Thiram

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:

08 Feb 1993 - 11 Jan 1994

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)

Qualifier:

according to guideline

Guideline:

other: FOCUS: Guidance Document on Estimating Persistence and Degradation Kinetics from Environmental Fate Studies on Pesticides in EU Registration. Report of the FOCUS Work Group on Degradation Kinetics, EU Document Sanco/10058/2005 version 2.0, 434 pp.

Version / remarks:

2006

Qualifier:

according to guideline

Guideline:

other: FOCUS: Generic guidance for estimating persistence and degradation kinetics from environmental fate studies on pesticides in EU registration. Version 1.0, 435 pp.

Version / remarks:

2011

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

high-performance liquid chromatography

Details on sampling:

- Sampling intervals of soil samples: 0, 1, 3, 7, 14 and 21 days
- Sampling method: After incubation, the soil was scraped off from the respective glass plates.
- Sampling method for CO2: Except for day 0, at each sampling interval, 14C02 was measured in the trap solutions for both the illuminated and non-illuminated plates. The KOH traps were exchanged at each time interval.
- Sampling methods for the volatile compounds, if any: Except for day 0, at each sampling interval, 14C-volatiles were measured in the trap solutions for both the illuminated and non-illuminated plates. Due to the low amounts of radioactivity trapped, the ethylene glycol was not exchanged.
- Measurement of moisture content: No measurements of soil humidity during the study were made to avoid any loss of radioactivity due to repeated opening of the incubation chambers or repeated weighing of the soil samples.
- Measurement of temperature: The actual temperature during illumination (20.0 ± 1.0 °C) was continuously monitored by means of a temperature element inside the metal chamber and remained constant, except for the transition period (variation: ± 5.0 °C for maximally 30 minutes).

Details on soil:

COLLECTION AND STORAGE
- Geographic location: Landis International Inc., Valdosta, Georgia, USA
- Storage conditions: After the arrival at RCC, the soil was stored in wooden boxes (layer: about 10 cm) at room temperature (winter period). In order to maintain a certain moisture content, the soil was periodically irrigated.
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): The selected soil was air-dried and sieved through a 2 mm sieve.

PROPERTIES
- Soil classification system: USDA
- Soil texture: Sandy loam
- % sand: 55.6
- % silt: 29.6
- % clay: 14.8
- pH: 6.7
- Organic carbon (%): 2.41
- CEC (meq/100 g): 14.44
- Initial moisture at 1/3 atm (%): 19.24
- Initial microbial biomass/microbial population (unit): 4.4 * 105/g soil
- Final microbial biomass/microbial population (unit): 1.8 * 105/g soil

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

< 800

Details on light source:

- Emission wavelength spectrum: Special UV-filter simulating sunlight outdoors (UV-edge 290 nm)
- Light intensity at sample and area irradiated: The light intensity was set to about 90 KLux (i.e. 89.7 KLux, on average) and was comparable to the light intensity of natural daylight in the summer with vertical incidence of the sun on a clear, cloudless day (about 90-100 KLux).
- Duration of light/darkness: 12 hours light, 12 hours dark

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test apparatus or thin layers: 16 clean, pre-weighed glass-plates (5 cm x 10 cm)
- Volume of test solution used/treatment: 1 mL application solution containing 80 pg 14C-THIRAM was applied to each of the 13 plates destined for incubation.
- Details of traps for volatile, if any: The outcoming air was passed through a C02-trapping system (2 flasks containing 1M KOH in methanol) and through ethylene glycol for absorption of volatiles. Additionally, a charcoal trap was installed.

PREPARATION OF THIN-LAYER PLATES:
Heavy cream-like slurry of sufficient density was obtained by mixing 100 g soil with 65 mL of bidistilled water. After homogenization using an ULTRA-TURRAX for about 2 minutes, the slurry was applied to the surface of the glass plates, using a TLC-plate coater (CAMAG No. 21251) adjusted to a layer-thickness of about 1.0 mm. After application, the plates were allowed to dry overnight and the sides and back were carefully cleaned.

REPLICATION
- No. of replicates (dark): 6
- No. of replicates (irradiated): 6
- Other: One plate was used as the day 0 sample.

MAINTENANCE OF TEST CONDITIONS SPECIFIED UNDER "DURATION"
- Temperature maintenance method: The temperature within the metal chamber under the photodegradation apparatus was thermocouple-regulated during the light/dark cycle by means of a water bath.
- Moisture maintenance method: The humidity within the metal chamber was increased by means of a moistened filter paper placed against the walls. Additionally, the incoming air was saturated by bubbling through a flask containing bidistilled water.

Duration:

21 d

Temp.:

20 °C

Initial conc. measured:

20.3 mg/kg soil d.w.

Reference substance:

no

Dark controls:

yes

% Degr.:

57.4

Sampling time:

21 d

Test condition:

Irradiated samples

% Degr.:

11.1

Sampling time:

21 d

Test condition:

Dark samples

DT50:

3.7 d

Test condition:

Irradiated samples

DT50:

15.9 d

Test condition:

Dark samples

DT50:

5.4 d

Test condition:

Corrected "net" photolytic degradation

DT50:

3.78 d

Test condition:

Kinetic re-evaluation according to FOCUS (2006, 2011)

Remarks on result:

other: based on SFO kinetic model

Remarks:

net photolytic degradation

Transformation products:

yes

Details on results:

HALF-LIFE
Irradiated samples: 3.7 days
Dark samples: 15.9 days
Corrected photodegradation: 5.4 days

MAJOR TRANSFORMATION PRODUCTS
Irradiated samples:
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: At least 3 radioactive fractions (M3, M5 and M6) were found during illumination. Fraction M3 transiently occurred only at day 1 (9.6 %) and day 7 (2.5 %). M3 disappeared fast and was not found anymore at days 14 and 21. Radioactive fraction M5 increased from 2.5 % at day 3 to 4.7 % at day 21. Radioactive fraction M6 increased from 6.2 % at day 1 to 8.4 % at day 3 and thereafter, decreased to 4.1 % at day 21. It was shown that fraction M6 consisted of at least 6 radioactive fractions.
Dark samples:
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: At least 4 radioactive fractions (M3-M6) were found. Radioactive fraction M3 occurred in minor amounts at day 3 (2 %) and day 14 (1.1 %). At day 21, M3 amounted to 5.8 %. Radioactive fraction M4 was found in a negligible amount of 0.5 % at day 14. Radioactive fraction M5 was found in minor amounts at day 1 (0.5 %) and day 7 (1.6 %). Thereafter M5 increased to 3.9 % at day 21. Radioactive fraction M6 increased from 4.7 % at day 1 to 15.2 % at day 21. M6 consisted in at least 6 radioactive fractions.

EXTRACTABLE RESIDUES
Irradiated samples:
- % of applied amount at day 0: 92.8 %
- % of applied amount at end of study period: 30.6 % at day 7 and 11.1 % at day 21
Dark samples:
- % of applied amount at day 0: 92.8 %
- % of applied amount at end of study period: 64.6 % at day 7 and 55.7 % at day 21

NON-EXTRACTABLE RESIDUES
Irradiated samples:
- % of applied amount at day 0: 11.0 %
- % of applied amount at end of study period: 35.8 % (day 14) to 30.7 % (day 21)
Dark samples:
- % of applied amount at day 0: 11.0 %
- % of applied amount at end of study period: 31.4 % (day 7) to 33.4 % (day 21)

MINERALISATION
Irradiated samples:
- % of applied radioactivity present as CO2 at end of study: 14 CO2 increased from 9.8 % at day 1 to 38.7 % at day 7 and 57.4 % at day 21.
Dark samples:
- % of applied radioactivity present as CO2 at end of study: 11.1 % at day 21

VOLATILIZATION (distinguish between dark and irradiated samples)
- % of the applied radioactivity present as volatile organics at end of study: No volatiles (<0.05 %) were trapped by means of ethylene glycol and charcoal.
Dark samples:
- % of the applied radioactivity present as volatile organics at end of study: No volatiles (<0.05 %) were trapped by means of ethylene glycol and charcoal.

Total recoveries of radioactivity (volatiles + extractable + bound residue) were characterised by average amounts of 104.3 ± 2.9 % and 103.5 ± 1.9 % of applied radioactivity (AR) in illuminated and darksamples, respectively.

Thiram was degraded on a soil surface exposed to artificial sunlight to form the major breakdown products CO2 (36.9 % of AR after 21 days) and CS2 (20.5 % of AR after 21 days).

For details on amounts of radioactivity applied, material balance and total recovery of radioactivitys see attachment.

Validity criteria fulfilled:

not applicable

Description of key information

Tetramethylthiuram disulfide (CAS No. 137-26-8) photodegrades rapidly in soil (DT50 = 3.78 hours, artificial sunlight, EPA 161-3 and FOCUS 2006).

Key value for chemical safety assessment

Half-life in soil:

3.78 d

Additional information

According to the EPA guideline 161-3, the phototransformation of the radiolabeled test substance was studied on a sandy loam soil (pH 6.7, organic carbon 2.41%) from Valdosta, Georgia, USA, with the substance being exposed in a concentration of 20.3 mg/kg soil dw, for 21 days. After 21 days and 20 °C 57.4% of the applied test substance was mineralized to 14CO2 in irradiated samples and 11.1% in dark control samples. The net photolytic degradation half-life was 5.4 days. This result was reevaluated according to the FOCUS guideline 2006, which resulted in a DT50 of 3.78 days.

 

In conclusion photodegradation in soil will contribute to the overall degradation of the test substance in the environment.