Mixture of isomers

Biodegradation in water: screening tests

Description of key information

Test substance (dipropylene glycol ethyl ether): inherently biodegradable based on studies available.

Structural analogues either side in homologous series (dipropylene glycol methyl ether and dipropylene glycol n-propyl ether: both readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

There are a limited number of degradation studies available on the substance dipropylene glycol ethyl (DPGEE) ether. In a guideline OECD301F study, DPGEE was not readily biodegradable, reaching only 38 -43% by day 28. However, the study showed a long lag phase of 10 -20 days and, more importantly, the reference substance did not reach the required level of degradation in 14 days required in the study guideline for the study to be valid. This result can be considered reliable as an indicator that the substance is degradable but does not provide unequivocal evidence of ready biodegradability . The substance was also assessed in a guideline inherent biodegradation study. A biodegradation rate greater than 70% (98%) in this test confirmed inherent ultimate biodegradability and therefore low potential for environmental persistency.

Biodegradation studies have also been performed on the two substances either side of DPGEE in the homologous series of dipropylene glycol n-alkyl ethers. Dipropylene glycol methyl ether (DPGME) was evaluated for ready biodegradability following the OECD Method 301F. Oxygen consumption and CO2evolution resulting from biodegradation of the compound was measured over a 28-day test. The average extent of biodegradation based on O2consumption at the end of the 10 day window was 75%. The extent of biodegradation based on CO2production (DCO2) and DOC removal for DPGME after 28 days was 76% and 96% respectively. DPGME can be classified as “readily biodegradable”,meeting the 10 day window.  In a guideline and GLP study, the substance dipropylene glycol monopropyl ether (DPGPE) was found to be readily biodegradable when tested according to guideline OECD301A study. A degradation of 92% was found at the end of the 23 day study.

 

In conclusion, DPGEE is clearly at least inherently biodegradable. In a ready biodegradation study 38-43% degradation was seen after 28 days but the innoculum was shown to be below acceptable levels of activity as the reference substance degraded more slowly than accepted for a valid study. There is data on the two glycol ethers either side of DPGEE in the homologous series, DPGME and DPGPE, that show that both of these substances are readily biodegradable. There is no credible scientific reason why these should be readily biodegradable and DPGEE not. Considering the weight of evidence, it is concluded that DPGEE is likely to be readily biodegradable.