Pirimiphos-methyl

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

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)

Version / remarks:

1992

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

Withdrawn on the 16th September 2021 (day of test start) from the sewage treatment plant Ruhrverband Kläranlage, Sunthelle 6, 57392 Schmallenberg, Germany, which is mainly fed with municipal wastewater.
The sludge samples were filtered (2 mm) to remove coarse particles and washed once with tap water. After the arrival in the laboratory, the sludge was kept aerobic until use. The sludge was left for settlement for ca. one hour. Subsequently the supernatant was discarded and the concentration of suspended solids was measured in the remaining sludge. The concentration was adjusted to 4.1 g/L in tap water and verified by dry mass measurement. The concentration of sludge used in the test was 29.5 mg dry mass/litre (7.38 mg dry mass/250 mL).

Duration of test (contact time):

28 d

Initial conc.:

40 mg/L

Based on:

test mat.

Remarks:

Corresponds to 88.0 mg theoretical oxygen demand (ThOD) considering total nitrification and 62.9 mg ThOD considering the total lack of nitrification.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium:
For the preparation of the stock solutions for mineral medium the following reagents (analytical grade) were used:
a) pH was found to be 7.4 ± 0.2
KH2PO4 8.50 g/L
K2HPO4 21.75 g/L
Na2HPO4 26.65 g/L
NH4Cl 0.50 g/L
b)
CaCl2·2H2O 6.39 g/L
c)
MgSO4·7H2O 22.50 g/L
d)
FeCl3·6H2O 0.25 g/L

The mineral medium prepared for the test contained 10 mL/L of the mineral stock solution (a) and 1 mL/L of the mineral stock solutions (b)–(d), diluted with deionized water free from inhibitory concentrations of toxic substances (e.g. Cu2+ ions). The organic carbon content was checked at regular intervals (monthly) by dissolved organic carbon (DOC) analysis. The maximum DOC content was verified in the last sampling before medium preparation and was found to be 0.41 mg/L, corresponding to 2.4% of the organic carbon content introduced by the test material (17.3 mg C per liter). According to the OECD 301 guideline, a value of 10% should not be surpassed.
- Additional substrate:
- Solubilising agent (type and concentration if used): none
- Test temperature: 22 °C
- pH: 7.2 to 7.3 at start, 7.3 to 7.8 at end of test
- pH adjusted: Before the start of the test, the pH values of all solutions were determined and adjusted to pH 7.4 ± 0.2 with H2SO4 (50 g/L)
- Aeration of dilution water: no
- Suspended solids concentration: 29.5 mg dry mas/L (concentration used in test)
- Continuous darkness: yes

TEST SYSTEM
The test flasks (500 mL reaction vessels, labeled with the necessary information to ensure unique identification) were incubated under continuous stirring in a SAPROMAT respirometer (VOITH Inc.). Oxygen consumption was measured and recorded continuously throughout the duration of the test.
Two replicates were used for test substance, inoculum control, procedure control, toxicity control and abiotic control.

SAMPLING
Oxygen consumption was measured and recorded continuously throughout the duration of the test.

CONTROL AND BLANK SYSTEM
- Inoculum blank: flasks with mineral medium only were prepared for inoculum controls
- Abiotic sterile control: were also prepared to measure any possible abiotic degradation; a solution of the test item at about 40 mg/L was sterilized by the addition of 10 mL/L NaN3 (100 g/L)
- Toxicity control: containing both test and reference item at the same concentrations as in the individual solutions (test item 40 mg/L, reference item 100 mg/L) was prepared to determine the possible toxicity of the test item against the inoculum
- Procedural control: Sodium benzoate was used as a reference item. The concentration in the test vessels with reference item (procedural control, toxicity control) was 100 mg per litre of mineral test medium (25 mg/250 mL)

Reference substance:

benzoic acid, sodium salt

Test performance:

The manometric respirometry test fulfilled all validity criteria of the guideline.

Key result

Parameter:

other: Theoretical oxygen demand with nitrification (ThODNO3) in %

Value:

-4

St. dev.:

1.7

Sampling time:

28 d

Key result

Parameter:

other: Theoretical oxygen demand without nitrification (ThODN3) in %

Value:

-5.6

St. dev.:

2.3

Sampling time:

28 d

Details on results:

The percent biodegradation of the test item was calculated based on the theoretical oxygen demand of 1.57 mg O2/mg test item (ThODNH3) and of 2.20 mg O2/mg test item (ThODNO3). The average percent biodegradation of the test item in the test media was found to be -5.6% (SD = 2.3%) based on ThODNH3 and -4.0% (SD = 1.7%) based on ThODNO3, respectively, after 28 days of incubation. No biodegradation within the 10-day-window could be calculated since the start criterium of the window (10% degradation) was not reached within the 28 days of incubation.

The percent biodegradation in the toxicity control, containing both the test item and the reference item, was calculated based on the sum of the ThOD of the test item and the reference item. Within 14 days of incubation, average biodegradation in the toxicity controls was 66% based on the ThODNH3 and 60% based on the ThODNO3. Thus, according to the test guidelines, the test item had no inhibitory effect on activated sludge microorganisms at the tested concentration of 100 mg/L because biodegradation in the toxicity control was >25% within 14 days.

No significant biodegradation was observed in the abiotic controls containing the test item and a sterilizing agent.

Results with reference substance:

A biodegradation of >90% was achieved with the reference substance sodium benzoate by day 14 of the test. The reference substance degraded by an average of 97% on day 28.

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The substance was not readily biodegradable under the test conditions.

Executive summary:

The ready biodegradability of the substance was investigated at a concentration of 40 mg/L in a manometric respirometry test using domestic aerobic activated sewage sludge incubated at 22 °C in the dark over 28 days under continuous stirring in a SAPROMAT respirometer (VOITH Inc.). The manometric respirometry test was carried out according to the OECD guideline for Testing of Chemicals No. 301 F (1992). The biochemical oxygen demand (BOD) was measured daily and the percentage degradation was calculated from the theoretical oxygen demand (ThOD) after correcting for the BOD of inoculum controls.
The average percent biodegradation of the test substance in the test media was found to be -5.6% (SD = 2.3%) based on ThODNH3 and -4.0% (SD = 1.7%) based on ThODNO3, respectively, after 28 days of incubation. No biodegradation within the 10-day window could be calculated since the start criterium of the window (10% degradation rate) was not reached within the 28 days of incubation. The difference of extremes of replicate values of the removal of the test item at the end of the test was less than 20%. The nitrate and nitrite concentrations were measured at Day 0 and Day 28 in the inoculum blanks and in the test item flasks to determine the effect of nitrification. As no biodegradation of the test item was observed, corrections to account for nitrification were not neccary. In the toxicity control, which contained both the test item and the reference item sodium benzoate, biodegradation was greater than 25% by Day 14. According to the guidelines, this indicates that the test item had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration. In the procedural controls, the reference substance sodium benzoate was degraded by an average of 92% by Day 14 and reached an average biodegradation of 97% by the end of the test (Day 28), thus confirming suitability of the activated sludge.

Description of key information

OECD TG 301F, GLP, Simon 2021: Not readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater