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Bis(2-ethylhexyl) adipate is readily biodegradable according to OECD criteria. The substances is thus expected to be rapidly degraded by microorganisms in both the aquatic and terrestrial environments, therefore in accordance with Regulation (EC) No. 1907/2006, –, further simulation testing for water and sediment or soil biodegradation tests are not necessary:

Several studies investigating the ready biodegradability of Bis(2-ethylhexyl) adipate (DEHA, CAS 103-23-1) are available.

Biodegradability of DEHA

The key study was performed under GLP conditions in a manometric respirometry test according to EU method C.4-D (equivalent to OECD 301F) (BASF 1987). Non-adapted domestic activated sludge was used as inoculum. The validity criteria were fulfilled. The pass level of 60% biodegradation was reached in less than 10 days. After 28 days a biodegradation of 90 – 100 % was observed. Thus, DEHA is readily biodegradable according to OECD criteria.

This result is confirmed by a QSAR calculation using BIOWIN v4.10, which predicted the ready biodegradability of the test substance (BPCN 2014), and six additional experimental results, which are used as supporting information only since original reports are not available (METI 1994, Hüls 1996) or adapted inoculum was used (Felder et al. 1986, Saeger et al. 1976). One study was performed by the Japanese Ministry of Economy, Trade and Industry according to OECD guideline 301C (METI 1994). 100 mg test substance /L was applied. Based on O2 consumption a biodegradation of 67 – 74% was reached after 28 days.

A second study was performed according EU method C.4-C and GLP using non-adapted domestic activated sludge as inoculum (Hüls 1996). 21 mg test substance /L was applied. The pass level of 60% biodegradation was reached in less than 10 days. After 28 days a biodegradation of 83% was observed.


Felder et al. (1986) and Saeger et al. (1976) investigated the inherent biodegradability of DEHA using on the one hand the semi-continuous activated sludge method (similar to OECD 302A) and on the other hand a 35d CO2 evolution test according to Thomson and Duthie (1968) and Sturm (1973). Both tests were performed with adapted inoculum. SCAS studies were carried out by a procedure described previously (SDA 1965) with suggested feed (Mausner et al. 1969) in magnetically stirred 1.5 L glass vessels. Activated sludge was obtained from a local domestic sewage treatment plant. Acclimation of the activated sludge was carried out by an incremental feeding schedule for each unit during the first 3 weeks (1, 3, and 5 mg/24h cycle). After the acclimation period, the primary biodegradation rate was determined each weak by analyzing 50 mL liquor samples withdrawn after feeding and at the end of the aeration cycle. Degradation was measured initially at a feed level of 5 mg (3.3 mg/L), and then this level was increased to 20 mg (13.3 mg/L). Disappearance of the test substance was measured by GC. Primary degradation of 65 - 96% and of 73 – 92% was observed by Felder et al. (1986) and Saeger et al. (1976), respectively. Boethling et al. (1997) has shown that results from SCAS tests adequately predict treatability in real-world wastewater treatment plants when the SCAS test results in a >90% removal rate.

Carbon dioxide evolution studies were carried out by the Sturm modification (Sturm 1993) of the Thompson and Duthie procedure (Thompson and Duthie 1968) (T-D-S) and a shake flask system similar to that described by Gledhill (1975). The seed for both systems was prepared by a 14-day die-away procedure (Bunch and Chambers 1967). A 2 L flask containing 20 mg of test material, 50 mg of yeast extract, 100 mL of settled SCAS supernatant, and 900 mL of standard biological oxygen demand (BOD) dilution water was prepared and stored in the dark under static conditions. Settled SCAS supernatant from a blank unit was employed in the seed preparation. The system was sealed, flasks were shaken on a rotary shaker in the dark at room temperature for 35 days.Ultimate degradation of 94% and of 93.8% (81.6% shake flask method) was observed by Felder et al. (1986) and Saeger et al. (1976), respectively.


Formation and degradation of metabolites

Several publications are available in the literature, which focus on DEHA degradation pattern of single bacterial/yeast species, such as Rhodococcus rhodochrous (Nalli et al. 2002, 2006) and Rhodotorula rubra (Gartshore et al. 2003), or monitoring DEHA and relevant metabolites in STP in- and effluents or activated sludge (Barnabe et al. 2008, Beauchesne et al. 2008). The studies show (i) that microorganisms are capable of degrading DEHA by extracellular esterases that could catalyze the initial hydrolysis of the ester (e.g., Gartshore et al. 2003, Nalli et al. 2002) and (ii) that DEHA is substantially removed in STPs with the solids and by bacterial degradation (e.g., Barnabe et al. 2008). Some of these studies indicate that biodegradation of DEHA by aquatic microorganisms can lead to the formation of intermediates (Barnabe et al. 2008, Nalli et al. 2002, Darraq et al. 2009), which are suspected to be more resistant to degradation than the parent compound. Relevant intermediates are adipic acid, 2-ethylhexanol, 2-ethylhexanal and 2-ethylhexanoic acid.

Adipic acid

The inherent biodegradability of adipic acid was assessed according to the EU Method C.9 (Biodegradation: Zahn-Wellens Test), showing more than 90% degradation after 5 days (Zahn 1980). Based on these results the subtsance is considered to be inherently biodegradable. In addition, several screening tests on biodegradation in water are available indicating the ready biodegradability of the substance. In one test conducted according to OECD guideline 301 D (Determination of the Ready biodegradability: Closed Bottle Test) 83 % degradation was observed after 30 days (Gerike 1979). The result is supported by an aerobic ready biodegradability test performed according to the national Japanese standard method comparable to the OECD TG 301 C guideline. After a period of 4 weeks more than 90% biodegradation of adipic acid was observed (MITI 2002). Based on these data adipic acid can considered to be readily biodegradable according to OECD citeria.

2 -ethylhexanol, 2 -ethylhexanal, 2 -ethylhexanoic acid

2-ethylhexanol and 2-ethylhexanal will disappear rapidly by oxidation to the acid (e.g., see Nalli et al. 2002, Nalli et al. 2006) or evaporation and subsequent photodegradation in air (AOPWIN v1.92: 2-ethylhexanol: DT50 = 29.1h; 2-ethylhexanal: 11.33h, see 5.1.1 for details). 2-ethylhexanoic acid showed to be readily biodegradable in a study performed according to OECD guideline 301E as given in the REACh Dossier for 2-ethylhecxanoic acid (CAS 149-57-5) submitted to ECHA and published on the ECHA webpage (Ekolab Environmental Oy 1998,  00144f67d249/AGGR-12dbca41-158c-4b51-aad6-81de7eaab902_DISS-9d899ce7-1bad-1a70-e044-00144f67d249.html#AGGR-12dbca41-158c-4b51-aad6-81de7eaab902). Primary effluent of a municipal treatment plant was used as inoculum. The validity criteria were fulfilled. After 28 days a DOC removal of 99% was measured. Preliminary abiotic and adsorption tests showed that these factors are not likely to interfere with the biodegradation of the test substance. This result is confirmed by a QSAR calculation using BIOWIN v4.10 (predicted to be readily biodegradable) and supporting studies given in the REACh dossier of 2-ethylhexanoic acid. In addition, Ejlertsson and Svensson (1996) showed that under anaerobic conditions 2-ethylhexanoic acid is completely and stoichiometrically degraded by microorganisms to methane indicating that the intermediate will neither resist the anaerobic activated sludge treatment nor will DEHA persist in sediments.


Based on the available data it can be concluded that DEHA and transient metabolites formed during the degradation process are readily biodegradable. 

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