polymeric zinc propylenebis(dithiocarbamate);propineb (ISO)

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:

2013-04-23 to 2014-04-28

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)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Remarks:

[propane-1-14C] label

Oxygen conditions:

anaerobic

Soil classification:

USDA (US Department of Agriculture)

Year:

2014

Soil no.:

#1

Soil type:

sandy loam

% Clay:

9

% Silt:

18

% Sand:

73

% Org. C:

1.7

CEC:

8.4 meq/100 g soil d.w.

Bulk density (g/cm³):

1.24

% Moisture content:

16.2

Soil no.:

#2

Soil type:

silt loam

% Clay:

17

% Silt:

62

% Sand:

21

% Org. C:

2

CEC:

11.9 meq/100 g soil d.w.

Bulk density (g/cm³):

1.12

% Moisture content:

21.6

Soil no.:

#3

Soil type:

loam

% Clay:

19

% Silt:

50

% Sand:

31

% Org. C:

3.1

CEC:

9.9 meq/100 g soil d.w.

Bulk density (g/cm³):

1

% Moisture content:

31.1

Soil no.:

#4

Soil type:

loam

% Clay:

27

% Silt:

42

% Sand:

31

% Org. C:

4.9

CEC:

19.8 meq/100 g soil d.w.

Bulk density (g/cm³):

0.98

% Moisture content:

39

Details on soil characteristics:

Soil #1: Laacher Hof AXXa
Soil #2: Hoefchen Am Hohenseh
Soil #3: Hanscheider Hof
Soil #4: Dollendorf II

The study was carried out using four different soils. The soils were taken from agricultural use areas representing different geographical origin and different soil properties as required by the guidelines. The plant protection product use history of the soils is known for at least 5 years.

Soil No.:

#1

Duration:

42 d

Soil No.:

#2

Duration:

42 d

Soil No.:

#3

Duration:

42 d

Soil No.:

#4

Duration:

42 d

Soil No.:

#1

Initial conc.:

0.487 other: mg/100 g soil

Based on:

test mat.

Soil No.:

#2

Initial conc.:

0.487 other: mg/100 g soil

Based on:

test mat.

Soil No.:

#3

Initial conc.:

0.487 other: mg/100 g soil

Based on:

test mat.

Soil No.:

#4

Initial conc.:

0.487 other: mg/100 g soil

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

19.7 °C

Humidity:

Maximum water holding capacity: 49.7 g H2O ad 100 g DW

Microbial biomass:

mg microbial carbon per kg dry weight of soil:
DAT 0: 1148
DAT 42: 578

Soil No.:

#2

Temp.:

19.7 °C

Humidity:

Maximum water holding capacity: 59.4 g H2O ad 100 g DW

Microbial biomass:

mg microbial carbon per kg dry weight of soil:
DAT 0: 1077
DAT 42: 812

Soil No.:

#3

Temp.:

19.7 °C

Humidity:

Maximum water holding capacity: 62.2 g H2O ad 100 g DW

Microbial biomass:

mg microbial carbon per kg dry weight of soil:
DAT 0: 949
DAT 42: 590

Soil No.:

#4

Temp.:

19.7 °C

Humidity:

Maximum water holding capacity: 80.2 g H2O ad 100 g DW

Microbial biomass:

mg microbial carbon per kg dry weight of soil:
DAT 0: 2504
DAT 42: 2257

Details on experimental conditions:

The soils were sampled freshly from the fields (upper horizon of 0 to 20 cm) and sieved to a particle size of = 2 mm. The soil moisture [g H2O ad 100 g soil dry weight] was determined using an automated halogen moisture analyzer by drying three aliquots of approximately 20 g of the sieved soils at 105 °C.
Static test systems (300-mL Erlenmeyer glass flasks) for degradation in soil under aerobic conditions were used as incubation vessels. Each flask was fitted with a trap attachment (permeable for oxygen) containing soda lime for absorption of carbon dioxide and a polyurethane (PU) foam plug for adsorption of volatile organic compounds (VOC).
For preparation of the test systems, 100 g dry weight equivalents of the sieved soils were weighed into each flask. Soil moisture was adjusted to approx. 55 ± 5% of the maximum water holding capacity (MWHC) for the individual test systems by addition of de-ionized water, taken into account the water content of the application solution. The flasks were then fitted with above-mentioned trap attachments.
The untreated test systems were equilibrated to study conditions for 7 days prior to application.
A study application rate of 0.487 mg per 100 g soil dry weight was applied as solid polymer well suspended in water. The applied amount was based on the intended maximum single field application rate of 1.825 kg Antracol per hectare. 400 µL of application suspension were applied dropwise onto the soil surface of the respective equilibrated test systems using a pipette. The application was performed with continous stirring of the application suspension using a magnetic stirrer.
After application, the test vessels (except DAT-0.06 samples) were fitted with trap attachments and placed into a temperature-controlled walk-in climatic chamber for incubation. The soil moisture was maintained since water loss from evaporation (determined by re-weighing of flasks) was replaced after 28 and 35 days of incubation. Soil microbial biomass was determined at the beginning start and at end of the study in untreated test systems (DAT-0 and DAT-42),

Soil No.:

#1

% Total extractable:

81.5

% Non extractable:

19.1

% Recovery:

100.6

Remarks on result:

other: 0.06 DAT

Soil No.:

#1

% Total extractable:

76.9

% Non extractable:

22.3

% CO2:

0.1

% Other volatiles:

< 0.1

% Recovery:

99.3

Remarks on result:

other: 0.21 DAT

Soil No.:

#1

% Total extractable:

65.7

% Non extractable:

32.7

% CO2:

0.8

% Other volatiles:

< 0.1

% Recovery:

99.2

Remarks on result:

other: 1 DAT

Soil No.:

#1

% Total extractable:

55.6

% Non extractable:

39.2

% CO2:

3.3

% Other volatiles:

< 0.1

% Recovery:

98

Remarks on result:

other: 3 DAT

Soil No.:

#1

% Total extractable:

44.1

% Non extractable:

42.1

% CO2:

9.5

% Other volatiles:

< 0.1

% Recovery:

95.7

Remarks on result:

other: 7 DAT

Soil No.:

#1

% Total extractable:

26.6

% Non extractable:

48.6

% CO2:

22.6

% Other volatiles:

< 0.1

% Recovery:

97.9

Remarks on result:

other: 14 DAT

Soil No.:

#1

% Total extractable:

6.9

% Non extractable:

50.5

% CO2:

39.5

% Other volatiles:

< 0.1

% Recovery:

96.9

Remarks on result:

other: 28 DAT

Soil No.:

#1

% Total extractable:

5.1

% Non extractable:

49.2

% CO2:

44

% Other volatiles:

< 0.1

% Recovery:

98.2

Remarks on result:

other: 42 DAT

Soil No.:

#2

% Total extractable:

79.2

% Non extractable:

21.5

% Recovery:

100.6

Remarks on result:

other: 0.06 DAT

Soil No.:

#2

% Total extractable:

73

% Non extractable:

24.4

% CO2:

0.1

% Other volatiles:

< 0.1

% Recovery:

97.6

Remarks on result:

other: 0.21 DAT

Soil No.:

#2

% Total extractable:

63

% Non extractable:

35.4

% CO2:

0.7

% Other volatiles:

< 0.1

% Recovery:

99.2

Remarks on result:

other: 1 DAT

Soil No.:

#2

% Total extractable:

54.2

% Non extractable:

41.9

% CO2:

3.4

% Other volatiles:

< 0.1

% Recovery:

99.6

Remarks on result:

other: 3 DAT

Soil No.:

#2

% Total extractable:

42.3

% Non extractable:

45.8

% CO2:

10.1

% Other volatiles:

< 0.1

% Recovery:

98.3

Remarks on result:

other: 7 DAT

Soil No.:

#2

% Total extractable:

25.4

% Non extractable:

49.4

% CO2:

23.2

% Other volatiles:

< 0.1

% Recovery:

97.9

Remarks on result:

other: 14 DAT

Soil No.:

#2

% Total extractable:

5.1

% Non extractable:

49.8

% CO2:

42.9

% Other volatiles:

< 0.1

% Recovery:

97.8

Remarks on result:

other: 28 DAT

Soil No.:

#2

% Total extractable:

3.8

% Non extractable:

44.8

% CO2:

46.5

% Other volatiles:

< 0.1

% Recovery:

95.1

Remarks on result:

other: 42 DAT

Soil No.:

#3

% Total extractable:

58.9

% Non extractable:

41.5

% Recovery:

100.3

Remarks on result:

other: 0.06 DAT

Soil No.:

#3

% Total extractable:

61.7

% Non extractable:

37.3

% CO2:

0.1

% Other volatiles:

< 0.1

% Recovery:

99.1

Remarks on result:

other: 0.21 DAT

Soil No.:

#3

% Total extractable:

58

% Non extractable:

43.1

% CO2:

0.3

% Other volatiles:

< 0.1

% Recovery:

101.4

Remarks on result:

other: 1 DAT

Soil No.:

#3

% Total extractable:

49.8

% Non extractable:

48.5

% CO2:

1.5

% Other volatiles:

< 0.1

% Recovery:

99.8

Remarks on result:

other: 3 DAT

Soil No.:

#3

% Total extractable:

42.1

% Non extractable:

53.6

% CO2:

4.4

% Other volatiles:

< 0.1

% Recovery:

100.1

Remarks on result:

other: 7 DAT

Soil No.:

#3

% Total extractable:

31.3

% Non extractable:

57.1

% CO2:

10.6

% Other volatiles:

< 0.1

% Recovery:

99

Remarks on result:

other: 14 DAT

Soil No.:

#3

% Total extractable:

16.1

% Non extractable:

59.3

% CO2:

21.3

% Other volatiles:

< 0.1

% Recovery:

96.6

Remarks on result:

other: 28 DAT

Soil No.:

#3

% Total extractable:

9.4

% Non extractable:

60.5

% CO2:

28.5

% Other volatiles:

< 0.1

% Recovery:

98.3

Remarks on result:

other: 42 DAT

Soil No.:

#4

% Total extractable:

70.1

% Non extractable:

30.5

% Recovery:

100.6

Remarks on result:

other: 0.06 DAT

Soil No.:

#4

% Total extractable:

63.5

% Non extractable:

34.3

% CO2:

0.1

% Other volatiles:

< 0.1

% Recovery:

97.9

Remarks on result:

other: 0.21 DAT

Soil No.:

#4

% Total extractable:

61.9

% Non extractable:

38.2

% CO2:

0.3

% Other volatiles:

< 0.1

% Recovery:

100.3

Remarks on result:

other: 1 DAT

Soil No.:

#4

% Total extractable:

53.5

% Non extractable:

41.5

% CO2:

2.5

% Other volatiles:

< 0.1

% Recovery:

97.4

Remarks on result:

other: 3 DAT

Soil No.:

#4

% Total extractable:

47.3

% Non extractable:

46.5

% CO2:

5.6

% Other volatiles:

< 0.1

% Recovery:

99.3

Remarks on result:

other: 7 DAT

Soil No.:

#4

% Total extractable:

21.6

% Non extractable:

53.3

% CO2:

22.1

% Other volatiles:

< 0.1

% Recovery:

97

Remarks on result:

other: 14 DAT

Soil No.:

#4

% Total extractable:

7.3

% Non extractable:

53.7

% CO2:

34.7

% Other volatiles:

< 0.1

% Recovery:

95.7

Remarks on result:

other: 28 DAT

Soil No.:

#4

% Total extractable:

4.3

% Non extractable:

51.5

% CO2:

39.9

% Other volatiles:

< 0.1

% Recovery:

95.7

Remarks on result:

other: 42 DAT

Soil No.:

#1

Remarks on result:

other: DT50 could not be derived for Propineb from this study

Soil No.:

#2

Remarks on result:

other: DT50 could not be derived for Propineb from this study

Soil No.:

#3

Remarks on result:

other: DT50 could not be derived for Propineb from this study

Soil No.:

#4

Remarks on result:

other: DT50 could not be derived for Propineb from this study

Transformation products:

yes

No.:

#4

No.:

#3

No.:

#2

No.:

#1

Details on transformation products:

Investigation of the route of degradation showed that Propineb is well degraded and mineralised in soils incubated under standardised aerobic laboratory conditions in the dark. Complete material balances found at all sampling intervals for each soil demonstrated that there was no significant loss of radioactivity from the test systems or during sample processing.

Evaporation of parent compound:

not specified

Volatile metabolites:

yes

Residues:

yes

Remarks:

Non-extractable residues (NER) quickly increased in all soils, slightly declining until DAT-42 (end of study).

Details on results:

Results indicated that the anticipated standardized aerobic laboratory conditions were maintained during the entire incubation period in the dark. The mean incubation temperature was 19.7 °C; the soil moisture was maintained on average at 54.2% of MWHC (min. 53.7%, max. 55.0%).
Determinations of microbial biomass demonstrated that the used soils were microbial viable. Under the conditions of a laboratory experiment a decrease of microbial biological activity is inevitable due to the absence of any further amendment of nutrients. Continued microbial respiration of nutrients in soil causes finally a lack of readily digestable organic matter.

Data:
The amount of applied test item for the degradation samples was determined to be 359.55 kBq (equal to 470 µg of test item) with a RSD of 0.7%, and this was set to 100% of applied radioactivity [% of AR]. It was confirmed that the application suspension remained homogeneous during the application procedure.
Complete material balances found at all sampling intervals for each soil demonstrated that there was no significant loss of radioactivity from the test systems or during sample processing. Mean material balance was 98.2% of AR (range from 95.7 to 100.6% of AR) for soil AX, 98.3% of AR (range from 95.1 to 100.6% of AR) for soil HF, 99.3% of AR (range from 96.6 to 101.4% of AR) for soil HN and 98.0% of AR (range from 95.7 to 100.6% AR) for soil DD.

Validation:
Due to its polymeric nature Propineb is practically insoluble in water and in organic solvents. Since the polymeric Propineb shows decomposition, i.e. if water is present, any observed solubility is caused by degradation but not by dilution. In consequence, the parent compound probineb cannot be analyzed itself. In case valid values of its content are to be determined it must be guaranteed that the entire Propineb polymer still present in a sample is degraded to products which are soluble and can be measured.

Verification of Sample Processing Method:
For the test item investigated in the current study a recovery, even shortly after the treatment of soils, cannot be given. Therefore, the overall mass balance and the distribution pattern of products received during the study (based on LSC and radio-TLC analysis data) are regarded as the important quality parameter for this study. Those results demonstrated that the sample processing method was gentle enough to recover quite short living degradates for a distinct period of time.
Further, the method was adequate to destroy the total amount of polymeric Propineb still present in a soil sample at the respective sampling interval. However, since the primary degradates of polymeric Propineb are highly reactive species the quick formation of comparatively high portions of NER cannot be avoided in any natural soil environment containing water.

Verification of Chromatographic Procedures:
A two-step radio-TLC method was used for data evaluation since experience was made that any concentration procedures (as needed prior to the use of radio-HPLC methods) did have an impact on the product pattern observed. A good selectivity and reproducibility demonstrated the suitability for separation and quantification of the major components of soil extracts.
The TLC limit of quantification (LOQ) for a single peak in the combined organic extracts was < 1% of applied radioactivity
Investigations were performed in order to confirm the results of the radio-TLC method with reversed phase radio-HPLC as second separation method. However, this was neither successful nor reproducible due to the need for concentrating the extract solutions. In principle, the metabolites itself could have been also analysed and verified by radio-HPLC, but for that a much higher concentration range of solutions and less content of matrix components would have been needed.

Volatiles:
The maximum amount of carbon dioxide was 44.0, 46.5, 28.5, and 39.9% of AR at study end (DAT-42) in soil AX, HF, HN and DD, respectively. Formation of volatile organic compounds (VOC) was insignificant as demonstrated by values of = 0.1% of AR at all sampling intervals for all soils.

Test Item and Degradation Products in Soil Extracts:
Until study termination (DAT-42) extractable residues decreased to 5.1, 3.8, 9.4 and 4.3 of AR in soils AX, HF, HN and DD, respectively.
Degradation of Propineb was accompanied by the formation of four major degradation products with the following maximum amounts observed: PTU with 31.3% of AR in soil AX at DAT-0.06, PU with 42.2% of AR in soil DD at DAT-3, Propineb-DIDT with 25.6% of AR in soil HF at DAT-0.06, and 4-methyl-imidazoline with 11.7% AR in soil AX at DAT-0.06. The compound propylene diamine (PDA) could not clearly be co-chromatographed with zones ROI 11 or ROI 12, a very polar peak area of chromatograms; if at all present it accounted for max. 1.6% of AR in soil DD at DAT-0.21, only.

Non-Extractable Residues:
Non-extractable residues (NER) quickly increased in all soils, slightly declining until DAT-42 (end of study). In soil AX the NER increased to max. 50.5% of AR at DAT-28, slightly declining to 49.2% of AR until DAT-42. In soil HF the NER increased to max. 49.8% of AR at DAT-28, declining to 44.8% of AR until DAT-42. In soil HN the NER increased to 60.5% of AR until DAT-42. In soil DD the NER increased to 53.7% of AR until DAT-28, slightly declining to 51.5% of AR at the end of study.

Until study termination (DAT-42) extractable residues decreased to less than 10% of AR in all soils. 14CO₂ up to 46.5% of AR was trapped until the end of study. Non-extractable residues (NER) quickly increased in all soils up to 60.5% of AR, slightly declining until DAT-42. A quite similar behavior observed in the metabolite degradation studies indicates that the NER formed from the parent is a major part of its entire route of degradation in soil, thus NER formation is not caused by an inadequate extraction of parent from the soil matrix.

Conclusions:

Investigation of the route of degradation showed that Propineb is well degraded and mineralized in soils incubated under standardized aerobic laboratory conditions in the dark. The quite fast degradation leads to four major degradation products in soil.
Propineb and its residues will be well degraded in aerobic soils if kept under usual moist conditions. Formation of significant amounts of non-extractable residues and carbon dioxide indicates a participation in the natural carbon cycle of soil and the potential for a complete mineralization of Propineb. From this study it is concluded that Propineb and its residues have no potential for accumulation in the environment.
Due to the fast degradation of Propineb and its metabolites observed under standardized laboratory conditions, no field dissipation or rotational crop studies are required.

Executive summary:

The route and rate of [propane-1-¹⁴C]Propineb was studied in four soils under aerobic conditions in the dark in the laboratory for 42 days at 19.7 °C and 54.2% of respective maximum water holding capacity. A study application rate of 0.487 mg per 100 g soil dry weight was applied as solid polymer well suspended in water. The applied amount was based on the intended maximum single field application rate of 1.825 kg Antracol per hectare. The test was performed in static systems consisting of Erlenmeyer flasks each containing 100 g soil (dry weight equivalents) and equipped with traps for the collection of carbon dioxide and volatile organic compounds. Duplicate samples were processed and analyzed 0.06, 0.21, 1, 3, 7, 14, 28 and 42 days after treatment (DAT). Due to the fast degradation of residues any longer interval was not regarded as necessary.

The following facts were considered for the processing of samples. Due to its polymeric nature Propineb is practically insoluble in water and in organic solvents. Since the polymeric Propineb shows decomposition, i.e. if water is present, any observed solubility is caused by degradation but not by dilution. In consequence, the parent compound probineb cannot be analyzed itself. In case valid values of its content are to be determined it must be guaranteed that the entire Propineb polymer still present in a sample is degraded to products which are soluble and can be measured.

At each sampling interval, the soil was extracted three times at ambient temperature, two times using acetonitrile / water 1/1 (v/v) and one time using acetonitrile. Further, two microwave-accelerated extraction steps were performed using acetonitrile / water 1/1 (v/v) at 70 °C and methanol / water 1/1 (v/v) at 50 °C. This entire procedure was adequate to decompose all polymeric residues of [¹⁴C]-Propineb contained in a soil sample.

The amount of degradation products in soil extracts was determined by liquid scintillation counting (LSC) and by TLC/radiodetection analysis. The amount of volatiles and non-extractable residues was determined by LSC and combustion/LSC, respectively. Degradation products were identified by co-chromatography with reference compounds.

Investigation of the route of degradation showed that Propineb is well degraded and mineralised in soils incubated under standardised aerobic laboratory conditions in the dark. Complete material balances found at all sampling intervals for each soil demonstrated that there was no significant loss of radioactivity from the test systems or during sample processing. Mean material balance was 98.2% of AR (range from 95.7 to 100.6% of AR) for soil AX, 98.3% of AR (range from 95.1 to 100.6% of AR) for soil HF, 99.3% of AR (range from 96.6 to 101.4% of AR) for soil HN and 98.0% of AR (range from 95.7 to 100.6% AR) for soil DD.

The maximum amount of carbon dioxide was 44.0, 46.5, 28.5, and 39.9% of AR at study end (DAT-42) in soil AX, HF, HN and DD, respectively. Formation of volatile organic compounds (VOC) was insignificant as demonstrated by values of ≤ 0.1% of AR at all sampling intervals for all soils.

Non-extractable residues (NER) quickly increased in all soils, slightly declining until DAT-42 (end of study).

It is concluded from this study that Propineb and its residues will be well degraded in aerobic soils kept under normal moisture conditions. However, this study cannot be kinetically evaluated for parent degradation with the usual tools since the starting point of polymer degradation is not to be defined. Same holds true for the kinetics of Propineb-DIDT and PTU degradation which must be determined by metabolite soil degradation studies.

Formation of significant amounts of non-extractable residues and carbon dioxide indicates a participation in the natural carbon cycle of soil and the potential for a complete mineralisation of Propineb. Propineb and its degradation products have no potential for accumulation in the environment. Due to the fast degradation of Propineb and its metabolites no field dissipation or rotational crop studies are required.

Description of key information

The route and rate of [propane-1-¹⁴C]Propineb was studied in four soils under aerobic conditions in the dark in the laboratory for 42 days at 19.7 °C and 54.2% of respective maximum water holding capacity. A study application rate of 0.487 mg per 100 g soil dry weight was applied as solid polymer well suspended in water. Investigation of the route of degradation showed that Propineb is well degraded and mineralised in soils incubated under standardised aerobic laboratory conditions in the dark.

Additional information

A DT₅₀ could not be derived for Propineb from this study due to the rapid degradation in soil.