Testing surfactants for ultimate biodegradability

Abstract

The development of screening biodegradability tests is briefly reviewed. The “new chemicals” screening methods according to the OECD (1981) and the EC (1984) are based upon ultimate biodegradability or mineralization by making use of some analytical parameter which is not specific for the chemical. The methods are now known as “ready biodegradability” tests (RBTs). Screening tests that are specifically designed for surfactants have been developed by the OECD earlier. In the latter tests primary biodegradation is monitored by means of a specific analytical parameter. Recent harmonization and improvement of RBTs are evaluated in order to see if their applicability can be extended to screen surfactants for ultimate biodegradability. It is shown that conditions for biotransformation of a surfactant in one of the revised RBTs, i.e. the Closed Bottle Test, are similar or even more favourable than in the screening tests for surfactants. Testing ultimate biodegradability is proposed as a supplement to primary biodegradation of surfactants, at the level of both Screening and Confirmatory. Several revised RBTs were applied to evaluate the ultimate biodegradability of twelve surfactants. Results are in agreement with previous studies and correspond to validated structure biodegradability relationships for surfactants. It is concluded that a positive result in a RBT can safely be extrapolated to aerobic environments in regions where domestic waste water is processed by sewage treatment plants. The proposed test system exclusively employs standardized methods that are published by the OECD and EC.