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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

A mixture of methyl borated glycol esters, with 44% B-TTEGME and 51% of their polyethylene glycol ethers was submitted to a valid GLP study to assess biodegradation (OECD 302 A). The results indicate 95% biodegradation within 3 days after incubation. According to the biodegradation criteria of the guideline, this finding provides evidence of ultimate biodegradation. The rapid degradation using non-adapted inoculum suggests the test material can be regarded as readily biodegradable. This is supported by an OECD 301A study with 88% pure B-TEGME (which forms 50% of B-TTEGME) which demonstrated ready biodegradability.

Key value for chemical safety assessment

Additional information

B-TTEGME is a mixture of three borated glycol esters which differ solely by the length of their "-CH2 -CH2 -O-" (glycol ether) side chains (homologues). Its major components are B-TEGME (50%) and B-tetraEGME (40%). Their basic chemical structure is identical: One boric acid molecule forms an ester with three polyethylene glycol ethers of different chain length, i.e., either three, four or five glycol ether entities. The following describes the typical composition of B-TTEGME (CAS 161907-80-8):

50 % B-TEGME (CAS 30989 -05-0) – three polyethylene glycol ether moieties with 3 glycols each (CAS 112 -35 -6)

40 % B-TetraEGME (CAS 57057-98-4) – three polyethylene glycol ether moieties with 4 glycols each (CAS 237 -42 -8)

10 % B-PentaEGME (CAS 75672 -72-9) - three polyethylene glycol ether moieties with 5 glycols each (CAS 23778 -52 -1)

Four studies are available to address the endpoint of B-TTEGME biodegradation.

Shell 1999 used a mixture of Methyl Borated Esters as test material, containing 44% B-TTEGME, to conduct a valid GLP OECD 302 A study. The purpose was to investigate the inherent biodegradability of the test material. The results show that 95% of DOC was lost within latest 3 days of incubation, providing evidence for ultimate biodegradation, according to the criteria of OECD 302 A (> 70% loss during 28 days). Although the test design allows the assessment of inherent biodegradability, the rapid biodegradation (95% within 3 days) using non-adapted inoculum suggests the test material can be regarded as readily biodegradable.

Ready biodegradation of borated glycol esters is supported by a ready biodegradation study of B-TEGME, which contributes 50% of B-TTEGME. BASF 1999b represents a valid study and was conducted with 88% pure B-TEGME, under GLP, and according to OECD 301A. It demonstrated that B-TEGME is readily biodegradable. B-TEGME is a homologue to the two other borated glycol esters of B-TEGME, namely B-TetraEGME (40% of B-TTEGME) and B-PentaEGME (10% of B-TTEGME). Hence, the results obtained with B-TEGME are considered relevant for the assessment of B-tetraEGME and B-pentaEGME biodegradability.

For the same reason the study of Shell 1986 provides evidence which support the biodegradation of borated glycol esters. A DOT 4 brake fluid was used in ready biodegradation testing.

The test material was a mixture of methyl and butyl borated esters, i.e., 35% B-TTEGME, 48% of their respective polyethylene glycol ethers, 13% butyl glycol ethers and 3% additives (not specificied).

The study was however conducted non-GLP, with reference to internal SOPs, which are not detailed in the report. Two different test designs were used to assess ready biodegradation, i.e. the Closed Bottle Test and the Modified Sturm Test. Both tests fulfilled the validity criteria with respect to performance of the reference substance. The results show biodegradation within 28 days, however at low extent. Depending on the study design, average 8 and 24% of the test material were degraded, respectively. It is reported that degradation was still proceeding steadily at the end of the Modified Sturm Test. Degradation observed in these two tests may reflect partial or complete degradation of a number of components of brake fluid DOT4.