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Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
.
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
The inoculum was prepared from a secondary effluent obtained from Peppers Ferry Wastewater Treatment Plant (Blacksburg, Virginia).
Duration of test (contact time):
28 d
Initial conc.:
28.5 mg/L
Based on:
test mat.
Initial conc.:
71 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
Apparatus
A standard constant-pressure respirometer was used to measure oxygen consumption. There were seven flasks as follows: two flasks contained inoculum (“Blank”); two flasks contained inoculum and test material (“Test”); one flask contained a reference substance and inoculum (“Ref”); one flask contained inoculum with test material and the reference substance (“Tox”); one flask contained test material and a sterilizing agent (“Sterile”).

A small open container of soda lime pellets in each flask removed evolved CO2 from the gas phase. Each flask was gently stirred continuously using a magnetic stirrer. Volume-change readings were made at least daily in the testing apparatus. Re-establishment of equilibrium was performed as needed. Gas volume changes in test and reference flasks were compared to volume changes in the blanks to determine net oxygen consumption in the test chambers.

Mineral Medium
Mineral medium was the growth medium and dilution water used for this study. It was prepared from four stock solutions in accordance with OECD 301F, using BMI deionized water and appropriate reagent grade compounds.

BMI deionized water was prepared by first dechlorinating Blacksburg, Virginia municipal water with activated carbon. The dechlorinated water was then deionized using mixed bed deionization tanks to a resistivity of > 1 megohm/cm, and polished with a Millipore Milli-Q UV Plus system with a 0.22-micron filter to a final resistivity of ≥ 18.1 megohm/cm.

Appropriate concentrations of mineral components (potassium and sodium phosphates plus ammonium chloride, calcium chloride, magnesium sulphate and iron (III) chloride) were added to BMI deionized water as specified in the OECD method (section 301A, paragraphs 5 and 6).

Test Environment
The test system was located in a secure area and was maintained at 22 ± 1 °C in near-darkness for the duration of the test.

Test Chronology
Testing proceeded as described in OECD 301F guidelines. Measurements of oxygen consumption were made daily. As oxygen consumption proceeded and/or atmospheric pressure changed, the cumulative volume change over those days was measured.

Re-establishment of equilibrium (reset) was performed at least daily, and more often when the extreme ranges of the graduated device were neared.

eference Substance
To ensure acceptable performance of the sludge, one reaction flask contained inoculum and the reference substance sodium acetate trihydrate (0.47 mg ThOD/mg). All calculations were based on 75 mg ThOD/L.

Data Analysis
The endpoint for the Manometric Respirometry test was percent degradation, which is the ratio of oxygen consumed to ThOD at test initiation. Percent biodegradation was determined at test conclusion. The 10-day window, defined by the method as the 10 days immediately following the attainment of 10% biodegradation, did not open in the study period. The test material would be deemed readily biodegradable by the method if degradation was at least 60% within the 10-day window and if the 10-day window closed by day 28 of the test.

All degradation calculations followed those presented in OECD 301F guidelines. Gas volume changes in all treatments were corrected to account for volume changes induced by changes in atmospheric pressure.


Reference substance:
acetic acid, sodium salt
Parameter:
% degradation (CO2 evolution)
Value:
8.2
Sampling time:
10 d
Parameter:
% degradation (CO2 evolution)
Value:
8.7
Sampling time:
20 d
Parameter:
% degradation (CO2 evolution)
Value:
8.9
Sampling time:
28 d
Details on results:
The Isophoronediamine-Cresyl Glycidyl Ether Adduct 10-day window of degradation did not open within the study period. The product reached a maximum of 9.2% degradation on Day 11, and 8.9% by test termination. Figure 2 presents a plot of test and reference material degradation.
No appreciable nitrification of Isophoronediamine-Cresyl Glycidyl Ether Adduct occurred. Nitrites were measured but not detected in any samples. All ThODs were calculated based on the absence of nitrification.

Pass Levels and Test Acceptability

Listed below are the test validity criteria and the results for this particular test. Criteria from the guideline are presented numerically, followed by our results noted with an asterisk.

 

1. The difference of extremes of replicate values of the removal of the test chemical at the plateau, at the end of the test or at the end of the 10-day window, as appropriate, is less than 20% and if the percentage degradation of the reference compound has reached the pass levels by day 14.

 

*At the end of the test (Day 28) replicate values varied by 7.9%, thus not exceeding 20%. The reference substance degradation reached the required 60% degradation by Day 7. 

 

2. If in a toxicity test, containing both the test substance and a reference compound, less than 35% degradation (based on total DOC) or less than 25% (based on total ThOD or ThCO2) occurred within 14 days, the test substance can be assumed to be inhibitory.  

 

*The toxicity control, containing both the test substance and reference compound, did not achieve 25% by day 14. Therefore, the test substance may be assumed to be inhibitory. 

 

3. The oxygen uptake of the inoculum blank is normally 20-30 mg O2/L and should not be greater than 60 mg/L in 28 days.

 

*The mean oxygen uptake of the inoculum blanks was 22.1 mg O2/L, and was not greater than 60 mg/L in the 28 days. 

 

4. If the pH value is outside the range 6-8.5 and the oxygen consumption by the test substance is less than 60%, the test should be repeated with a lower concentration of test substance. 

 

*At test initiation the pH values were 7.50 in Test Replicate A and 7.50 in Test Replicate B. At the end of the test, the pH values were 8.97 in Test Replicate A and 8.31 in Test Replicate B. 

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The isophoronediamine-cresyl glcidyl ether adduct did not reach pass levels for biodegradation within the 28-day period of the test, indicating that it is not readily biodegradable. The toxicity control treatment reached pass levels for biodegradation by day 7, indicating that the test substance is not inhibitory.
Executive summary:

The isophoronediamine-cresyl glcidyl ether adduct did not reach pass levels for biodegradation within the 28-day period of the test, indicating that it is not readily biodegradable. The toxicity control treatment reached pass levels for biodegradation by day 7, indicating that the test substance is not inhibitory.

Description of key information

The isophoronediamine-cresyl glcidyl ether adduct did not reach pass levels for biodegradation within the 28-day period of the test, indicating that it is not readily biodegradable. The toxicity control treatment reached pass levels for biodegradation by day 7, indicating that the test substance is not inhibitory.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information