Zinc Chelate Complex

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

April - August 2020

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

- Storage conditions: Controlled room temperature (15-25°C, ≤70% relative humidity), protected from light and humidity (stored in a tightly closed container)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: local wastewater treatment plant, ARA Birs (Birsfelden / Switzerland), which treats predominantly domestic sewage
- Concentration of sludge: 30 mg dry material per liter
- Preparation of Inoculum: The aerobic activated sewage sludge was washed three times by centrifugation, decantation of the supernatant (liquid phase) and resuspension of the solid material in tap water and finally in mineral medium. Aliquots of the homogenized final sludge suspension were weighed and dried (using a halogen moisture analyzer HS153 from Mettler Toledo) and the dry weight of the suspended solids was determined. Based on the sludge dry weight, a calculated amount of wet sludge was suspended in mineral medium to obtain a concentration equivalent to 4 g dry material per liter. During the holding period of two days prior to use, the sludge was aerated at room temperature. Prior to use, the dry weight of the sludge was again determined and the sludge was diluted with mineral medium. Defined volumes of this diluted activated sludge were added to the mineral medium in the test vessels to obtain a final concentration of 30 mg dry material per liter

Duration of test (contact time):

28 d

Initial conc.:

82 mg/L

Based on:

ThOD

Initial conc.:

100 mg/L

Based on:

test mat.

Details on study design:

A measured volume of inoculated mineral medium, containing a known concentration of test item (100 mg test item/L giving at least 50 - 100 mg Theoretical Oxygen Demand/L) as the nominal sole source of organic carbon was stirred in closed vessels at a constant temperature for 28 days. The biodegradation process consumed dissolved oxygen in the test vessel and generated carbon dioxide, which was absorbed by sodium hydroxide pellets. The consumption of oxygen was determined from the change in pressure in the incubation vessels. The amount of oxygen taken up by the microbial population during biodegradation of the test item (corrected for the uptake by blank inoculum, run in parallel) was expressed as a percentage of Theoretical Oxygen Demand (ThOD).

Reference substance:

benzoic acid, sodium salt

Remarks:

50 mg/l

Preliminary study:

Solubility Pre-Experiment:
Prior to test start, the solubility/dispersibility of the test item in mineral medium was checked,and the test item was found to be not soluble at a concentration of 100 mg/L. The pH of thedispersion with very fine, homogeneously distributed, gray particles was measured to be 7.6.Therefore, a test item stock solution could not be prepared and in the main test the test item wasadded directly to the test vessels.

Key result

Parameter:

% degradation (O2 consumption)

Value:

33

Sampling time:

28 d

Remarks on result:

other: not ready biodegradable

Details on results:

Test item:
The Biochemical Oxygen Demand (BOD) of the test item in the test media significantly increased from the test start until approximately day 5 of incubation, where biodegradation reached a mean value of 28 % (average of two replicates). Afterwards the biodegradation values remained in a plateau phase, with mean values in the range of 28 % to 35 %, until the end of the test, on day 28, when the mean biodegradation value of LZ 61000 amounted to 33 %. At the end of the 10-day window, the mean biodegradation of the test item reached approximately 30 %. Therefore, the pass level for ready biodegradability, i.e. biodegradation of at least 60 % of the ThOD in a 10-day window within a 28-day period of the test, was not reached. In conclusion the test item LZ 61000 was considered as not readily biodegradable under the test conditions within 28 days. The obtained biodegradation value of 33 % may be regarded as evidence of inherent, primary biodegradability.

Procedure and toxicity controls:
In the procedure controls, the average biodegradation of the reference item sodium benzoate was 63 % and 68 % reached by day 5 and day 14, respectively. Therefore, the suitability of the activated sludge was confirmed (≥ 60 % degradation was reached at day 14). At the end of the test (day 28), the average biodegradation was 69 %.
In the toxicity control containing both LZ 61000 and the reference item sodium benzoate, the biodegradation amounted to 59 % by day 14 and reached 64 % at the end of the test period (day 28). Therefore, according to the test guidelines, the test item LZ 61000 was considered to have no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration of 100 mg/L.

Remarks on result:

not measured/tested

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The test item showed a biodegradation rate of 33% after 28 days and was therefore considered as not readily biodegradable under the test conditions.

Executive summary:

The test item was investigated for its ready biodegradability in a manometric respirometry test according to the OECD Guideline for Testing of Chemicals, No. 301F and EU-Method C.4-D. The test was performed in closed vessels containing a known concentration of test item (100 mg test item/L giving 82 mg Theoretical Oxygen Demand/L) incubated at constant temperature (23 °C) for 28 days.

The percent of biodegradation of the test item was calculated based on the Theoretical Oxygen Demand (ThOD) of 0.82 mg O2/mg test item.

The Biochemical Oxygen Demand (BOD) of LZ 61000 in the test media significantly increased from the test start until approximately day 5 of incubation, where biodegradation reached a mean value of 28 % (average of two replicates). Afterwards the biodegradation values remained in a plateau phase, with mean values in the range of 28 % to 35 %, until the end of the test, on day 28, when the mean biodegradation value of LZ 61000 amounted to 33 %. At the end of the 10-day window, the mean biodegradation of the test item reached approximately 30 %. Therefore, the pass level for ready biodegradability, i.e. biodegradation of at least 60 % of the ThOD in a 10-day window within a 28-day period of the test, was not reached. In conclusion the test item LZ 61000 was considered as not readily biodegradable under the test conditions within 28 days. The obtained biodegradation value of 33 % may be regarded as evidence of inherent, primary biodegradability.

Description of key information

The test item was investigated for its ready biodegradability in a manometric respirometry test according to the OECD Guideline for Testing of Chemicals, No. 301F and EU-Method C.4-D. The test was performed in closed vessels containing a known concentration of test item (100 mg test item/L giving 82 mg Theoretical Oxygen Demand/L) incubated at constant temperature (23 °C) for 28 days. The biodegradation values remained in a plateau phase, with mean values in the range of 28 % to 35 %, until the end of the test, on day 28, when the mean biodegradation value amounted to 33 %. At the end of the 10-day window, the mean biodegradation of the test item reached approximately 28 %. Therefore, the pass level for ready biodegradability, i.e. biodegradation of at least 60 % of the ThOD in a 10-day window within a 28-day period of the test, was not reached. In conclusion the test item was considered as not readily biodegradable under the test conditions within 28 days.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater