Butane, 2-ethoxy-2-methyl-

Endpoint summary

Additional information

Data on experimental determination of hydrolysis in water is not available. However, based on physical-chemical properties of TAEE and the properties of other structurally related aliphatic ethers TAEE is not expected to significantly hydrolyse in natural waters under environmentally relevant pH conditions (pH 4-10).

In the troposphere TAEE is photochemically oxidised by hydroxyl radicals abstracting H atoms. The degradation half-life of TAEE in the air is 1.01 days depending on environmental conditions (predominantly OH-radical concentration). Using a degradation rate constant of1.06E-11cm3/molecule/2 and an OH-radical concentration of 5E05 radicals/cm3 a half-life of 1.51 days is calculated. This half-life for degradation in air will be used in further assessment.

Data on experimental determination of photolysis in water is not available. However, because of structural reasons, TAEE is not expected to be photolysed directly. Significant photooxidation in water via reactions with photochemically produced hydroxyl radicals is unlikely to occur.

TAEE is not readily biodegradable in the aquatic environment according to a GLP-compliant standardised aerobic ready-biodegradation test (OECD 301D guideline; Closed Bottle test).The percentage of biodegradation observed is ca. 5% after 28 days.Therefore, TAEE should be classified as “not biodegradable”. However, certain adapted micro-organisms are capable of degrading the structurally related aliphatic ether TAME (Kharoune et al., 2002). These studies show that at least some microbial species are capable to degrade the structurally related aliphatic ether TAME and to use it even as their sole carbon source.It may be concluded that TAEE is inherently biodegradable under certain conditions in the aquatic aerobic environment. In contrast, adapted sewage sludge is able to rapidly degrade TAEE.

Therefore, a distinction will be made between biodegradation in non-adapted municipal STPs which will be classified as“inherently biodegradable, not fulfilling criteria”and adapted industrial STPs where there are continuous releases of TAEE which will be classified as “readily biodegradable”. For these adapted STPs, Monod kinetics are used for the degradation of TAEE in the STP instead of the more simplified first-order kinetics.

No simulation tests are available for TAEE, but data are available for the structurally related aliphatic ether TAME.In anaerobic, static sediment/water microcosms, TAME does not biodegrade (Suflita and Mormile, 1993; Mormile et al., 1994; Somsamak et al., 2001).Based on the few studies available it should be concluded that rapid and reliable biodegradation of TAME in soil can not be assumed in any normal environmental conditions indicating very slow degradation in soil (Jensen and Arvin, 1990; Mormile et al., 1994; Zenker et al., 1999). The biodegradability of TAME in soil in aerobic and anaerobic conditions seems to be very slow and favourable conditions for degradation are difficult to attain.

The rate constants used in the assessment are:

Degradation for hydrolysis	0 d^-1
Degradation for photolysis	0 d^-1
Degradation rate in air	0.458 d^-1
Degradation in a non-adapted STP	0 d^-1
Degradation in an adapted STP	Monod kinetics (default values)
Degradation rate in surface water	4.62·10^-3d^-1
Degradation rate in aerated sediment	2.31·10^-3d^-1
Degradation rate in soil	2.31·10^-3d^-1

No bioconcentration tests are available for TAEE, but data are available for the structurally related aliphatic ether MTBE. Whole-body bioconcentration factors (BCF) of 1.5 and 1.4 l/kg were reported for Japanese carp (Cyprinus carpio) exposed to 10 and 80 mg/l MTBE in a flow-through system at 25 ºC. Fish exposed for 28 days and then transferred to clean water eliminated almost all MTBE residues within 3 days. However, as TAEE has a higher log Kow than MTBE (3.15 and 1.06, respectively), it is expected that the bioaccumulation of TAEE will be higher than the bioaccumulation observed for MTBE. QSAR calculations have been performed for both substances using the program BCFWIN™ v3.00. For TAEE the estimated BCF was 55.6 l/kg, for MTBE it was 2.32 l/kg. As the calculated BCF for TAEE and MTBE differ approximately a factor of ca. 25, this factor is used as the safety factor for the experimental BCF of 1.5 l/kg for MTBE. A BCF in fish of 37.5 l/kg for TAEE is used in the assessment.

The distribution coefficient in soil (log Koc) was estimated to be between 2.16 and 3.73 at 25 °C using the HPLC simulation technique, all within a 95% confidence range of 1.74 to 4.12.The log Koc was also calculated with the program KOCWIN™ v2.00 (2008) using an average log Kow of 3.15, which resulted in a log Koc of 2.58. The experimental average log value of 2.95 (Koc of 891 l/kg) will be used in the assessment.

The Henry's law constant (H) estimated using the vapour pressure of 4,361 Pa at 20 °C and water solubility 3,917 mg/l at 20 °C, is 129 Pa m3/mol (log H = 2.11). The calculated Henry's law constant value indicates that TAEE volatises easily from water to air. The value of 72.9 Pa m3/mol at 12 °C will be used in the assessment.

Using a fugacity model (level I), the theoretical distribution of TAEE based on physico-chemical properties between four environmental compartments at equilibrium can be calculated. The results indicate that 93.1% is distributed to the atmosphere and that volatilisation may be expected from water and soil. Adsorption to particulate matter is unlikely to occur.