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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Qualifier:
according to
Guideline:
other: ABC Laboratories Method (1984)
Deviations:
no
GLP compliance:
yes
Specific details on test material used for the study:
- Lot number: NC06-107
- Trade name: Santocure NS
Analytical monitoring:
yes
Details on sampling:
The compound was stored at ambient tmperature. Primary stock solutions of 1.00 mg/mL TBBS was prepared in nanograde acetone.
Test sample:
Due to the hydrophobic nature of TBBS, a preliminary solubility study was conducted in Phase I. This involved introducing an excess amount of TBBS into water then stirring for several hours. The excess solid was filtered off and the water solution was extracted with methylene chloride, quantification was determined using an HPLC method.
TBBS was introduced into the test system as a solution using a water miscible carrier solvent, HPLC grade acetonitrile. The final concentration of co-solvent did not exceed one percent by volume for the test system. Test concentrations were established on the basis of the approximate
determination of solubility. The concentration was 0.30 µg/mL, approximately 50 % of the solubility value determined in the water solubility determination.
Experimental method:
Deionized and environmental (approximately 8.2 L) water employed in the study was filtered through a 0.45 µ filter to inhibit microbial degradation or particulate catalyzed hydrolysis.
The pH was measured with a Corning pH meter using a one-point calibration method and an appropriate standard buffer. A 25.0 mL aliquot 100 µg/mL of TBBS stock solution was pipetted into 8.3 L of aqueous phase after being buffered with 100 mL of the appropriate buffer, and allowed to stir for approximately 15 minutes. The test solution was divided into 10-700 mL aliquots using 1 L clear glass jars. In order to exclude all artificial sunlight (provided by a mercury vapor lamp) from five of the glass jars, they were wrapped in aluminum foil. The reactions were extracted at intervals of 2-5 hours apart. The frequency of extraction for pH 9.0 was slower to conform with the slower rate of hydrolysis. The quartz mercury arc transmits light from 185-4000 mm. The intensity of the emitted wavelength ranged from 27-980 watts depending on the wavelength. The reactions were run at ambient temperature 25 °C ± 5 °C.
The aliquots of test solution were transferred to separatory funnels for extraction. The water samples were extracted with 3 portions of methylene chloride in a 1:10 ratio. The organic layers were then dried by passing through a cotton plug into a 500 mL flat-bottom flask. The cotton was washed
with an additional 50 mL of methylene chloride which was also collected. The combined organic extracts were evaporated to near-dryness with a
vacuum rotary evaporator. Approximately 5 mL of acetonitrile were then added to the flask and this was evaporated to near-dryness. This step was added to remove any residual methylene chloride. The residues were transferred with anhydrous acetonitrile to a 10 mL volume. Quality control spikes were prepared at the estimated sample concentrations with 700 mL of D.I. or environmental water which had been filtered and buffered in the same manner as the reaction solvent.






Buffers:
0.1 M Potassium Hydrogen Phthalate/0.1 M NaOH fot pH 5
0.1 M KH2PO4/0.1 M NaOH for pH 7
0.025 M Na2B4O7/0.1 M HCl for pH 9
Transformation products:
yes
No.:
#1
No.:
#2
pH:
5
Temp.:
25 °C
DT50:
>= 11.3 - <= 12.6 h
pH:
7
Temp.:
25 °C
DT50:
>= 7.76 - <= 9.53 h
pH:
9
Temp.:
25 °C
DT50:
>= 40.5 - <= 42.1 h
Details on results:
reported temperature was 25 °C+/-5 °C

Test results confirm the results obtained in Monsanto report AB-84-X128.  TBBS has a hydrolysis half-life less than 24 hours in water.

Presence of sunlight did not impact rate of disappearance of TBBS. Data suggest that TBBS hydrolyzes to yield mercaptobenzthiazole.

Validity criteria fulfilled:
yes
Conclusions:
At pH 7 and 25 °C, the half-life for hydrolysis of the TBBS was in between 7.76 and 9.53 hours.
Executive summary:

At pH 7 and 25 °C, the half-life for hydrolysis of the TBBS was in between 7.76 and 9.53 hours.

Description of key information

The key study was performed at three different pH-values. The half-life under pH 7 of 7.76 to 9.53 hours is taken into account for further risk assessment due to the environmental relevance. In this key study MBT is identified as degradation product. However in other similar supporting studies, tert-butylamine was also identified as hydrolysis product.

Key value for chemical safety assessment

Half-life for hydrolysis:
9.53 h
at the temperature of:
25 °C

Additional information

should read "7.76 to 9.53 h"