Zinc isodecyl phosphorodithioate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 August 2017- 22 September 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Remarks:

Toxicity control conducted as part of an OECD 301B study

Qualifier:

according to guideline

Guideline:

other: Toxicity control conducted as part of an OECD Guideline 301B, Section 3. Degradation and Accumulation. "Ready Biodegradability: CO2 Evolution Test"

Version / remarks:

17 July, 1992

Deviations:

no

Principles of method if other than guideline:

Result taken from a toxicity control conducted as part of an OECD 301B study.

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Toxicity control: Test item and sodium acetate (reference item)
- Method: On the day of testing weighed amounts of the test item were added to the 2-litres test bottles containing medium with microbial organisms and mineral components (toxicity control bottle: 44.2 mg). To this end, 10 mL of Milli-RO water was added to each weighing bottle containing the test item. After vigorous mixing (vortex) the resulting suspension was added quantitatively to the test medium. The test solutions were continuously stirred during the test, to ensure optimal contact between the test item and the test organisms.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Source of inoculum/activated sludge: An activated sludge freshly obtained from a municipal sewage treatment plant: 'Waterschap Aa en Maas', 's-Hertogenbosch, The Netherlands, receiving predominantly domestic sewage.
- Preparation of inoculum for exposure: Before use the sludge was allowed to settle (33 minutes) and the supernatant liquid was used as inoculum at the amount of 10 mL/L of mineral medium.
- Concentration of suspended solids: 4.2 g/L

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

14 d

Test temperature:

22.2 - 23.2°C

pH:

Test start: 7.6
Test end: 8.0

Nominal and measured concentrations:

Target test item concentration: 22 mg/L (12 mg TOC/L)

Details on test conditions:

TEST SYSTEM
- Test vessel: 2 litre brown coloured glass bottle
- Aeration: Test media were aerated and stirred continuously
- No. of vessels per concentration (replicates): 1

OTHER TEST CONDITIONS
- Adjustment of pH: None
- Photoperiod: Excluded from light

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Inhibition of microorganisms leading to decreased CO2 production

TEST CONCENTRATIONS
- Range finding study : Not applicable
- Test concentrations: 22 mg/L

Reference substance (positive control):

yes

Remarks:

sodium acetate

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

22 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: Inhibition of microorganisms leading to decreased CO2 production in a toxicity control conducted as part of a ready biodegradation study

Remarks on result:

other: Toxicity control in an OECD 301B study did not demonstrate the test item is toxic to microorganisms

Details on results:

In the toxicity control, more than 25% biodegradation occurred within 14 days (36%, based on ThCO2). Therefore, the test item was assumed not to inhibit microbial activity.

Results with reference substance (positive control):

In the same biodegradation study, the positive control demonstrated 79% degradation after 14 days, therefore meeting the validity criteria,

Table 1 CO₂Production and Percentage Biodegradation of the Toxicity Control

Day	HCl(0.05 N) titrated (mL)		Produced CO2 (mL HCl)	Produced CO2 (mg)	Cumulative CO2 (mg)	Biodegradation^1) (%)
	Blank (mean)	Toxicity control
1	48.23	47.94	0.29	0.3	0.3	0
4	46.49	26.83	19.66	21.6	21.9	13
6	46.30	36.69	9.61	10.6	32.5	19
8	46.03	40.91	5.12	5.6	38.1	22
11	46.92	40.30	6.62	7.3	45.4	26
15^2)	45.89	29.41	16.48	18.1	63.6	36
^1): Calculated as the ratio between CO2produced (cumulative) and the sum of the ThCO2of the test item and positive control: 174.5 mg CO2/2L (ThCO2test item: 88.8 mg CO2/2L + ThCO2sodium acetate: 85.7 mg CO2/2L). ^2): CO2measured on day 15 is actually part of CO2production of day 14, since microbial activity was ended on day 14 by addition of HCl.

Validity criteria fulfilled:

yes

Conclusions:

The toxicity control in an OECD 301B study demonstrated that the test item is not toxic to microorganisms at 22 mg/L. This is therefore considered to be the NOEC for toxicity to STP microorganisms.

Executive summary:

Toxicity to microorganisms was assessed based on the toxicity control included as part of an OECD 301B ready biodegradation study (Timmer 2017). The toxicity control consisted of test item (22 mg/L) and reference item (sodium acetate). As 36% degradation was demonstrated after 14 days for the toxicity control it was concluded that the test item is not inhibitory to microorganisms at this concentration. The NOEC for toxicity to STP microorganisms is therefore taken as 22 mg/L.

Description of key information

The toxicity control in an OECD 301B study demonstrated that the test item was not toxic to microorganisms at 22 mg/L. This is therefore considered to be the NOEC for toxicity to STP microorganisms.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

22 mg/L

Additional information

Toxicity to microorganisms was assessed based on the toxicity control included as part of an OECD 301B ready biodegradation study (Timmer 2017). The toxicity control consisted of test item (22 mg/L) and reference item (sodium acetate). As 36% degradation was demonstrated after 14 days for the toxicity control it was concluded that the test item is not inhibitory to microorganisms at this concentration. The NOEC for toxicity to STP microorganisms is therefore taken as 22 mg/L.