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Environmental fate & pathways

Phototransformation in soil

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Administrative data

Endpoint:
phototransformation in soil
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2010
Report Date:
2010

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
EPA Guideline Subdivision N 161-3 (Photodegradation Studies on Soil)
Deviations:
no
Qualifier:
according to
Guideline:
other: U.S. EPA OPPTS 835.2410 (Photodegradation on Soil)
Deviations:
no
Qualifier:
according to
Guideline:
OECD Guideline draft (Phototransformation of Chemicals on Soil Surfaces)
Deviations:
no
Qualifier:
according to
Guideline:
other: Procedures for Assessing the Environmental Fate and Ecotoxicology of Pesticides, Society for Environmental Toxicology and Chemistry-Europe (SETAC-Europe), Brussels, Belgium
Deviations:
no
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid
Details on test material:
Purity: 85-99%
Specific details on test material used for the study:
[Triazine-14C]test substance (Radiochemical purity: 97.0% and specific activity: 49.61 μCi/mg)
[Phenyl-14C]test substance (Radiochemical purity: 97.1% and specific activity: 39.55 μCi/mg)
Radiolabelling:
yes
Remarks:
[Triazine-14C] and [Phenyl -14C]

Study design

Analytical monitoring:
yes
Analytical method:
high-performance liquid chromatography
other: Thin layer chromatography
Light source:
Xenon lamp
Light spectrum: wavelength in nm:
> 290 - < 800
Duration of test at given test condition
Duration:
30 d
% Moisture:
20.03
Temp.:
20 °C
Initial conc. measured:
0.3 mg/kg soil d.w.
Reference substance:
yes
Remarks:
unlabeled test substance
Dark controls:
yes
Computational methods:
Optimization of model parameters, including estimation of parameter standard errors, was performed using the software ModelMaker 4.0 (Cherwell Scientific, 2000)

Results and discussion

Dissipation half-life of parent compoundopen allclose all
Key result
DT50:
24 d
Test condition:
irradiated samples
Key result
DT50:
150 d
Test condition:
non-irradiated (dark control) samples
Key result
DT50:
28 d
Test condition:
the DT50 value corrected for non-irradiated degradation
Transformation products:
yes
Remarks:
IN-N7468 (N-Demethyl DPX-A7881), IN-B9161 (Triazine Urea), IN-D7556 (Triazine Amine). A further 12 minor degradation products were detected, none of which accounted for greater than 5% AR at any time point.
Details on results:
The DT50 and DT90 values for the test substance in irradiated samples were 24 days and 78 days, respectively. In non-irradiated (dark control) samples the DT50 and DT90 values were 150 days and 500 days, respectively. To determine the rate of degradation of the test substance due to photolysis only, the first-order rate of degradation constant (k) in the non-irradiated samples was subtracted from the first-order rate of degradation constant in the irradiated samples. The resulting corrected DT50 and DT90 values were 28 days and 92 days respectively. These estimated DT90 values are extrapolated well beyond the limits of the observed data.

Photolytic degradation of the test substance was observed with one significant degradation product, IN-N7468 (N-Demethyl DPX-A7881), being detected in irradiated samples and reaching a maximum of 29.2% by the end of the study.

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
Results of this intermittent irradiation experiment support that photolysis of the test substance on the surface of moist soil will be a dissipation pathway in the environment.
Executive summary:

The photodegradation of radiolabeled test substance on the surface of a clay loam soil (pH 8.00, 2.0% organic carbon) from Nambsheim, France was investigated at 20 ± 1°C for up to 30 days while being exposed to simulated sunlight and intervening dark cycles.

The study was conducted in accordance with the OECD Guideline, Proposal for a New Guideline, Phototransformation of Chemicals on Soil Surfaces; SETAC Procedures for Assessing the Environmental Fate and Ecotoxicology in Pesticides; U.S. EPA OPPTS 835.2410; EPA Guideline Subdivision N 161-3.

[Phenyl-14C]- and [Triazine-14C]-test substance were applied by pipette to thinly-layered soil (ca 2 mm thick) to achieve a nominal concentration of 0.3 mg a.i./kg soil (300 ppb) and irradiated (light and dark cycles) using a SunTest® accelerated exposure table unit with Xenon light source and equipped with filters to eliminate wavelengths of <290 nm. An identical treatment group of the same soil for each radiolabel was also made and kept in the dark as a control. The two sites of radiolabel of the test substance served as duplicate replicates.

The material balance (Day 0-Day 30) ranged from 91.87% to 103.45% and 97.68% to 103.45% of the applied radioactivity (AR) in the irradiated and dark (non-irradiated) samples, respectively. The total extractable radioactivity for irradiated samples decreased during the irradiation period, from a mean of 102.32% AR at Day 0 to a mean of 85.68% AR after 30 days. Non-extractable 14C-residues increased from levels below the limit of quantification (LOQ) to a maximum mean value of 10.00% AR after 30 days light/dark cycles. Throughout the experimental phase, evolved 14CO2 and 14C-organic volatile radioactivity were not detected or below the limit of quantification. In the non-irradiated (dark control) samples the total extractable radioactivity decreased during the study, from a mean of 102.32% AR at Day 0 to 96.63% AR at Day 30. Non-extractable 14C-residues increased from <LOQ at Day 0 and Day 3 to 3.29% AR after 30 days. Throughout the experimental phase, evolved 14CO2 and 14C-organic volatile radioactivity were not detected or below the limit of quantification.

In the irradiated samples test substance decreased from a mean value of 100.8% AR at Day 0, to a mean of 38.8% AR after 30 days. One significant degradation product, IN-N7468 (N-Demethyl DPX-A7881), was detected over the course of the study and increased from a mean value of 3.5 % AR at Day 1 to a maximum mean value of 29.2 % AR by the end of the study. Two minor degradation products were identified in the Triazine label samples only. IN-B9161 (Triazine Urea) reached a maximum of 3.3% AR at Day 30. IN-D7556 (Triazine Amine) reached a maximum of 4.9% AR at Day 30. A number of minor degradation products were also detected, none of which accounted for greater than 5% AR at any time point.

In the non-irradiated samples, the parent compound decreased from a mean of 100.8 % AR at Day 0 to 85.7% AR at Day 30. No significant degradation products were detected and IN-N7468 (N-Demethyl DPX-A7881) reached a mean maximum level of 2.8% AR. Two further minor degradation products were also identified in the dark control Triazine label samples. IN-B9161 (Triazine Urea) reached a maximum of 4.1% AR at Day 30. IN-D7556 (Triazine Amine) reached a maximum of 2.6% AR at Day 30. All other degradation products were also minor and accounted for less than 5% AR at any time point.

The DT50 and DT90 values of the test substance were calculated using a simple firstorder (SFO) model. The DT50 and DT90 values for the test substance in irradiated samples were 24 days and 78 days, respectively. In non-irradiated (dark control) samples the DT50 and DT90 values were 150 days and 500 days, respectively.

To calculate the rate of degradation of the test substance due to photolysis only, the first-order rate of degradation constant (k) in the non-irradiated samples was subtracted from the first-order rate of degradation constant in the irradiated samples. The resulting corrected DT50 and DT90 values were 28 days and 92 days respectively. This estimated DT90 value is extrapolated well beyond the limits of the observed data. However, results of this experiment support that photolysis of the test substance on the surface of moist soil will be a dissipation pathway in the environment.