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Environmental fate & pathways

Phototransformation in water

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Description of key information

[Isothiazol-3-14C, Carboxamide-14C]S-2310: DT50 (days) = 1.8 (irradiated samples, natural water) to 2.2 (irradiated samples, distilled water)
[Isothiazol-3-14C, Carboxamide-14C]S-2310: DT50 (days) = 66.6 (dark controls, distilled water) to 990 (dark controls, natural water)
[Phenyl(U)-14C]S-2310: DT50 (days) = 2.2 (irradiated samples, distilled water) to 2.3 (dark controls, natural water)
[Phenyl(U)-14C]S-2310: DT50 (days) = 56.8 (dark controls, distilled water) to 187.3 (dark controls, natural water)

Key value for chemical safety assessment

Additional information

Phototransformation of [Isothiazol-3-14C, carboxamide-14 C]S-2310 and [Phenyl(U)-14C]S-2310 in water was studied by Lentz (2006). The study was not conducted according to OECD GLP and did follow an inhouse protocol to fulfill registration requirements for Japan MAFF Guideline (ID #2-6-2, 12 Nousan No. 8147 November 24, 2000. However, the study is comparable to the OECD Guideline draft (Phototransformation of Chemicals in Water - Direct and Indirect Photolysis).

The purpose of this study was to determine the rate and route of photolysis of [14C]S-2310 (3,4-dichloro-N-(2-cyanophenyl)isothiazole-5-carboxamide). The photolysis of radiolabeled S-2310, labeled uniformly on the phenyl ring or on the 3 position of the isothiazole and the carboxamide groups was determined using a xenon arc lamp. The test materials were applied to sterile natural water and sterile distilled water solutions containing <1% acetonitrile as the co-solvent at an application rate of 0.2 (µg/mL (0.2 ppm). The sterile samples were incubated under continuous irradiation while dark control samples in sterile natural water and sterile distilled water were used for comparison with the irradiated samples.

The irradiated samples were continuously exposed to simulated sunlight from a xenon arc lamp, which had been filtered to remove wavelengths less than 290 nm. Using the Suntest sunlight simulator the average intensity was measured to be 2.751 and 2.415 MJ/m /day for the sterile natural water and sterile distilled water samples, respectively. The samples were irradiated continuously for 9 days at 25 ± 2 °C. The total irradiation was calculated to be 24.8 and 21.7 MJ/m² for the sterile natural water and sterile distilled water samples which were equivalent to 37- and 32-day irradiation under natural sunlight (Tokyo, 35 °N; April-June), respectively.

At selected intervals, duplicate samples were analyzed directly by high-performance liquid chromatography with radiochemical flow detection (HPLC-RAD) to determine the distribution of radioactivity.

The material balance of radioactivity for the sterile natural water and sterile distilled water samples throughout the study ranged from 91.2 - 101.6% of the applied radioactivity (%AR).

Based on the data generated in this study, S-2310 degraded very fast by photolysis in sterile natural water and sterile distilled water with greater than 90% degradation observed after 9 days of continuous irradiation. The DT50 (half-lives) and DT90 values of S-2310 under natural sunlight (Tokyo, spring) were estimated to be 7.4 - 9.4 and 24.2 - 31.5 days in sterile natural water and 7.9 and 25.9 days in sterile distilled water, respectively as summarized in the following tables:

Table 1: Observed DT50 and DT90 values of S-2310; [Isothiazol-3-14C, carboxamide-14 C]S-2310

[lsothiazole-3-14C, Carboxamide-14C]S-2310

Rate Constant (days1)

Observed DT50 (days)

Observed DT90 (days)

r2

Irradiated Natural Water

0.3927

1.8

5.9

0.9912

Irradiated Distilled Water

0.3186

2.2

7.2

0.9753

Dark Control Natural Water

0.0007

990

3290

0.0315

Dark Control Distilled Water

0.0104

66.6

221

0.9106

Table 2: Observed DT50 and DT90 values of S-2310; [Phenyl(U)-14C]S-2310

[Phenyl(U)-14C]S-2310

Rate Constant (days1)

Observed DT50(days)

Observed DT90 (days)

r2

Irradiated Natural Water

0.3009

2.3

7.7

0.9894

Irradiated Distilled Water

0.3208

2.2

7.2

0.9501

Dark Control Natural Water

0.0037

187.3

622

0.2524

Dark Control Distilled Water

0.0122

56.8

189

0.9287

Table 3: Estimated DT50 and DT90 values of S-2310 in Tokyo, spring

[lsothiazole-3-14C, Carboxamide-14C]S-2310

DT50 (days)

DT90 (days)

Irradiated Sterile Natural Water

7.4

24.2

Irradiated Sterile Distilled Water

7.9

25.9

[Phenyl(U)-14C]S-2310

 

 

Irradiated Sterile Natural Water

9.4

31.5

Irradiated Sterile Distilled Water

7.9

25.9

The values for the DT50 and DT90 calculations were in good agreement between the phenyl and the isothiazole labels. S-2310 was rapidly and extensively degraded during aqueous photolysis at 25 ± 2 °C. The photolysis of S-2310 produced a complex mixture of components from both the natural water and distilled water solutions. The major degradate was anthranilonitrile amounting for up to 14.5% of the applied radioactivity via amide cleavage. A number of minor degradates were also formed and they were gradually mineralized to 14CO2. Based on the results of this study, photolysis will be a major route of elimination of S-2310 from the aquatic environment.