2-nitrotoluene

Phototransformation in water

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

other: BUA report

Rationale for reliability incl. deficiencies:

other: No reliability is given as this is a summary entry for the BUA report.

Principles of method if other than guideline:

BUA report

GLP compliance:

not specified

Specific details on test material used for the study:

- Analytical purity: not specified

BUA report (1989):

 

For the direct photolysis of o-nitrotoluene in water (near the surface, at 40 degrees latitude, throughout the year) a quantum yield of 0.0022 and a corresponding half-life period of 18.9 h was found by Simmons and Zeep, 1986. Photolysis is accelerated by indirect degradation mechanisms (the effects of humic acids, nitrates, etc. in natural waters). This is especially true for o-nitrotoluene, for which the degradation rate in natural waters was increased by a factor of 6-7.

Executive summary:

BUA report (1989):

For the direct photolysis of o-nitrotoluene in water (near the surface, at 40 degrees latitude, throughout the year) a quantum yield of 0.0022 and a corresponding half-life period of 18.9 h was found by Simmons and Zeep, 1986. Photolysis is accelerated by indirect degradation mechanisms (the effects of humic acids, nitrates, etc. in natural waters). This is especially true for o-nitrotoluene, for which the degradation rate in natural waters was increased by a factor of 6-7.

Reference 2

Endpoint:

phototransformation in water

Type of information:

other: EU Risk Assessment

Adequacy of study:

other information

Reliability:

other: EU Risk Assessment

Rationale for reliability incl. deficiencies:

other: No reliability is given as this is a summary entry for the EU RAR.

Principles of method if other than guideline:

EU Risk Assessment

GLP compliance:

not specified

Specific details on test material used for the study:

- Analytical purity: not specified

EU Risk Assessment (2008):

 

Chemical hydrolysis and oxidation of 2-nitrotoluene are not expected to be important removal processes. However, 2-nitrotoluene may be susceptible to photolysis. Because nitroaromatic compounds absorb sunlight strongly in the ultraviolet and blue spectral region, they are generally susceptible to photochemical transformation in aquatic systems. In a study by Simmons and Zeep (1986), carried out through the year under full exposure to sunlight and surface conditions at 40 ºN latitude, the photodegradation rates of several nitroaromatic compounds were determined. Saturated solutions of 2-nitrotoluene were made up in distilled water (organic-free water) and were centrifuged at 15,000 rpm for 30 min. The supernatant was removed carefully, this stock solution was diluted to concentration levels of 10 ^-6 - 10 ^-5 M and then exposed to midday sunlight. The kinetic results for 2-nitrotoluene indicated a half life of 0.79 days.

 

The effect of humic substances in natural waters on photolysis was investigated in the same study and it was shown that they enhanced the sunlight-induced photodegradation rates compared to distilled water results. This was especially pronounced for 2-nitrotoluene, for which the degradation rate in natural waters was increased by a factor of 6 - 7.5.

 

Photoreaction in seawater may differ from those occurring in other aqueous media. The photolysis rate for 2-nitrotoluene in filter-sterilised seawater was 5.3×10^-3 min^-1 (t_1/2 = 130 min). In unsterilised seawater, the rate was not significantly different, 5.5×10 ^-3 min^-1 (t_1/2= 126 min), and in neither case any loss of nitrotoluene was observed in the dark. The rate in unsterilised seawater collected from a more polluted site, which was presumed to have a larger microbial population, was also determined. Again, no degradation was observed in the dark, and a half-life of 5.7×10 ^-3 min^-1 (t_1/2 = 122 min) was determined in the light, which is within 3% of that calculated in unsterilised seawater (Toole, 1988).

 

The studies referred above are based on direct photolysis under laboratory conditions. As half life under environmental conditions is not available, it was assumed that only 3.3% of the solved substance is exposed to photodegradation, since the Handbook of Estimation Methods for Chemicals (eds Boethling and Mackay, Lewis Publishers) suggests a diffuse attenuation coefficient of 0.1 cm^-1 as an average. For a depth of 3 metres as in the TGD regional model, the average rate over this depth would be 1/30th of the rate at the surface (3.3%). Considering the lowest photodegradation rate (0.79 days) as a worst case, an effective half-life of 24 days is estimated. The corresponding Kphotowater of 1.2×10 ^-3 h^-1 has been used in the risk assessment.

Executive summary:

EU Risk Assessment (2008):

Chemical hydrolysis and oxidation of 2-nitrotoluene are not expected to be important removal processes. However, 2-nitrotoluene may be susceptible to photolysis. Because nitroaromatic compounds absorb sunlight strongly in the ultraviolet and blue spectral region, they are generally susceptible to photochemical transformation in aquatic systems. In a study by Simmons and Zeep (1986), carried out through the year under full exposure to sunlight and surface conditions at 40 ºN latitude, the photodegradation rates of several nitroaromatic compounds were determined. Saturated solutions of 2-nitrotoluene were made up in distilled water (organic-free water) and were centrifuged at 15,000 rpm for 30 min. The supernatant was removed carefully, this stock solution was diluted to concentration levels of 10 ^-6 - 10 ^-5 M and then exposed to midday sunlight. The kinetic results for 2-nitrotoluene indicated a half life of 0.79 days.

 

The effect of humic substances in natural waters on photolysis was investigated in the same study and it was shown that they enhanced the sunlight-induced photodegradation rates compared to distilled water results. This was especially pronounced for 2-nitrotoluene, for which the degradation rate in natural waters was increased by a factor of 6 - 7.5.

 

Photoreaction in seawater may differ from those occurring in other aqueous media. The photolysis rate for 2-nitrotoluene in filter-sterilised seawater was 5.3×10^-3 min^-1 (t1/2 = 130 min). In unsterilised seawater, the rate was not significantly different, 5.5×10 ^-3 min^-1 (t1/2= 126 min), and in neither case any loss of nitrotoluene was observed in the dark. The rate in unsterilised seawater collected from a more polluted site, which was presumed to have a larger microbial population, was also determined. Again, no degradation was observed in the dark, and a half-life of 5.7×10 ^-3 min^-1 (t1/2 = 122 min) was determined in the light, which is within 3% of that calculated in unsterilised seawater (Toole, 1988).

The studies referred above are based on direct photolysis under laboratory conditions. As half life under environmental conditions is not available, it was assumed that only 3.3% of the solved substance is exposed to photodegradation, since the Handbook of Estimation Methods for Chemicals (eds Boethling and Mackay, Lewis Publishers) suggests a diffuse attenuation coefficient of 0.1 cm^-1 as an average. For a depth of 3 metres as in the TGD regional model, the average rate over this depth would be 1/30th of the rate at the surface (3.3%). Considering the lowest photodegradation rate (0.79 days) as a worst case, an effective half-life of 24 days is estimated. The corresponding Kphotowater of 1.2×10 ^-3 h^-1 has been used in the risk assessment.

Description of key information

For transported isolated intermediates according to REACh, Article 18, this endpoint is not a data requirement. However, data is available for this endpoint and is thus reported under the guidance of "all available data".

EU Risk Assessment (2008)

Chemical hydrolysis and oxidation of 2-nitrotoluene are not expected to be important removal processes. However, 2-nitrotoluene may be susceptible to photolysis. Because nitroaromatic compounds absorb sunlight strongly in the ultraviolet and blue spectral region, they are generally susceptible to photochemical transformation in aquatic systems. In a study by Simmons and Zeep (1986), carried out through the year under full exposure to sunlight and surface conditions at 40 ºN latitude, the photodegradation rates of several nitroaromatic compounds were determined. Saturated solutions of 2-nitrotoluene were made up in distilled water (organic-free water) and were centrifuged at 15,000 rpm for 30 min. The supernatant was removed carefully, this stock solution was diluted to concentration levels of 10 ^-6 - 10 ^-5 M and then exposed to midday sunlight. The kinetic results for 2-nitrotoluene indicated a half life of 0.79 days.

The effect of humic substances in natural waters on photolysis was investigated in the same study and it was shown that they enhanced the sunlight-induced photodegradation rates compared to distilled water results. This was especially pronounced for 2-nitrotoluene, for which the degradation rate in natural waters was increased by a factor of 6 - 7.5.

Photoreaction in seawater may differ from those occurring in other aqueous media. The photolysis rate for 2-nitrotoluene in filter-sterilised seawater was 5.3×10^-3 min-1 (t1/2 = 130 min). In unsterilised seawater, the rate was not significantly different, 5.5×10 ^-3 min^-1 (t1/2= 126 min), and in neither case any loss of nitrotoluene was observed in the dark. The rate in unsterilised seawater collected from a more polluted site, which was presumed to have a larger microbial population, was also determined. Again, no degradation was observed in the dark, and a half-life of 5.7×10 ^-3 min^-1 (t1/2 = 122 min) was determined in the light, which is within 3% of that calculated in unsterilised seawater (Toole, 1988).

The studies referred above are based on direct photolysis under laboratory conditions. As half life under environmental conditions is not available, it was assumed that only 3.3% of the solved substance is exposed to photodegradation, since the Handbook of Estimation Methods for Chemicals (eds Boethling and Mackay, Lewis Publishers) suggests a diffuse attenuation coefficient of 0.1 cm^-1 as an average. For a depth of 3 metres as in the TGD regional model, the average rate over this depth would be 1/30th of the rate at the surface (3.3%). Considering the lowest photodegradation rate (0.79 days) as a worst case, an effective half-life of 24 days is estimated. The corresponding Kphotowater of 1.2×10 -³ h^-1 has been used in the risk assessment.

BUA report (1989):

For the direct photolysis of o-nitrotoluene in water (near the surface, at 40 degrees latitude, throughout the year) a quantum yield of 0.0022 and a corresponding half-life period of 18.9 h was found by Simmons and Zeep, 1986. Photolysis is accelerated by indirect degradation mechanisms (the effects of humic acids, nitrates, etc. in natural waters). This is especially true for o-nitrotoluene, for which the degradation rate in natural waters was increased by a factor of 6-7.