Zinc isodecyl phosphorodithioate

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:

21 August 2017- 22 September 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

Version / remarks:

301 Adopted: 17.07.92

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

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.
- Concentration of suspended solids: 4.2 g/L
- 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.

Duration of test (contact time):

28 d

Initial conc.:

22 mg/L

Based on:

test mat.

Initial conc.:

12 mg/L

Based on:

TOC

Initial conc.:

2.01 mg/L

Based on:

ThCO2

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: The following stock solutions of mineral components were used
A)8.50 g KH2PO4
mineral components 21.75 g K2HPO4, 67.20 g Na2HPO4.12H2O and 0.50 g NH4Cl
dissolved in Milli- RO water and made up to 1 litre, pH 7.4 ± 0.2.
B)22.50 g MgSO4.7H2O dissolved in Milli- RO water and made up to 1 litre.
C)36.40 g CaCl2.2H2O dissolved in Milli- RO water and
made up to 1 litre.
D)0.25 g FeCl3.6H2O dissolved in Milli- RO water and made up to 1 litre.
The mineral medium (1L) contained 10ml of solution (A), 1ml of solutions (B) to (D) and Milli-RO water.
- Addition of test item: 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 (test item bottle A: 44.2 mg; test item bottle B: 44.0 mg and 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 temperature: 22.2 and 23.2⁰C.
- pH: 7.6-8.0
- pH adjusted: No
- Suspended solids concentration: 4.2g/L
- Continuous darkness: The test media was excluded from light.


TEST SYSTEM
- Test performed in open system: No, closed bottle.
- Number of culture flasks: Test item and inoculum (2 bottles); inoculum blank (2 bottles); positive control (1 bottle); toxicity control (1 bottle)

SAMPLING
- Sampling frequency: 10,14, 28 days.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes
- Abiotic sterile control: No
- Toxicity control: Yes (test item and reference item, sodium acetate)

Information on reporting of results:

ThCO2, expressed as mg CO2/mg test item, was calculated from the results of carbon analysis. The first step in calculating the amount of CO2 produced is to correct for background (endogenous) CO2 production. Thus the amount of CO2 produced by a test item is determined by the difference (in mL of titrant) between the experimental and blank Ba(OH)2 traps.
The amount of 0.05 N HCl titrated is converted into mg of CO2 produced:
mg CO2=(0.05×∆ mL HCl titrated)/2×44=1.1×∆ mL HCl titrated

Relative biodegradation values were calculated from the cumulative CO2 production relative
to the total expected CO2 production, based on the total carbon content of the amount of test
item present in the test bottles. A figure of more than 10% biodegradation was considered
biologically relevant. The relative biodegradation values were plotted versus time together with the relative biodegradation of the positive control.

When applicable, the number of days is calculated from the attainment of 10% biodegradation until 60% biodegradation. Should this period be ≤ 10 days (10-day window), then the test item is designated as readily biodegradable.

For the toxicity control: if less than 25% biodegradation (based on ThCO2 of the test and positive
control items combined) occurred within 14 days, the test item was assumed to be inhibitory.

The total CO2 evolution in the inoculum blank was determined by the cumulative difference
(in mL of titrant) between the blank Ba(OH)2 traps and untreated Ba(OH)2 (background).

Reference substance:

other: Sodium acetate

Test performance:

In parrallel preparations with the reference substance sodium acetate, degradation of 79% was achieved within 14 days.

Key result

Parameter:

% degradation (CO2 evolution)

Value:

1

Sampling time:

28 d

Results with reference substance:

The reference substance has reached the level for ready biodegradability by 14 days (79%).

Table 1       
CO₂Production and Percentage Biodegradation of the Positive Control Item

Day		HCl (0.05 N) titrated (mL)			Produced CO2 (mL HCl)		Produced CO2 (mg)		Cumulative CO2 (mg)		Biodegradation^1) (%)
		Blank (mean)		Positive control
1		48.23		47.51		0.72		0.8		0.8		1
4		46.49		26.41		20.08		22.1		22.9		27
6		46.30		32.61		13.69		15.1		37.9		44
8		46.03		36.70		9.33		10.3		48.2		56
11		46.92		39.84		7.08		7.8		56.0		65
15^2)		45.89		35.06		10.83		11.9		67.9		79
^1): Calculated as the ratio between CO2produced (cumulative) and the ThCO2of sodium 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.

 

Table 2    
CO₂Production and Percentage Biodegradation of the Test Item (Bottle A)

Day	HCl (0.05 N) titrated (mL)		Produced CO2 (mL HCl)	Produced CO2 (mg)	Cumulative CO2 (mg)	Biodegradation^1) (%)
	Blank (mean)	Bottle A
1	48.23	49.01	0.00	0.0	0.0	0
4	46.49	46.14	0.35	0.4	0.4	0
6	46.30	46.80	0.00	0.0	0.4	0
8	46.03	48.06	0.00	0.0	0.4	0
11	46.92	47.83	0.00	0.0	0.4	0
15	45.89	47.45	0.00	0.0	0.4	0
18	46.13	47.88	0.00	0.0	0.4	0
22	44.43	46.60	0.00	0.0	0.4	0
25	45.63	47.03	0.00	0.0	0.4	0
29^2)	45.53	46.30	0.00	0.0	0.4	0
29^2)	46.58	46.11	0.47	0.5	0.9	1
29^2)	47.84	48.91	0.00	0.0	0.9	1
^1): Calculated as the ratio between CO2produced (cumulative) and the ThCO2of the test item: 88.8 mg CO2/2L. ^2): CO2measured on day 29 is actually part of CO2production of day 28, since microbial activity was ended on day 28 by addition of HCl.

Table 3
CO₂Production and Percentage Biodegradation of the Test Item (Bottle B)

Day		HCl (0.05 N) titrated (mL)			Produced CO2 (mL HCl)		Produced CO2 (mg)		Cumulative CO2 (mg)		Biodegradation^1) (%)
		Blank (mean)		Bottle B
1		48.23		47.74		0.49		0.5		0.5		1
4		46.49		46.29		0.20		0.2		0.8		1
6		46.30		46.90		0.00		0.0		0.8		1
8		46.03		48.52		0.00		0.0		0.8		1
11		46.92		48.00		0.00		0.0		0.8		1
15		45.89		47.41		0.00		0.0		0.8		1
18		46.13		47.68		0.00		0.0		0.8		1
22		44.43		46.38		0.00		0.0		0.8		1
25		45.63		46.99		0.00		0.0		0.8		1
29^2)		45.53		45.28		0.25		0.3		1.0		1
29^2)		46.58		48.22		0.00		0.0		1.0		1
29^2)		47.84		48.94		0.00		0.0		1.0		1
^1): Calculated as the ratio between CO2produced (cumulative) and the ThCO2of the test item: 88.4 mg CO2/2L. ^2): CO2measured on day 29 is actually part of CO2production of day 28, since microbial activity was ended on day 28 by addition of HCl.

 

Table 4
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.

 

Table 5
Comparison of Biodegradation of the Test Item in Bottles A and B

Day	Biodegradation (%)
	Bottle A	Bottle B	Mean A and B	∆ A-B^1)
1	0	1	1	1
4	0	1	1	1
6	0	1	1	1
8	0	1	1	1
11	0	1	1	1
15	0	1	1	1
18	0	1	1	1
22	0	1	1	1
25	0	1	1	1
29^2)	0	1	1	1
29^2)	1	1	1	0
29^2)	1	1	1	0
^1): Absolute difference in biodegradation between bottles A and B ^2): Biodegradation is ended on day 28 by addition of HCl. Therefore, differences observed on day 29 are actually differences of day 28.

 

 

Validity criteria fulfilled:

yes

Remarks:

All criteria for the acceptability of the test were met and the study was considered to be valid. An abiotic control was not used but was not considered to have impacted the intergrity of the study.

Interpretation of results:

not readily biodegradable

Remarks:

Under test conditions 1% biodegradation was observed.

Conclusions:

The test item was shown to have degraded by 1% at 28 days. In conclusion, Zinc, bis(O,O-diisodecyl phosphorodithioato-.kappa.S,.kappa.S') is not readily biodegradable under the conditions of the modified Sturm test performed.

Executive summary:

The study (Timmer 2017) is assigned a reliability score of 1 (reliable without restrictions) as it followed OECD guideline 301 B: CO2 Evolution (Modified Sturm Test) and it is compliant with GLP. A blank inoculum control, reference item control and toxicity control were included in the test set up. 2 bottles were used for the inoculum blanks, 2 bottles were used for the test item, 1 bottle was used for the positive control (Reference item) and 1 bottle was used for the toxicity control (Test item and reference item). Activated sludge obtained from a sewage treatment plant was used as the inoculum. The reference substance achieved 79% degradation within 14 days and the toxicity control showed more than 25% degradation after 14 days, therefore meeting the required criteria. Degradation of 1% was determined for the test item within the test period of 28 days. This concludes that the test item is not readily biodegradable.

Description of key information

Within the test period of 28 days, 1% degradation was determined for the test item. The test item is therefore not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

The ready biodegradability study is reliable as it complies with GLP and was performed in accordance with OECD guideline 301 B: CO2 Evolution (Modified Sturm Test) (Timmer 2017). Throughout the study six bottles were used. There were 2 inoculum blanks, 2 test bottles, 1 positive control and 1 toxicity control. For the inoculum, activated sludge originating from a municipal sewage treatment plant was used. The reference substance that was used showed 79% degradation within 14 days and the toxicity control achieved more than 25% degradation after 14 days, therefore both met the required criteria. For the test item, 1% degradation was determined within the test period of 28 days.