Ziram

Phototransformation in water

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

key study

Study period:

29 November 1994 - 15 August 1995

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Study type:

direct photolysis

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water)

Version / remarks:

1982

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Analytical method:

other: HPLC and LSC

Details on sampling:

- Duplicate samples of each sample interval were harvested at 0, 1, 4, 6, 12, 18, and 24 hours post treatment. At each interval, the sample tube was wrapped with aluminum foil as soon as it was taken out of the photolysis chamber. All the low-dose samples were first analyzed within 15 minutes after the harvest. Dark control samples were harvested 24 hours post treatment. The high-dose sample was first analyzed approximately 24 hours after removal from the photolysis chamber. The high-dose sample tube, which had been wrapped in aluminum foil after being harvested, was maintained in a refrigerator at -2 °C until analysis.

Buffers:

- Buffered solution at pH 9 was prepared using 0.01 M dibasic sodium phosphate (Na2HPO4) in water adjusted to pH 9 with monobasic sodium phosphate (NaH2PO4).
- Buffered solution and glassware used in the study were sterilized using an autoclave (Market Forge Company) to minimize the possibility of microbial degradation of the test substance.

Light source:

Xenon lamp

Remarks:

equipped with a UV filter

Light spectrum: wavelength in nm:

> 290

Details on light source:

- The lamp intensity was comparable to that of the average local sunlight. The average light flux in the wavelength range of 330—800 nm was used for comparison. The average light flux for the xenon lamp over this spectral region, which was measured within the sample chamber at the same distance as the samples, was 166.0 W/m^2. The light flux of natural sunlight in the same spectral range was 138.1 W/m^2, as measured on June 13, 1990.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test apparatus/vessels: A two-compartment, stainless steel chamber (with one compartment designated as “A“ and the other as B) equipped with a flat glass window lid and coolant insulation was used for the study. A thermocouple was placed inside the chamber next to the samples, and readings were taken by an automatic temperature monitoring program. To simulate outdoor field application conditions, the system was designed to experience alternating 12-hour Iight and dark cycles every 24 hours by switching the position of compartments A and B. In the preliminary study, alternating 12-hour Iight and dark cycles every 24 hours were applied. In the definitive study, the light cycle was continued for 24 hours by keeping compartments A and B at the same position. - All prepared sample tubes were placed horizontally in the photolysis sample chamber, half-way submerged in a water bath maintained at 25 ± 1 °C for irradiation. The temperature was monitored using an automatic monitoring system.
- Type of test system: closed (tubes were capped with a Teflon®-lined septum cap and Teflon® tape).
- Details on test procedure for unstable compounds: The pH 9 solution was used instead of the more commonly used pH 7 buffered solution because Ziram was determined to be most stable at pH 9 based on a previous Ziram hydrolysis study (see Key hydrolysis study, 1995).

TEST SOLUTIONS
- Volume used/treatment: 42 mL (test item + solubilizing agent + buffer)
- Preparation of test solution: 3.1 mg/kg test solution concentration with less than 1% acetone as a co-solvent were prepared. Additionally, a higher test concentration of 40 mg/kg with 4.8 % acetonitrile as a co-solvent was prepared for identification of major degradates.
- Identity and concentration of co-solvent: acetonitrile
- Concentration of solubilising agent: 1%

REPLICATION
- No. of replicates (dark): 2 (wrapped in aluminium foil)
- No. of replicates (irradiated): 2 per sampling interval

Duration:

24 h

Temp.:

25 °C

Initial conc. measured:

3.1 mg/L

Dark controls:

yes

Preliminary study:

A preliminary study was conducted with scheduled sampling intervals of 0, 3, and 7 days post treatment. Since on day 3 complete degradation of Ziram took place, further samples were not harvested. In view of these results, shorter sampling intervals under a continuous light cycle were scheduled for the definitive study (0, 1, 4, 6, 12, 18 and 24 hours).

% Degr.:

ca. 84.89

Sampling time:

24 h

Test condition:

25°C, pH 9

Remarks on result:

other:

Remarks:

After 24 h, the parent compound accounted for an average of 15.11%

Key result

DT50:

8.66 h

Predicted environmental photolytic half-life:

DT50 = 8.66 h

Transformation products:

yes

Remarks:

Refer to field "Any other information on results incl. tables".

Details on results:

HALF-LIFE: 8.66 h

TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes

MAJOR TRANSFORMATION PRODUCTS
- Refer to field "Any other information on results incl. tables".

MINOR TRANSFORMATION PRODUCTS
- Refer to field "Any other information on results incl. tables".

Under the given test conditions, the tested substance was stable up to 1 hour, then it rapidly degraded to an average of 15.1 % of the total radioactivity in the test solution within 24 hours of irradiation. Under dark conditions the substance was found to be fairly stable in the pH 9 buffer throughout the duration of the study. 15 major transformation products were observed in the 24 hour-duration of the study.

MAJOR DEGRADATION PRODUCTS

The two major degradates were identified as N,N-dimethylformamide and N,N-dimethylthioformamide.

Degradate B, which amounted to an average of 20.98 % at the 24-hour sampling interval, was composed of six degradates identified as N,N-dimethylthioformamide (Degradate B-1), N,N-dimethyl-N-formyl sulfinic acid (Degradate B-2), N,N-dimethyl-N-thioformyl sulfinic acid (Degradate B-3), N,N-dimethyl-N-thioformyl sulfonic acid (Degradate B-4), N,N-dimethyl-N-thioformyl-O-sulfonic acid (Degradate B-5), dimethyldithiocarbamic acid (Degradate B-7), and one unknown (Degradate B-6).

MINOR DEGRADATION PRODUCTS

Five minor degradates (C, D, G, Hand I) were detected accounting for average max. values of 0.9 %, 3.4 %, 1.4 %, 1.6 % and 4.4 %, respectively. Due to the extremely short half-life ofziram under aqueous photolysis, the identification of the other minor degradates (Degradates C, D, G, H and I) was not pursued further.

Dimethyldithiocarbamic acid (DDC, component of Degradate B) was an intermediate degradate in this study. DDC further degraded to N,N-dimethylthioformamide (N,N-DMTF), which then degraded to N,N-dimethylformamide (N,N-DMF).

Validity criteria fulfilled:

not applicable

Remarks:

No validity criteria mentioned in guideline.

Reference 2

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Study type:

direct photolysis

Qualifier:

according to guideline

Guideline:

other: OECD/GD(97)21: Guidance Document on Direct Phototransformation of Chemical in Water.

GLP compliance:

yes (incl. QA statement)

Remarks:

Federal Office of Public Health, Swiss Agency for the Environment, Forests and Landscape and the Intercantonal Office for the Control of Medicines, Switzerland

Radiolabelling:

yes

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

> 290 - < 400

Relative light intensity:

17.4

Duration:

21 h

Reference substance:

no

Dark controls:

yes

Quantum yield (for direct photolysis):

0.024

DT50:

3.51 h

Transformation products:

not measured

Remarks:

several products were observed but not specified

The substance decreased continuously from 98.2% at the start to 13.1% after 6 hours of irradiation.

In dark controls, no degradation was observed in the course of the experiment.

Description of key information

Photolytic half-life in water = 8.66 hours (pH 9)

Key value for chemical safety assessment

Half-life in water:

8.66 h

Additional information

The photolysis of zinc bis dimethyldithiocarbamate (CAS No. 137-30-4) in water was investigated (1995)according to US EPA Guideline, Subdivision N (161-2, Photodegradation Studies in Water, 1988) andGLP. Photolysis of 14C-labeled Ziram was investigated in a pH 9 buffered solution as this substance is known to be more stable under alkaline conditions. Vessels were incubated at 25.0 ± 1 °C and a continuous light cycle. Test substance and a dark control were incubated for 24 hours. Samples were analysed by liquid scintillation counting (LSC) and high-performance liquid chromatography (HPLC) with radiometric detection. Overall recoveries of the applied radiochemical in the irradiated samples and the dark controls were 97.7 % and 103.2 %, respectively. The substance was stable up to 1 hour, then it rapidly degraded to an average of 15.1 % of the total radioactivity in the test solution within 24 hours of irradiation. Under dark conditions the substance was found to be fairly stable in the pH 9 buffer. Based on pseudo-first-order kinetics, the photolytic half-life of Ziram under irradiated aqueous test conditions was calculated to be 8.66 hours at pH 9. In addition to the parent compound, 15 degradation products were observed during the 24-hour duration of the study. Major degradation products were identified as N,N-dimethylformamide and N,N-dimethylthioformamide based on the HPLC, thin-layer chromatography (TLC), gas chromatography/radioactivity monitoring (GC/RAM), gas chromatography/mass spectrometry (GC/MS), and liquid chromatography/mass spectrometry (LC/MS) analyses. 

A further study investigating the phototransformation of the substance in water is available (2000). The study was conducted according to the OECD guideline (97)21 (Guidance Document on Direct Phototransformation of Chemical in Water) and GLP. The rate of photodegradation of about 1.2 mg 14C Ziram per litre aqueous buffer solution (pH 9), could be satisfactorily described by linear-order reaction kinetics. The substance decreased continuously from 98.2% at the start to 13.1% after 6 hours of irradiation. The test item degraded to several photoproducts. The experimental photolytic half-life was determined to be 3.51 hours after continuous irradiation. In dark controls, no degradation was observed in the course of the experiment.

An additional study is available for this endpoint (1985). However, due to methodological deficiencies, it is not further considered for assessment.