Indole

Endpoint summary

Description of key information

Biodegradation in water

Biodegradation study was conducted under anaerobic conditions for evaluating the percentage biodegradability of test chemical (from peer reviewed journal (D. F. Berry et. al., 1987) and authoritative databases). Municipal sewage sludge collected from primary anaerobic digesters was used as a test inoculum. Before used for the study, test inoculum was filtered through cheese cloth. Test chemical concentration used for the study was 0.43µmol/ml (50µg/ml). Serum bottles of 160 ml volume was used as a test vessel. Test vessel was closed with butyl rubber stoppers and aluminum crimp seals. Mineral salt medium (with 1 ml of 0.1% resazurin solution added) was used as a test medium for the study. 1.2 mg of Na2HCO3 and 0.12 mg of Na2S 9H20 per ml were added as an additional substrate in the test medium. After test medium has been autoclaved for 15 min to remove 02, the medium was maintained under a positive pressure of N2 gas which was previously passed through copper filings at 300°C to remove traces of O2. Test chemical was added to the medium when the medium temperature had cooled to 50°C. The pH of the medium was 7.0 which was adjusted with a solution of HCl. Later, 100 ml portions of inoculated medium were dispensed to N2-flushed serum bottles. Control bottles were sterilized by being autoclaved on three successive days. All bottles were incubated stationary in the dark at a temperature of 35°C for a period of 18 days. All samples (sterile, non-sterile, and with & without added test chemical) were run in duplicates, Additional bottles were frozen after various time intervals for subsequent chemical analysis. The disappearance of test chemical in test sludge was monitored by HPLC. The complete disappearance of test chemical required 10 days. As the test chemical concentration declined, the formation of an intermediate metabolite was observed. Subsequently, this intermediate was isolated by thin-layer chromatography and identified as oxindole (1,3-dihydro-2H-indol-2-one). Mass-spectral analysis, UV absorbance (Xmax, 247 nm), and HPLC retention time of the intermediate were identical to the same analyses performed with an authentic oxindole standard. Additional evidence for the conversion of test chemical to oxindole was obtained in experiments with radioactive test chemical. During 52 days of incubation period, the amount of radioactivity initially added as test chemical declined from 100 to 7.2%. Simultaneously, the radioactivity in the oxindole fraction rose from 0 to 42%. In a sterile control, the initial 14C in the indole fraction remained constant throughout the incubation. The oxindole concentration reached a maximum at approximately day 7 and then declined below detection levels by day 10. During the incubation period, net methane production was increased, indicating the metabolism of test chemical. The percentage degradation of non-radioactive and radioactive test chemical was determined to be 100 and 87% after a period of 10 & 29 days, respectively. Oxindole was isolated and identified as an initial intermediary metabolite and methane was also formed during the degradation study. Thus,test chemical was considered to be readily biodegradable in water.

Biodegradation in water and sediment

Biodegradation study in sediment was conducted for a period of 35 days under anaerobic conditions for evaluating the degradability of the test chemical in freshwater sediment (from peer reviewed journal (E. L. Madsen et. al., 1988) and authoritative databases). Freshwater sediments collected from Buffalo Run stream (Bellefonte, Pa.) were used as a test inoculum. Test chemical concentration used for the study was in the range of 32 to 50 mg/l (0.27 to 0.43 mmol/l). Serum bottles of 160 ml volume was used as a test vessel. Test vessel was closed with butyl rubber stoppers and aluminum crimp seals. Mineral salt medium was used as a test medium for the study. 1.2 mg of Na2HCO3 and 0.12 mg of Na2S 9H20 per ml were added as an additional substrate in the test medium. After test medium has been autoclaved for 15 min to remove 02, the medium was maintained under a positive pressure of N2 gas which was previously passed through copper filings at 300°C to remove traces of O2. Freshwater sediment was diluted with media, stirred vigorously, and dispensed as slurries to N2-flushed serum bottles (160 ml). Test chemical was added to the medium when the medium temperature had cooled to 50°C. The pH of the medium was 7.0 which was adjusted with a solution of HCl. Later, 100 ml portions of inoculated medium were dispensed to N2-flushed serum bottles. Control bottles were sterilized by being autoclaved on three successive days. All bottles were incubated stationary in the dark at a temperature of 22°C for a period of 35 days. All experiments were performed in triplicates, Additional bottles were frozen after various time intervals for subsequent chemical analysis. The disappearance of test chemical in test sludge was monitored by HPLC. The percentage degradation of test chemical was determined to be 100% after a period of 33 days, respectively. As the test chemical disappeared, stoichiometric amounts of oxindole appeared in the sediment suspensions and persisted for over 4 weeks. Subsequently, oxindole was eliminated by the inocula over 110 days. This, indicates that test chemical is not persistent in sediment and the exposure to sediment dwelling animals is moderate to low.

Biodegradation in soil

Biodegradation study in soil was conducted for a period of 75 days under anaerobic conditions for evaluating the degradability of the test chemical in organic soil (from peer reviewed journal (E. L. Madsen et. al., 1988) and authoritative databases). Organic soil (Carlisle muck) was obtained from State College, Pa. Test chemical concentration used for the study was in the range of 32 to 50 mg/l (0.27 to 0.43 mmol/l). Serum bottles of 160 ml volume was used as a test vessel. Test vessel was closed with butyl rubber stoppers and aluminum crimp seals. Mineral salt medium was used as a test medium for the study. 1.2 mg of Na2HCO3 and 0.12 mg of Na2S 9H20 per ml were added as an additional substrate in the test medium. After test medium has been autoclaved for 15 min to remove 02, the medium was maintained under a positive pressure of N2 gas which was previously passed through copper filings at 300°C to remove traces of O2. Organic soil were diluted with media, stirred vigorously, and dispensed as slurries to N2-flushed serum bottles (160 ml). Test chemical was added to the medium when the medium temperature had cooled to 50°C. The pH of the medium was 7.0 which was adjusted with a solution of HCl. Later, 100 ml portions of inoculated medium were dispensed to N2-flushed serum bottles. Control bottles were sterilized by being autoclaved on three successive days. All bottles were incubated stationary in the dark at a temperature of 22°C for a period of 35 days. All experiments were performed in triplicates, Additional bottles were frozen after various time intervals for subsequent chemical analysis. The disappearance of test chemical in test sludge was monitored by HPLC. The percentage degradation of test chemical was determined to be 100% after a period of 67 days. Oxindole was formed as one of the product of test chemical which gradually degraded during the study. This, indicates that test chemical is not persistent in soil and the exposure to soil dwelling animals is moderate to low.

Additional information

Biodegradation in water

Various experimental key and supporting studies of the test chemical were reviewed for the biodegradation end point which are summarized as below:

 

In an experimental key study from peer reviewed journal (D. F. Berry et. al., 1987) and authoritative databases,biodegradation study was conducted under anaerobic conditions for evaluating the percentage biodegradability of test chemical. Municipal sewage sludge collected from primary anaerobic digesters was used as a test inoculum. Before used for the study, test inoculum was filtered through cheese cloth. Test chemical concentration used for the study was 0.43µmol/ml (50µg/ml). Serum bottles of 160 ml volume was used as a test vessel. Test vessel was closed with butyl rubber stoppers and aluminum crimp seals. Mineral salt medium (with 1 ml of 0.1% resazurin solution added) was used as a test medium for the study. 1.2 mg of Na2HCO3 and 0.12 mg of Na2S 9H20 per ml were added as an additional substrate in the test medium. After test medium has been autoclaved for 15 min to remove 02, the medium was maintained under a positive pressure of N2 gas which was previously passed through copper filings at 300°C to remove traces of O2. Test chemical was added to the medium when the medium temperature had cooled to 50°C. The pH of the medium was 7.0 which was adjusted with a solution of HCl. Later, 100 ml portions of inoculated medium were dispensed to N2-flushed serum bottles. Control bottles were sterilized by being autoclaved on three successive days. All bottles were incubated stationary in the dark at a temperature of 35°C for a period of 18 days. All samples (sterile, non-sterile, and with & without added test chemical) were run in duplicates, Additional bottles were frozen after various time intervals for subsequent chemical analysis. The disappearance of test chemical in test sludge was monitored by HPLC. The complete disappearance of test chemical required 10 days. As the test chemical concentration declined, the formation of an intermediate metabolite was observed. Subsequently, this intermediate was isolated by thin-layer chromatography and identified as oxindole (1,3-dihydro-2H-indol-2-one). Mass-spectral analysis, UV absorbance (Xmax, 247 nm), and HPLC retention time of the intermediate were identical to the same analyses performed with an authentic oxindole standard. Additional evidence for the conversion of test chemical to oxindole was obtained in experiments with radioactive test chemical. During 52 days of incubation period, the amount of radioactivity initially added as test chemical declined from 100 to 7.2%. Simultaneously, the radioactivity in the oxindole fraction rose from 0 to 42%. In a sterile control, the initial 14C in the indole fraction remained constant throughout the incubation. The oxindole concentration reached a maximum at approximately day 7 and then declined below detection levels by day 10. During the incubation period, net methane production was increased, indicating the metabolism of test chemical. The percentage degradation of non-radioactive and radioactive test chemical was determined to be 100 and 87% after a period of 10 & 29 days, respectively. Oxindole was isolated and identified as an initial intermediary metabolite and methane was also formed during the degradation study. Thus, test chemical was considered to be readily biodegradable in water.

 

In an another supporting study,biodegradation study was conducted for 28 days for evaluating the percentage biodegradability of test chemical (J-CHECK, 2020). Activated sludge was used as a test inoculums for the study. Concentration of inoculum i.e, sludge used was 30 mg/l and initial test substance conc. used in the study was 100 mg/l, respectively. The percentage degradation of test chemical was determined to be 91, 98 and 100% by O2 consumption, TOC removal and HPLC parameter in 28 days. Thus, based on percentage degradation, test chemical was considered to be readily biodegradable in water.

 

For the test chemical, biodegradation study was conducted under anaerobic conditions for evaluating the percentage biodegradability of test chemical (Yi-Tin Wang et. al., 1984). Synthetic sewage from a laboratory, granular activated carbon, anaerobic filter was used as a test inoculum. Initial test chemical concentrations used for the study was 42 mg/l which increase gradually during the experiment upto 289 mg/l. Serum bottles of 125 ml volume was used as a test vessel. Test vessel was sealed with butyl rubber stoppers. Defined medium was used for the study. The pH of the medium was 7.0 which was adjusted with a solution of sodium bicarbonate under a 30% CO2-70% N2 gas mixture. Resazurin was used as an indicator of reduced conditions. Sodium sulfide and L-cysteine hydrochloride were each added to 0.5 g/liter to provide reducing environment. Oxygen in the purge gas mixture was removed by passing this gas through a heated (450°C) silica glass tube filled with light copper turnings. A 100-ml volume of prereduced defined medium was transferred anaerobically to each bottle. Subsequently, activated carbon inocula ranging in weight from 2 to 4 g were added to each bottle. Finally, test chemical was added to each of two bottles as substrate. The final liquid-phase volume in every bottle was 110 ml. The serum bottles were then sealed with butyl rubber stoppers and shaken at 35°C. All bottles were incubated at a temperature of 35°C for a period of 117 weeks. All experiments were performed in duplicates. Controls (which contained only the defined medium and activated carbon inoculum) were also run simultaneously during the study. The concentration of the polycyclic N-aromatic substrate was measured on aqueous samples filtered through a membrane filter (pore size, 0.45µm). These samples were alkalified to pH 12 and extracted with ether. The solvent phase was analyzed with a Hewlett-Packard model 5750 gas chromatograph with a glass coil column (10 ft long [ca. 3.05 m]) packed with 10% OV-101 on 80/100 Supelcoport. The oven temperature was maintained at 160°C. Both injection port and detector temperatures were set at 200°C. During the metabolism of test chemical by inoculum, total 84% of methane was produced in 18 weeks followed by CO2 indicating that the test chemical has undergone upto 84% degradation. Thus, test chemical was considered to be readily biodegradable in water.

 

Another biodegradation study from peer reviewed journal (E. L. Madsen et. al., 1988) and authoritative database (2019) was conducted for a period of 50 days under anaerobic conditions for evaluating the percentage biodegradability of test chemical. Municipal sewage sludge collected from primary anaerobic digesters was used as a test inoculum. Before used for the study, test inoculum was filtered through cheese cloth. Test chemical concentration used for the study was in the range of 32 to 50 mg/l (0.27 to 0.43 mmol/l). Serum bottles of 160 ml volume was used as a test vessel. Test vessel was closed with butyl rubber stoppers and aluminum crimp seals. Mineral salt medium was used as a test medium for the study. 1.2 mg of Na2HCO3 and 0.12 mg of Na2S 9H20 per ml were added as an additional substrate in the test medium. After test medium has been autoclaved for 15 min to remove 02, the medium was maintained under a positive pressure of N2 gas which was previously passed through copper filings at 300°C to remove traces of O2. Test chemical was added to the medium when the medium temperature had cooled to 50°C. The pH of the medium was 7.0 which was adjusted with a solution of HCl. Later, 100 ml portions of inoculated medium were dispensed to N2-flushed serum bottles. Control bottles were sterilized by being autoclaved on three successive days. All bottles were incubated stationary in the dark at a temperature of 35°C for a period of 50 days. All experiments were performed in triplicates, Additional bottles were frozen after various time intervals for subsequent chemical analysis. The disappearance of test chemical in test sludge was monitored by HPLC. The percentage degradation of test chemical was determined to be 100% after a period of 24 days, respectively. Oxindole was formed as one of the product of test chemical. Thus, based on percentage degradation, test chemical was considered to be readily biodegradable in water.

 

In a supporting study, biodegradation study was conducted for evaluating the percentage biodegradability of test chemical (from handbook, 2009). Sewage sludge was used as a test inoculums for the study. The percentage degradation of test chemical was determined to be 84% by O2 consumption parameter in 5 days. Thus, based on percentage degradation, test chemical was considered to be readily biodegradable in water.

 

Thus, on the basis of this available information, test chemical was considered as readily biodegradable in water.

Biodegradation in water and sediment

Experimental study and predicted data of the test chemical were reviewed for the biodegradation in water & sediment end point which are summarized as below:

 

In an experimental study from peer reviewed journal (E. L. Madsen et. al., 1988) and authoritative databases, biodegradation study in sediment was conducted for a period of 35 days under anaerobic conditions for evaluating the degradability of the test chemical in freshwater sediment. Freshwater sediments collected from Buffalo Run stream (Bellefonte, Pa.) were used as a test inoculum. Test chemical concentration used for the study was in the range of 32 to 50 mg/l (0.27 to 0.43 mmol/l). Serum bottles of 160 ml volume was used as a test vessel. Test vessel was closed with butyl rubber stoppers and aluminum crimp seals. Mineral salt medium was used as a test medium for the study. 1.2 mg of Na2HCO3 and 0.12 mg of Na2S 9H20 per ml were added as an additional substrate in the test medium. After test medium has been autoclaved for 15 min to remove 02, the medium was maintained under a positive pressure of N2 gas which was previously passed through copper filings at 300°C to remove traces of O2. Freshwater sediment was diluted with media, stirred vigorously, and dispensed as slurries to N2-flushed serum bottles (160 ml). Test chemical was added to the medium when the medium temperature had cooled to 50°C. The pH of the medium was 7.0 which was adjusted with a solution of HCl. Later, 100 ml portions of inoculated medium were dispensed to N2-flushed serum bottles. Control bottles were sterilized by being autoclaved on three successive days. All bottles were incubated stationary in the dark at a temperature of 22°C for a period of 35 days. All experiments were performed in triplicates, Additional bottles were frozen after various time intervals for subsequent chemical analysis. The disappearance of test chemical in test sludge was monitored by HPLC. The percentage degradation of test chemical was determined to be 100% after a period of 33 days, respectively. As the test chemical disappeared, stoichiometric amounts of oxindole appeared in the sediment suspensions and persisted for over 4 weeks. Subsequently, oxindole was eliminated by the inocula over 110 days. This, indicates that test chemical is not persistent in sediment and the exposure to sediment dwelling animals is moderate to low.

 

For the test chemical, Estimation Programs Interface prediction model was run to predict the half-life in water and sediment for the test chemical. If released in to the environment, 24.8% of the chemical will partition into water according to the Mackay fugacity model level III and the half-life period of test chemical in water is estimated to be 15 days (360 hrs). The half-life (15 days estimated by EPI suite) indicates that the chemical is not persistent in water and the exposure risk to aquatic animals is moderate to low whereas the half-life period of test chemical in sediment is estimated to be 135 days (3240 hrs). However, as the percentage release of test chemical into the sediment is less than 1% (i.e, reported as 0.761%), indicates that test chemical is not persistent in sediment.

 

Thus, on the basis of this available information, test chemical was considered to be not persistent in sediment.

 

In addition to this, biodegradation in water and sediment endpoint can also be considered for waiver as per in accordance with column 2 of Annex IX of the REACH regulation, testing for this end point is scientifically not necessary and does not need to be conducted since the test chemical is readily biodegradable in water.

Biodegradation in soil

Experimental study and predicted data of the test chemical were reviewed for the biodegradation in soil end point which are summarized as below:

 

In an experimental study from peer reviewed journal (E. L. Madsen et. al., 1988) and authoritative databases,biodegradation study in soil was conducted for a period of 75 days under anaerobic conditions for evaluating the degradability of the test chemical in organic soil. Organic soil (Carlisle muck) was obtained from State College, Pa. Test chemical concentration used for the study was in the range of 32 to 50 mg/l (0.27 to 0.43 mmol/l). Serum bottles of 160 ml volume was used as a test vessel. Test vessel was closed with butyl rubber stoppers and aluminum crimp seals. Mineral salt medium was used as a test medium for the study. 1.2 mg of Na2HCO3 and 0.12 mg of Na2S 9H20 per ml were added as an additional substrate in the test medium. After test medium has been autoclaved for 15 min to remove 02, the medium was maintained under a positive pressure of N2 gas which was previously passed through copper filings at 300°C to remove traces of O2. Organic soil were diluted with media, stirred vigorously, and dispensed as slurries to N2-flushed serum bottles (160 ml). Test chemical was added to the medium when the medium temperature had cooled to 50°C. The pH of the medium was 7.0 which was adjusted with a solution of HCl. Later, 100 ml portions of inoculated medium were dispensed to N2-flushed serum bottles. Control bottles were sterilized by being autoclaved on three successive days. All bottles were incubated stationary in the dark at a temperature of 22°C for a period of 35 days. All experiments were performed in triplicates, Additional bottles were frozen after various time intervals for subsequent chemical analysis. The disappearance of test chemical in test sludge was monitored by HPLC. The percentage degradation of test chemical was determined to be 100% after a period of 67 days. Oxindole was formed as one of the product of test chemical which gradually degraded during the study. This, indicates that test chemical is not persistent in soil and the exposure to soil dwelling animals is moderate to low.

 

For the test chemical, the half-life period of test chemical in soil was estimated using Level III Fugacity Model by EPI Suite version 4.1 estimation database. If released into the environment, 74.3% of the chemical will partition into soil according to the Mackay fugacity model level III. The half-life period of test chemical in soil is estimated to be 30 days (720 hrs). Based on this half-life value of test chemical, it is concluded that the chemical is not persistent in the soil environment and the exposure risk to soil dwelling animals is moderate to low.

 

Thus, on the basis of this available information, test chemical was considered to be not persistent in soil.

 

In addition to this, biodegradation in soil endpoint can also be considered for waiver as per in accordance with column 2 of Annex IX of the REACH regulation, testing for this end point is scientifically not necessary and does not need to be conducted since the test chemical is readily biodegradable in water.