Ziram

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

19 August 1994 - 13 November 1995

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-1 (Hydrolysis)

Version / remarks:

1982

GLP compliance:

yes

Radiolabelling:

yes

Remarks:

labeled with carbon-14 at both thiocarbonyl positions

Analytical monitoring:

yes

Remarks:

liquid scintillation counting (LSC) and high-performance liquid chromatography (HPLC)

Details on sampling:

- Sampling intervals for the parent/transformation products: The pH 5 samples were taken for assay at 30, 300, 420, 600, 1200, and 3600 seconds post-treatment (i.e., 0.5, 5, 7, 10, 20, and 60 minutes post-treatment, respectively). The pH 7 samples were taken for assay at 0, 1, 4, 16, 24, 48, and 72 hours post-treatment. The pH 9 samples were taken for assay at 0, 1, 3, 7, 14, 21, and 30 days posttreatment.
- Sampling method: Each aqueous test sample was withdrawn from the vial and directly injected into the Rheodyne injector, which was equipped with either a 100 mL size loop, during analysis of pH 5 and 7 samples or a 10 mL size loop during the analysis of pH 9 samples. After the sample was withdrawn, the on-off valve for the syringe was closed and the needle was replaced with a flat-bottom HPLC needle before injection. The major degradation product formed in each pH solution was analyzed by injecting the headspace sample into an HPLC system.
- Sampling methods for the volatile compounds, if any: At certain internvals for pH 7 and 9 samples, the headspace gas was withdrawn using the gas-tigh syringe and dissolved in chilled acetonitrile for quantitative analyses of the content of the headspace gas.
- Sampling intervals/times for pH measurements: The pH of all buffered test solutions was monitored during the course of the stud
- Sample storage conditions before analysis: Samples were analyzed immediately, except of one at pH 9.

Buffers:

- Buffered solutions at pH 5, 7 and 9 were prepared as follows:

pH 5: 0.01 M sodium acetate (NaOAc) in water adjusted to pH 5 with acetic acid (HOAc)
pH 7: 0.01 M tris(hydroxymethyl)aminomethane in water adjusted to pH 7 with hydrochloric acid (HCI)
pH 9: 0.01 M boric acid (H3BO3) in 0.01 M potassium chloride (KCI) adjusted to pH 9 with sodium hydroxide (NaCH)

- All buffered solutions and glassware used in the study were sterilized to minimize the possibility of microbial degradation of the test substance. After sterilization, the pH levels of the pH 5 and 7 buffered solutions were measured. The pH level of the pH 9 buffered solution was measured before sterilization.

- Other: The study was conducted using a test solution concentration of approx. 2.8 ppm for pH 5 and 7 and 2.9 ppm for pH 9 of the test substance with less than 1% acetone as a cosolvent. For the higher concentration-dosed samples to be used for identification of low-level degradates the test solution concentration of approx. 10 ppm was used with 3.9% acetone as a cosolvent. Due to the spontaneous degradation of the test substance upon mixing with buffers, each test system was prepared individually.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: sterilized 12 or 45 mL-capacity glass vials/tubes
- Sterilisation method: All water used throughout the experiment was processed through a NANOPure II (Bamstead Co.) water purification system and sterilized using an autoclave (Market Forge Company).
- Details on test procedure for unstable compounds: due to the spontaneous degradation of Ziram upon mixing with buffers, each test system was prepared individually. First, a stock solution was prepared by dissolving the entire test substance ([14C]Ziram) kept in an amber glass vial (5 mCi) with approximately 15 mL of acetone. The entire contents of the amber glass vial was transferred into a 50-mL-size tube and closed with a screw cap. The dosing solution used for pH 5 and 7 samples was prepared by diluting 2 mL of the stock solution with 2.8 mL of acetone. The dosing solution used for pH 9 samples was prepared in a similar way.
- Details of traps for volatile, if any: At certain intervals for pH 7 and 9 samples, the headspace gas was withdrawn using the gas-tight syringe and dissolved in chilled acetonitrile for qualitative analyses of the content of the headspace gas.

TEST MEDIUM
- Test solutions:
- Low-dose treatments: 100 µL of the radiolabeled test material in acetone was applied to empty, labeled and sterilized 12 mL-capacity glass vials. Subsequently, 11 mL of the respective buffered solution was added to the vial and the vial was sealed with a Teflon-lined septum cap before shaking. Most vials of the pH 7 samples and all pH 9 samples were capped with a Teflon®-lined septum cap, mixed well, and incubated in a constant temperature incubator at 25 ± 1 °C in the dark.
- High-dose treatments: For the 10 ppm sample, 1600 mL of the radiolabeled test material isotopically diluted with unlabeled Ziram in acetone was applied individually, to two 45 mL capacity glass test tuebes, then 39.4 mL of pH 9 buffer solution was added to each tube and the tubes were sealed. Samples were incubated in a constant temperature incubator at 25 ± 1 °C in the dark. For the 100 ppm sample, 176 mg of the labeled test material and 4250 mg of the nonlabled test substance in 2.5 mL acetonitrile was applied to a 45 mL capacity glass test tube. Then, 39 mL of pH 9 buffer solution was added to the tube, and the tube was sealed. An additional 0.5 mL of acetone was added to the tube in order to enhance the solubility of hte chemicals. The test tube was incubated in a water bath at 50 ± 1 °C.
- The vials were covered with aluminium foil before the test solution was prepared.
- The high-dosed samples were prepared only using the pH 9 buffered solution. The high-dose pH 9 samples fortified at 10 mg/L were incubated for 30 days at 25 ± 1 °C in the dark and stored in a refrigerator for 5 days until the first analyses. The second high-dose pH 9 samples fortified at ea. 67 mg/L were incubated in the dark for up to 6 days at 50 ± 1 °C in order to achieve an accelerated degradation of the test item.
- Identity of co-solvent: acetone

Duration:

1 h

pH:

5

Initial conc. measured:

2.8 mg/L

Duration:

72 h

pH:

7

Initial conc. measured:

2.8 mg/L

Duration:

30 d

pH:

9

Initial conc. measured:

2.9 mg/L

Transformation products:

yes

Remarks:

For details see field "Details on hydrolysis and appearance of transformation product".

No.:

#1

Details on hydrolysis and appearance of transformation product(s):

- A total of 11 degradates were observed during the entire study. Degradates A and D, found in pH 5 and 7 test solutions, were considered to be DDC and Thiram based on HPLC. Degradates G ard F, also found in pH 5 and 7 test solutions, were considered to be different metallic complexes of DDC. Further confirmation efforts on those degradates was not attempted due to the extreme short half-life of Ziram under either pH. Degradate C was identified as carbon disulfide by HPLC ard GC. lt was the most predominant degradate in both pH 5 and 7 samples and a minor degradate in pH 9 samples. lt is well known that when a dithiocarbamate is protonated, it can be easily decomposed to carbon disulfide and the protonated amine. The formation of carbon disulfide, therefore, is more favored in the acidic medium, which agrees with the finding that the formation rate of CS2 was significantly higher in pH 5 test solutions than in pH 7 and 9 test solutions. Degradates H and 1 were characterized as DDC and DDC related compounds by comparing the HPLC, TLC, and LC/MS data with these obtained from the analyses of reference standard DDC. In addition, DDC-Na salt also showed to appear as several complexation forms in HPLC. Degradate O, designated as R-t9 min eluate in pH 9 samples, was composed of three degradates. They were identified 23 carbon oxysulfide, thiocyanic acid er isothiocyanic acid, and N, N-dimethylformamide by LC/MS. Each component was designated as Degradate O-1, G-2, and O-3. Under the hydrolysis in-life quantitation conditions, all Degradates O-1 to O-3 appeared as unretained products. Therefore, the percent distribution of the three degradates was not individually monitored.

pH:

5

Temp.:

25 °C

DT50:

ca. 10.4 min

Type:

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

Key result

pH:

7

Temp.:

25 °C

DT50:

ca. 17.67 h

Type:

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

pH:

9

Temp.:

25 °C

DT50:

ca. 6.31 d

Type:

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

Ziram was rapidly degraded in all three buffered solutions. At pH 5, 7, and 9 buffered solutions, the half-life was calculated to be 624.32 seconds (10.4 minutes), 17.67 hours, anti 6.31 days, respectively. Eleven degradates were observed. Some short-lived degradates that were formed initially eventually converted to CS2. Efforts to identify minor unstable intermediate degradates were hindered due to the extremely short half-life; however, the final observed major degradate was confirmed and identified as CS2 in pH 5 and 7 buffered solutions. CS2 was also observed in the ph 9 buffered solution. In addition, dimethyldithiocarbamic acid (DDC), carbon oxysulfide, isothiocyanic acid or thiocyanic acid, anti N, N-dimethylformamide also were detected in the pH 9 buffered solution.

Validity criteria fulfilled:

not applicable

Remarks:

No validity criteria mentioned in guideline.

Description of key information

Hydrolysis is a relevant degradation pathway for zinc bis dimethyldithiocarbamate (CAS No. 137-30-4) in aquatic systems: DT50 (pH 5) = 10.4 min, DT50 (pH 7) = 17.67 h, DT50 (pH 9) = 6.31 d

Key value for chemical safety assessment

Half-life for hydrolysis:

17.67 h

at the temperature of:

25 °C

Additional information

The determination of the hydrolysis (1995) of zinc bis dimethyldithiocarbamate (CAS No. 137-30-4) was performed according to US EPA Guideline, Subdivision N (161-1, Hydrolysis, 1988), and GLP. Hydrolysis of the test substance (14C-labeled Ziram) was investigated at pH 5, 7 and 9 and 25°C. Test vessels were incubated for up to 30 days (depending on pH) under sterile conditions in the dark. Samples were analysed immediately by liquid scintillation counting (LSC) and high-performance liquid chromatography (HPLC) with radiometric detection. Overall recoveries of the applied radioactivity were 98.8 %, 93.7 %, and 95.8 % for pH 5, 7, and 9, respectively. Rapid degradation of the parent compound occurred under acidic and neutral conditions (DT50 = 10.4 min and 17.67 h, respectively). At pH 9, hydrolysis took place at a lower pace (DT50 = 6.31 d) but eventually complete degradation was achieved within 30 days. In addition to the parent compound a total of 11 degradation products were observed during the study. Four intermediate degradation products appeared and disappeared in the pH 5 samples during the 60 min duration of the study. Eventually, the intermediate degradation products were converted to carbon disulfide as the final degradation product. Six intermediate degradation products appeared and disappeared in the pH 7 samples during the 72 hour duration of the study. Degradation products similar to those found in the pH 5 samples were observed in the pH 7 samples, although two additional transient degradation products were found. Due to the extremely short half-life of Ziram at pH 5 and 7, identification of the intermediate unstable degradation products was impossible. The identity of CS2 as a major degradation product was confirmed by gas chromatography/radioactivity monitoring (GC/RAM). Four intermediate degradation products were observed in the pH 9 samples. The major intermediate hydrolytic degradation product in the pH 9 sample was identified and confirmed as dimethyldithiocarbamic acid (DDC) by HPLC, one-dimensional (1-D) thin-layer chromatography (TLC), and liquid chromatography/mass spectrometry (LC/MS). CS2 was also found as a major degradation product in the pH 9 samples. Minor degradation products identified in pH 9 samples were carbon oxysulfide, isothiocyanic acid or thiocyanic acid, and N,N-dimethylformamide.

An additional study is available for this endpoint (1987), however, due to methodological deficiencies was disregarded for further assessment.

In conclusion, hydrolysis is a relevant degradation pathway for Ziram in aquatic systems.