Ziram

Phototransformation in soil

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

key study

Study period:

24 April 1996 - 14 February 1997

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-3 (Photodegradation Studies on Soil)

Version / remarks:

1982

GLP compliance:

yes

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

high-performance liquid chromatography

other: liquid scintillation counting (LSC)

Details on sampling:

- Sampling intervals of soil samples: Samples were taken for assay at 0, 2, 4, 8, 16, and 24 hours post-treatment. At each harvest interval, the trapping solutions were exchanged with fresh solution.

Details on soil:

COLLECTION AND STORAGE
- Soil source: Almond Grove sandy loam obtained from Research For Hire, Porterville, California, USA.
- Soil preparation: The soil was sieved through a 2mm mesh and placed into a stainless steel tray. The soil was treated 2-3 times per week with deionized water and aerated until the initiation of the preliminary study.The same procedure was applied before the performance of the definitive study.

PROPERTIES
- Soil classification system: sandy loam
- Soil texture
- % sand: 61
- % silt: 32
- % clay: 7
- pH in H2O: 5.4
- Organic matter (%): 3.1
- CEC (meq/100 g): 9.0
- Bulk density (g/cm3): 1.14
- Initial moisture at 1/3 bar (%): 15.4
- Moisture content (%): 7.2

Light source:

Xenon lamp

Remarks:

Heraeus SUNTEST CPS (Controlled Power System)

Light spectrum: wavelength in nm:

> 290

Details on light source:

- A xenon lamp equipped with a UV filter was used (in order to filter out wavelengths < 290 nm)
- Light flux wavelength: 330-800 nm
- Light flux test chamber: 165.7 W/m^2 (natural measured light flux in the same spectral range was 138.1 W/m2, as measured on June 13 and August 7, 1990)

Details on test conditions:

- A two-compartment, stainless steel chamber (with one side 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, and readings were taken by an automatic temperature monitoring program. Readings were taken every hour, and average daily values were reported. The system was designed to experience alternating 12-hour light and dark cycles, simulating outdoor field application conditions. The light flux during the light cycle was measured to be 165.7 W/m^2
- The radiolabeled test material which had been dissolved in CH3CN, was applied evenly to each soil layered tube using a wiretrol. The solvent was allowed to evaporate. The tubes were capped and sealed with tape. The soil-layered tubes were placed into the “B“ side of the photolysis chamber
- A total of 22 tubes were dosed at the rate of 3 and 15 mg/kg soil. All tubes were sealed with caps, placed in sample chamber “A,“ and maintained at approximately 25 °C for alternating 12-hour light and dark cycles. Ten of the 22 tubes dosed were wrapped with aluminum foil before placement into the photolysis chamber to serve as dark controls for each sampling interval except at 0 time. The treatment rate was calculated based on dry soil weight basis (dwb).
- Off gases were collected from the tube by piercing the tube septum with a pair of needles connected to another tube, which allowed air to displace the volatiles as they are removed by vacuum. The vacuum pump was used to purge individually sealed soil tubes using CO2-free and moistened air for approximately 20 minutes. The off gases were trapped in a series of traps consisting of 0.1 N KOH solution (for acidic volatiles, including carbon dioxide (14CO2), Vlies‘ reagent (for 14CS2), ancf 0.1 N H2S04 (for basic volatiles)
- A mixture of 0.01 M phosphate buffer (pH 9)/CH3CN (1:2, v/v) was chosen as a soil extraction solvent

Duration:

24 h

% Moisture:

75

Temp.:

25 °C

Initial conc. measured:

3 mg/kg soil d.w.

Duration:

24 h

% Moisture:

75

Temp.:

25 °C

Initial conc. measured:

15 mg/kg soil d.w.

Reference substance:

no

Dark controls:

yes

Preliminary study:

A preliminary study treated at 10 mg/kg soil was conducted using the 14C-Ziram test substance. Samples were harvested at 0 and 25 hours post-treatment. The half-life of the test substance in this study was 9.6 hours.

DT50:

>= 8 - <= 8.9 h

Test condition:

Irradiated samples (3 and 15 mg/kg soil respectively)

DT50:

>= 16.2 - <= 20.5 h

Test condition:

dark control samples (3 and 15 mg/kg soil respectively)

Transformation products:

yes

Remarks:

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

Details on results:

HALF-LIFE: between 8 - 8.9 h

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

MAJOR TRANSFORMATION PRODUCTS
- Thiram, Thiram-Oxide

MINOR TRANSFORMATION PRODUCTS
- N,N-DMF (N,N-dimethylformamide), DOC (dimethyldithio-carbamic acid, sodium salt)

EXTRACTABLE AND NON-EXTRACTABLE RESIDUES (distinguish between dark and irradiated samples)
- The percentage of 14C in the bound residues (PES) increased steadily in both the irradiated and dark control samples, reaching its highest mean level of 29 % and 20.4 % at 24 hours, respectively. By 24 hours, 40.7 % of the applied radioactivity was extracted from the
irradiated samples into the Buffer/CH3CN fraction, whereas 67 % of the total applied radioactivity was extracted from the dark control samples. The level of radioactivity associated with the bound residues (PES fraction) increased to a maximum of 33 % (irradiated samples) and 28 % (dark control samples) at 24 hours. A total of 2.1 % of the dose was found to be associated with the fulvic acid and 2 % was found to be associated with humic acid. Bound residues that could not be extracted are assumed to be associated with the humins fraction of the soil, which totaled only 1.6 % of the initial 33.2 % of the applied radioactivity in the bound residues (PES).

MINERALISATION AND VOLATILIZATION (distinguish between dark and irradiated samples)
- 3 mg/kg treatments: At 24 hours, the level of radioactivity trapped in the KOH solution and the Viles' reagent of the 3 mg/kg treated sample was 9.3 % and 1.7 %, respectively, for the irradiated samples and 2.8 % and 0.5 %, respectively, for the dark control samples. Less than 0.1 % of the total dose was observed in the trap containing H2SO4.
- 15 mg/kg treatments: During the study, the evolved acidic volatiles, including 14CO2, trapped in the KOH solution of the 15 mg/kg dosed samples gradually increased, reaching a maximum of 9.6 % of the total applied radioactivity in the irradiated samples and 3.9 % in the dark control samples by 24 hours. 99% of the radioactivity trapped in the KOH solution was attributable to 14CO2. The radioactivity trapped in the Viles' reagent ranged from 6.1 % in the irradiated samples to 3.2 % in the dark control samples of the total applied radioactivity at 24 hours. The results from the barium salt precipitation test on the Viles' reagent from the 24-hour irradiated samples, indicated that 26.5 -32.7 % of the radioactivity trapped in the Viles' reagent was attributable to 14CO2 in addition to 14CS2. Less than 0.1 % of the total applied radioactivity in basic volatiles was detected in the H2SO4 trap.

TRANSFORMATION PATHWAY
- Description of biotransformation pathway: Under the given test conditions, Ziram decreased rapidly when exposed to light from 68.4 % (0 time) of the applied radioactivity to 9.4 % at 24 hours of the 15mg/kg dosed samples. Under dark conditions ziram decreased from 49.8 % (2 hours) of the applied radioactivity to 21.4 % at 24 hours. 10 degradates were detected in the Buffer/CH3CN fraction of the 15 mg/kg dosed samples during the 24-hour sampling period. The major degradate was thiram. The level of thiram (D 1) detected in the irradiated samples decreased rapidly from 25 % at 0 time to 1.4 % at 8 hours and was not detected in the later samplings. The level of thiram (D 1) detected in the dark control samples ranged from 26.7 % at 2 hours to 0.3 % at 24 hours. Two other degradates, D4 and D5, identified as N,N-DMF (N,N-dimethylformamide) and DOC (dimethyldithio-carbamic acid, sodium salt), respectively, were detected, but neither one exceeded 4.5 % of the total applied radioactivity in the irradiated or dark control samples. None of the other degradates exceeded 5.5 % of the applied radioactivity were not found 2 times above 5 % AR or above 5 % AR at the end of the incubation period in either the irradiated or dark control samples. The degradation of ziram of the 3 mg/kg dosed samples was very similar to the 15 mg/kg dosed samples.

The total 14C recoveries for the 15 mg/kg treated samples ranged from 86.1 % to 98.0 % for irradiated samples and from 99 % to 102.1 % for dark control samples. In the 3 mg/kg treated samples, recoveries ranged from 84.6 % to 104.4 % for the irradiated samples and from 98.3 % to 107.2 % for the dark controls.

10 degradates were detected at various time points in the extractable residue : Major compounds >10 % RR are thiram and thiram oxide. Other compounds accounting for less than 10% RR were dithiocarbamic acid, N,N-dimethylformamide.

Thiram oxide which appeared in both irradiated and dark samples was considered as an artifact from the test system because its ‘levels depend upon the volume of solvent used to dose the soil with ziram’.

The significant degradates were identified in other studies by MS analysis. The significant transformation products in this study correspond to the same observed in the previous environmental fate studies (with one exception) and were confirmed by chromatography.

Validity criteria fulfilled:

not applicable

Remarks:

No validity criteria mentioned in guideline.

Description of key information

Half-lives of zinc bis dimethyldithiocarbamate (CAS No. 137-30-4) in soil = 8 and 8.9 hours (at 3 and 15 mg/kg dw soil concentrations respectively).

Key value for chemical safety assessment

Half-life in soil:

8 h

Additional information

The photolysis of zinc bis dimethyldithiocarbamate (CAS No. 137-30-4) in soil was investigated in a study (1997) according to US EPA Guideline, Subdivision N (161-3, Photodegradation Studies on Soil, 1988) andGLP. 14C-labeled Ziram at concentrations of 3 and 15 mg /kg dw soil was incubated in sandy loam soil for 24 hours, 25°C and simulated sunlight (xenon arc lamp). Dark controls were used in parallel to the irradiated samples. Harvested samples were extracted and analysed by liquid scintillation counting (LSC) and high-performance liquid chromatography (HPLC) with radiometric detection. Further characterization was conducted using liquid chromatography electrospray ionization mass spectrometry (LC/ESI-MS). The total 14C recoveries for the 3 and 15 mg/kg treated samples ranged from 84.6 % to 104.4 % and from 98.3 % to 107.2 % for the dark control samples. Under the given test conditions, Ziram decreased rapidly when exposed to light from 68.4 % (0 time) of the applied radioactivity to 9.4 % at 24 hours of the 15mg/kg dosed samples. Under dark conditions Ziram decreased from 49.8 % (2 hours) of the applied radioactivity to 21.4 % at 24 hours. 10 degradates were detected in the Buffer/CH3CN fraction of the 15 mg/kg dosed samples during the 24-hour sampling period. The major degradate was thiram, which decreased rapidly from 25 % at 0 time to 1.4 % at 8 hours and was not detected in the later samplings. Two other degradates, identified as N,N-DMF (N,N-dimethylformamide) and DOC (dimethyldithio-carbamic acid, sodium salt), respectively, were detected, but neither one exceeded 4.5 % of the total applied radioactivity in the irradiated or dark control samples. None of the other degradates exceeded 5.5 % of the applied radioactivity. The degradation of Ziram of the 3 mg/kg dosed samples was very similar to the 15 mg/kg dosed samples. The resulting half-lifes were 8 and 8.9 hours for the 3 and 15 mg /kg dw soil concentrations respectively.

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