Thiram

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

28 February 2000

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.23 (Aerobic and Anaerobic Transformation in Soil)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

not specified

Soil no.:

#1

Soil type:

sandy loam

% Clay:

5.6

% Silt:

10.9

% Sand:

83.5

% Org. C:

1.05

pH:

6.1

CEC:

5.62 meq/100 g soil d.w.

Soil no.:

#2

Soil type:

sandy clay loam

% Clay:

26.6

% Silt:

26.2

% Sand:

47.2

% Org. C:

3.8

pH:

6.9

CEC:

24.9 meq/100 g soil d.w.

Soil no.:

#3

Soil type:

clay

% Clay:

48

% Silt:

30

% Sand:

22

% Org. C:

1.8

pH:

7.8

CEC:

39.9 meq/100 g soil d.w.

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: The sandy loam (Borstel, RJ-93) soil was collected from the top 30 cm of the surrounding area of a barley field in the Lower Saxony (Niedersachsen) D-23057 Borstel, Germany on June, 1998. The sandy clay loam (UK-1, RJ-94) and clay (IT01, RJ-95) soil were sampled on March, 1998 and October, 1997 from the upper 20 cm of a field 3 miles south of Droitwich, Worcestshire, England and Piacentino, Italy, respectively
- Pesticide use history at the collection site: The barley field from where the sandy soil was collected, was treated with the herbicides diflufenican and isoproturon which are not structurally or by mode of action similar to that of the test substance (thiram). The other two soils were not treated with any pesticide for at least 3 years
- Storage conditions: kept at ca. 4°C
- Soil preparation: prior to incubation, each soil was acclimated for several days at the approximate temperature (i.e., either 20 ± 2 °C or 10 ± 2 °C). The soil (approximately 10 g per tube, dry weight equivalent) was adjusted to 45% of MWC before treatment.

Soil No.:

#1

Duration:

120 d

Soil No.:

#2

Duration:

120 d

Soil No.:

#3

Duration:

120 d

Soil No.:

#1

Initial conc.:

26.6 mg/kg soil d.w.

Based on:

test mat.

Remarks:

measured concentration

Soil No.:

#2

Initial conc.:

26.6 mg/kg soil d.w.

Based on:

test mat.

Remarks:

measured concentration

Soil No.:

#3

Initial conc.:

26.9 mg/kg soil d.w.

Based on:

test mat.

Remarks:

measured concentration

Soil No.:

#1

Initial conc.:

26.9 mg/kg soil d.w.

Based on:

test mat.

Remarks:

measured concentration

Parameter followed for biodegradation estimation:

radiochem. meas.

test mat. analysis

Soil No.:

#1

Temp.:

20°C

Humidity:

45% MWC

Microbial biomass:

0.27 g C/kg soil

Soil No.:

#2

Temp.:

20°C

Humidity:

45% MWC

Microbial biomass:

0.43 g C/kg soil

Soil No.:

#3

Temp.:

20°C

Humidity:

45% MWC

Microbial biomass:

0.44 g C/kg soil

Soil No.:

#1

Temp.:

10°C

Humidity:

45% MWC

Microbial biomass:

0.11 g C/kg soil

Details on experimental conditions:

PRELIMINARY EXPERIMENT:
- Prior to initiation of the definitive study, a preliminary investigation on the sandy loam, sandy clay loam and clay soils was conducted for 12 days to estimate the approximate degree of degradation of 14C-thiram in the soils, and to establish method recoveries, material balance, and the efficiency of trapping volatiles using the test apparatus. The definitive study was conducted for 120 days under aerobic conditions at a temperature of 20 ± 2 °C for the three agriculturally relevant soils (sandy loam, sandy clay loam and clay). An additional incubation with one of the soils was perforrned at
10 ± 2 °C.

EXPERIMENTAL DESIGN
- The test apparatus was comprised of individual 50-mL Teflon® incubation tubes equipped with a manifold having fourteen inlet valves connected to the incubation tubes. Each incubation tube contained approximately 10 g (dry soil weight equivalent) sieved (2mm) soil adjusted to a soil moisture content of 45% of maximum water holding capacity (MWC) and was connected to a series of traps consisting of two sodium hydroxide, one methanolic KOH, and one ethylene glycol, in that order. The aerobicity of the test system was maintained by continuously passing, via positive pressure, humidified air (approximately 2 mL/ min/tube) through each incubation tube and its trapping solutions.
- With the exception of two tubes, radiolabeled test substance was added to the soil of each incubation tube. The two incubation tubes containing untreated soil were used for checking soil moisture content periodically. These two incubation tubes having untreated soil were removed from the environmental chamber once a week and were weighed to determine the loss of water during incubation. The calculated amount of deionized water (Milli-Q) was added to eaeh test incubation tube to maintain the soil mojsture content at 45% of MWC.

Test material application
- For the sandy loam (RJ-93) and sandy clay loam(RJ-94) soil, 3.10 mg of 14C-thiram (Lot# 98120A, specific activity 60 mCi/mmol) and
12.10 mg of non-radioactive thiram (Lot# AC-1 315-148, purity 99.80%) were dissolved in 4 mL of acetone (Lot # 960165, purity 99.6%, Fisher Scientific) and sonicated for approximately 3 minutes to be sure all test substance was in solution. For the clay soil (RJ-95) and the sandy loam soil (RJ-93) incubated at 10 ± 2 °C, the dosing solution was prepared by dissolving 3.00 mg of ‘4C-thiram (Lot# 98120A, specific activity 60 mCi/mmol) and 12.50 mg of non-radioactive thiram (Lot# AC-1315-148, purity 99.80%) in 4 mL of acetone (Lot # 960165, purity 99.6%, Fisher Scientific) and sonicating for approximately 3 minutes to be sure all test substance was in solution.

Experimental conditions
- Moisture maintenance method: yes
- Continuous darkness: Yes

SAMPLING DETAILS
- Sampling intervals: Single soil samples were harvested and analyzed at 0, 1, 2, 4, 8, 16, 31, 64, and 120 days post treatment for the sandy loam and sandy clay loam soil. For the clay and sandy loam soil (10 °C), single soil samples were harvested and analyzed at 0, 1, 2, 4, 8, 16, 32, 64, and 120 days post treatment. Sampling intervals for the high-dose samples were selected at 3, 6 (clay), 7 and 14 days (sandy loam) post treatment.
- Sampling method for soil samples: At the time of sampling, sample incubation tubes were removed from the environmental chamber along with their respective traps. Before disassembling the test apparatus, approximately 5 mL of extraction solvent (acetone) was added to the soil in each incubation tube using a syringe and then extracted
- Method of collection of CO2 and volatile organic compounds: Triplicate aliquots (100 µL) of 1N sodium hydroxide, 1M methanolic KOH and ethylene glycol trapping solutions were quantified for radioactivity by LSC.
- Sample storage before analysis: All soil extracts were refrigerated immediately after extraction and the post-extraction solids (PES), after air drying in a hood, were also refrigerated. The refrigerator containing the samples was maintained at approximately 4 °C.

Soil No.:

#1

Sampling day(s):

120 d

% Total extractable:

1.18

% Non extractable:

24.47

% CO2:

66.46

% Other volatiles:

3.16

% Recovery:

95.27

Soil No.:

#2

Sampling day(s):

120 d

% Total extractable:

1.59

% Non extractable:

21.98

% CO2:

71.87

% Other volatiles:

2.01

% Recovery:

97.45

Soil No.:

#3

Sampling day(s):

120 d

% Total extractable:

16.69

% Non extractable:

18.53

% CO2:

59.16

% Other volatiles:

1.75

% Recovery:

96.13

Soil No.:

#1

Sampling day(s):

120 d

% Total extractable:

3.2

% Non extractable:

26.58

% CO2:

65.95

% Other volatiles:

3.49

% Recovery:

99.22

Remarks on result:

other:

Remarks:

soil #1 incubated at 10 °C

Parent/product:

parent

Soil No.:

#1

% Degr.:

66.46

Parameter:

radiochem. meas.

Sampling time:

120 d

Remarks on result:

other:

Remarks:

Mineralization to 14CO2

Parent/product:

parent

Soil No.:

#2

% Degr.:

71.87

Parameter:

radiochem. meas.

Sampling time:

120 d

Remarks on result:

other:

Remarks:

Mineralization to 14CO2

Parent/product:

parent

Soil No.:

#3

% Degr.:

59.16

Parameter:

radiochem. meas.

Sampling time:

120 d

Remarks on result:

other:

Remarks:

Mineralization to 14CO2

Parent/product:

parent

Soil No.:

#1

% Degr.:

65.95

Parameter:

radiochem. meas.

Sampling time:

120 d

Remarks on result:

other:

Remarks:

Mineralization to 14CO2; soil #1 incubated at 10 °C

Soil No.:

#1

DT50:

3.7 d

Type:

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

Temp.:

20 °C

Remarks on result:

other: DT90= 12.4 d

Soil No.:

#1

DT50:

7.86 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of the parent compound, based on results at 20 °C

Soil No.:

#2

DT50:

5.5 d

Type:

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

Temp.:

20 °C

Remarks on result:

other: DT90= 18.3 d

Soil No.:

#2

DT50:

11.7 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of the parent compound, based on results at 20 °C

Soil No.:

#3

DT50:

6.8 d

Type:

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

Temp.:

20 °C

Remarks on result:

other: DT90= 61.3 d

Soil No.:

#3

DT50:

14.4 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of the parent compound, based on results at 20 °C

Soil No.:

#1

DT50:

9.8 d

Type:

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

Temp.:

10 °C

Remarks on result:

other: DT90=32.7 d (10°C)

Transformation products:

yes

Evaporation of parent compound:

not measured

Volatile metabolites:

not measured

Residues:

yes

N,N dimethyl carbamosulfonic acid (DMCS) was a major metabolite in the study, accounting for 12.12% at maximum (day 32). However, the metabolite exceeded 10% AR only in two soils and in each at one sampling event. Another degradate (< 7% AR), tetramethylthiuram monosulfide (TMTMS), was investigated in each soil, however, the compound is also an impurity of the radiolabelled test substance.

CO₂as final mineralisation product was formed at amounts between 59.2 to 71.9% until study termination. Soil bound residues increased to maxima between 24.2 and 33.0 %. A fractionation indicated these residues to be mainly distributed among humic and fulvic acids. 

Reference 2

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

15 January 1993-18 May 1995

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

other: US-EPA 540/9-82-021

Deviations:

no

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

Version / remarks:

2006

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

not specified

Soil No.:

#1

Duration:

205 d

Initial conc.:

2.04 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

DT50:

2 d

Type:

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

Temp.:

20 °C

Remarks on result:

other: DT90= 7 days

Soil No.:

#1

DT50:

4.25 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of the parent compound, based on results at 20 °C

Soil No.:

#1

DT50:

4.89 d

Type:

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

Temp.:

20 °C

Remarks on result:

other: geom. mean value for persistence

Remarks:

Calculated with SFO, DFOP and FOMC models

Transformation products:

yes

Thiram was mineralised to a high extent. The CO₂formation accounted for 74.9% of the applied radioactivity (AR) at study termination (65.9% after 84 days). The extractable radioactivity declined from 103.1% at study initiation to 56.3% and 5.7% at days 2 and 14 (1.1% at day 84). Vice versa, non-extractable residues increased up to day 14 (47.6%), thereafter a decrease was observed to 30.9% at day 205 (36.1% at day 84). Soil organic matter fractionation indicated that up to 72.1% of the non-extractable radioactivity was bound to the humin fraction and humin acids after 205 days. Analysis of the extractable radioactivity showed that besides¹⁴C-thiram, 11 radioactive fractions were present, however, at any time below 10% AR. Thiram presented the main fraction of extracted radioactivity until day 21. The major transient radioactive fraction was N,N dimethyl carbamosulfonic acid. It was present from day 1 onwards, increasing to a maximum of 8.7% AR on day 4, thereafter quickly decreasing to 0.4% on day 42. All other radioactive breakdown products were ≤ 3.1% AR.

Reference 3

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

21 Oct 2013 - 06 Jun 2014

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Version / remarks:

2002

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.4200 (Anaerobic Soil Metabolism)

Version / remarks:

2008

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

anaerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

clay loam

% Clay:

33

% Silt:

36

% Sand:

31

% Org. C:

2.4

pH:

7.6

CEC:

19.3 meq/100 g soil d.w.

Bulk density (g/cm³):

1.11

% Moisture content:

31.1

Soil No.:

#1

Duration:

42 d

Soil No.:

#1

Initial conc.:

12.8 mg/kg soil d.w.

Based on:

test mat.

Remarks:

equivalent to a maximum single application rate of 3.2 kg/ha

Parameter followed for biodegradation estimation:

radiochem. meas.

test mat. analysis

Soil No.:

#1

Temp.:

20 °C

Microbial biomass:

342.0 µg C/g soil

Soil No.:

#1

Sampling day(s):

42 d

% Total extractable:

29.69

% Non extractable:

46.56

% CO2:

6.01

% Other volatiles:

1.35

% Recovery:

92.26

Parent/product:

parent

Soil No.:

#1

% Degr.:

95.65

Parameter:

test mat. analysis

Sampling time:

42 d

Soil No.:

#1

DT50:

3.91 d

Type:

other: Modified single first order (SFO)

Temp.:

20 °C

Remarks on result:

other:

Remarks:

best fit DT50 of parent compound

Soil No.:

#1

DT50:

8.3 d

Type:

other: Modified single first order

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 of the parent compound, based on results at 20 °C

Transformation products:

yes

Remarks:

dimethylamino(oxo) methanesulfonic acid (DMCS) and 1-(dimethylamino)-1-thioxomethanesulfinic acid (DMTSA)

DMCS and DMTSA reached maximum averages of 16.15% at Day 2.4 and 16.46% at Day 8, which declined to 5.82% and 5.85% of the applied dose, respectively at the final sampling interval (42 days).

Description of key information

-       DT50 of parent substance in soil: 4.7 – 45.1 days at 20 °C based on test material analysis (recalculated to 9.98 – 98.75 d at 12°C, aerobic, OECD 307 and FOCUS 2006, soil).

-       38.69 - 54.28% of AR mineralization (CO2 and CS2) after 30 to 120 days in key study and clearly > 50% of AR in supporting studies.

Additional information

The degradation of tetramethylthiuram disulfide (CAS No. 137-26-8) in soil was investigated in several simulation studies under aerobic and anaerobic conditions.

 

In the key study (2016), conducted according to OECD guideline 307 and GLP, the formation and identity of metabolite P8 (chromatographic region around 29 minutes) after application of thiram to soil was investigated. In parallel, the degradation rate of the substance was investigated in four european soils at 20°C for 30 to 120 days (depending on the soil) under aerobic test conditions. The recoveries for the duration of the study were 100.4 % of AR (EFS546), 94.9 % of AR (EFS558), 98.2 % of AR (EFS559) and 102.2 % of AR (EFS567). The test substance degraded rapidly in all four soils based on test material analysis. Mineralization to 14CO2 reached a maximum average of 51.8, 53.0, 40.7 and 35.1% AR for the Bologna (EFS546), Bologna (EFS558), Parma (EFS559) and Bologna (EFS567) soils, respectively, by the end of the soil incubations. Mineralization to 14CS2, reached a maximum of 1.8, 1.3, 8.9 and 3.6% AR for the Bologna (EFS546), Bologna (EFS558), Parma (EFS559) and Bologna (EFS567) soils, respectively, by the end of the soil incubations. The P8 metabolite was not detected in the soil extracts analyzed by HPLC. Therefore, it could be concluded that the P8 metabolite detected in old studies was an artifact peak due to poor chromatography and not a true metabolite. Data from this study were retrospectively used to calculate DT50 values for thiram based on the FOCUS guideline (2006). The normalized test item DT50 value obtained based on the SFO kinetic model were between 4.7 and 45.1 d at 20°C (9.98 – 98.75 d, recalculated to 12°C) depending on the soil. 

 

In the supporting study (2000), which was conducted according to the EU Method C.23 (Aerobic and Anaerobic Transformation in Soil) and GLP the degradation behaviour of thiram in three European soils was investigated at 20 ± 2 °C and 10 ± 2 °C (one soil). 14C-volatiles steadily increased to a maximum between 60.9 and 73.9 % of AR during the incubation period showing a high mineralization of the test substance. DMCS was a main metabolite with > 10 % of AR. A non-polar metabolite (P8) was observed although it was only found at a significant level in one soil, reaching a maximum of 11.41 %. This metabolite was further investigated in the key study described above. The DT50 values based on test material analysis ranged between 3.7 and 6.8 d at 20°C and 9.8 d at 10°C.

 

In the supporting study (1995), according to US-EPA 540/9-82-021 and GLP the DT50 values based on test material analysis was 2 d at 20°C (recalculated to 4.25 d at 12°C). Mineralisation exceeded 50% on Day 21 and reached 74.9% after 205 d. The recovery of the radiolabeled test substance was always > 90% of AR. A retrospective kinetic analysis according to the FOCUS guideline (2006), resulted in a geom. mean DT50 value for degradation of 4.89 d.

 

The leaching characteristics of 14C-thiram and its degradates was studied in a sandy soil following aerobic incubation for ~3 days according to Commission Directive 95/36/EC (1995). Thiram was aged in the sandy soil to its approximate half-life and added to the top of two replicate soil columns containing the identical soil. Simulated rainfall (0.01 M calcium chloride; 200 mm) was added to each column dropwise over a two-day period. Overall, 14C-thiram showed no mobility in the soil at an artificial rainfall of about 200 mm over a period of approximately 2 days. The main degradate corresponded to DMCS at a maximum of 4.35% of the applied dose.

 

Finally, a study is available evaluating the degradation potential of the substance under anaerobic conditions and 20°C in one soil. The test resulted in a maximum mineralization of 6.01% CO2 at test termination (42 d). The test material DT50 was 3.91 d at 20°C (recalculated to 8.3 d at 12°C). Dimethylamino(oxo) methanesulfonic acid (DMCS) and 1-(dimethylamino)-1-thioxomethanesulfinic acid (DMTSA) were the major degradation products.

 

In view of these results and the high mineralization rates (mostly > 50%), it can be expected that tetramethylthiuram disulfide will not persist in the soil compartment.