diuron (ISO); 3-(3,4-dichlorophenyl)-1,1-dimethylurea

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP Guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

Time course concentrations were determined from duplicate sampling at any observation time. Samples were taken at the beginning of the test and after 6, 24, 48, 75, 96 and 120 hours.

Buffers:

- pH: 4
- Type and final molarity of buffer: 0.05M citrate buffer
- pH: 7
- Type and final molarity of buffer: 0.05M phosphate buffer
- pH: 9
- Type and final molarity of buffer: 0.05M borate buffer

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: Amber glass vials with PTFE seals were used as test vessels
The test was carried using a thermostatically controlled enclosure at ¿ 0.5 ºC the chosen temperature, which was kept within ¿ 0.1 ºC. Photolytic interference was avoided all precautions were taken to exclude dissolved oxygen.

Duration:

120 h

pH:

4

Temp.:

50 °C

Initial conc. measured:

14.4 mg/L

Duration:

120 h

pH:

7

Temp.:

50 °C

Initial conc. measured:

14.4 mg/L

Duration:

120 h

pH:

9

Temp.:

50 °C

Initial conc. measured:

14.4 mg/L

Number of replicates:

Each sample was prepared in duplicate

Preliminary study:

A preliminary test was performed with sufficient number of samples in order to be able to estimate whether the hydrolysis was lower than 10 % after 120 hours or not

Transformation products:

no

% Recovery:

95.6

pH:

4

Temp.:

50 °C

Duration:

120 h

% Recovery:

99.3

pH:

7

Temp.:

50 °C

Duration:

120 h

% Recovery:

99.3

pH:

9

Temp.:

50 °C

Duration:

120 h

pH:

4

Temp.:

25 °C

DT50:

> 1 yr

Type:

(pseudo-)first order (= half-life)

pH:

4

Temp.:

50 °C

DT50:

ca. 91 d

Type:

(pseudo-)first order (= half-life)

pH:

7

Temp.:

25 °C

DT50:

> 1 yr

Type:

(pseudo-)first order (= half-life)

pH:

7

Temp.:

50 °C

DT50:

ca. 477 d

Type:

(pseudo-)first order (= half-life)

pH:

9

Temp.:

25 °C

DT50:

> 1 yr

Type:

(pseudo-)first order (= half-life)

pH:

9

Temp.:

50 °C

DT50:

ca. 425 d

Type:

(pseudo-)first order (= half-life)

Almost no degradation of Diuron at the tested pH was observed to occur

Table 1: Time course of Diuron tech. concentrations at 50 ºC and different pH values
	pH 4			pH 7			pH 9
Time [h]	pH	[mg/L]	[%] of initial	pH	[mg/L]	[%] of initial	pH	[mg/L]	[%] of initial
0	4.01	13.7	100	7.01	14.4	100	9.01	14.0	100
2	4.01	13.7	100	-	-	-	9.01	14.0	100
4	4.02	13.7	100	-	-	-	9.01	14.0	100
6	4.02	13.7	100	7.01	14.4	100	9.01	14.0	100
24	4.01	13.7	100	7.00	14.4	100	9.01	14.0	100
48	4.01	13.6	99.3	7.02	14.4	100	9.00	14.0	100
75	4.01	13.6	99.3	7.01	14.4	100	9.02	13.9	99.3
96	-	-	-	7.02	14.3	99.3	-	-	-
120	4.02	13.1	95.6	7.02	14.3	99.3	9.01	13.9	99.3

 

 

 

Table 2:   Degradation rate and half-life of Diuron tech. at 25 ºC / 50 ºC and different pH values *
Temperature [ ºC]	pH	Kobs	t1/2
25	4	< 0.693 y^-1	> 1 year
50	4	0.00762 d^-1	2181 hours
25	7	< 0.693 y^-1	> 1 year
50	7	0.00145 d^-1	11436 hours
25	9	< 0.693 y^-1	> 1 year
50	9	0.00163 d^-1	10206 hours
*             Degradation rate calculated according to Arrhenius equation

 

Executive summary:

A GLP guideline study (OECD 111) is available for this test substance. The hydrolytic stability of Diuron under abiotic conditions is not dependent on pH. The degradation of Diuron being less 10 % at Ph 4, 7 and 9 and the corresponding half life at ambient temperature (calculated using Arrhenuis equation) estimated to be longer than 1 yr.

Description of key information

Diuron is not susceptible to abiotic hydrolysis, is hydrolytically stable at pH 5, 7 and 9 for 120 hours at 50 °C, in the dark. Therefore, chemical hydrolysis can be excluded as a dissipation mechanism of Diuron in environmental systems.

Additional information

A GLP guideline study (OECD 111) is available for this test substance. The hydrolytic stability of Diuron under abiotic conditions is not dependent on pH. The degradation of Diuron being less than 10 % at pH 4, 7 and 9 and the corresponding half life, at ambient temperature (calculated using Arrhenuis equation), estimated to be longer than 1 yr (Wilfinger, 2007)