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Environmental fate & pathways

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
Study period:
2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reference:
Composition 0
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
Qualifier:
equivalent or similar to
Guideline:
EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Test material information:
Composition 1
Specific details on test material used for the study:
Name: 9-Octadecenoic acid (9Z)-, propyl ester
Product Description: Propyl oleate
CAS No.: 111-59-1
Physical state: pale yellow to yellow liquid at 20 °C
Batch No.: 37584
Re-certification date of batch: 08 March 2018
Purity: > 99 % (fatty acid propyl esters, max water content 0.3 % (w/w))
Free Fatty Acid, % Oleic: 0.1
Color, Gardner: 3
Iodine Value, cg I2/g 75
Cloud Point, degrees C 0
Saponification Number, mg KOH/g 177
Moisture, % 0,07
Stability: stable under test conditions
Storage condition of test material: Room temperature, protected from light
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, predominantly domestic, non-adapted
Details on inoculum:
Activated sludge from the municipal wastewater treatment plant Breisgauer Bucht was used as inoculum with a concentration corresponding to 30 mg dry solids per litre. The treatment plant clarifies predominantly domestic wastewater and has a capacity of 600.000 inhabitant equivalents. Sampling date of activated sludge was on 4 July 2017. The dry solid content of the activated sludge was 3.9 g/L. It was determined by weight measurements after drying at 105°C for 5 hours (mean of triplicate measurements). The activated sludge was washed twice with tap water by settling the sludge, decanting the supernatant and re-suspending the sludge.
Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
TOC
Parameter followed for biodegradation estimation:
CO2 evolution
Reference substance:
benzoic acid, sodium salt
Test performance:
Toxicity control: The degradation extent in the toxicity control was 73.5% within 14 days. According to the criterion of the guideline, the test substance had no inhibitory effect on the inoculum.

Reference item: The reference compound sodium benzoate reached the pass levels for ready biodegradability within 4 days (see table 1).

Blank: The mean CO2-evolution of the blank flasks was 31.6 mg/L on day 28 after acidification.

Test parameters:
- Before adding the test item, the IC in the reactor was determined, but only insignificant amounts of IC (0.39 mg/L) were found.
- The IC-concentration of the NaOH in the second CO2-absorber flasks in line, used as protective flasks, was below 7 ppm and was not considered in the data processing, because CO2 absorption from room air was its source.
- The temperature was 19.2 – 22.3°C throughout the whole study and therefore temporarily below the required range of 22 ± 2°C. Since the CO2 evolution in the blank flasks was in the tolerated range and the biodegradation of the reference compound reached 60% within 4 days, it is concluded that the deviation had no effect on the validity of the test.
- The aeration rate was in the tolerated range of 1.6 – 5.5 bubbles/second (counted bubbles: 2.8 – 5.4 bubbles/second).

Criteria of validity
- The IC content in the test vessel was less than 5% of the TOC introduced with the test item.
- The CO2 evolution in the inoculum blank at the end of the test was below 40 mg/L.
- The difference of extremes of replicate values of the test item at the end of the test was less than 20%.
- The biodegradation of the reference compound reached the pass level of 60% ThCO2 by day 4.
- The degradation extent in the toxicity control was above 25% in 14 days based on ThCO2.

The test is valid according to OECD Test Guideline 301 B (July 1992).
Key result
Parameter:
% degradation (CO2 evolution)
Value:
88
Sampling time:
28 d
Remarks on result:
other: mean of three replicate values
Parameter:
% degradation (CO2 evolution)
Value:
72.9
Sampling time:
7 d
Remarks on result:
other: mean of three replicate values
Details on results:
The degradation of the test item at the end of the test was 88.0% (28 d after acidification, mean of three replicates). The test item reached the criteria for ready biodegradability (60% of ThCO2 within a 10-d window).
The degradation of the toxicity control after 14 days was 73.5%. The test item had no inhibitory effect on the inoculum according to the criterion of the guideline.

Results with reference substance:
The biodegradation of the reference compound reached the pass level of 60% ThCO2 by day 4.

Results

Table 1: Ultimate biodegradation after x days [% of ThCO2]

 reactor  day  0  4  7  11  14  21  28  29
                   
 19  Test flasks  0  19.6  65.5  77.9  76.0  80.1  81.7  80.3
 20    0  58.7  75.9  88.4  84.8  90.2  94.2  91.1
 21    0  55.6  77.0  89.6  88.3  90.0  95.9  92.5
 4  Reference flasks  0  75.4  86.3  88.4  89.5  90.6  93.1  96.8
 5

 0

 77.7

 82.7

 84.7

 87.1

 86.0

 90.4

 94.6

 6

 

 0

 72.8

 80 .7

 86.7

 87.8

 87.6

 88.9

 91.8

 22

 Toxicity control - test item & reference item

 0

 41.1

 58.9

 72.6

 73.5

 78.4

 83.5

 81.1

Table 2: Mean CO2 evolution of blanks after x days

 Day  0  4  7  11  14  21  28  29
 CO2 -evolution [mg/l]  0  9.6  14.2  18.5  21.7  25.6  30.5  31.6
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
In a Klimisch 1 OECD 301 B study the degradation of the test item at the end of the test was 88.9 % (28 d after acidification, mean of three replicates). The test item reached the criteria for ready biodegradability (60% of ThCO2 within a 10-d window).
Executive summary:

In a Klimisch 1 OECD 301 B study the degradation of the test item at the end of the test was 88.9 % (28 d after acidification, mean of three replicates). The test item reached the criteria for ready biodegradability (60% of ThCO2 within a 10-d window). The degradation of the toxicity control after 14 days was 73.5%. The test item had no inhibitory effect on the inoculum according to the criterion of the guideline. The test is valid according to OECD 301 B (July 1992).

Description of key information

In a Klimisch 1 OECD 301 B study the degradation of the test item at the end of the test was 88.9 % (28 d after acidification, mean of three replicates). The test item reached the criteria for ready biodegradability (60% of ThCO2 within a 10-d window).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information