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Environmental fate & pathways

Phototransformation in water

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Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study
Study type:
direct photolysis
Principles of method if other than guideline:
The photolysis experiment was conducted as part of a two-phase study, the second phase of which was OECD 301D biodegradation study.
GLP compliance:
yes
Specific details on test material used for the study:
Non-labelled BIT: Analytical Grade BIT
Batch number: Identification Code ODAS 235.
Purity of non-labelled BIT is 99.5%.

Radiolabelled BIT: [carbonyl-14C]BIT ; [ring-14C]BIT
Purity of [carbonyl-14C]BIT was 93.3%
Purity of [ringl-14C]BIT was 90.5%
Details on sampling:
Aqueous samples were taken from each flask at 0, 1, 3 and 10 days and the concentration of BIT remaining in solution determined by means of high performance liquid chromatography (HPLC) using UV and radiochemical detectors and liquid scintillation counting (LSC).
Light source:
sunlight
Initial conc. measured:
10 mg/L
Key result
DT50:
4 h
Transformation products:
not measured
Details on results:
The photolysis rate constant (kcp) for BIT was 0.172. This was determined from a non-linear regression plot of the overall mean concentration obtained from [carbonyl 14C]BIT and [ring14C]BIT LSC and HPLC data against exposure period.
t1/2E: The half life of BIT was calculated from the equation: t1/2 = (ln(2)/k), where t1/2 was expressed in hours.
t1/2 = 4 hours. t1/2E was not calculated since solar irradiance was not measured.
Validity criteria fulfilled:
not specified
Conclusions:
In aqueous solution the substance was readily photolysed by the action of natural sunlight. The calculated half-life was 4 h. Therefore it is unlikely that the substance will be persistent in the aquatic environment. A minimum of three metabolites were formed all of which eluted before the substance suggesting that they were more polar.
Executive summary:

A study was conducted to determine the photodegradation of the substance in water as part of a two-phase study, the second phase of which was OECD 301D biodegradation study. In aqueous solution the substance was readily photolysed by the action of natural sunlight. The calculated half-life was 4 h. Therefore it is unlikely that the substance will be persistent in the aquatic environment. A minimum of three metabolites were formed all of which eluted before the substance suggesting that they were more polar (Gilbert, 2000).

Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Study type:
direct photolysis
Qualifier:
according to
Guideline:
OECD Guideline 316 (Phototransformation of Chemicals in Water - Direct Photolysis)
Version / remarks:
JMAFF Agchem Test Guidelines 12 Nohsan N. 8147, 24 November 2000, revised 26 June 2001: Photodegradation in water (2-6-2) EPA-540/9-82-021, Section 161-2, October 18, 1982 EPA 540/09-90-
Deviations:
no
GLP compliance:
yes
Specific details on test material used for the study:
Radio labelled BIT
Batch number: 2259PJS014-1
Purity: 98.4% radiochemically pure
Radiolabelling:
yes
Details on sampling:
0, 0.17 (4 h), 0.33 (8 h), 1, 4, 7 and 15 days.
Buffers:
0.05 M buffer solution at pH 7 was prepared by diluting 500 mL 0.1 M potassium dihydrogen phosphate with 0.1 N sodium hydroxide and bi-distilled water to reach a final volume of 1 litre.
Light source:
Xenon lamp
Light spectrum: wavelength in nm:
> 290 - <= 400
Relative light intensity:
ca. 48.7
Details on light source:
“Suntest CPS, Original Hanau” apparatus (Heraeus, Germany).
Details on test conditions:
The direct and indirect photochemical degradation of 14C-BIT, i.e. 1,2-Benzisothiazolin-3(2H)-one, were investigated under simulated sunlight in sterilised buffer solution at pH 7 and sterilised natural pond water at about pH 8.
A “Suntest” apparatus equipped with a xenon lamp and filters to remove wavelengths below 290 nm was used to simulate sunlight during the study. Its intensity within the visual light spectrum (300 to 400 nm) was measured by a spectrophotometer to be 43.7 W/m2. Above 400 nm, the test item asorbed practically no light. This light intensity was slightly higher than the intensity of natural daylight with vertical incidence under temperate climates measured in summer with the same spectrophotometer at RCC Ltd. facility, 47.5°N latitude (43.7 W/m2).
Duplicate 100 mL samples of sterile pH 7 buffer solution or pond water treated with the test item at a mean initial concentration of 5 mg/L (significantly less than half of its water solubility) were irradiated for a continuous period of 15 days (corresponding to 32 days of midsummer sunlight at latitude 50°N and 94 days of spring sunlight at latitude 35°N (Tokyo, Japan)) and at a mean temperature of 25.0 ± 0.1°C. Concurrently, a sample of each treated test solution was incubated under the same conditions but in the dark (control samples).
Aliquots from each sample were taken at seven time intervals during the irradiation/incubation period and directly submitted to radiochemical quantification by Liquid Scintillation Counting and chromatographic analysis by High Performance Liquid Chromatography. The results were confirmed by Thin Layer Chromatography on selected samples and metabolite identification was performed by LC-MS and LC-MS/MS .
Duration:
15 d
Temp.:
25 °C
Reference substance:
yes
Remarks:
1,2-Benzisoxazole; 2,6- Dihydrobenzoic acid; Salicylic acid; Salicylamide; 1,2-Benzisothiazolin-3-one
Dark controls:
yes
Key result
% Degr.:
< 1.5
Sampling time:
4 h
Predicted environmental photolytic half-life:
14C-BIT was instantly photo-degraded in a buffered solution at pH 7 and in natural pond water. Due to its very rapid rate of photodegradation, an accurate photolytic Suntest half-life could not be calculated. Photodegradation involved cleavage of the isothiazolone ring to form principally 14CO2 and several major metabolites (M2, 2-sulfobenzoic acid (M4), 1,2-benzisothiazol-3(2H)-one-1,1-dioxide (M6), M10, B1, benzamide (B3) and 2-carbamoyl-benzenesulfonic acid (M13)). M2, M4, M10 and B1 were very rapidly photolysed with Suntest half-lives of 1.2 days or less, whereas M6 and B3 degraded at a much slower rate (87-89 Suntest days).
Transformation products:
yes
No.:
#7
Details on results:
The total mean recoveries of radioactivity for the irradiated samples were 93.4 ± 3.0% and 99.9 ± 1.0% of the applied radioactivity for the buffer solution and pond water samples, respectively. The corresponding values for the control samples were 95.9 ± 2.7% and 98.8 ± 1.6%.
14C-BIT was instantly photolyzed in both aqueous media. The test item represented 1.5% of applied or less after just 4 hours of irradiation in both test systems. 14C-BIT was photodegraded mainly to M4 (identified by LC-MS as 2-sulfobenzoic acid), which was further degraded to many fractions and carbon dioxide.
The formation of radioactive carbon dioxide was high, accounting for 31% and 22% of the applied radioactivity in the irradiated buffer solution and pond water samples, respectively, on day 15. The evolution of 14CO2 demonstrates that photodegradation involved the cleavage of the isothiazolone ring.
Besides the parent compound and 14CO2, numerous radioactive fractions were detected, some accounted for more than 10% of the applied radioactivity. Only one degradate was formed in both pond water and buffer solution, indicating essentially a different photolytic process in the two test systems. The major radioactive fractions formed in buffer solution were M4, B1 and B3 whereas in pond water, they were M2, M4, M6, M10 and M13. Most of the major metabolites were identified by LC-MS and MS/MS. Namely, M4 was identified as 2-sulfobenzoic acid, M6 as 1,2-benzisothiazol-3(2H)-one-1,1-dioxide, M13 as 2-carbamoyl-benzenesulfonic acid and B3 as benzamide. The very transient fractions M2, M10 and B1 could not be identified with the current methods and might consist of several compounds.
Under non-irradiated conditions (dark controls), the test item remained stable in the buffer test system, accounting for 101.1% of applied on day 15. In the pond water however, microbial degradation was observed, with BIT representing 43% of applied on day 1. However, BIT was photodegraded within less than four hours. Up to seven radioactive fractions were formed including the major ones detected in the corresponding irradiated samples, 2-sulfobenzoic acid (M4), 1,2-benzisothiazol-3(2H)-one-1,1-dioxide (M6) and 2-carbamoylbenzenesulfonic acid (M13). M4 reached its maximum of 41% on day 1 before declining rapidly (it was not detected at the end of the study). M6 and M13 formed at a later stage, accounting for up to 14% and 87% of the applied radioactivity on days 4 and 15, respectively. Another fraction M12 remained stable between days 1 and 7 at between 9-12% of applied before rapidly declining to 3% on day 15. None of the used reference substances co-eluted with the observed fractions.
The amount of carbon dioxide formed in the non-irradiated samples was negligible (<0.1% of applied).
The rate of photodegradation of 14C-BIT and its major photodegradates was described using first order kinetics.
The photodegradation of BIT was rapid and similar in both systems. However, the irradiation of its photoproducts showed that direct and indirect photolysis involved a different photolytic pathway.

Validity criteria fulfilled:
not specified
Conclusions:
14C-BIT was instantly photo-degraded in a buffered solution at pH 7 and in natural pond water. Due to its very rapid rate of photodegradation, an accurate photolytic Suntest half-life could not be calculated. Photodegradation involved cleavage of the isothiazolone ring to form principally 14CO2 and several major metabolites (M2, 2-sulfobenzoic acid (M4), 1,2-benzisothiazol-3(2H)-one-1,1-dioxide (M6), M10, B1, benzamide (B3) and 2-carbamoyl-benzenesulfonic acid (M13)). M2, M4, M10 and B1 were very rapidly photolysed with Suntest half-lives of 1.2 days or less, whereas M6 and B3 degraded at a much slower rate (87-89 Suntest days).
Executive summary:

A study was conducted to determine the phototransformation of the substance according to OECD Guideline 316. The 14C-radiolabelled substance was instantly photo-degraded in a buffered solution at pH 7 and in natural pond water. Due to its very rapid rate of photodegradation, an accurate photolytic Suntest half-life could not be calculated. Photodegradation involved cleavage of the isothiazolone ring to form principally 14CO2 and several major metabolites (2 -sulfobenzoic acid, 1,2 -benzisothiazol-3(2H)-one-1,1 -dioxide, benzamide (B3) and 2 -carbamoyl-benzenesulfonic acid), were very rapidly photolysed with Suntest half-lives of 1.2 days or less, whereas other metabolites degraded at a much slower rate (87-89 Suntest days).

Description of key information

Key value for chemical safety assessment

Half-life in water:
4 h

Additional information

A study was conducted to determine the phototransformation of the substance according to OECD Guideline 316. The 14C-radiolabelled substance was instantly photo-degraded in a buffered solution at pH 7 and in natural pond water. Due to its very rapid rate of photodegradation, an accurate photolytic Suntest half-life could not be calculated. Photodegradation involved cleavage of the isothiazolone ring to form principally 14CO2 and several major metabolites (2 -sulfobenzoic acid, 1,2 -benzisothiazol-3(2H)-one-1,1 -dioxide, benzamide (B3) and 2 -carbamoyl-benzenesulfonic acid), were very rapidly photolysed with Suntest half-lives of 1.2 days or less, whereas other metabolites degraded at a much slower rate (87-89 Suntest days).

A study was conducted to determine the photodegradation of the substance in water as part of a two-phase study, the second phase of which was OECD 301D biodegradation study. In aqueous solution the substance was readily photolysed by the action of natural sunlight. The calculated half-life was 4 h. Therefore it is unlikely that the substance will be persistent in the aquatic environment. A minimum of three metabolites were formed all of which eluted before the substance suggesting that they were more polar (Gilbert, 2000).