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Biodegradation is the most important mechanism for the total removal of chemicals from the environment. It is nature's way of getting rid of wastes by breaking down organic matter into nutrients that can be used by other organisms. As a result, the ability of a chemical to biodegrade is an indispensable element in the understanding of any risk posed by that chemical on the environment.

DEFINITIONS

LAS "Primary Biodegradation" is the transformation induced by microorganisms with formation of sulphophenyl carboxylates (SPCs) as biodegradation intermediates. This biodegradation stage corresponds to the disappearance of the parent molecule and the loss of interfacial activity as well as the toxicity to aquatic organisms.

Biodegradation proceeds further with the cleavage of the aromatic ring and the complete conversion of LAS and SPCs into water, CO2, inorganic sulphates and biomass. This step is also known as "Ultimate Biodegradation" or mineralization.

biodegradation

Field studies, which monitor the real-world behaviour of a substance, indicate that linear alkylbenzene sulphonate biodegrades rapidly and completely and does not accumulate in the environment. Extensive aquatic toxicity and safety evaluation data from more than 30 years of use as a detergent surfactant confirm that LAS is safe for aquatic populations. Field studies also confirm that even after 30 years of use, LAS has not accumulated in these environments, providing further scientific support for aerobic metabolism through oxygen diffusion in natural anaerobic environments.

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ANAEROBIC BIODEGRADATION OF LAS

Some policy makers use anaerobic biodegradability of surfactants as a criterion for determining their environmental acceptability. In this regard, the industry and the European Commission have conducted the following studies:

The ERASM report

The relevance of anaerobic biodegradability cannot be separated from other important properties of surfactants such as their sorptive behaviour, ecotoxicity profile and above all their aerobic biodegradation. In order to study these factors ERASM (Environmental Risk Assessment Management), a joint Research Group of AISE (International Association for Soaps, Detergents and Maintenance Products) and CESIO (European Council of Surfactant Producers), has conducted a comprehensive program to assess the relevance of Anaerobic Biodegradability as an environmental criterion of surfactants.

The ERASM report concludes that:

"It is therefore concluded that anaerobic biodegradability as a strict pass/fail criterion is not in line with the environmental interpretation and significance that should be given to the lack of this property for surfactants. For surfactants used today in detergents, rapid aerobic biodegradation as well as their sorptive and ecotoxicological properties, are key to making a realistic assessment of environmental compatibility. If a surfactant is rapidly degradable under aerobic conditions, and its transitory presence in anaerobic environments does not affect the function and structure of that environment (e.g. it is not inhibitory), then its anaerobic degradability is of minor importance."

view the ERASM report -

The Fraunhofer study

In the general context of the EU policy to modernise the European legislation on detergents, the Commission has undertaken to examine the anaerobic issues of surfactants. To this end, the Fraunhofer Institute was contracted to research the phenomenon of anaerobic biodegradation in the context of the total environmental impact of detergent surfactants.

The study was completed in July 2003 and covered the fifteen Member States of the European Union and 3 of the accession countries (Poland, Hungary, and Czech Republic).

The study concluded that the anionic surfactant (such as LAS) concentrations are low in surface water and are similar in all countries. These results also corroborate the high performance of the Waste Water Treatment Plant for removing surfactants. Moreover, no accumulation of the measured surfactants (mainly LAS, NP and derivatives, AE, DTDMAC/DSDMAC) has been observed in water bodies.

With regard to sediments, no accumulation of aerobically ready biodegradable surfactants has been observed, in particular for LAS, even over a period of several decades.

Regarding soil fertilisation, when the anaerobically treated sludge is used as fertiliser in agriculture, the surfactant concentration in sludge-amended soil is predicted to decrease rapidly because of the aerobic biodegradation process that occurs in soil.

Overall, the data analysis confirms that all surfactants must be ultimately and readily biodegradable under aerobic condition in order to prevent major environmental impact. This seems to confirm that aerobic biodegradation plays the main role in eliminating organic compounds.

According to the report, LAS is still the most cost-effective surfactant and the most flexible one for many cleaning purposes. Apart from the excellent performance in all household detergent or cleaning formulations, LAS can be produced, stored and transported in high concentrations, leading to lower storage and transport cost compared to the main potential alternatives.

The Fraunhofer study conducted for the European Commission corroborates the findings of industry's ERASM study of the year 2000.

Click here to view or download the study at the web site of the European Commission -

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USEFUL INFORMATION

The most relevant data on LAS biodegradability are summarized in the table below :

LAS

Protocol

Results

Screening, confirmatory

OECD 301
DOECD 303 A

> 99 (% primary biod.)

Ready test

OECD 301 B, D, E

Readily biodegradable

>70 (ultimate biod. % DOC removal)
>60 (ultimate biod. % CO2evolution)
>60 (ultimate biod. % O2 uptake)

Inherent test

OECD 302 A, B

95-98
(ultimate biod., % DOC removal)

Simulation test

OECD 303 A

80 -> 95
(ultimate biod., % DOC removal)

Biodegradation rate in activated sludge

Die-away

t0.5=0.6-0.7 hours (primary biod.)
t0.5=1.3-1.4 hours (ultimate biod.)

Biodegradation rate in river water

Die-away

Die-away

River monitoring

t0.5 = 12 hours (primary biod.)

t0.5 = 18 hours (ultimate biod.)

t0.5 = 1-3 hours (primary biod.)

Anaerobic biodegradation

ECETOC

ca.0 (% ultimate biod.)
30-90 (% primary biod.)

Biodegradation rate in soil

Field study

Laboratory study

t0.5 = 3-7 days (primary biod.)

t0.5 = 13-26 days (ultimate biod.)

Hydrolysis*

Research study

Decomposition:
60-70% in presence of inorganic acids at 150-200°C

Photolysis*

Research study

Degradation:
> 95% after 20 min. under mercury lamp (200-450 nm)

* :Not environmentally relevant experimental conditions

Ultimate Biodegradability of Commercial LAS (Na salt) as requested under Regulation (EC) Nº 648/2004 of 31 March 2004 on Detergents
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Useful references

Kimerle RA, RD Swisher, Reduction of aquatic toxicity of LAS by biodegradation, Water Res.
11: 31, 1977 Moreno A, J Ferrer, Toxicity towards Daphnia m. during biodegradation of various LAS, Tenside Surf. Det. 28: 129-131, 1991

Swisher RD, Surfactant biodegradation, 2° Edition, Marcell Dekker, New York, 1987

Fraunhofer Institut UMSICHT, Anaerobic Biodegradation of Detergent Surfactants, Oberhausen, 2003

ERASM, Report on the relevance of Anaerobic Biodegradation of Surfactants, Brussels, 1999