Captan

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

29 October 2001 to 18 March 2002

Reliability:

1 (reliable without restriction)

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Identity: THPI
Batch: ASW01685-01A
Purity: 99.51 % (GC/FID)
Appearance: Pale, tan flakes
Expiration Date: June 07,2002
Storage: At room temperature (about 20 °C)

Radiolabelling:

no

Analytical monitoring:

yes

Buffers:

Buffer pH 4, Biphthalate: Baker Art. No. 5657Buffer pH 7, Phosphate: Baker Art. No. 5656Buffer pH 9, Borate: Baker Art. No. 7145. The buffer solutions were sterilized for 25 minutes In an autoclave prior to first use. Nitrogen was passed through the buffer soIutions for 5 minutes except when freshly sterilized.

Number of replicates:

two

Key result

pH:

7

Temp.:

25 °C

DT50:

3 658 h

Key result

pH:

7

Temp.:

50 °C

DT50:

137 h

Key result

pH:

7

Temp.:

60 °C

DT50:

44 h

Key result

pH:

7

Temp.:

70 °C

DT50:

15 h

Key result

pH:

9

Temp.:

25 °C

DT50:

76 h

Key result

pH:

9

Temp.:

50 °C

DT50:

6 h

Key result

pH:

9

Temp.:

60 °C

DT50:

2 h

Key result

pH:

9

Temp.:

70 °C

DT50:

1 h

The hydrolysis preliminary test was performed with THPI at 50.0 ± 0.1°C at each of pH 4.0, pH 7.0 and pH 9.0 in duplicate. The test solutions of THPI were thermostated to 50.0°C and analysed in time intervals.

The concentrations of THPI found in the test solutions after Incubation times of 2.4 hours, 24 hours and 5 days are given in the following table. The tabulated values represent rounded results which were obtained by calculation using the exact raw data (please look at attached background material).

Validity criteria fulfilled:

yes

Conclusions:

THPI is stable at pH 4.0. Its half-life time is longer than one year at 25 °C.THPI at pH 7.0 has a half-life time of 3658 hours (152 days) at 25 °C.THPI at pH 9.0 has a half-life time of 76 hours (3 days) at 25 °C.

Executive summary:

The hydrolysis of the test item was performed at 50.0°C ± 0.1 °C at each of pH 4.0, pH 7.0 and pH 9.0.

THPI was found to be stable at pH 4.0 and 50°C. Therefore no further testing was performed at this pH-value.

THPI was not stable at pH 7.0 and at pH 9.0, further testing was performed at elevated temperatures in order to calculate the rate constant (k25) and the half-life time of the hydrolysis at pH 7.0, pH 9.0 at 25°C.

Reference 2

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 April 1989 to 26 May 1989

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

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

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-1 (Hydrolysis)

GLP compliance:

yes

Specific details on test material used for the study:

- Name of test material: Captan, N-(trichloromethylthio)cyclohex-4-ene-1,2-dicarboximide
- Physical state: white solid
RADIOLABELLED TEST SUBSTANCE
- Position of radiolabel: [Ring-l-14C]captan
- Specific activity: 40.4 mCi/mmol.
- Source: Chevron Chemical Company
- Batch number: Inventory No. 171
- Radiochemical purity: 98.0 %

NON RADIOLABELLED TEST SUBSTANCE
- Source: ICIA Analytical
- Batch number: Reference Standard No. M
-1053C- Purity: 98.9 %

Radiolabelling:

yes

Remarks:

14C labelled within trichloromethylgroup

Buffers:

pH: 5, 7, 9

Duration:

25.3 h

pH:

5

Temp.:

25 °C

Initial conc. measured:

2.15 mg/L

Duration:

6.35 h

pH:

7

Temp.:

25 °C

Initial conc. measured:

2.15 mg/L

Duration:

10 h

pH:

9

Temp.:

25 °C

Initial conc. measured:

2.15 mg/L

Number of replicates:

2

Transformation products:

yes

No.:

#1

No.:

#2

% Recovery:

97

St. dev.:

8

pH:

5

Temp.:

25 °C

Duration:

ca. 25.3 h

% Recovery:

92

St. dev.:

2

pH:

7

Temp.:

25 °C

Duration:

ca. 6.2 h

% Recovery:

103

St. dev.:

3

pH:

9

Temp.:

25 °C

Duration:

ca. 10 h

Key result

pH:

5

Temp.:

25 °C

Hydrolysis rate constant:

0.037 h-1

DT50:

18.8 h

Type:

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

Key result

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0.14 h-1

DT50:

4.9 h

Type:

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

Key result

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.083 min-1

DT50:

8.3 min

Type:

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

Several unknown degradation products were found by HPLC analysis. Decomposition products depend on pH (refer to tables attched).

Validity criteria fulfilled:

not specified

Conclusions:

Captan is hydrolysing with half-life times from 18.8 hours at pH 5 to 8.3 minutes at pH 9. PH dependence is also found for the hydrolysis products. At pH 5 the major hydrolytic degradate was found to be CO2. At pH 7 and 9 also CO2 (as sodium carbonate) was found with two additional degradates. Captan exhibited rapid first-order hydrolysis at all pH values in sterile water, the rate of degradation increasing with pH. Two unidentified products were observed which were presumed to be sodium thiocarbonate and sodium-(tetrahydrophthalimido) thiocarbonate, both of which rapidly degrade to carbon dioxide.

Executive summary:

The hydrolysis of [trichloromethyl-¹⁴C]captan has been examined at 25°C in aqueous solutions buffered at pH 5, 7, and 9. The studies were carried out in the dark, under sterile conditions, with concentrations of labeled captan at 2.15 mg/L. At 25°C, captan degraded rapidly in water with a half-life of 18.8 hours at pH 5, 4.9 hours at pH 7, and 8.3 minutes at pH 9.

At pH 5, the major hydrolytic degradate was identified as CO₂.

At pH 7 and pH 9, CO₂was also formed in addition to two other degradates. Available evidence suggested that the latter, too unstable to be characterized fully, are presumably sodium thiocarbonate and sodium S-(tetrahydrophthalimido)thiocarbonate, both of which rapidly degraded to produce CO₂ -recovery, obtained from the analysis of radioactivity, was nearly quantitative; 97% at pH 5, 92% at pH 7, and 103% at pH 9.

In the present study, characterizations were attempted only for those products containing the trichloromethyl moiety leading to carbon dioxide and sodium carbonate as transformation products.

Addtionally it is well known from studies on captan as active substance in plant protection products that further transformation products are THPI and THPAM.

Description of key information

Captan is hydrolysing with half-life times from 18.8 hours at pH 5 to 8.3 minutes at pH 9. The major hydrolytic degradation product was found to be CO2 and THPI.

THPI is stable at pH 4.0. Its half-life time is longer than one year at 25 °C.THPI at pH 7.0 has a half-life time of 3658 hours (152 days) at 25 °C.THPI at pH 9.0 has a half-life time of 76 hours (3 days) at 25 °C.

Key value for chemical safety assessment

Half-life for hydrolysis:

4.9 h

at the temperature of:

25 °C

Additional information

Hydrolysis of captan is in a range from 18.8 hours in acidic to 8.3 minutes in alkaline water. At pH 7 a half-life time of 4.9 hours was determined. Fast hydrolysis and low solubility of 3.8 mg/L has to be considered for formulation uses and subsequent cleaning processes

Captan exhibited very rapid first order hydrolysis at all pH values in sterile water, the rate of degradation increasing with pH. The first order half-lives were in the range 11 to 18.8 hours at pH 5, 2.6 to 4.9 hours at pH 7 and 3.6 to 8.3 minutes at pH 9 at 25°C in various experiments. Carbon dioxide was evolved at acidic and neutral pH´s, and dissolved in solution as carbonate at alkaline pH´s. At neutral and alkaline pH, three unidentified degradates were observed, containing radiolabel derived from the trichloromethyl [14C] position, two of which did not contain the tetrahydrophthalate moiety.