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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:
16th November 1995 to 15th December 1995
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Study conducted in compliance with agreed protocols, with no or minor deviations from standard test guidelines and/or minor methodological deficiencies, which do not affect the quality of the relevant results. The study report was conclusive, done to a valid guideline and the study was conducted under GLP conditions.
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge: Fresh activated sludge from a biological waste water treatment plant treating predominantly domestic sewage (City of Geneva, Aïre). The sludge was collected in the morning, washed three times in the mineral medium (by centrifuging at 1000 g for 10 minutes, discarding the supernatant and resuspending in mineral medium) and kept aerobic until being used on the same day.
- Dry weight of suspended solids: The dry weight of suspended solids was determined by taking two 50 mL samples of the homogenised sludge, evaporating water on a steam bath, drying in an oven at 105-110°C for two hours and weighing the residue.
- Concentration of sludge: Dry weight of suspended solids 3.891 g/L. To obtain a concentration of 30 mg/L (dry weight) in a 250 mL flask, 1.93 mL of sludge was needed (inoculum).
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium:
*Solution A*
KH2PO4 8.5 g
K2HPO4 21.75 g
Na2HPO4.2H2O 33.4 g
NH4Cl 0.5 g
dissolved in water and made up to 1 litre
*Solution B*
CaCl2 27.5 g
dissolved in water and made up to 1 litre
*Solution C*
MgSO4.7H2O 22.5 g
dissolved in water and made up to 1 litre
*Solution D*
FeCl3.6H2O 0.25 g
HCl Conc. one drop
dissolved in water and made up to 1 litre.

The mineral medium was prepared by mixing 50 mL of solution A and 2000 mL deionised water, adding 5 mL of each of the solutions B, C and D and making up to 5 litres with deionised water. The water used during the study was deionised water containing less than 10 mg/L dissolved organic carbon.

- Test temperature: 22 °C
- pH: 7.34-8.60
- pH adjusted: yes, the pH of each flask was measured and if necessary was adjusted to 7.4 ± 0.2 with phosphoric acid or potassium hydroxide.
- Suspended solids concentration: 3.891 g/L

TEST SYSTEM
- Culturing apparatus: 250 mL volumetric flask
- Number of culture flasks/concentration: 2 flasks containing test material, 2 flasks containing reference substance, two flasks with reference substance and test material and 2 control flasks (inoculum only)
- Measuring equipment: The respirometers used during the study was a SAPROMAT D 12 (J. M. VOITH GmbH, D-7920 Heidenheim)
- Test performed in closed vessels: Yes

OBSERVATIONS
- Frequency of observations: Oxygen consumption of each flask was measured daily.
- Calculation of oxygen uptake: Oxygen uptakes as read on the SAPROMAT meters were corrected by deducting the basic oxygen uptake of sludge (flasks 2/3 and 2/4) proportionally to account for the differences between actual and nominal concentrations of test and reference substances. Averages of identical flasks were used to obtain the graph of BOB versus time, percentage versus time and biodegradation rates.

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2 flasks
- Toxicity control: 2 flasks (reference substance and test material)
Reference substance:
aniline
Parameter:
% degradation (O2 consumption)
Value:
89
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
82
Sampling time:
10 d
Details on results:
Hexenyl-3-cis salicylate underwent 89% biodegradation, under the conditions of the test, after 28 days. Biodegradation started on day 2 and reached 82% at the end of the 10-day window. The curve obtained with aniline alone and with hexenyl-3-cis salicylate + aniline showed no toxic effect of hexenyl-3-cis salicylate of the micro-organisms at the test concentration.
Results with reference substance:
Degradation of Aniline exceeded 40% after 7 days and 65% after 14 days. The activity of the inoculum was therefore verified and the test was considered valid.

Table 2: Biodegradability of test material

     Days  2  7  12  14  21  28
 BOD sludge  1st flask  B1  9.0  20.0  24.0  25.0  29.0  32.0
   2nd flask  B2  11.0  23.0  28.0  29.0  33.0  36.0
   Mean  B  10.0  21.5  26.0  27.0  31.0  34.0
 BOD test substance  1st flask  C1  80.1  181.3  213.3  219.3  229.3  235.3
   2nd flask  C2  90.4  168.9  206.6  212.6  225.5  233.5
   1st flask corr.  C1 -B  70.1  159.8  187.3  192.3  198.3  201.3
   2nd flask corr.  C2 -B  80.4  147.4  180.6  185.6  194.5  199.5
 % degradation  1st flask  D1  31  71  83  85  88  89
   2nd flask  D2  36  66  80  82  86  89
   Mean  D  33  68  82  84  87  89

ThOD of test material: 2.25 mg O2/mg

B = (B1 + B2)/2

D1 = 100 * (C1 - B)/ThOD*[S]

D2 = 100 * (C2 - B)/ThOD*[S]

D = (D + D2)/2

[S] = initial test material concentration (mg/L)

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
Under the conditions of the study, the biodegradation of hexenyl-3-cis salicylate was determined to be 89% after 28 days. Biodegradation started on day 2 and reached 82% at the end of the 10-day window. Hexenyl-3-cis salicylate is considered to be readily biodegradable.
Executive summary:

In a GLP-compliant ready biodegradation study conducted in line with OECD 301F, the biodegradation of hexenyl-3-cis salicylate was determined using the Manometric Respirometry Test. The biodegradation of the substance was determined to be 89% after 28 days. Biodegradation started on day 2 and reached 82% at the end of the 10-day window. The substance is considered to be readily biodegradable.

Description of key information

Biodegradation was determined to be 82% biodegradation within 10 days, 89% biodegradation within 28 days; study conducted in accordance with OECD 301F; Rudio (1995b)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

In a GLP-compliant ready biodegradation study conducted in line with a standardised guideline, the biodegradation of (z)-3-hexenyl salicylate was determined using the Manometric Respirometry Test. The biodegradation of the substance was determined to be 89% after 28 days. Biodegradation started on day 2 and reached 82% at the end of the 10-day window. The substance is considered to be readily biodegradable. As the study was performed to GLP and standardised guidelines, it was allocated a reliability score of 1 and considered to be the key study.

Supporting information includes two studies performed to standardised guidelines. One study performed to GLP concluded that hexenyl-3-cis salicylate appears to be readily biodegradable but that this could not be determined. Limitations on the methodology meant that this study was allocated a reliability score of 3. The other study, a concluded that (z)-3-hexenyl salicylate was readily biodegradable. This study was allocated a reliability score of 2 due to the limited detail in the reporting of the methods and results.