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Environmental fate & pathways

Biodegradation in soil

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Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
14 Oct 2013 - 23 Feb 2015
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
Deviations:
no
Qualifier:
equivalent or similar to guideline
Guideline:
EPA OPPTS 835.4100 (Aerobic Soil Metabolism)
Version / remarks:
2008
GLP compliance:
yes (incl. QA statement)
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
USDA (US Department of Agriculture)
Soil no.:
#1
Soil type:
loamy sand
% Clay:
>= 7.9 - <= 8.2
% Silt:
>= 15.3 - <= 16.3
% Sand:
>= 75.8 - <= 76.5
% Org. C:
>= 1.61 - <= 1.74
pH:
5.5
CEC:
>= 10 - <= 10.2 other: mmol/100 g soil
Details on soil characteristics:
SOIL COLLECTION AND STORAGE
- Geographic location: near Hanhofen, Germany, latitude 49° 19’ N, longitude 08° 20’ E
- Pesticide use history at the collection site: The soil had not been subjected to any pesticide or organic fertilizer treatment for at least the past four years.
- Collection procedures: Collected from the field from the top layer (about 20 cm). The top plant cover was removed and thereafter, the soil top layer was put in plastic bags with free access to air.
- Storage conditions: stored at approximately 4 °C
- Storage length: about 2.5 weeks
- Soil preparation: 2 mm sieved
Soil No.:
#1
Duration:
28 d
Soil No.:
#1
Initial conc.:
4.58 mg/kg soil d.w.
Based on:
test mat.
Parameter followed for biodegradation estimation:
radiochem. meas.
test mat. analysis
Soil No.:
#1
Temp.:
21 °C
Humidity:
pF 2
Microbial biomass:
491 - 513 mg org. C/kg soil dw
Details on experimental conditions:
1. PRELIMINARY EXPERIMENTS: not reported

2. EXPERIMENTAL DESIGN
- Soil condition: Soil was conditioned to room temperature for about 3 days, the moisture content of the soil was determined and adjusted with purified water to values of pF 2.0.
- Soil (g/replicate): 100 g
- No. of replication controls, if used: Duplicate samples were taken for extraction and analysed
- No. of replication treatments: Duplicate samples were taken for extraction and analysed
- Test apparatus (Type/material/volume): all glass metabolism flasks (inner diameter: about 10.6 cm, volume: approx. 1 L) equipped with an air inlet and outlet
- Details of traps for CO2 and organic volatile, if any: trapping system equipped with three absorption traps (one trap containing ethylene glycol and two traps containing 2N NaOH/methanol (1:1; v:v), in this sequence)
- Identity and concentration of co-solvent: acetone 830 µL/100 g soil

Test material application
- Volume of test solution used/treatment: 830 µL
- Application method: applied drop-wise to the soil surface and mixed thoroughly by turning the flasks containing the applied soils
- Is the co-solvent evaporated: not reported

Any indication of the test material adsorbing to the walls of the test apparatus: not reported

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: moisture content of the soil samples was controlled regularly during the study and adjusted to the original moisture content with water, followed by mixing after weighing
- Continuous darkness: yes

3. OXYGEN CONDITIONS
- Methods used to create the aerobic conditions: The flasks were equipped with an air inlet and outlet and the system was continuously ventilated with moistened air.

4. SUPPLEMENTARY EXPERIMENTS: not reported

5. SAMPLING DETAILS
- Sampling intervals: after 0.25, 0.67, 1, 2, 3, 7, 14 and 28 days of incubation
- Sampling method for soil samples: duplicate samples were taken for extraction and analysed
- Method of collection of CO2 and volatile organic compounds: radioactivity in the sodium hydroxide/methanol traps was precipitated with barium hydroxide with selected samples: 0.5 mL of alkaline solution was diluted with 10 mL of Milli-Q® water and
precipitations were induced by adding 5 mL of saturated barium hydroxide solution. The suspensions were centrifuged for 5 to 10 minutes and the supernatants were tested for quantitative precipitation by adding saturated Ba(OH)2 solution. If no turbidity developed upon the second addition of Ba(OH)2, the supernatants were counted by LSC measurement. If turbidity was observed, LSC measurements were performed after another precipitation step. The absence of radioactivity in the supernatants after
precipitation was taken as proof that only 14CO2 was present in the sodium hydroxide solutions, whereas radioactivity remaining in the supernatants after precipitation was accounted to CS2.
- Sampling intervals/times for:
> Moisture content: not reported
> Sample storage before analysis: not reported
Soil No.:
#1
Sampling day(s):
28 d
% Total extractable:
12.4
% Non extractable:
29.8
% CO2:
53.2
% Other volatiles:
0.1
% Recovery:
97.1
Parent/product:
parent
Soil No.:
#1
% Degr.:
100
Parameter:
radiochem. meas.
Sampling time:
28 d
Soil No.:
#1
DT50:
0.6 d
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Soil No.:
#1
DT50:
1.4 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other: re-calculated to 12 °C using Arrhenius equation
Transformation products:
yes
Remarks:
For further details see field "any other information on results incl. tables".
No.:
#1
Details on transformation products:
- Formation and decline of each transformation product during test: Two major fractions, Thiram and M1.1, were detected: Thiram was identified by co-chromatography on HPLC and initially detected after 6 hours (day 0.25) with maximum mean amounts of 42.5% AR, then subsequently decreased to 7.5% AR on day 3, and dissipated after 7 days of incubation. M1.1 was initially detected at time 0 with mean amounts of 11.5% AR, reaching maximum mean amounts of 34.9% AR on day 1, and subsequently decreased to 11.1% AR at the end of incubation (day 28). Besides, a number of minor fractions were detected. None of the remaining fractions exceeded a mean amount of 5.7% AR (M1.11, day 1) at any time throughout the study.
- Pathways for transformation: The main degradation pathway of [14C] Ziram in soil proceeded through formation of major metabolite Thiram, major fraction M1.1, and several minor fractions with ultimate formation of bound residues and radioactive carbon dioxide.
Evaporation of parent compound:
no
Volatile metabolites:
yes
Remarks:
CO2, CS2
Residues:
yes
Details on results:
TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes

MAJOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: Thiram: initially detected after 6 hours (day 0.25) with maximum mean amounts of 42.5% AR, then subsequently decreased to 7.5% AR on day 3, and dissipated after 7 days of incubation. M1.1: initially detected at time 0 with mean amounts of 11.5% AR, reaching maximum mean amounts of 34.9% AR on day 1, and subsequently decreased to 11.1% AR at the end of incubation (day 28).

MINOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: A number of minor fractions were detected. None of these fractions exceeded a mean amount of 5.7% AR (M1.11, day 1) at any time throughout the study.

TOTAL UNIDENTIFIED RADIOACTIVITY (RANGE) OF APPLIED AMOUNT:

EXTRACTABLE RESIDUES
- % of applied amount at day 0: 99.7%
- % of applied amount at end of study period: 12.4%

NON-EXTRACTABLE RESIDUES
- % of applied amount at day 0: not performed
- % of applied amount at end of study period: 29.8%

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: 53.2

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: 0.1%

Table 1: Radioactivity balance in soil Speyer 2.2 treated with the test item. Values in percent of applied radioactivity.

(% AR)

 

 

Sample

INCUBATION TIME IN DAYS

 

0

 

0.25

 

0.67

 

1

 

2

 

3

 

7

 

14

 

28

 

Extractables*

A

 

B

98.4

 

101.1

79.4

 

82.8

70.5

 

70.3

59.3

 

58.3

35.6

 

35.4

24.9

 

30.1

3.2

 

4.6

1.2

 

1.3

1.1

 

1.1

 

Soxhlet**

A

 

B

n.p.

 

n.p.

2.6

 

2.5

3.6

 

2.9

2.2

 

2.1

2.9

 

2.6

2.3

 

2.4

2.2

 

3.2

2.0

 

1.9

2.2

 

2.0

 

Reflux***

A

 

B

n.p.

 

n.p.

9.4

 

8.3

10.3

 

11.7

12.9

 

11.0

16.6

 

12.2

11.5

 

11.6

12.9

 

13.8

11.0

 

12.1

9.1

 

9.4

 

 

Total Extractables

A

 

B

98.4

 

101.1

91.3

 

93.6

84.4

 

84.9

74.4

 

71.5

55.0

 

50.3

38.7

 

44.1

18.3

 

21.5

14.2

 

15.4

12.4

 

12.5

Mean

99.7

92.5

84.7

72.9

52.7

41.4

19.9

14.8

12.4

 

 

Non-extractables

A

 

B

n.p.

 

n.p.

10.9

 

10.6

14.2

 

15.0

18.1

 

20.2

28.2

 

31.5

30.5

 

26.1

27.9

 

27.2

28.7

 

30.0

30.4

 

29.1

Mean

n.p.

10.7

14.6

19.2

29.8

28.3

27.6

29.4

29.8

 

14CO2

A

 

B

n.p.

 

n.p.

1.6

 

<0.1

2.6

 

2.4

0.3

 

3.5

9.7

 

22.1

26.4

 

19.8

46.6

 

42.2

51.5

 

50.3

55.1

 

51.3

Mean

n.p.

0.8

2.5

1.9

15.9

23.1

44.4

50.9

53.2

 

 

Other volatiles in EG

A

 

B

n.p.

 

n.p.

<0.1

 

<0.1

<0.1

 

<0.1

<0.1

 

<0.1

<0.1

 

0.1

0.1

 

<0.1

0.2

 

0.2

0.2

 

0.2

0.2

 

<0.1

Mean

n.p.

<0.1

<0.1

<0.1

<0.1

<0.1

0.2

0.2

0.1

 

T O T A L

A

 

B

98.4

 

101.1

103.8

 

104.3

101.4

 

102.4

92.8

 

95.3

93.0

 

104.0

95.7

 

90.1

93.1

 

91.1

94.6

 

95.8

98.1

 

93.0

MEAN ± SD

 

 

 

97.1

±

4.7

 

 

 

* Acetonitrile/buffer (2:1,v:v), up to four times.Preparation of the buffer solution: (0.01 M Na2HPO4 + 0.01 M NaH2PO4 adjusted to pH 9 with NaOH.

** Soxhletextraction using acetonitrile/water (9:1;v/v) for four hours

*** Reflux extraction using acetonitrile/0.1 M HCl (1:1, v:v) for four hours.

 

n.p.  =  Not performed

SD = Standard deviation

Table 2: Pattern of degradation and formation of fractions in soil Speyer 2.2 treated with test item. Values in percent of applied radioactivity.

(% AR)

 

Sample

INCUBATION TIME IN DAYS

0

0.25

0.67

1

2

3

7

14

28

 

Parent

A

B

83.7

83.5

22.6

32.5

21.1

19.6

*

*

*

*

*

*

*

*

*

*

*

*

Mean

83.6

27.5

20.4

*

*

*

*

*

*

 

M1.1

A

B

11.3

11.7

14.7

13.9

25.2

25.0

43.5

26.2

32.4

23.3

18.5

29.2

14.9

17.3

12.3

13.6

10.9

11.4

Mean

11.5

14.3

25.1

34.9

27.9

23.9

16.1

13.0

11.1

 

M1.3

A

B

*

*

1.8

1.6

3.3

2.6

4.1

4.5

*

1.1

0.9

1.1

*

*

*

*

0.4

0.6

Mean

*

1.7

3.0

4.3

0.6

1.0

*

*

0.5

 

M1.4

A

B

*

*

*

*

*

*

*

*

*

1.2

*

*

*

*

*

*

0.4

*

Mean

*

*

*

*

0.6

*

*

*

0.2

 

M1.5

A

B

*

*

*

1.4

0.3

*

*

*

*

*

0.9

*

1.0

0.8

0.9

0.8

0.2

0.3

Mean

*

0.7

0.2

*

*

0.4

0.9

0.8

0.2

 

M1.6

A

B

*

*

*

1.5

1.2

2.2

*

*

*

*

*

*

*

*

*

*

*

*

Mean

*

0.7

1.7

*

*

*

*

*

*

 

M1.7

A

B

*

*

*

*

*

*

*

*

*

*

*

*

0.8

0.7

0.6

0.5

0.2

0.3

Mean

*

*

*

*

*

*

0.8

0.5

0.2

 

M1.8

A

B

*

*

3.8

1.7

3.0

2.5

* 2.3

1.4

1.4

*

*

*

*

*

*

0.2

*

Mean

*

2.7

2.7

1.2

1.4

*

*

*

0.1

 

M1.9

A

B

*

*

2.2

2.4

*

1.3

3.5

*

*

2.0

1.7

1.7

* 0.8

0.5

0.5

*

*

Mean

*

2.3

0.7

1.7

1.0

1.7

0.4

0.5

*

* Not detected

Table 3: Pattern of degradation and formation of fractions in soil Speyer 2.2 treated with test item. Values in percent of applied radioactivity (continued)

 (% AR)

 

Sample

INCUBATION TIME IN DAYS

0

0.25

0.67

1

2

3

7

14

28

 

M1.10

A

B

*

*

*

*

3.6

4.1

*

3.6

*

*

*

*

*

*

*

*

*

*

Mean

*

*

3.8

1.8

*

*

*

*

*

 

M1.11

A

B

*

*

*

*

*

*

8.5

2.8

2.0

2.5

1.6

2.9

*

*

*

*

*

*

Mean

*

*

*

5.7

2.3

2.2

*

*

*

 

M1.12

A

B

*

*

*

*

*

*

2.9

3.1

1.1

8.1

7.9

1.4

*

*

*

*

*

*

Mean

*

*

*

3.0

4.6

4.6

*

*

*

 

Thiram (M1.13)

A

B

*

*

46.3

38.6

26.7

27.6

8.5

10.6

9.4

8.5

7.2

7.8

*

*

*

*

*

*

Mean

*

42.5

27.1

9.6

9.0

7.5

*

*

*

 

M1.16

A

B

*

*

*

*

*

*

*

1.1

2.4

1.0

*

*

1.6

2.0

*

*

*

*

Mean

*

*

*

0.5

1.7

*

1.8

*

*

 

M1.17

A

B

*

*

*

*

*

*

*

3.4

*

*

*

*

*

*

*

*

*

*

Mean

*

*

*

1.7

*

*

*

*

*

 

M1.18

A

B

*

*

*

*

*

*

*

6.9

4.8

*

*

*

*

*

*

*

*

*

Mean

*

*

*

3.4

2.4

*

*

*

*

 

M1.19

A

B

*

*

*

*

*

*

3.3

7.0

1.4

1.1

*

*

*

*

*

*

*

*

Mean

*

*

*

5.1

1.3

*

*

*

*

 

M1.20

A

B

3.4

5.9

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

Mean

4.7

*

*

*

*

*

*

*

*

Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
18 May 1996 - 24 February 1997
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
only one type of soil tested, anaerobic conditions were not created according to SETAC recommendations
Qualifier:
according to guideline
Guideline:
other: 40 CFR 158 Environmental Fate, USEPA Pesticide Assessment Guidelines Subdivision N; Series 162-1.
Deviations:
no
GLP compliance:
yes
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic/anaerobic
Soil classification:
USDA (US Department of Agriculture)
Soil no.:
#1
Soil type:
sandy loam
% Clay:
7
% Silt:
32
% Sand:
61
% Org. C:
1.8
pH:
5.4
CEC:
9 meq/100 g soil d.w.
Details on soil characteristics:
Soil origin: Almond grove
Soil No.:
#1
Duration:
30 d
Initial conc.:
2.99 mg/kg soil d.w.
Based on:
act. ingr.
Soil No.:
#1
Temp.:
25 °C
Details on experimental conditions:
- Following 2 days of aerobic incubation, the treated soil was flooded with water and the atmosphere replaced with nitrogen to establish anaerobic conditions. This procedure is not in accordance with the SETAC guidelines which recommend to maintain the soil for 30 days under anaerobic conditions prior to application of the a.s. No indication is given about the determination of the redox potential of the sacrificed samples.
Anaerobic incubation in the laboratory at 25 ± 1 °C in the dark; Application rate was 2.99 mg a.s./kg soil.
DT50:
14.12 d
Type:
(pseudo-)first order (= half-life)
Temp.:
25 °C
DT50:
47 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other: re-calculated to 12 °C using Arrhenius equation
Transformation products:
yes
No.:
#1
No.:
#2
Details on transformation products:
Ten metabolites, designated as M1-M10, were observed during both the aerobic and anaerobic phases of the study. M9 was the highest in concentration at an average of 7.98% at day 0 during the aerobic phase and then quickly declined to less than 2% by day 1. M9 steadily decreased throughout the anaerobic phase to a final value of 0.41% by day 30. Degradate D1, was characterized as thiram by crochromatography with the thiram reference chemical. M1 possessed the second highest concentration starting at time zero (2.75% of the dose) under aerobic conditions but was then stabilized between 4.3% and 4.7% of the applied radioactivity throughout 30 days under anaerobic conditions. This metabolite was identified as dimethyldithiocarbamic acid (DDC).
Evaporation of parent compound:
no
Volatile metabolites:
yes
Residues:
yes
Details on results:
Volatiles, which included 14CO2 and 14CS2, accounted for 37.64% of the applied dose. The majority (>35.20% of applied radioactivity) of the evolved volatiles was confirmed to be 14C02 by barium salt precipitation.

Volatiles (mainly 14CO2) accounted for ca. 38% AR. The main metabolite dimethyldithiocarbamic acid was detected at a level of ~ 4.5% AR during the whole study. None of the other metabolites exceeded 4.67% AR during the anaerobic study. No unique metabolites were detected in anerobic soil samples.

Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
25 January 2001 - 12 October 2001
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
other: Commision Directive 95/36/EC of July 14, 1995, Annex I, 7.1.1.2.1 laboratory studies - aerobic degradation
Deviations:
no
Principles of method if other than guideline:
Based on:
- SETAC (Europe): Procedures for assessing the enviromental fate and ecotoxicity of pesticides, March 1995, Part 1 - Aerobic degredation
- OECD TG: Aerobic - Anaerobic Transformation in Soil (Draft proposal, October 1999)
GLP compliance:
yes (incl. QA statement)
Remarks:
The Swiss GLP Monitoring Authorities
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
USDA (US Department of Agriculture)
Soil no.:
#1
Soil type:
loamy sand
% Clay:
8.2
% Silt:
17
% Sand:
74.8
% Org. C:
2.28
pH:
5.8
CEC:
11 meq/100 g soil d.w.
Soil no.:
#2
Soil type:
sandy loam
% Clay:
6.4
% Silt:
21.9
% Sand:
71.7
% Org. C:
1.2
pH:
7.5
CEC:
7.3 meq/100 g soil d.w.
Soil no.:
#3
Soil type:
silt loam
% Clay:
18
% Silt:
51.3
% Sand:
26.8
% Org. C:
2
pH:
7.5 - 8.2
CEC:
15.3
Details on soil characteristics:
SOIL COLLECTION AND STORAGE
- Geographic location: Speyer, Germany (Soil I), VS, Switzerland (Soil II) and Nambsheim, France (Soil III)
- Pesticide use history at the collection site: no pesticide, organic or inorganic treatment at least for the last two years
- Collection procedures: the soils were freshly collected from the sampling sites (0-20 cm top layer)
- Sampling depth (cm): 20 cm
- Storage conditions and length: soil samples were acclimatised to room temperature in the laboratory for 3-4 weeks. The soils were crumbled and turned over to avoid excessive drying of the surface and water was added if needed. The remaining soil aliquots were stored then at 4°C in the dark
- Soil preparation: after removal of vegetation, stones and soil fauna, the soils were passed through a 2 mm sieve

PROPERTIES OF THE SOILS (in addition to defined fields)
- Moisture at 1/3 atm (%): adjusted to about 40% Maximum Water holding Capacity
Duration:
28 d
Initial conc.:
2.99 mg/kg soil d.w.
Based on:
act. ingr.
Soil No.:
#1
Temp.:
20 °C
Humidity:
40-50% of MWC
Microbial biomass:
319 mg carbon/kg dry soil (start of incubation period)
Soil No.:
#2
Temp.:
20°C
Humidity:
40-50% of MWC
Microbial biomass:
204 mg carbon/kg dry soil (start of incubation period)
Soil No.:
#3
Temp.:
20°C
Humidity:
40-50% MWC
Microbial biomass:
225 mg carbon/kg dry soil (start of incubation period)
Soil No.:
#1
Temp.:
10°C
Humidity:
40-50% of MWC
Microbial biomass:
319 mg carbon/kg dry soil (start of incubation period)
Details on experimental conditions:
- Aliquots of 100 g soil samples based on dry weight of the soil were filled in all-glass cylindrical metabolism flasks (volume: ca. 1 L) in the dark at 20 ± 1 °C. The flasks were equipped with an air inlet and outlet. The System was continuously ventilated with moistened air. The outcoming air was passed through a trapping system, equipped with two absorption traps containing 50 mL of ethylene glycol and 50 mL 2 M NaCH/methanol (1:1; v/v) to trap organic volatiles and 14CO2/14CS2, respectively. Additionally, one soll type (soil 1) was also incubated at 10°C.
- 300 uL of the application solution was added dropwise to the soil surface of each sample by means of a Hamilton syringe. After each addition (drop), the soil was thoroughly mixed to ensure a homogeneous distribution of the test item and to allow the organic solvent to evaporate. The control samples were treated with an equal amount of acetone without test item. The applied concentration corresponded to 2.99 mg a.i./kg soil assuming an even distribution of the test item in the top 10 cm soil layer and a soil bulk density of 1.0 g/cm3

DT50:
< 1 h
Type:
(pseudo-)first order (= half-life)
Transformation products:
yes
No.:
#1
Details on transformation products:
Besides the main degradation product Thiram, at least 13 unknown degradation products of minor importance were detected.
Evaporation of parent compound:
no
Volatile metabolites:
yes
Residues:
yes

Ziram degraded very rapidly with DT50 values of less than 1 hour and DT90 values of about 1 to 3 days in all soils tested.

The metabolic pathway of Ziram was similar in all soils tested. 14C-Ziram was rapidly degraded to at least 13 radioactive fractions. The main degradation product was carbon dioxide ( 51 -58% and 40% of AR after 28 days at 30,°C and 10°C respectively).

Additionally to 14CO2 one degradate exceeded 10% of the applied radioactivity (M1, characterised as Thiram). Thiram reached amounts of up to 49.8% AR However, it was rapidly degraded in all soils (DT50 = 1 -3 days).

Incorporation into the organic matter of soil played also a significant role on the degradation of the test substance.

Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
17 November 1994- 17 April 1996
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: GLP study with acceptable restrcitions (one soil tested)
Qualifier:
according to guideline
Guideline:
other: 40 CFR 158 Environmental Fate, USEPA Pesticide Assessment Guidelines Subdivision N; Series 162-1.
GLP compliance:
yes
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
USDA (US Department of Agriculture)
Soil type:
sandy loam
% Clay:
7
% Silt:
32
% Sand:
61
% Org. C:
1.8
pH:
5.4
CEC:
9 meq/100 g soil d.w.
Details on soil characteristics:
- Soil origin: Almond Grove
Duration:
60 d
Initial conc.:
3.05 mg/kg soil d.w.
Based on:
act. ingr.
Temp.:
25°C
Details on experimental conditions:
- Aerobic incubation at 25 ± 1°C in the dark and application rate was 3.05 mg a.s./kg soil. The experiment was performed in duplicate.
DT50:
1.7 d
Type:
(pseudo-)first order (= half-life)
Transformation products:
yes
Evaporation of parent compound:
no
Volatile metabolites:
yes
Residues:
yes

Metabolite 8 (1,1'-dimethylurea) was found as the major metabolite. Nine other metabolites were detected but none exceeded an average of 8.67% of the applied radioactivity. They were generally in the range ‘not detected’ to ‘< 1% of applied radioactivity’.

A metabolic pathway for ziram was proposed. After cleavage of the molecule to dimethyldithiocarbamic ions, 1,1-dimethylurea is formed. Final metabolites of ziram are CS2 + CO2 (48.35% after 60 d) and bound residue (max 48.16 % after 7 d, 42% after 60 d).

DT50 of 41.9 hours (1.7 days) was calculated for ziram.

Description of key information

- DT50 = 0.6 days based on test material analysis (1.4 days, recalculated to 12 °C, OECD 307 under aerobic conditions in soil)

- 53.2% mineralisation after 28 days


- DT50 = 14.1 days based on test material analysis (47 days, recalculated to 12 °C, 40 CFR 158 Environmental Fate, USEPA Pesticide Assessment Guidelines Subdivision N; Series 162-1, under anaerobic conditions)

Key value for chemical safety assessment

Additional information

The biodegradation of zinc bis dimethyldithiocarbamate (CAS No. 137-30-4) in soil was investigated in several studies under both aerobic and anaerobic conditions.

The key aerobic study (2015) assessed the degradation of 14C labelled zinc bis dimethyldithiocarbamate in soil Speyer 2.2 (loamy sand) following a treatment with the test item at a rate of 4.58 mg/kg soil dw according to OECD 307 and GLP. The soils were incubated at a temperature of 21.0 ± 0.1 °C for up to 28 days under dark conditions. Duplicate samples treated with the test item were extracted from each soil after 0.25, 0.67, 1, 2, 3, 7, 14 and 28 days of incubation. Concentrated extracts were analysed for the test item and degradation products by High Performance Liquid Chromatography (HPLC). Selected extracts were additionally analysed by Thin Layer Chromatography (TLC). Total mean recovery of radioactivity during the 28-day incubation period accounted for 97.1% ± 4.7% of applied radioactivity (AR). Mineralization of [14C] zinc bis dimethyldithiocarbamate was considerably with 14CO2 reaching maximum mean amounts of 53.2% at study end (28 d). Degradation of [14C] zinc bis dimethyldithiocarbamate was very rapid. On Day 0, the test item represented 83.6% AR, and was completely dissipated by Day 1. Besides the test item, two major fractions, Thiram and M1.1, were detected. M1.1 was initially detected at time 0 with mean amounts of 11.5% AR, reaching maximum mean amounts of 34.9% AR on day 1, and subsequently decreased to 11.1% AR at the end of incubation (day 28). Furthermore, a number of minor fractions were detected. None of the remaining fractions exceeded a mean amount of 5.7% AR (M1.11, day 1) at any time throughout the study. The calculated DT50 value based on test material analysis was determined to be 0.6 day, corresponding to 1.4 days at 12 °C. 

A supporting aerobic study (2001) is available and was conducted according to US EPA Guideline, Subdivision N162-1, Aerobic Soil Metabolism Studies (1986) and GLP conditions. 14C-labeled zinc bis dimethyldithiocarbamate was incubated in three different soil types (loamy sand, sandy loam and silt loam) at 20°C (with an additional 10°C loamy sand incubation group) for 28 days. The resulting half-life was determined to be below 1 hour for all three soil types at both tested temperatures. Several metabolites originated from the degradation of the parent compound. The main products from this degradation process were 14CO2 and Thiram (substance degraded within 3 days since first detected). CO2 reached 51-58% and 40% of AR after 28 d at 30°C and 10°C, respectively. An additional supporting study (1996) investigated the biodegradation of 14C-labeled zinc bis dimethyldithiocarbamate in soil under aerobic conditions. This test was conducted also according to US EPA Guideline, Subdivision N162-1 under GLP conditions and it was extended to 60 days. Final metabolites of Ziram were CS2 and CO2 (48.35% after 60 d). A half-life of 1.7 days was reported, with 1,1-dimethylurea and 14CO2 as major metabolites.

Investigations under anaerobic conditions (1997), showed that the measured half-life of 14C-labeled zinc bis dimethyldithiocarbamate was 14.12 days. The metabolite profile of this substance did not differ between aerobic and anaerobic conditions, being 14CO2 a relevant product of the degradation process.

Additional studies are available regarding biodegradation of zinc bis dimethyldithiocarbamate in soil but due to methodological deficiencies were disregarded for further assessment (1987a and 1987b).