3-iodo-2-propynyl butylcarbamate

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: sediment simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1989-08-08 to 1992-08-24

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA Subdivision N Pesticide Guideline 162-3 (Anaerobic Aquatic Metabolism)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: N.J. AS-2; 3D-95-C; 30-142-A; 9010-5951; 910261.11

SOURCE OF TEST MATERIAL RADIOLABELLED
- Source and lot/batch No.of test material: NSN/1/77/1
- Radiochemical purity: 99.4%

Radiolabelling:

yes

Oxygen conditions:

anaerobic

Inoculum or test system:

natural water / sediment: freshwater

Details on source and properties of surface water:

- Details on collection: Pond water and sediment were collected from the same location in Macon County, IL on three separate occasions
- pH at time of collection: 7.5 - 7.8
- Electrical conductivity: 394.4 - 644 umhos/cm
- Redox potential measured: yes
- Hardness (CaCO3):346.0 - 138.0 mg CaCO3 equiv/L

Duration of test (contact time):

> 118 - < 244 d

Initial conc.:

1.04 other: ppm

Based on:

test mat.

Remarks:

Test A

Initial conc.:

1.02 other: ppm

Based on:

test mat.

Remarks:

Test B

Initial conc.:

0.94 other: ppm

Based on:

test mat.

Remarks:

Test C

Parameter followed for biodegradation estimation:

CO2 evolution

test mat. analysis

other: metabolite formation; bound residues accumulation

Details on study design:

Three tests were performed:
Test A (nonsterile and sterile static samples)
Test B (nonsterile, enclosed static samples)
Test C (nonsterile continuous N2 flow samples)

For Nonsterile and Sterile Static Samples 20 g sediment were added to 250 mL polycarbonate centrifuge bottles and flooded with 100 mL N2-purged pond water. The bottles were sealed with a Teflon gasket. Sample headspace was purged with N2 at regular intervals to remove and trap volatile 14C components.

Set-up for the Nonsterile Enclosed Static Samples was the same as for the previous samples except that the 250 mL Polycabonate bottles were placed in individual chambers constructed of polyvinyl chloride (PVC). An air flow stream passed through the PVC chambers and into a 1 M NaOH solution to trap any CO2 which escaped from the sealed bottles.

For the Continuous N2 Flow Samples, 50 g of sediment were added to 500 mL sidearm filter flasks and flooded with 250 mL of N2-purged pond water. The filter flask sidearms were connected to a N2 inlet with Tygon tubing. The N2 outlet from each sample passed through a silica solid phase extraction column and a polyurethane foam plug and a gas washing bottle containing 1 M NaOH.

TEST CONDITIONS
- Test temperature: 22 +/- 2 °C

SAMPLING
- Sampling frequency:
Test A: 0, 2, 4, and 8 hours, 1, 7, 14, 28, 59, 93, 162 and 244 days
Test B: 28, 45, 90, 119 and 180 days
Test C: 104 and 118 days

- Sampling method used per analysis type:
Headspace of samples was purged with nitrogen passing through a polyurethane foam plug and a 1 M NaOH solution to trap organic volatiles and CO2
NaOH solutions of the PVC chambers were radioassayed by LSC. Selected NaOH samples were precipitated with BaCl2 to confirm the presence of CO2.
Polyurethane foam plugs were extracted with methanol and radioassayed.
The silica solid phase extraction columns were eluted with methanol/1 N HCl (9/1 v/v). Aliquots were radioassayed and extracts partitioned with methylene chloride. Organic extracts were concentrated.
Water layers were separated from the sediment by filtration, and extracted twice with methylene chloride after acidification with 1N HCl. Aliquots of the aqueous and organic fractions were radioassayed by LSC.
Sediment samples were extracted with methanol for 18 hours in Soxhlet tubes. Aliquots of the extracts were radioassayed by LSC.
All sample extracts containing > 1 % of applied radioactivity were analysed by HPLC with UV and 14C detector. Confirmatory analyses were performed on isolated metabolites using GC/MS.
All extracted sediment samples were combusted and analysed by LSC to determine the amount of non-extractable residues.

STATISTICAL METHODS:
The half life of the test item and its degradation product propargyl butyl carbamate (PBC) was calculated assuming pseudo first-order kinetics.

Test performance:

Material Balance:
In Nonsterile Static Samples the material balance values averaged 99.2 % through the day 14 sampling interval but had decreased to 62.1 % by the day 59 and 46.7 % by the day 244 sampling interval. The low material balance values from the later samplings was most probably related to CO2 evolution.

To accomplish this, Nonsterile Enclosed Static Samples were placed in individual PVC chambers which were connected to an air flow passing through 1 M NaOH solution to trap any CO2 that had escaped the sealed incubation flasks. However, despite these efforts, the material balance declined rapidly between the 28 and 90 days sampling intervals. Based on this data it was assumed that the unaccounted 14C appears to be a volatile, low molecular weight molecule (e.g. CH4) formed by bacteria which are able to convert CO2 to methane.
Additional samples were incubated under a continuous N2 flow to limit CO2 conversion to CH4 by removal of the CO2 as it was formed and/or by inhibition of the methanogenic bacterial population. The material balance from the continuous flow samples were significantly greater than from static samples ranging from 75.4 to 81.7 % of applied radioactivity. Again, it is likely that the unaccounted 14C was in the form of 14CH4. Although the continuous N2 flow appeared to inhibit CH4 formation, it did not stop it completely.
The material balance in Sterile Static Samples averaged 95.3 % of applied radioactivity.

Key result

Compartment:

natural water: freshwater

DT50:

1.5 h

Type:

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

Temp.:

22 °C

Key result

Compartment:

natural water: freshwater

DT50:

34.8 d

Type:

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

Temp.:

22 °C

Remarks on result:

other: DT90

Transformation products:

yes

No.:

#1

Details on transformation products:

The initial degradation product of the test item was propargyl butyl carbamate (PBC) accounting for > 97 % of the applied radioactivity one day after treatment. PBC was further degraded to 2-propenyl-butyl carbamate and several non-identified compounds prior to complete mineralisation. Residue levels of 2-popenyl-butyl carbamate in sediment and water of nonsterile static systems peaked at 8.0 and 34.7 % of the applied radioactivity, respectively, at day 59. Total residue levels of either of the non-identified metabolites accounted for less than 3 % at any sampling interval.
Under sterile conditions PBC was again the main degradation product accounting for maximum values of >80 % of applied radioactivity in the total system 29 days after treatment.

Evaporation of parent compound:

no

Volatile metabolites:

no

Residues:

yes

Remarks:

Residues remained predominantly in the water layer. Less than 21 % of the applied radioactivity was associated with the sediment (extractable and bound residues) at any sampling interval

Validity criteria fulfilled:

yes

Conclusions:

The test item was rapidly degraded in anaerobic aquatic systems with a half-life of 1.5 hours. The major degradation product was propargyl butyl carbamate (PBC) which degraded itself with a half-life of 11.5 days. The terminal degradation products of the test item in anaerobic aquatic systems appear to be CO2 and CH4. The test item degradation in anaerobic aquatic systems was primarily microbially mediated but nonbiological mechanisms also contribute to the degradative process.

Executive summary:

A laboratory study was performed to investigate the anaerobic aquatic metabolism of the test item at a temperature of 22 +/- 2 °C. The test item was rapidly degraded in anaerobic aquatic systems with a half-life of 1.5 hours. Propargyl butyl carbamate was the initial degradation product, and 2-propenylbutylcarbamate was a secondary degradation product. Due to the rapid, and nearly complete, degradation of the test item to propargyl butyl carbamate, the longevity of propargyl butyl carbamate under anaerobic aquatic conditions was estimated using the day one sample interval as the initiation point for propargyl butyl carbamate dissipation. A half-life of 11.5 days was calculated for propargyl butyl carbamate based on the data collected up to 59 days after treatment. Beginning with the 93 day sampling interval, no extractable metabolites were detected at levels greater than 4 % of the applied 14C in Nonsterile Static Samples. The terminal degradation products of the test item in anaerobic systems appear to be carbon dioxide and methane. The test item degradation in anaerobic aquatic systems was primarily microbially mediated but nonbiologically mechanisms also contribute to the degradation process.

Description of key information

The test item was rapidly degraded in anaerobic aquatic systems with a half-life of 1.5 hours. The major degradation product was propargyl butyl carbamate (PBC) which degraded itself with a half-life of 11.5 days. The terminal degradation products of the test item in anaerobic aquatic systems appear to be CO2 and CH4.

Test item degradation in anaerobic aquatic systems was primarily microbially mediated but nonbiological mechanisms also contribute to the degradative process.

Key value for chemical safety assessment

Half-life in freshwater:

1.5 h

at the temperature of:

22 °C

Additional information

A laboratory study was performed to investigate the anaerobic aquatic metabolism of the test item at a temperature of 22 +/- 2°C. The test item was rapidly degraded in anaerobic aquatic systems with a half-life of 1.5 hours. Propargyl butyl carbamate was the initial degradation product, and 2-propenylbutylcarbamate was a secondary degradation product. Due to the rapid, and nearly complete, degradation of the test item to propargyl butyl carbamate, the longevity of propargyl butyl carbamate under anaerobic aquatic conditions was estimated using the day one sample interval as the initiation point for propargyl butyl carbamate dissipation. A half-life of 11.5 days was calculated for propargyl butyl carbamate based on the data collected up to 59 days after treatment. Beginning with the 93 day sampling interval, no extractable metabolites were detected at levels greater than 4 % of the applied 14C in Nonsterile Static Samples. The terminal degradation products of the test item in anaerobic systems appear to be carbon dioxide and methane. The test item degradation in anaerobic aquatic systems was primarily microbially mediated but nonbiologically mechanisms also contribute to the degradation process.