Biodegradability Performance of Surfactants

Biodegradation Performance of Innospec's Light, Sulfate-Free Surfactants *Eigenmann & Veronelli is the distributor of Innospec in Turkey.

Background

Many personal care products end their life cycles in aquatic ecosystems as a result of "waste disposal" processes, where the toxicity and biodegradation performance of ingredients are critical to ensuring environmental safety. In recent years, biodegradability has become a fashionable term among environmentally conscious consumers, and many major brands in the industry are shifting toward more sustainable products by committing to ambitious targets for transitioning to 100% biodegradable formulations within the next 10 years. Innospec offers a wide range of primary surfactants for personal care products, including our light, sulfate-free isethionate and taurate product lines:

Biodegradation Test Methods

Typically, the biological degradation of organic substances by microorganisms in sewers, wastewater treatment plants (WWTPs) and receiving environments (surface water, soil and sediments) occurs under aerobic conditions, that is, in the presence of oxygen. However, since aerobic biological degradation requires high amounts of oxygen, under certain conditions the availability of oxygen can become rate-limiting. Low oxygen levels can be encountered in sludge digestion tanks at WWTPs or in deeper sediments where anaerobic biological degradation can occur by more specialized microorganisms. To determine the biodegradation performance of Innospec's isethionate and taurate surfactants under aerobic and anaerobic conditions, a series of internationally standardized screening-level tests were applied. These methods range between OECD 301A-F (Ready Biodegradability under Aerobic Conditions) and OECD 311 (Anaerobic Biodegradability of Organic Compounds in Digested Sludge). OECD 301 tests are used to screen for ready (rapid) biodegradability of chemicals in aerobic aqueous solutions. Isethionate and taurate surfactants are incubated for 28 days in mineral medium containing a microorganism inoculum. The degradation of test substances over time is measured using CO₂ production (OECD 301B) or O₂ consumption (OECD 301D) as an indicator of complete (ultimate) biological degradation to water, CO₂ and nutrients. Positive controls/reference substances are included in the test to control test results and demonstrate inoculum viability. OECD 311 test is a stringent screening for the biodegradability of chemicals in anaerobic aqueous solution. Washed and diluted digested sludge was incubated for 60 days in sealed containers in mineral test medium, separately with isethionate and taurate surfactants. CO₂ and CH₄ production, as a measure of anaerobic degradation, was determined by measuring the increase in pressure in the headspace of the test containers. A significant portion of the produced CO₂ dissolves in the aqueous phase or is converted to carbonates. This inorganic carbon (IC) is also measured at the end of the test. Positive controls/reference substances are included in the test to control test results and demonstrate inoculum viability.

Results

The Innospec range of isethionate and taurate surfactant products has been shown to demonstrate impressive performance in OECD 301 and 311 biodegradability tests, as seen in the figures below: All isethionate and taurate surfactants meet the criteria for readily biodegradable classification according to OECD 301 test guidelines. SLMI (Sodium Lauroyl Methyl Isethionate) has been found to be anaerobically biodegradable according to OECD 311, which is also applicable to SLI (Sodium Lauroyl Isethionate) on a read-across basis (because both substances exhibit similar chemical structure). For SCI, historical OECD 311 data is also available demonstrating that the substance is anaerobically biodegradable (data not shown in the figures). SMOT (Sodium Methyl Oleoyl Taurate) was actually anaerobically biodegradable under OECD 311 test conditions, passing the positive control (sodium benzoate). Since SMOT has a longer alkyl chain length compared to SMCT (Sodium Methyl Cocoyl Taurate) and SMLT (Sodium Methyl Lauroyl Taurate), both of the latter substances are considered anaerobically biodegradable on a read-across basis.

Conclusion

Innospec's light, sulfate-free anionic isethionate and taurate surfactants are an ideal choice for skin and hair cleansing applications. These surfactants are not classified as environmentally hazardous according to EU CLP/GHS, and they demonstrate excellent biodegradation performance in screening tests, meeting criteria to be considered readily biodegradable under both aerobic and anaerobic conditions. James Dawick Head of Toxicology and Risk Assessment Innospec Limited Gonca Tuncer Head of Personal Care Business Unit Eigenmann&Veronelli İrem Ulusaraç Essence Products Manager Eigenmann&Veronelli