Thiophanate-methyl

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2001-10-08 to 2002-05-14

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: SETAC (Europe): Procedures for assessing the environmental fate and ecotoxicity of pesticides, Part 1, Section 1.1, Aerobic Degradation

Version / remarks:

March 1995

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Version / remarks:

August 2000

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Remarks:

Phenyl-UL-14C-labelled thiophanate-methyl

Oxygen conditions:

aerobic

Soil classification:

other: ISO 10381-6 “(Soil quality-Sampling-Guidance on the collection, handling and storage of soil for the assessment of microbial processes in the laboratory)”

Year:

2001

Soil no.:

#1

Soil type:

silt loam

% Clay:

19.5

% Silt:

61.2

% Sand:

19.3

% Org. C:

2

pH:

5.8

CEC:

8.5 meq/100 g soil d.w.

Bulk density (g/cm³):

1.04

Soil no.:

#2

Soil type:

clay loam

% Clay:

34.2

% Silt:

44.3

% Sand:

21.5

% Org. C:

3

pH:

7.5

CEC:

36.2 meq/100 g soil d.w.

Bulk density (g/cm³):

1.04

Soil no.:

#3

Soil type:

sandy loam

% Clay:

9

% Silt:

33.3

% Sand:

57.8

% Org. C:

1.3

pH:

6.5

CEC:

10 meq/100 g soil d.w.

Bulk density (g/cm³):

1.26

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: France: Soil I - Bretagne soil & Soil II – Mussing soil
- Pesticide use history at the collection site: No pesticide treatments for at least 5 years prior to soil sampling. No cultivation in these fields since 1995.
- Geographic location: Germany: Soil III – Speyer 2.3
- Pesticide use history at the collection site: No pesticides between 1997 and 2001.
- Collection procedures: The soils selected are representative field soils and were freshly collected from the top layer.
- Sampling depth (cm): 0 - 20 cm
- Storage conditions: Acclimation at 20 °C for about 5 days before study.
- Storage length: Soil I &II - Stored for about 3 weeks at 4 °C; Soil III - Stored for about 8 weeks at 4 °C.
- Soil preparation: Sieved (2 mm)

Soil No.:

#1

Duration:

120 d

Soil No.:

#2

Duration:

120 d

Soil No.:

#3

Duration:

120 d

Soil No.:

#1

Initial conc.:

1.48 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#2

Initial conc.:

1.48 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#3

Initial conc.:

1.48 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Soil No.:

#1

Temp.:

20 ± 2 °C

Microbial biomass:

Day 0: 23.5; Day 120: 18.7

Soil No.:

#2

Temp.:

20 ± 2 °C

Microbial biomass:

Day 0: 34.1; Day 120: 36.5

Soil No.:

#3

Temp.:

20 ± 2 °C

Microbial biomass:

Day 0: 21.33; Day 120: 13.93

Details on experimental conditions:

EXPERIMENTAL DESIGN
Soil Preparation
The vegetation, larger soil fauna and stones, were removed prior to passing through a 2 mm sieve. During acclimation to room temperature, the soils were finger crumbled and turned over frequently to avoid excessive surface drying. Before use, the soil moisture content was determined for triplicate subsamples by oven drying and weighing. The moisture content was adjusted with bi-distilled water to about 46 % of its corresponding maximum water holding capacity (MWHC).

Test System
The study was carried out in glass metabolism flasks connected to an open air-flow-through system.
- Soil condition: fresh
- Soil (g/replicate): 100 g
- Control condition: untreated soil samples
- No. of replication controls: 6
- No. of replication treatments: 22
- Test apparatus (Type/material/volume): all-glass metabolism flasks
- Details of traps for CO2 and organic volatile: flasks were equipped with an air inlet and outlet. The system was continuously ventilated with moistened air. The out coming air was passed through a trapping system, equipped with absorption traps containing 50 mL of ethylene glycol and 50 mL of 2N NaOH, in this order, to collect organic volatiles and 14CO2, respectively.

Test material application
- Volume of test solution used/treatment: 6.98 mg/25 mL (labeled test item); 10.28 mg /25 mL unlabeled test item
- Application method: dropwise by using a Hamilton syringe

Experimental conditions
- Moisture maintenance method: The moisture content of the soil samples was controlled by weighing and adjusting to about 46 % of the soil maximum water holding capacity with water. The water content was controlled in selected samples every week and adjusted about every 14 days.
- Continuous darkness: Yes

OXYGEN CONDITIONS
- Methods used to create the aerobic conditions: The system was continuously ventilated with moistened air

SAMPLING DETAILS
- Sampling intervals: 0, 1, 3, 7, 14, 28, 56, 120 days
- Moisture content: 46 % of the soil maximum water holding capacity

Soil No.:

#1

% Recovery:

97.3

St. dev.:

2.1

Remarks on result:

other: 1.440 ± 0.032 mg/kg dry soil

Soil No.:

#2

% Recovery:

97.3

St. dev.:

1.8

Remarks on result:

other: 1.440 ± 0.027 mg/kg dry soil

Soil No.:

#3

% Recovery:

97.3

St. dev.:

2.6

Remarks on result:

other: 1.439 ± 0.038 mg/kg dry soil

Soil No.:

#1

% Degr.:

25.7

Parameter:

CO2 evolution

Sampling time:

120 d

Remarks on result:

other: Applied radioactivity evolved as 14CO2

Soil No.:

#2

% Degr.:

7.6

Parameter:

CO2 evolution

Sampling time:

120 d

Remarks on result:

other: Applied radioactivity evolved as 14CO2

Soil No.:

#3

% Degr.:

7.3

Parameter:

CO2 evolution

Sampling time:

120 d

Remarks on result:

other: Applied radioactivity evolved as 14CO2

Key result

Soil No.:

#1

DT50:

0.44 d

Type:

other: Single First Order (SFO) (DT50)

Temp.:

20 °C

Key result

Soil No.:

#2

DT50:

0.7 d

Type:

other: Single First Order (SFO) (DT50)

Temp.:

20 °C

Key result

Soil No.:

#3

DT50:

0.59 d

Type:

other: Single First Order (DT50)

Temp.:

20 °C

Transformation products:

yes

No.:

#3

No.:

#2

No.:

#1

Details on transformation products:

Please refer to the attached tables for the details representation of the formation and decline of each major and minor metabolite for each label and test dose.

Evaporation of parent compound:

yes

Volatile metabolites:

no

Residues:

no

Details on results:

TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes

MAJOR TRANSFORMATION PRODUCTS
The metabolite carbendazim was formed in all soils in large amounts already after 1 day (42.2 – 58.7 % AR) and reached maxima of 62.8 - 75.8 % in the different soils after 3 or 7 days, respectively. Two additional metabolites were detected in concentrations ≥5 % at a minimum of two consecutive sampling intervals in at least one soil: CM-0237 and 2-AB. Metabolite CM-0237 reached a maximum of 9.8 % AR (after 3 days). The metabolite 2-AB reached a maximum of 6.1 % with standard extraction at day 14 in soil Mussig (soil II) and was 5.0 % on average at the following sampling interval (day 28). A maximum of 18 % AR was extracted with the additional harsh extraction at day 120 from soil Speyer 2.3 (soil III).

MINOR TRANSFORMATION PRODUCTS
The metabolite DX-105 and up to 9 unknown other metabolites were detected. None of them exceeded 4.7 % AR.

EXTRACTABLE RADIOACTIVITY
Immediately after treatment (day 0), mean amounts of 98.6 %, 98.7 % and 99.4 % of the applied radioactivity could be extracted from soils I, II and III, respectively.
The extractable radioactivity decreased continuously to mean amounts of 31.2 %, 15.3 % and 23.3 % on day 120 in soils I, II and III, respectively. Soxhlet extractions were performed from day 1 onwards and recovered up to 22.3 % of the applied radioactivity.
High amounts of radioactivity were recovered by harsh extraction of selected samples (day 120; sample A) accounting for 14.7 % (soil I), 5.6 % (soil II) and 30.3 % (soil III) of the applied radioactivity, due to the very drastic conditions used.

NON-EXTRACTABLE RADIOACTIVITY
The amount of non-extractable radioactivity increased continuously for all soils until the end of incubation (day 120). On day 120, mean amounts of 39.7 %, 73.2 % and 65.9 % of the applied radioactivity were non-extractable from soils I to III, respectively

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: Volatile radioactivity other than 14CO2 did not exceed 0.1 % of the applied radioactivity until the end of incubation.

Table 1: Distribution and characterisation of radioactivity in the Bretagne soil (soil I) treated with phenyl-14C-labelled thiophanate-methyl and incubated at 20 ± 2 ºC and 46 % MWHC. Mean of duplicates is given. For the parent and the metabolites that occurred in highest concentrations, results from the two individual replicates are also presented.* All values as % of applied radioactivity (AR).

		days after application
		0	1	3	7	14	28	56	120
Parent		85.7 81.1	15.9 23.5	1.4 1.7	0.9 4.6	- -	0.6 -	- -	- -
	Mean	83.4	19.7	1.6	2.7	-	0.3	-	-
Carbendazim		8.3 10.2	63.0 54.5	72.6 74.2	76.2 75.4	68.0 69.1	53.5 50.8	38.9 36.7	23.0 25.2
	Mean	9.3	58.7	73.4	75.8	68.5	52.1	37.8	24.1
DX-105		1.7 1.6	4.0 4.6	1.3 1.5	- -	2.5 -	- -	- -	- -
	Mean	1.6	4.3	1.4	-	1.2	-	-	-
2-AB		- -	- -	0.6 0.4	1.3 -	3.4 3.7	3.2 2.9	3.3 3.2	2.6 2.8
	Mean	-	-	0.5	0.6	3.6	3.0	3.3	2.7
CM-0237 (M2) ^a		1.3 1.3	3.6 4.7	2.3 2.0	1.3 1.6	1.0 1.0	0.3 0.2	- 0.1	- -
	Mean	1.3	4.1	2.1	1.4	1.0	0.3	0.1	-
CM-0238 (M1) ^a		-	-	-	-	-	-	-	-
M3		-	-	1.7	1.9	1.2	0.7	0.5	0.3
M6		-	0.6	1.2	1.7	1.3	2.4	1.0	1.6
M7		0.7	0.8	0.6	-	0.5	0.3	0.5	0.3
M8		-	1.5	0.3	-	-	0.2	0.4	0.1
Extractable		98.6	86.0	77.1	69.3	57.5	47.7	31.6	10.5
Soxhlet		n.p.	6.6	8.6	16.2	21.9	12.9	14.4	20.7
Total extractable		98.6	92.6	85.7	85.5	79.4	60.6	46.0	31.2
Non-extractable		3.2	4.9	11.2	12.2	17.5	30.1	39.3	39.7
^14CO2		n.p.	<0.1	<0.1	0.2	0.8	3.5	10.3	25.7
Other Volatiles		n.p.	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1
Total recovery		101.8	97.5	97.0	97.9	97.7	94.2	95.6	96.6
97.3 ± 2.1

* Results for additional radioactive fractions (M5, M12, M13, M14), individually not exceeding 1.3 %, were not presented in detail by the author.

- Not detected

^a Amounts of M1 and M2 were corrected for mean amounts of M1 (2.7 %) and M2 (1.3 %) detected in the application solution before and after application.

Table 2: Distribution and characterisation of radioactivity in the Mussig soil (soil II) treated with phenyl-14C-labelled thiophanate-methyl and incubated at 20 ± 2 ºC and 46 % MWHC. Mean of duplicates is given. For the parent and the metabolites that occurred in highest concentrations, results from the two individual replicates are also presented.* All values as % of applied radioactivity (AR).

	days after application
		0	1	3	7	14	28	56	120
Parent		89.9 90.4	41.5 32.0	0.8 3.3	2.5 2.1	0.8 -	0.4 0.4	- -	- -
	Mean	90.1	36.7	2.1	2.3	0.4	0.4	-	-
Carbendazim		5.2 4.6	39.9 44.5	62.6 63.0	55.8 59.1	45.3 44.7	30.3 28.2	13.1 13.0	3.1 3.3
	Mean	4.9	42.2	62.8	57.4	45.0	29.2	13.1	3.2
DX-105		0.9 0.6	1.1 1.2	0.5 0.7	- -	- -	- -	- -	- -
	Mean	0.7	1.2	0.6	-	-	-	-	-
2-AB		- -	- -	1.6 1.3	3.1 2.3	5.5 6.7	5.9 4.2	3.4 3.9	1.5 1.3
	Mean	-	-	1.5	2.7	6.1	5.0	3.7	1.4
CM-0237 (M2) ^a		- -	2.9 4.3	5.6 6.1	8.0 5.2	4.4 5.5	5.0 4.9	3.2 3.4	2.7 3.1
	Mean	-	3.6	5.9	6.6	4.9	4.9	3.3	2.9
CM-0238 (M1) ^a		0.2	2.6	-	-	-	-	-	-
M3		-	-	2.8	-	2.3	1.3	1.3	0.6
M6		-	-	-	-	0.6	0.7	-	1.2
M7		-	0.7	3.9	4.6	4.0	2.7	2.8	2.5
M8		-	1.7	-	-	0.3	0.2	0.4	0.4
Extractable		98.7	86	69.9	57.7	48.1	32.3	11.8	3.4
Soxhlet		n.p.	6.7	11.7	17.2	17.3	13.9	16	11.9
Total extractable		98.7	92.7	81.6	74.9	65.4	46.2	27.8	15.3
Non-extractable		2.1	5.1	16.3	22.5	31.0	48.1	63.3	73.2
^14CO2		n.p.	<0.1	0.2	0.5	0.9	1.5	3.7	7.6
Other Volatiles		n.p.	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1
Total recovery		100.7	97.8	98.1	97.9	97.4	95.8	94.8	96.1
97.3 ± 1.8

* Results for additional radioactive fractions (M5, M11, M12, M13), individually not exceeding 0.8 %, were not presented in detail by the author.

- Not detected

^a Amounts of M1 and M2 were corrected for mean amounts of M1 (2.7 %) and M2 (1.3 %) detected in the application solution before and after application.

 

Table 3: Distribution and characterisation of radioactivity in the Speyer 2.3 soil (soil III) treated with phenyl-14C-labelled thiophanate-methyl and incubated at 20 ± 2 ºC and 46 % MWHC. Mean of duplicates is given. For the parent and the metabolites that occurred in highest concentrations, results from the two individual replicates are also presented.* All values as % of applied radioactivity (AR).

	days after application
		0	1	3	7	14	28	56	120
Parent		89.2 90.3	31.1 29.0	1.5 1.6	1.0 -	- -	- -	- -	- -
	Mean	89.7	30.0	1.6	0.5	-	-	-	-
Carbendazim		5.4 5.9	44.6 45.4	68.0 64.3	58.4 58.3	51.1 51.6	37.6 39.1	23.1 23.2	13.0 11.7
	Mean	5.7	45.0	66.1	58.4	51.4	38.3	23.1	12.3
DX-105		0.7 0.6	1.0 0.9	- -	- -	- -	- -	- -	- -
	Mean	0.6	1.0	-	-	-	-	-	-
2-AB		- -	- -	0.7 0.7	- -	2.3 2.2	1.6 1.8	1.9 1.8	2.6 -
	Mean	-	-	0.7	-	2.3	1.7	1.8	1.3
CM-0237 (M2) ^a		- -	5.4 6.0	11.2 8.5	7.2 9.6	7.9 8.3	6.6 6.2	3.3 3.7	2.3 2.3
Mean	Mean	-	5.7	9.8	8.4	8.1	6.4	3.5	2.3
CM-0238 (M1) ^a		0.4	5.0	-	0.5	-	-	-	-
M3		-	-	2.1	0.9	1.4	1.0	0.8	0.4
M6		-	-	0.3	-	1.1	1.5	0.1	1.6
M7		0.2	1.1	2.0	2.2	2.1	1.5	1.4	0.8
M8		-	0.2	0.2	-	0.2	0.4	0.2	0.2
Extractable		99.4	86.3	73.3	58.5	50.8	36.8	20.7	5.1
Soxhlet		n.p.	6.5	11.8	16.4	17.7	15.9	15.6	18.2
Total extractable		99.4	92.8	85.1	74.9	68.5	52.7	36.3	23.3
Non-extractable		1.4	5.7	14.8	20.1	27.2	39.8	56.7	65.9
^14CO2		n.p.	<0.1	0.1	0.4	0.7	1.4	3.4	7.3
Other Volatiles		n.p.	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1	<0.1
Total recovery		100.8	98.5	100.1	95.4	96.4	93.9	96.4	96.5
97.3 ± 2.6

* Results for additional radioactive fractions (M5, M11, M12, M13, M15), individually not exceeding 1.9 %, were not presented in detail by the author.

- Not detected

^a Amounts of M1 and M2 were corrected for mean amounts of M1 (2.7 %) and M2 (1.3 %), which were detected in the application solution before and after application

 

Table 4: Recovery of radioactivity as % AR in the different extraction steps, characterisation of the extractable radioactivity after harsh extraction and radioactivity in organic matter fractions, analysed in one sample taken at day 120.

	Bretagne Soil I	Mussig Soil II	Speyer 2.3 Soil III
Non-extractable after extraction at room temperature and Soxhlet extraction	40.3	72.5	63.8
Extractable radioactivity by “harsh extraction”	14.7	5.6	30.3
Carbendazim	7.2	1.1	9.0
2-AB	6.3	1.2	18.1
CM-0237 (M2)	0.8	1.9	0.6
CM-0238 (M1)	0.2	0.1	0.3
Others	0.2	1.3	2.3
Non-extractable after “harsh extraction”	25.6	66.9	33.5
Soluble fraction at low pH (fulvic acids)	10.1	8.3	7.7
Soluble fraction at high pH (humic acids)	7.5	1.1	11.7
Insoluble fraction (humins)	8.1	57.5	14.1

 

Table 5: Summary of kinetic re-analysis by Kiesel and Geibel (2016a,b) of the data from Völkl (2002); for the Bretagne soil the final pathway fit was done by Kiesel, Drechsler & Geibel (2017a,b). For thiophanate-methyl, only results for parent-only fit are shown. For the metabolites, the results from pathway-fit with thiophanate-methyl and the major metabolites (carbendazim, CM-0237 and 2-AB) are given.

Substance	Soil	Kinetic model	Mo	Parameter	χ^2, %-error	Prob>t	Lower CI	Upper CI	DT50 [days]	DT90 [days]
Thiophanate-methyl	Bretagne (soil I)	SFO	96.34	k = 1.5826	5.0	1.4E-08	1.4	1.8	0.44	1.5
		FOMC	96.34	α = 5.584 β = 3.034	5.2	n.r.	-9.4 -6.4	20.6 12.5	- a	- a
	Mussig (soil II)	SFO	96.22	k = 0.9936	5.8	7.0E-11	0.9	1.1	0.70	2.3
		FOMC	96.22	α = 1.25E+5 β = 1.26E+5	6.3	n.r.	1.2E+5 1.2E+5	1.3E+5 1.3E+5	0.70	2.3
	Speyer 2.3 (soil III)	SFO	96.77	k = 1.1812	1.9	1.9E-10	1.1	1.2	0.59	1.9
		FOMC	96.77	α = 2.55E+5 β = 2.16E+5	2.2	n.r.	2.5E+5 2.1E+5	2.6E+5 2.2E+5	0.59	1.9
Carbendazim	Bretagne (soil I)	SFO-SFO	0	k = 0.01096	4.7	2.0E-16	9.3E-3	0.013	63.2	210
	Mussig (soil II)	SFO-SFO	0	k = 0.03144	2.1	<2E-16	0.029	0.034	22.0	73.2
	Speyer 2.3 (soil III)	SFO-SFO	0	k = 0.01843	5.0	<2E-16	0.016	0.021	37.6	125
CM-0237	Bretagne (soil I)	SFO-SFO	0	k = 0.2438	30.2	2.7E-05	0.14	0.35	2.8	9.4
	Mussig (soil II)	SFO-SFO	0	k = 0.00801	8.5	2.8E-05	0.004	0.01	86.5	287
	Speyer 2.3 (soil III)	SFO-SFO	0	k = 0.01491	7.7	1.2E-08	0.010	0.019	46.5	154
2-AB	Bretagne (soil I)	SFO-SFO ^b	0	k = 0.05135	20.0	1.6E-05	0.03	0.07	13.5	44.8
	Mussig (soil II)	SFO-SFO ^b	0	k = 0.06027	16.1	1.3E-07	0.04	0.08	11.5	38.2
	Speyer 2.3 (soil III)	SFO-SFO b	0	k = 0.02961	33.6	9.7E-3	0.0056	0.054	- ^c	- ^c

n.r Not relevant.

n.p Not provided.

^a Author considered the results statistically not reliable.

^b Carbendazim as pre-cursor.

^c Result considered as not reliable at experts’ consultation (September, 2017).

 

Table 6: Formation fractions of carbendazim, CM-0237 and 2-AB, according to kinetic re-analysis by Kiesel and Geibel (2016a,b) of the data from Völkl (2002); for the Bretagne soil the final pathway fit was done by Kiesel, Drechsler & Geibel (2017a,b).

Formation	Soil	Formation fraction	St. dev.
Thiophanate-methyl → Carbendazim	Bretagne (soil I)	0.79	0.02
	Mussig (soil II)	0.72	0.02
	Speyer 2.3 (soil III)	0.69	0.015
Thiophanate-methyl → CM-0237	Bretagne (soil I)	0.055	0.01
	Mussig (soil II)	0.064	0.007
	Speyer 2.3 (soil III)	0.099	0.008
Carbendazim → 2-AB	Bretagne (soil I)	0.36	0.07
	Mussig (soil II)	0.33	0.04
	Speyer 2.3 (soil III)	0.12 a	0.03 ^a

^a Result considered as not reliable at experts’ consultation (September, 2017).

Conclusions:

Under aerobic conditions in soil the test item degraded to its major metabolite Carbendazim and several minor metabolites. Two of the metabolites showing the highest amounts were identified by LC-MS. Two further metabolites were characterized as DX-105 and 2-AB by co-chromatography. The degradation products were eventually mineralized to carbon dioxide or bound to soil organic matter.
The test item degraded rapidly with half-lives (DT50) of 0.44, 0.7 and 0.59 days in soils I, II and III, respectively. The corresponding DT90 values were 1.5, 2.3 and 1.9 days in soils I, II and III, respectively. The amount of 14CO2 evolved increased continuously with the incubation time. Maximum values of 25.7 %, 7.6 % and 7.3 % of the applied radioactivity were evolved as 14CO2 from soils I, II and III, respectively. Volatile radioactivity other than 14CO2 did not exceed 0.1 % of the applied radioactivity until the end of incubation.

Executive summary:

The degradation and metabolism of ¹⁴C-labeled test item was investigated in three soils under aerobic conditions according to OECD 307 for a period of up to 120 days. The following freshly sampled soils were selected: soil I (Bretagne I/France; silt loam), soil II (Mussig/France; clay loam) and soil III (Speyer 2.3/Germany; sandy loam). For this purpose, the test item was applied to the soils at the concentration of 1.48 mg test item/kg soil dry weight. The soil samples were incubated at 20 ± 2 °C and at a moisture content of about 46 % of the soils maximum water holding capacity (MWHC). During the whole incubation period the soil samples were aerated by a constant air-flow passing through the incubation flasks sequentially followed by ethylene glycol and sodium hydroxide solutions to collect organic volatiles and CO₂, respectively.

Duplicate samples from all three soils were taken for analysis after 0, 1, 3, 7, 14, 28, 56 and 120 days of incubation. All samples were subjected to exhaustive solvent extractions, and the concentrated extracts were analyzed by HPLC and TLC. The total radioactivity balance and the distribution of radioactivity in every incubation sample was established on each sampling day. The following results were obtained:

The total mean recoveries were 97.3 % ± 2.1 % (1.440 ± 0.032 mg/kg dry soil), 97.3 % ± 1.8 % (1.440 ± 0.027 mg/kg dry soil) and 97.3 % ± 2.6 % (1.439 ± 0.038 mg/kg dry soil) of the applied radioactivity for soils I, II and III, respectively.

Individual recoveries ranged from 93.3 % (1.381 mg/kg) to 102.9 % (1.523 mg/kg) for soils I to III.

Immediately after treatment (day 0), mean amounts of 98.6 %, 98.7 % and 99.4 % of the applied radioactivity could be extracted from soils I, II and III, respectively. With increasing incubation time, the amount of extractable radioactivity decreased continuously amounting to 31.2 %, 15.3 % and 23.3 % of the applied radioactivity on day 120 in soils I, II and III, respectively. Soxhlet extractions performed from day 1 onwards recovered up to 22.3 % of the applied radioactivity.

Further harsh extractions using acetonitrile/2N hydrochloric acid performed for selected samples on day 120, recovered additional amounts of 14.7 %, 5.6 % and 30.3 % of the applied radioactivity in soils I to III, respectively.

The amount of non-extractable radioactivity increased continuously until the end of incubation (day 120), representing 39.7 %, 73.2 % and 65.9 % of the applied radioactivity in soils I, II and III, respectively

Organic matter fractionation of the non-extractable radioactivity (day 120 samples after harsh extraction) indicated that the major part of the radioactivity was incorporated into the immobile humic acids and humin fraction representing 15.6 %, 58.6 % and 25.8 % of the applied radioactivity in soils I to III, respectively. The minor part of the bound radioactivity was associated with the more mobile fulvic acids amounting to 10.1 %, 8.3 % and 7.7 % of the applied radioactivity in soils I to III, respectively.

The mineralization of ¹⁴C-labelled test item, i.e. the formation of carbon dioxide reached maximum values of 25.7 %, 7.6 % and 7.3 % of the applied radioactivity for soils I to III at the end of incubation (day 120), respectively. Other volatile radioactivity did not exceed 0.1 % of the applied radioactivity.

In soil I, ¹⁴C-labelled test item amounted to a mean of 83.4 % of the applied radioactivity immediately after treatment (day 0) and decreased rapidly to 2.7 % of the applied radioactivity after 7 days of incubation. Thereafter, it was only detected once, amounting to 0.3 % of the applied radioactivity.

Radioactive fraction M9 characterized as Carbendazim - methyl benzimidazol-2-yl carbamate - represented the main degradation product. M9 amounted to a maximum of 75.8 % of applied radioactivity after 14 days of incubation. Thereafter it degraded continuously amounting to 24.1 % of the applied radioactivity at the end of incubation (day 120). Two degradation products characterized as DX-105 (M4) and 2-AB (M10) and up to nine unknown radioactive fractions were detected. None of them exceeded 4.3 % (M4) of the applied radioactivity.

In soil II, ¹⁴C-labelled test item amounted to a mean of 90.1 % of the applied radioactivity immediately after treatment (day 0). It degraded rapidly representing 36.7 % on day 1 and 2.3 % of the applied radioactivity on day 7.

M9 characterized as Carbendazim and representing the main degradation product, increased continuously during the incubation reaching a maximum of 62.8 % of the applied radioactivity after 3 days of incubation and decreasing thereafter to 3.2 % of the applied radioactivity at the end of incubation (day 120).

Radioactive fractions M1 and M2 characterized by LC-MS amounted to maximum amounts of 2.6 % and 6.6 % of the applied radioactivity after 1 and 7 days, respectively. Additionally, up to eleven degradation products of minor importance were detected, none of them exceeding 6.1 % (M10, characterized as 2-AB) of the applied radioactivity.

In soil III, ¹⁴C-labelled test item amounted to 89.7 % of the applied radioactivity immediately after treatment (day 0) and decreased continuously to 30.0 % on day 1 and 0.5 % of the applied radioactivity on day 7.

Carbendazim (M9) representing the main degradation product reached a maximum of 66.1 % on day 3 and decreased to 12.3 % at the end of incubation (day 120). Radioactive fractions M1 and M2 amounted to maximum amounts of 5.0 % and 9.8 % after 1 and 3 days of incubation, respectively. M1 decreased rapidly and represented 0.5 % of the applied radioactivity after 7 days of incubation. M2 decreased continuously to 3.6 % of the applied radioactivity at the end of incubation (day 120).

Up to eleven radioactive fractions were detected, none of them exceeding an amount of 2.3 % (M10, characterized as 2-AB) of the applied radioactivity.

In this current study, DT₅₀s were calculated for the test item and the metabolites carbendazim and the unknown M2 using first-order kinetic model (non-linear curve fitting). These results were superseded by the re-evaluation by Kiesel and Geibel (2015a, b) which during the evaluation was replaced by Kiesel and Geibel (2016a,b). The kinetic re-evaluation was performed according to FOCUS Degradation kinetics report (2006, 2014) with KinGUI version 2.1. Parent only data were fitted to SFO and FOMC kinetic models. Degradation pathway-fits were performed for thiophanate-methyl and the metabolites carbendazim, CM-0237 and 2-AB in a sequential fitting approach, using SFO-SFO. The optimization method IRLS and the optimization algorithm LM were used. The results were normalised to standard conditions (20 °C and pH 2) to fulfil requirements for modelling endpoints according to FOCUS Groundwater (2000, 2014).

Under aerobic conditions in soil the test item degraded to its major metabolite Carbendazim and several minor metabolites. Two of the metabolites showing the highest amounts were identified by LC-MS. Two further metabolites were characterized as DX-105 and 2-AB by co-chromatography. The degradation products were eventually mineralized to carbon dioxide or bound to soil organic matter.

The test item degraded rapidly with half-lives (DT₅₀) of 0.44, 0.7 and 0.59 days in soils I, II and III, respectively. The corresponding DT₉₀ values were 1.5, 2.3 and 1.9 days in soils I, II and III, respectively. The amount of ¹⁴CO₂ evolved increased continuously with the incubation time. Maximum values of 25.7 %, 7.6 % and 7.3 % of the applied radioactivity were evolved as ¹⁴CO₂ from soils I, II and III, respectively. Volatile radioactivity other than ¹⁴CO₂ did not exceed 0.1 % of the applied radioactivity until the end of incubation.

Description of key information

Biodegradation in soil (n=3 (SFO))

DT₅₀ Soil I = 0.44 days

DT₅₀ Soil II = 0.70 days

DT₅₀ Soil III = 0.59 days

DT₉₀ Soil I = 1.5 days

DT₉₀ Soil II = 2.3 days

DT₉₀ Soil III = 1.9 days

Mineralisation (¹⁴CO₂): 7.3 – 25.7 % (day 120) (source: 815051, Völkl S. 2002)

Key value for chemical safety assessment

Half-life in soil:

0.7 d

at the temperature of:

20 °C

Additional information

Biodegradation in soil (n=3 (SFO)): The degradation of the ¹⁴C-labled test item was determined in three soil samples soil I (Bretagne I/France; silt loam), soil II (Mussig/France; clay loam) and soil III (Speyer 2.3/Germany; sandy loam) under aerobic conditions according to OECD 307. Since the study meets validity criteria, it was concluded to be reliable. The endpoint is the rapid degradation of the test item after 120 with half-lives (DT50) of 0.44, 0.7 and 0.59 days in soils I, II and III, respectively. The corresponding DT90 values were 1.5, 2.3 and 1.9 days in soils I, II and III, respectively. (Source: 815051, Völkl S. 2002)

 

Biodegradation in soil (n=1 (SFO)): The degradation of the ¹⁴C-labled test item was determined in one soil sample Speyer 5M (sandy loam) under aerobic conditions according to OECD 307. Since the study meets validity criteria, it was concluded to be reliable. The study provided additional information for risk assessment. The endpoint is the degradation of the test item after 120 days with a half-life (DT₅₀) of 0.29 and a corresponding DT₉₀ of 0.57 days. (Source: 20110080, Dr. Daniel Adam, 2014)