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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The substance is regarded to be readily biodegradable, but failing the 10-d window (according to OECD criteria).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window
Type of water:
freshwater

Additional information

Based on a weight-of-evidence approach, di-(2-ethylhexyl)amine is considered to be readily biodegradable but failing the 10-day window (according to OECD criteria) taking into account results from an enhanced biodegradation test according to OECD 301B (BASF SE, 2016; report no.: 22G0454/11G208), which was extended to an exposure period of 60 days. However, the test conditions during the first 28 days of this test properly correspond to the test conditions described in OECD TG 301B for ready biodegradability testing (see table below): 

 

Method

Required conditions according to

OECD TG 301B

Applied test conditions

(BASF SE, 2016)

Flasks:

(1) test suspension

(2) inoculum blanks

(3) reference control

(4) toxicity control

 

(1)  2 replicates

 (2)  2 replicates

 (3)  1 replicate

 (4)  1 replicate

 

 (1)  3 replicates

 (2)  2 replicates

 (3)  1 replicate

 (4)  1 replicate

Vessel-/ fill volume

Flasks 2 – 5 L;

The description of OECD 301B refers to a 5-L flask containing 3 L of suspension.  

5-L flask;

fill volume 3L

Agitation

Magnetic stirrers, when assessing poorly soluble chemicals

Test assays were stirred on magnetic stirrers.

Mineral medium preparation

According to OECD 301A (paragraphs 5 & 6)

Consistently prepared according to OECD 301A

Inoculum

May be derived from a variety of sources (e.g. activated sludge, sewage effluents; surface waters; soils)

Activated sludge from a municipal sewage plant, collected at experimental starting date

Inoculum volume

≤ 30 mg suspended solids/L

Activated sludge concentration of 30 mg/L (dry weight)

Test temperature

22 ±2 °C

22 ±2 °C

pH

7.4 ±0.2

7.4

Test concentration

10-20 mg/L TOC

10 mg/L TOC

(approx. 12.6 mg/L test substance)

CO2 determination interval

≤ 5 d

(During the first 10 d, determination is recommended every second or third day)

Determination interval:

4 ±1 d

 

In a further test conducted according to OECD 301B, DOC-measurements revealed that adsorption of the amine to activated sludge is likely to occur (BASF SE, 2012; report no.: A12-00901). The high adsorption rate to activated sludge was confirmed in a Simple Treat v4.0 calculation using the following input parameter:

- Molecular weight: 241.46 (EPISuite v4.11)

- log Kow: 6.56 (estimation for uncharged molecule; KOWWIN v1.68; BASF SE, 2015)

- log Koc: 5.5 (measured; at pH 7.0; OECD 121; BASF SE, 2013; report no.: 11L00538)

- Water solubility: 14 mg/L (measured; at 20 °C and pH 4.8; OXEA GmbH, 2010; report no.: AN-ASB 0496)

- Vapor pressure: 0.0023 hPa (measured; at 20 °C; BASF SE, 2013; report no.: 11L00538)

- Henry’s Law Constant: 3.97 Pa*m³/mol (estimation based on measured vapor pressure and water solubility)

- pKa: 10.59 (estimated using SPARC; BASF SE, 2011)

- biodegadation rate constant: 0.3 (hr-1; readily biodegradable, failing 10-d window)

 

According to the Simple Treat calculation 90.9% of the amine is absorbed to the sludge.

 

The assessment of the biodegradation potential is based on experimental data as well as on calculated data from (Q)SAR estimations, summed up in the two tables below.

 

Experimental data on the biodegradation potential of the substance (CAS 106-20-7):

Test Guideline

Reference

Inoculum

Result: Elimination

Enhanced OECD 301B

(CO2-Evolution-Test)

BASF SE (2016)

Report no.:

22G0454/11G208

domestic activated sludge; non-adapted

94% after 60 days

(based on DOC)

 

69% after 28 days

(based on CO2-evolution; slightly failing the 10day window)

 

91% after 60 days

(based on CO2-evolution)

Enhanced OECD 301B

(CO2-Evolution-Test)

BASF SE (2012)

Report no.: A12-00901

domestic activated sludge; non-adapted

83% after 28 days

(based on DOC; most likely due to adsorption)

 

0.9% after 60 days

(based on CO2-evolution)

OECD 301B

(CO2-Evolution-Test)

BASF AG (1997)

Report no.: 97/0028/22/1

domestic activated sludge; non-adapted

~50% after 39 days

(based on CO2-evolution)

Similar to OECD 302B

(Zahn-Wellens-Test)

Hoechst AG (1977)

Report no.: TO2623

activated sludge; non-adapted (source unknown)

93% after 15 days

(based on COD)

 

Estimated data on the biodegradation potential of the substance (CAS 106-20-7):

Estimation model

Reference

Applicability Domain

Prediction

CATALOGIC 301C v11.16,

(OASIS Catalogic v5.14.1.5)

BASF SE (2020)

100% within the applicability domain

44% degraded after 28 days (based on BOD)

BIOWIN v4.10,

(EPISuite v4.11)

BASF SE (2015)

within the applicability domain

not readily biodegradable

 

Conclusion based on weight-of-evidence approach:

The substance (CAS 106-20-7) is readily biodegradable, but failing the 10-day window (according to OECD criteria).

 

Experimental data for the target compound:

Experimental data are available from an enhanced ready biodegradability test according to OECD 301B, conducted with non-adapted, domestic activated sludge as inoculum (BASF SE, 2016). Elimination of the test item was determined to be 94% after 60 days of exposure, based on DOC removal; based on CO2 evolution, biodegradation 91% after 60 days. However, after 28 days, biodegradation was determined to be 69%, but the pass level of the 10-day window was slightly failed as biodegradation was approximately 58% at the end of the 10-day window.

 

In addition, the results from an enhanced ready biodegradability test according to OECD 301B, conducted with non-adapted, domestic activated sludge as inoculum are available (BASF SE, 2012). Elimination of the test item was determined to be 83% after 28 days based on DOC removal. However, this value was regarded to be most likely due to adsorption to sludge and/or to the test vessels. Based on CO2 evolution, biodegradation was determined to be 0.9% after 60 days.

 

Additional experimental data are available from a CO2 evolution test conducted similar to OECD 301B (BASF AG, 1997; report no. 97/0028/22/1) with non-adapted, domestic activated sludge as inoculum. The substance was degraded to approximately 50% after 39 days of incubation. However, the plateau phase of the biodegradation curve was not reached after 39 days. The biodegradation curve still showed an upward trend indicating that the biodegradation of the molecule was not completed.

  

There are further experimental data from a Zahn-Wellens test (conducted similar to OECD 302B) with non-adapted, activated sludge as inoculum (Hoechst AG, 1977). Based on COD, the degradation was determined to be 93% after 15 days. However, as no 3-h value is available, no discrimination between adsorption to sludge and real biodegradation is possible.

 

(Q)SAR estimation data for the target compound:

Calculated data are available from estimations by BIOWIN v4.10 implemented in EPISuite v4.11. The model predicted the substance to be not readily biodegradable. The substance is within the applicability domain of the model (BASF SE, 2015).

 

Further data are available from estimations by the model CATALOGIC 301C v.11.16 implemented in the platform OASIS CATALOGIC v.5.14.1.5. The model’s endpoint is Biological Oxygen Demand (BOD) according to OECD 301C Modified MITI I test conditions. Based on BOD, the model calculated 44% degradation after 28 days. The substance is 100% within the applicability domain (BASF SE, 2020).

 

Overall conclusion:

The biodegradability of bis-(2-ethylhexyl)amine was assessed in a weight-of-evidence approach including experimental and estimated data on the biodegradability of the substance. Due to limited water solubility (14 mg/L; Oxea GmbH, 2012) of bis(2-ethylhexyl)amine (CAS# 106-20-7), the bioavailability of the substance may be reduced. However, as the substance is soluble in water to a certain extent, the impact of water solubility on experimental biodegradation results is not regarded to be crucial. Based on the available data for bis-(2-ethylhexyl)amine (CAS 106-20-7) is concluded to be readily biodegradable, but failing the 10-day window (according to OECD criteria).