- Inputs for modeling have been updated with 2005 LAS use data (collected by the HERA project, p. 10) and with LAS melting point and boiling point data from the 2005 OECD assessment ( The CLER Review , Vol. 10, Number 1, December 2005). This has resulted in updating of all of PEC values based on modeling. However, real world monitoring data are used for PEC/PNEC calculations.
- New data from US and European monitoring studies ( Sanderson et al., The CLER Review , p. 110; Temmink & Klapwijk, The CLER Review , p. 136 ) have been added to the section on environmental monitoring studies (p. 16), providing a fuller discussion of the available real world data. The US and European data is consistent in indicating that LAS concentrations in river water below sewage treatment plants are generally below 0.05 mg/L, the PEC concentration used in environmental risk assessment cited above.
- Additional data ( Versteeg & Rawlings, The CLER Review , p. 82 ) and discussion have been added to the section on the potential bioaccumulation of LAS in aquatic organisms (pp. 21-2). These data strongly support the calculated bioconcentration factor for commercial LAS (LAS having an average alkyl chain length of C11.6) of 87 L/kg, a value that indicates low concern for LAS bioaccumulation in aquatic organisms.
Sewage Treatment Plants, Sludge and Soil
- For modeling of environmental exposures, the distribution of LAS in sewage treatment plants (79% biodegradation, 20% to sludge and 1% release to water) are explicitly stated (p. 15).
- Extensive additional data (pp. 17-8) are also provided on the levels of LAS in sewage sludge, leading to more refined LAS PEC values for sludge (5.56 g/kg dw for the mean; 15.07 g/kg dw at the upper 95 percentile of the distribution, Schowanek et. al. The CLER Review , p. 42 ). These PEC values are used in the PEC/PNEC calculations for environmental risk assessment mentioned above.
Updates to Substance Characterization
- Manufacturing methods for linear alkylbenzene (LAB), the key intermediate in the manufacture of LAS, have been updated (p. 9) to indicate that 75% of the production in the European Union uses the HF process, 20% uses the fixed bed process and 5% uses the AlCl 3 process, based on 2005 ECOSOL4 data.
- LAS use (demand) in Europe in 2005 was 430 kilotons with over 80% used for household products, based on AISE data (p. 10).
- New data is provided on a key physical-chemical property of LAS, the critical micelle concentration (pp. 7-8).
Updates to the Executive Summary
The Executive Summary has been updated to reflect the updates to the environmental assessment section, including:
• New data on LAS concentrations in sludge,
• Clarification of the LAS biodegradation rate in sludge-amended soil,
• Updating the PNEC value for LAS in the terrestrial environment, and
• Calculation of a PNEC value for LAS in sludge.
The new data and analysis strongly supports the environmental assessment conclusion that:
“The risk characterisation as expressed by the PEC/PNEC ratio was below 1 for all environmental compartments. It was concluded that the ecotoxicological parameters of LAS have been adequately and sufficiently characterized and that the ecological risk of LAS is judged to be low.”
Belanger SE, JW Bowling, DM Lee, EM LeBlanc, KM Kerr, DC McAvoy, SC Christman, DH Davidson (2002), Integration of aquatic fate and ecological responses to LAS in model stream ecosystem, Ecotoxicol. Environ. Safety 52 : 150-171.
Human and Environmental Risk Assessment, LAS, Linear Alkylbenzene Sulfonate
(CAS No. 68411-30-3), October 2007, Version 3.0
Van de Plassche EJ, JHM de Bruijn, RR Stephenson, SJ Marshall, TCJ Feijtel, SE Belanger (1999), Predicted no-effect concentrations and risk characterization of four surfactants: LAS, AE, AES, and soap, Environ. Toxicol. Chem. 18 : 2653-2663.
1. AISE, the international Association for Soaps, Detergents and Maintenance Products is the official representative body of this industry in Europe. See: http://www.aise.eu/
2. Cefic, the European Chemical Industry Council, see: http://www.cefic.be/ .
3. Research in this area is continuing as demonstrated by the recent paper by P.A Lara-Martin et al. included in this volume of The CLER Review, p.98.
4. ECOSOL is a sector group of the European Chemical Industry Council (CEFIC) and represents the European producers of LAB. See: http://www.lasinfo.org/
1. Screening Information Data Set, the OECD name for the minimum data requirements for evaluation of the properties of any chemical submitted for health and environmental assessment.
2. OECD member countries include: Australia, Austria, Belgium, Canada, Czech Republic, Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Japan, Korea, Luxembourg, Mexico, Netherlands, New Zealand, Norway, Poland, Portugal, Slovak Republic, Spain, Sweden, Switzerland, Turkey, United Kingdom, and the United States.