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Environmental fate & pathways

Phototransformation in air

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Reference
Endpoint:
phototransformation in air
Type of information:
experimental study
Adequacy of study:
key study
Study period:
21 September 1992 to 23 March 1992
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EPA Guideline Subdivision N 161-4 (Photodegradation Studies in Air)
Deviations:
no
GLP compliance:
yes
Light source:
Xenon lamp
Duration:
10 d
Temp.:
33 °C
Quantum yield (for direct photolysis):
0.06
Key result
DT50:
2.8 d
Test condition:
in the SUNTEST (1.4 days of natural sunlight at 50 ºN latitude)
Transformation products:
yes
No.:
#1

In the control samples, 99 % of the radioactivity could be recovered as unchanged [14C]-2,6-dichlorobenzonitrile.

In the irradiated samples, the recovered total amount of [14C] decreased rapidly. After 10 days, only 22% of the total radioactivity could be recovered, caused by the formation of volatile products that could not be condensed at -70°C to the glass wall of the ampoule.

The radioactivity that was condensed was analysed by reversed-phase HPLC. After 10 days of irradiation, 45.5 % of the condensate was recovered as the parent compound. The remainder of the radioactivity was characterised as a major peak with the same retention time as 2,6-dichlorobenzamide comprising about 60 % in the condensate and at least 5 minor compounds, each comprising about 2-5 % of the condensate.

Considering the volatile products, [14C]-2,6-dichlorobenzonitrile comprises 10.3 % of the initial added amount after 10 days irradiation. Therefore, the calculated half-time of [14C]-2,6-dichlorobenzonitrile in air is 2.8 days in the SUNTEST, which equals 1.4 days of natural sunlight at 50 º Northern latitude as specified by the US-EPA. The quantum yield was 0.06 mole/Einstein.

Because of the incomplete mass-balance in the study, GC-MS was used to elucidate the structure of the volatile compounds that could not be condensed. For this purpose, 100 mg of unlabelled test material in 1 L of air was irradiated for 7 days under the same conditions as for the samples. A second gas flask was kept for the same period in the dark. After 1 week, the air of the samples was pumped through a Tenax tube, which was completely eluted and linked to a GC-MS system.

In the dark sample, only H20 and parent compound were recovered. The gas phase of the irradiated sample contained parent compound, 5 major degradation products and a number of minor compounds. These five major degradation products were diethyl ether, ethanol, possibly acetamide and unknown mixtures. No small volatile chlorinated compounds were found.

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the test, the test material degrades rapidly in air under the influence of light to form a number of volatile photodegradation products. The calculated half-life of the test material in air is 2.8 days in the SUNTEST, which equals 1.4 days of natural sunlight at 50 º Northern latitude as specified by the US-EPA. The quantum yield was 0.06 mole/Einstein.
Executive summary:

In a GLP compliant photolysis study conducted in accordance with standardised guideline EPA 161-4, the rate and route of dichlobenil degradation in the air was investigated. Under the conditions of the test, the test material degrades rapidly in air under the influence of light to form a number of volatile photodegradation products. The calculated half-life of the test material in air is 2.8 days in the SUNTEST, which equals 1.4 days of natural sunlight at 50 º Northern latitude as specified by the US-EPA. The quantum yield was 0.06 mole/Einstein.

Description of key information

The half-life of the test material was determined to be 2.8 days in the SUNTEST which is equivalent to 1.4 days of natural sunlight at 50 º Northern latitude according to a study performed in line with EPA 161-4.

Key value for chemical safety assessment

Half-life in air:
2.8 d

Additional information

See 'Environmental Fate and Pathways' endpoint summary.