2,6-di-tert-butyl-p-cresol

Phototransformation in water

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Study type:

direct photolysis

Principles of method if other than guideline:

Two kinds of experiments were conducted:
1.- photolysis in distilled water
2.- photolysis in aqueous solution in the presence of soil.

In the former experiments, methanol solution (55 µl) of 14C-BHT was added aseptically to 750 ml distilled water in a 1 liter quartz flask to give a concentration of 0.6 ppm. Prior to addition of 14C-BHT, the quartz flask and distilled water were sterilized by autoclaving at 20 psi and 120 ºC for 1 hour.
In the latter experiments, a 1 liter quartz flask containing 750 ml of distilled water and 120 g of fine powdered Kodaira, Azuchi or Takarazuka soil with ca. 20% moisture content was kept at 25 ºC for a week in the dark. After preincubation, methanol solution of 14C-BHT was added to each aqueous layer to attain a level of 0.6 ppm. Each of these flasks was exposed to natural sunlight for 30 days (8 hour per day).

GLP compliance:

no

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Synthetized by A. Yoshitake et al (unpublished).

RADIOLABELLING INFORMATION
- Radiochemical purity: 99 %
- Specific activity: 2.97 mCi/mmol
- Locations of the label: 4-methyl group

Radiolabelling:

yes

Analytical method:

other: TLC

Details on sampling:

- Sampling intervals for the parent/transformation products: 8 and 30 days after the application of labeled BHT.
- Sampling method: The 14C trapped in alkaline solution was counted in 10 mL of Aquasol-II..
- Sampling methods for the volatile compounds, if any: Volatile radiocarbon was trapped by polyurethane plugs and 0.5N NaOH solutions.
- Sampling intervals/times for sterility check: Two series of experiments were conducted: One in distilled water in which prior to addition of 14C-BHT, the quartz flask as well as distilled water were sterilized by autoclaving at 20 psi and 120 ° C for 1 hour.
The other series of experiments assessed the photolysis in aqueous solution in the presence of soil. In these series of assays, the above-mentioned sterilization process was not conducted.

Light source:

sunlight

Light spectrum: wavelength in nm:

>= 310 - <= 400

Details on light source:

- Emission wavelength spectrum: Between 310 and 400 nm.
- Filters used and their purpose: None.
- Relative light intensity based on intensity of sunlight: Sunlight intensity was approximately 310, 1300 and 190 µw/cm2 at the beginning, middle and end of the day.
- Duration of light/darkness: 8 hours light and 18 hours dark per day.
- Other: In all cases, a dark control was used to distinguish the products of photochemical process.

Details on test conditions:

Two kinds of experiments were conducted:
1.- photolysis in distilled water
2.- photolysis in aqueous solution in the presence of soil.

TEST SYSTEM
- Type, material and volume of test apparatus/vessels: 1 liter quartz flask containing 750 mL of water with and without 120 g of powdered powdered Kodaira, Azuchi or Takarazuka soil.
- Sterilisation method: In the photolysis in distilled water prior to addition of 14C-BHT, the quartz flask and distilled water were sterilized by autoclaving at 20 psi and 120 ºC for 1 hour.
- Measures to saturate with oxygen: The study conducted with soil had 20 % moisture content in the bottom and was kept at 25 ° C for a week in the dark.
- Details on test procedure for unstable compounds: Not reported.
- Details of traps for volatile, if any: Volatile radiocarbon was trapped by polyurethane plugs and 0.5N NaOH solutions
- Indication of test material adsorbing to the walls of test apparatus: no data.

TEST MEDIUM
- Volume used/treatment: 750 mL water.
- Kind and purity of water: Distilled water.
- Source of natural water (if applicable) in terms of geographical location, site characteristics and date of collection: No data.
- Preparation of test medium:
In the experiment 1, methanol solution (55 µL) of 14C-BHT was added aseptically to 750 mL distilled water in a 1 liter quartz flask to give a concentration of 0.6 ppm. Prior to addition of 14C-BHT, the quartz flask and distilled water were sterilized by autoclaving at 20 psi and 120 ºC for 1 hour.
In the experiment 2, a 1 liter quartz flask containing 750 mL of distilled water and 120 g of fine powdered Kodaira, Azuchi or Takarazuka soil with ca. 20% moisture content was kept at 25 ºC for a week in the dark. After preincubation, methanol solution of 14C-BHT was added to each aqueous layer to attain a level of 0.6 ppm.
- Renewal of test solution: None.
- Identity and concentration of co-solvent: Not applicable.
- Concentration of solubilising agent: Not applicable.

REPLICATION
- No. of replicates (dark): In all cases, a dark control was used to distinguish the products of photochemical process.
- No. of replicates (irradiated): Not specified.

OTHER
Each of the flasks was exposed to natural sunlight for 30 days (8 hour per day).

Duration:

30 d

Reference substance:

not specified

Dark controls:

yes

Key result

Remarks on result:

not measured/tested

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

No.:

#4

No.:

#5

Details on results:

After 8 days of exposure to natural sun light 98.5 % of applied radioactivity could be recovered from the aqueous solution. As BHT is not stable under the applied conditions, only 25 % of this sum were unchanged BHT. BHT-OOH (5.7 %), BHT-OH (4.2 %), BHT-CH2OH (7.5 %), BHT-CHO (2.7 %), BHT-COOH (4.7 %) were determined as degradation products. Polar unidentified products amounted to approx. 48 % of applied radioactivity. A dark control was used to examine the products of the photochemical process. In the control experiment 59.6 % unchanged BHT, 2.6 % BHT-OOH, 8.8 % BHT-OH, 1.1 % BHT-CH2OH, 3.0 % BHT-CHO, 1.4 % BHT-COOH, and 22.9 % unidentified polar compounds were observed.

Validity criteria fulfilled:

not applicable

Conclusions:

From the results it can be concluded that BHT is unstable in water with and without irradiation. Volatilization from the system was very low. The authors assume that BHT-OOH and BHT-OH were mainly derived from autoxidation of BHT in water, while oxidation of the methyl group is accelerated by sunlight. Furthermore sunlight irradiation appreciably increased the amounts of the unidentified polar products.

Executive summary:

Two kinds of experiments were conducted:

1.- photolysis in distilled water;

2.- photolysis in aqueous solution in the presence of soil.

In the former experiments, methanol solution (55 µl) of 14C-BHT was added aseptically to 750 mL distilled water in a 1 liter quartz flask to give a concentration of 0.6 ppm. Prior to addition of 14C-BHT, the quartz flask and distilled water were sterilized by autoclaving at 20 psi and 120 ºC for 1 hour. In the latter experiments, a 1 liter quartz flask containing 750 mL of distilled water and 120 g of fine powdered Kodaira, Azuchi or Takarazuka soil with ca. 20% moisture content was kept at 25 ºC for a week in the dark. After preincubation, methanol solution of 14C-BHT was added to each aqueous layer to attain a level of 0.6 ppm. Each of these flasks was exposed to natural sunlight for 30 days (8 hour per day). From the results it can be concluded that BHT is unstable in water with and without irradiation. Volatilization from the system was very low. The authors assume that BHT-OOH and BHT-OH were mainly derived from autoxidation of BHT in water, while oxidation of the methyl group is accelerated by sunlight. Furthermore sunlight irradiation appreciably increased the amounts of the unidentified polar products.

Description of key information

From the results it can be concluded that BHT is unstable in water with and without irradiation. Volatilization from the system was very low. The authors assume that BHT-OOH and BHT-OH were mainly derived from autoxidation of BHT in water, while oxidation of the methyl group is accelerated by sunlight. Furthermore sunlight irradiation appreciably increased the amounts of the unidentified polar products.

Additional information

Key study: Experimental data from a scientific article.