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For predicting the environmental fate of a chemical a knowledge of its biodegradability is essential. Several kinds of tests, standardized by the OECD and EEC for the determination of ultimate biodegradability (mineralization), are available. The degradation is determined by nonspecific analyses such as the measurement of DOC (e.g. modified OECD screening test), microbial oxygen uptake (modified MITI test; manometric respirometry test) or the microbial release of COsub2 (modified Sturm test). For testing the biodegradability of two stroke engine oils a special test was developed by the CEC (Co-Ordination European Council): the CEC L-33-T-82. In this test the criterion for biodegradability is the elimination of the characteristic CHsub3CHsub2- groups as determined by IR-spectroscopy. Comparative studies with three synthetic lubricant base stocks revealed that significant differences may occur for this substance class. The degradation of the three substances was 100 percent in the CEC-te st, whereas in the manometric respirometry test degradation levels below 40 percent were obtained; in the modified Sturm test the degradation was between 44 and 85 percent. In the manometric respirometry test no substance fulfilled the criterion of ready biodegradability, whereas all three substances reached the pass level in the CEC- test. Results obtained in the CEC-test and in mineralization tests should be in good agreement when no significant formation of microbial biomass and no formation of hydrophilic metabolites takes place. Both parameter contribute to a high percentage of biodegradation in the CEC-test, but low apparent biodegradability in tests for ultimate biodegradability. |
