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EC number: 212-783-8 | CAS number: 868-85-9
Biodegradation in water: screening tests
Administrative data
Link to relevant study record(s)
Description of key information
Not readily biodegradable.
50% DOC in 28 days (EU Method C.4-B)
48% BOD, 50% TOC and 86% test material in 28 days (OECD TG 301 C)
Key value for chemical safety assessment
Additional information
Biodegradation was investigated in a ready test system according to the EU-Method C.4-B. Based on DOC measurements the initial test substance concentration was reduced to 50% after 28 d by activated sludge from predominantly domestic origin. The degradation rate was fastest at the beginning of the test (ca. 45% degradation at the first measurement after 7 d) (Bayer AG, 1992).
A study according to OECD TG 301 supports the findings of the Bayer AG and even gives more detailed results. Using a non adapted mixture of sewage, soil and natural water a biodegradation of 48% was found after 28 d based on BOD. In contrast gas chromatographic analysis revealed a decrease of the test substance of 86%. The TOC was 50% after 28 days. These different results may be attributed to the hydrolysis of the test substance in test medium. While the major part of dimethyl phosphonate hydrolyzed, individual hydrolysis products remained in test medium at about 50% and were not degraded during the test period of 28 days (MITI, 1992).
Based on the degradation results, dimethyl phosphonate is classified as being not readily biodegradable.
It has to be considered that under the conditions used in both tests dimethyl phosphonate hydrolyses to monomethyl phosphonate and methanol. Monomethyl phosphonate hydrolyses further to phosphonic acid and methanol. The high carbon contents at the end of both tests presumably cannot be attributed to the hydrolysis products methanol and phosphonic acid, since methanol is known to be readily biodegradable and phosphonic acid is an inorganic substance. The carbon measured after 28 days should mainly be based on monomethyl phosphonate. Hydrolysis of dimethyl phosphonate is relatively fast at neutral pH which should be used in both tests (DT50 = 3.09 h). Monomethyl phosphonate however remains longer in solution (DT50 not determined). Hydrolysis of dimethyl phosphonate and monomethyl phosphonate is the determining factor for the speed at which biodegradation of dimethyl phosphonate occurs.
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