5-Isothiazolecarboxamide, 3,4-dichloro-N-(2-cyanophenyl)-

Biodegradation in water and sediment: simulation tests

Description of key information

Isotianil and its degradation products have no potential for accumulation in the aquatic environment. The half-lives for the degradation of Isotianil in the total water/sediment system are 2.0 to 3.1 days. Consequently, Isotianil will not persist in the environment.

Additional information

Since Isotianil showed to be not readily biodegradable further simulation studies in water and sediment were conducted under aerobic and anaerobic conditions.

In an aerobic aquatic metabolism study (Ströch & Junge, 2014) the route and rate of degradation of [isothiazol-3-14C, carboxamide-14C]Isotianil (isotianil) were studied in two water/sediment systems under aerobic conditions in the dark in the laboratory for 100 days at 19.9 °C. The study followed the OECD Guideline for the Testing of Chemicals No. 308. A study application rate of 53.0 µg per test system (corresponding to 101.9 µg/L) was applied based on a 5-fold maximum single field application rate of isotianil of 200 g/ha due to analytical reasons. The test was performed in static systems consisting of cylindrical glass containers containing a water-to-sediment volume ratio of 3/1 (v/v) and equipped with traps for the collection of carbon dioxide and volatile organic compounds. During incubation, the water was in smooth motion. Duplicate samples were processed and analyzed 0, 1, 3, 7, 14, 30, 58 and 100 days after treatment (DAT). DAT-0 samples were processed approximately 1 to 2 hours after application. At each sampling interval, the water was separated from the sediment by decantation. The sediment was extracted three times at ambient temperature using acetonitrile/water 4/1 (v/v). Furthermore, two microwave-accelerated extraction steps were performed using acetonitrile/water 4/1 (v/v) at 70 °C and methanol/water 1/1 (v/v) at 50 °C. The amounts of test item and degradation products in water and sediment extracts were determined by liquid scintillation counting (LSC) and by HPLC/radiodetection analysis. The amount of volatiles and non-extractable residues were determined by LSC and combustion/LSC, respectively. Test item and degradation products were identified by HPLC-MS(/MS) including accurate mass determination and by co-chromatography with reference items. Mean material balances were 103.6% AR for system Anglersee (range from 101.4 to 106.9% AR) and 102.6% AR for system Wiehltalsperre (range from 99.0 to 110.2% AR). The maximum amount of carbon dioxide was 21.8 and 31.5% AR at study end (DAT-100) in system Anglersee and Wiehltalsperre, respectively. Formation of volatile organic compounds (VOC) was insignificant as demonstrated by values of ≤ 0.1% AR at all sampling intervals for both water/sediment systems. Residues in water decreased from DAT-0 to DAT-100 from 91.3 to 51.7% AR in system Anglersee and from 92.5 to 25.5% AR in system Wiehltalsperre. Extractable residues in sediment increased from 14.8 and 14.2% AR at DAT-0 to 25.5 and 46.6% AR at DAT-14 and decreased then to 15.6 and 22.0% AR at DAT-100 in system Anglersee and Wiehltalsperre, respectively. Extractable residues in the total system (water and sediment extracts) decreased from DAT-0 to DAT-100 from 106.1 to 67.3% AR in system Anglersee and from 106.8 to 47.5% AR in system Wiehltalsperre. Non-extractable residues (NER) increased in system Anglersee from DAT-0 to DAT-100 from 0.9 to 12.4% AR. In system Wiehltalsperre, NER increased from DAT-0 to DAT-58 from 3.4 to 21.2% AR and slightly decreased to 20.0% AR at DAT-100. Isotianil dissipated from the water due to degradation and translocation into the sediment. The amount of isotianil in the water decreased from 88.8 and 91.3% at DAT-0 to below LOD or not detectable from DAT-14 or DAT-30 onwards in system Anglersee and Wiehltalsperre, respectively. The amount of isotianil in the sediment extracts increased from 13.3 and 13.7% AR at DAT-0 to 16.3 and 32.6% AR at DAT-1 and decreased then to 1.3 and 3.0% AR at DAT-100 in system Anglersee and Wiehltalsperre, respectively. The amount of isotianil in the total system decreased from DAT-0 to DAT-100 from 102.1 to 1.3% AR in system Anglersee and from 105.0 to 3.0% AR in system Wiehltalsperre. Besides the formation of carbon dioxide, two degradation products were identified with the following maximum occurrences: DCIT-acid with 92.3% AR at DAT-14 (system Anglersee) and 4-CIT-acid with 20.6% AR at DAT-100 (system Wiehltalsperre). The total unidentified residues for both water/sediment systems amounted to a maximum of 6.5% AR only at one single sampling interval and were below 5% AR at all following sampling intervals. The experimental data could be well described by single first order (SFO) and double first order in parallel (DFOP) kinetic models. The half-life for the dissipation of isotianil from the water was 1.3 and 0.9 days in system Anglersee and Wiehltalsperre, respectively. The half-life for the degradation of isotianil in the total water/sediment system was 2.0 and 3.1 days in system Anglersee and Wiehltalsperre, respectively. It is concluded that isotianil and its degradation products have no potential for accumulation in the aquatic environment.

In the second study the anaerobic biotransformation of radiolabeled isotianil was studied in two pond (sediment/water) systems (McConnell et al., 2014). One system was collected from a pond near Hughson, CA, USA (water: pH 9.0, sediment: texture loamy sand, pH 7.7) and the other was taken from a pond in Wilson, NC, USA (water: pH 6.9; sediment: texture loam). The application rate used in the study was based on the anticipated single maximum field application rate for this compound of 200 g a.i./ha. To achieve analytical sensitivity, the test rate used in the study was 3-fold the proposed maximum rate or 0.06 µg a.i. per mL pond water. The study was conducted for 104 days in the dark at 20 ± 2 °C. The experiment was conducted in accordance with US EPA OCSPP 835.4300 and 835.4400, Aerobic and Anaerobic Aquatic Metabolism, OECD: Guideline 308, Aerobic and Anaerobic Transformation in Water-Sediment Systems. The test systems consisted of an Erlenmeyer flask containing 60 g (dry weight) sediment and 180 mL pond water to achieve a water/sediment ratio of 1:3 (sediment depth of approximately 2.5 cm). Eight sampling intervals were conducted and included 0, 2, 8, 16, 36, 56, 78, and 104 days post treatment. The water samples were centrifuged and analyzed by HPLC direct injection equipped with 14C detector. The aqueous and sediment extracts were characterized for 14C-isotianil residues. Identification of isotianil and major degradates was achieved by co-chromatography or retention time comparisons to reference standards and by liquid chromatography-electrospray ionization mass spectrometry (LC/ESI-MS). In the CA test systems, the mean material balances per sampling interval ranged from 96.8 to 99.1% of the applied radioactivity, with an overall mean material balance of 97.7%. The radioactive residues in the water phase decreased from an average of 90.7% at Day 0 to 57.4% at Day 8 and then increased to 73.9% by the end of the study (Day 104). The radioactive residues in the sediment increased from an average of 6.7% on Day 0 to 39.2% on Day 8 then decreased to 18.8 at the end of the study. Nonextractable residues increased over the course of the study to 4% of the applied radioactivity. Organic volatiles and 14CO2 remained ≤0.4% of the

applied radioactivity. In the NC test systems, the mean material balances per sampling interval ranged from 91.3 to 98.8% of the applied radioactivity, with an overall mean material balance of 95.2%. The radioactive residues in the water phase decreased from an average of 91.5% at Day 0 to 25.5% at Day 36 and increased to 36.5% at the end of the study. The radioactive residues in the sediment increased from an average of 3.5% on Day 0 to 59.9% at Day 36 and decreased to 42.8% at the end of the study. Unextractable residues increased from 0.2% at Day 0 to 18.1% at Day 104. Organic volatiles and 14CO2 remained at ≤0.5% of the applied radioactivity. In the water phase of the CA test systems, isotianil decreased from 90.7% of the applied radioactivity at Day 0, to 0.5% at Day 36, and was below the limit of detection at Days 56, 78 and 104. DCIT-acid formed at 5.3% of the applied radioactivity at Day 2 and reached a maximum level of 73.9% in the water at the end of the study. In the sediment phase of the CA test systems, isotianil increased from 6.7% of the applied radioactivity at Day 0 to 18.4% at Day 2 and then decreased to 0.7% by the end of the study. DCIT-acid formed at 21.1% of the applied radioactivity at Day 8 and increased to 22.2% at Day 36, and then and declined to 17.4 to 18.2% in the sediment by Days 78 and 104, respectively. In the CA total water/sediment systems, isotianil decreased from 97.4% of the applied radioactivity at Day 0 to 0.7% by Day 104. DCIT-acid formed at 5.3% of the applied radioactivity at Day 2, increased to 91.9% by Day 36 and remained at 90.4 to 92.1% through Day 104. Individual unidentified minor degradates were detected on Days 56 and 78 but did remained at ≤1.4% of the applied radioactivity. In the water phase of the NC test systems, isotianil decreased from 91.5% of the applied radioactivity at Day 0 to 0.9% at Day 36, and was below the limit of detection beginning on Day 56 through the end of the study (Day 104). DCIT-acid detected at 11.4% of the applied radioactivity at Day 8 and reached a maximum level of 23.0% in the water at Day 36, and declined to 0% in the water at Day 104. The degradate 4-CIT-acid was detected at 1.6% at Day 36 and increased to 36.5% at Day 104. In the sediment phase of the NC test systems, isotianil occurred at 3.5% of the applied radioactivity at Day 0, increased to 45.3% by Day 36, and decreased to 21.5% at the end of the study. DCIT-acid formed at 13.3% of the applied radioactivity at Day 16, increased to 14.6% by Day 36, decreased below the limit of detection by Day 104. 4-CIT-acid was detected at 8.6% of the applied radioactivity at Day 56, increasing to 21.3% by the end of the study. In the NC total water/sediment systems, isotianil decreased from 95.0% of the applied radioactivity at Day 0 to 21.5% at Day 104. DCIT-acid formed at 11.4% of the applied radioactivity at Day 8, reached a maximum level of 37.6% in the total system at Day 36, and declined to below the limit of detection in the total system at Day 104. 4-CIT-acid was detected at 1.6% of the applied radioactivity at Day 36 and increased to 57.8% by the end of the study. There were no unidentified degradates. The half-lives calculated for isotianil in anaerobic water were 3.5 and 6.3 days for CA and NC, respectively. The half-lives of isotianil in the total system were 6.5 and 27.9 days for CA and NC, respectively. Isotianil degrades rapidly in anaerobic aquatic water/sediment environment, and, thus, will not persist under this type of environmental conditions.