Paraquat-dichloride

Phototransformation in water

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1988

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water)

Version / remarks:

1982

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Remarks:

14C-pyridyl-labelled

Remarks on result:

not determinable

Remarks:

The results of these analyses showed that after exposure to the equivalent of 36 days Florida Summer sunlight no detectable photodegradation had occurred

Virtually all the radioactivity recovered was detected in the photolysis vial. Only very minute traces of radioactivity were recovered from the polyurethane bungs and traps. The largest fraction of radioactivity recovered outside the photolysis vessels, 0.13%, was detected in the first ethanolamine trap. This trap was designed to trap carbon dioxide. At the start of the study the purity of the 14C-labelled test material was measured and found to be 95.3%. After exposure to the equivalent of 36 days Florida Summer Sunlight the average total recovery, based on two samples, was 103.3%. The vast majority of the radioactivity, 103.2%, was recovered from the photolysis vials. Analysis of the photolysis vials by Thin Layer Chromatography (TLC) and High Performance Liquid Chromatography (HPLC) showed that 94.0% and 94.8% of the recovered radioactivity was due to unchanged test material. Thus no detectable photodegradation of the test material had occurred. After being maintained in the dark at 25 ± 1°C for the same length of time as the samples exposed to the xenon burner, for theequivalent of 36 days of Florida Summer sunlight, 105.9% of the radioactivity initially present was recovered from the dark control samples. Also the purity of the test material in the dark control samples measured by TLC and HPLC, showed no real change at 95.8% and 94.6%.

Validity criteria fulfilled:

not specified

Conclusions:

The purpose of this study was to evaluate the possible photodegradation of the test material when introduced into an aqueous environment. Very good recovery of the radioactivity initially present in the photolysis vessels was achieved for all the samples analyzed. Virtually all the radioactivity recovered was detected in the photolysis vial. Only very minute traces of radioactivity were recovered from the polyurethane bungs and traps. The largest fraction of radioactivity recovered outside the photolysis vessels, 0.13%, was detected in the first ethanolamine trap. This trap was designed to trap carbon dioxide. At the start of the study the purity of the 14C-labelled test material was measured and found to be 95.3%. After exposure to the equivalent of 36 days Florida Summer Sunlight the average total recovery, based on two samples, was 103.3%. The vast majority of the radioactivity, 103.2%, was recovered from the photolysis vials. Analysis of the photolysis vials by Thin Layer Chromatography (TLC) and High Performance Liquid Chromatography (HPLC) showed that 94.0% and 94.8% of the recovered radioactivity was due to unchanged test material. Thus no detectable photodegradation of the test material had occurred. After being maintained in the dark at 25 ± 1°C for the same length of time as the samples exposed to the xenon burner, for the equivalent of 36 days of Florida Summer sunlight, 105.9% of the radioactivity initially present was recovered from the dark control samples. Also the purity of the test material in the dark control samples measured by TLC and HPLC, showed no real change at 95.8% and 94.6%. This result was consistent with the results obtained from the test material hydrolysis study. The hydrolysis study showed that the test material was stable to hydrolysis at pH7 when maintained at 25°C and 40°C in the absence of light for 30 days.

Executive summary:

This study was conducted to evaluate the possible photodegradation of the test material when introduced into an aqueous environment. The study was designed to conform to the Pesticide Assessment Guidelines for photodegradation studies in water, published by the US Environmental Protection Agency. A sample concentration of 28 ppm 14C-pyridyl-labelled test material was used in the study. Samples were prepared in a 0.01 M pH7 phosphate buffer solution, made from glass distilled water. All samples and apparatus were autoclaved prior to setting up the study, and sterile techniques were observed to prevent the ingress of microorganisms into the system. The light source used to irradiate the samples was a Heraeus Suntest Accelerated Exposure Machine. This machine consisted of a xenon burner surrounded by a combination of mirrors and filters, producing an emission spectrum which closely approximated to the global radiation of natural sunlight. Samples were continuously irradiated and duplicate samples were removed at specific time intervals. The final duplicate samples were removed after an irradiation period equivalent to 36 days of Florida Summer Sunlight. During the irradiation period samples were maintained at 25 ± 1°C.A further two sets of duplicate samples were prepared for dark control and time zero samples. The dark control samples were maintained in the dark at 25 ± 1°C until all irradiation periods were completed. The time zero samples were prepared and immediately stored in the dark at 15 ± 5°C. All the samples were analyzed by Thin Layer Chromatography (TLC) and High Performance Liquid Chromatography (HPLC). The results of these analyses showed that after exposure to the equivalent of 36 days Florida Summer sunlight no detectable photodegradation had occurred.

Reference 2

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

01 June 2000 to 31 Jul 2000

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with national standard methods

Qualifier:

according to guideline

Guideline:

other: Japanese Ministry of Agriculture, Forestry and Fisheries guideline: Photolysis of a Pesticide in Water

Deviations:

no

GLP compliance:

yes

Radiolabelling:

no

Remarks on result:

not determinable

Remarks:

not significantly photodegraded in natural river water after 33 days of natural spring sunlight in Tokyo (latitude 35°N).

The test item was not significantly photodegraded in natural river water after 33 days of natural spring sunlight in Tokyo (latitude 35°N). There was no degradation of the test item in dark control solutions.

Validity criteria fulfilled:

not specified

Conclusions:

The test item was not significantly photodegraded in natural river water after 33 days of natural spring sunlight in Tokyo (latitude 35°N).

Executive summary:

Natural river water, fortified with test item at a nominal concentration of 5 µg/ml test substance cation, was continuously irradiated with light from a xenon arc lamp that was filtered to give a spectral distribution close to that of natural sunlight. Samples were maintained at 25 ± 2°C and irradiated for defined periods up to 6 days (equivalent to approximately 33 days of Tokyo spring sunlight). Duplicate samples were analysed at zero-time and at 1, 2, 3, 4, 5 and 6 days after test item application. 'Dark control' samples were also prepared and maintained at 25 ± 2°C. A single dark control sample was analysed at the same time intervals as the irradiated samples. The test item was determined in sampled solutions by a second derivative spectrophotometric method following appropriate dilution of the treated water with saturated ammonium chloride.

The test item was not significantly photodegraded in natural river water after 33 days of natural spring sunlight in Tokyo (latitude 35°N). There was no degradation of the test item in dark control solutions.

Description of key information

It is shown that the test item when introduced into an aqueous environment is found to be stable and no photodegradation occurs, EPA 161 -2, Parker & Leahey, 1988 and Japanese guidance Dean 2000