8-Chloro-6-(trifluoromethyl)imidazo[1,2-a]pyridine-2-carboxylic acid

Phototransformation in soil

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:

2014

Report date:

2014

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline draft (Phototransformation of Chemicals on Soil Surfaces)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: Photodegradation on Soil, U.S. Environmental Protection Agency Assessment Guidelines, OPPTS 835.2410

Deviations:

no

GLP compliance:

yes

Test material

Test material information

1

Reference substance name:

8-chloro-6-(trifluoromethyl)imidazo[1,2-a]pyridine-2-carboxylic acid

Cas Number:

353258-35-2

Molecular formula:

C9H4ClF3N2O2

IUPAC Name:

8-chloro-6-(trifluoromethyl)imidazo[1,2-a]pyridine-2-carboxylic acid

Specific details on test material used for the study:

Test substance: [Phenyl-14C(U)]-DPX-Q8U80
Lot Number: 3631265
Radiochemical Purity: 99.7%
Specific Activity: 38.94 µCi/mg

Test substance: [Imidazo[1,2-a]pyridine-5,8a-14C]-DPX-Q8U80
Lot Number: 1572459
Radiochemical Purity: 99.2%
Specific Activity: 38.46 µCi/mg

Radiolabelling:

yes

Study design

Analytical monitoring:

yes

Analytical method:

high-performance liquid chromatography

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 290 - <= 800

Duration of test at given test condition

Duration:

15 d

% Moisture:

75

Temp.:

20 °C

Initial conc. measured:

1 mg/kg soil d.w.

Dark controls:

yes

Results and discussion

% Degradation

Key result

Remarks on result:

other: IN-QEK31 was rapidly degraded by simulated sunlight

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

IN-QEK31 was rapidly degraded by simulated sunlight

Executive summary:

The photodegradation of [14C]-DPX-Q8U80 on the surface of a sandy loam soil (Sassafras, pH 6.3, 1.16% organic carbon) from Maryland, USA was investigated at 20 ± 2°C for 15 days while being exposed to continuous simulated sunlight. Test item ([phenyl-14C]-DPX-Q8U80 and [imidazo[1,2-a]pyridine-5,8a-14C]-DPX-Q8U80, abbreviated as [PH-14C]-DPX-Q8U80 and [IP-14C]-DPX-Q8U80) was applied to thinly-layered moist soil (at ca 9.1% moisture, 75% field capacity) at a nominal concentration of 1.0 mg a.i./kg soil. The samples were irradiated under artificial irradiation using a SunTest accelerated exposure table unit equipped with filters to eliminate wavelengths of <290 nm. An identical treatment to the same soil for each radiolabel was also made and kept in the dark as a control. In each case the soil samples were maintained at ca 9.1% moisture by checking and adjusting the moisture level at each sampling. The two sites of radiolabelled [14C]-DPX-Q8U80 served as replicates.

The soil samples were analyzed at 0, 2, 4, 8, 12 and 15 days after application. Soil samples were extracted 3 times. The extraction solvents were acetonitrile: 2% formic acid (aq) (9:1 v/v) followed by acetonitrile: 2% formic acid (aq) (4:1 v/v) and then acetonitrile: 2% formic acid (aq) (1:1 v/v). Radioactive components in soil extracts were quantified by reversed phase HPLC with on-line radiodetection. Non-extractable 14C-residues were quantified by combustion analysis.

The material balance for the moist irradiated test systems were quantitative (except for the samples irradiated for 12 and 15 days with IP label; 86.17% and 85.85% AR, respectively). In all other cases, individual values ranged between 91.35% AR to 104.12% AR. The material balance for the non-irradiated (dark control) test systems were also quantitative, individual values ranged between 98.70% AR to 109.55% AR. Extractable radioactivity declined from ca 99-104% for the two radiolabels to ca 72% to 86% AR by Day 15 in irradiated samples, and non-extractable residues reached a maximum of ca 14% AR by the end of the study. Radioactivity associated with 14CO2 accounted for 1.28% AR in the moist irradiated samples, and radioactivity associated with volatile organics remained at levels close to or below the limit of quantification throughout the incubation period. Extractable radioactivity recovered from moist dark control soil samples was quantitative at most sampling intervals (ca 99-104% at zero time for the two radiolabels and ca 98-103% on day 15 for both radiolabels). Non-extractable residues was minimal, ca 2.5% AR or less in moist dark control samples.

Radioactivity associated with 14CO2 and volatile organics remained at levels below the limit of quantification throughout the incubation period. HPLC analysis of moist irradiated soil extracts indicated that [PH-14C]-DPX-Q8U80 declined from quantitative levels at Day 0 to ca 48-53% AR following 15 days total irradiation. One significant degradation product was detected in progressively increasing amounts over the course of the study and was identified as IN-F4106. It was detected in the PH-label samples only and reached a maximum value of 24.15% AR (0.236 ppm) following 15 days total irradiation Multiple minor metabolites were detected but not identified as none of these individually accounted for greater than 5.53% AR (0.058 ppm) at any sampling interval. Corresponding dark control soil extracts indicated that [PH-14C]-DPX-Q8U80 also declined from quantitative levels at Day 0 to ca 44-58% AR following 15 days in dark conditions. Just like the light exposed sample extracts, dark control soil extracts also displayed one main degradation product identified as IN-F4106. Once again, it was detected in the phenyl label samples only and reached a maximum value of 36.53% AR (0.357 ppm) following 15 days

incubation.

The IP-Label samples displayed a decline of DPX-Q8U80 in dark control as well as irradiated soil extracts, and one main degradation product was identified in dark control samples. This degradation product co-eluted with IN-QEK31 and it was detected in the imidazo-pyridine label samples only. It reached a maximum value of 28.97% AR (0.305 ppm) following 12 days incubation, before declining slightly to 26.45% AR (0.279 ppm) at 15 days incubation dark control soils.

However this degradate was not detected in substantial amounts in irradiated soils. Absence of IN-QEK31 in irradiated soils suggested that it was degraded by light almost as readily as it was generated. Multiple minor metabolites were detected in the IP-Label samples as well, but not identified as none of these individually accounted for greater than 5% AR (0.054 ppm) at any sampling interval. Based on the decline kinetics, degradation of [14C]-DPX-Q8U80 in irradiated soil samples occurred primarily via non-photolytic degradation because the rate of degradation in irradiated and dark control soils did not differ appreciably. In addition, both degradation products observed, IN-F4106 and IN-QEK31 are known to be produced in aerobic soil degradation (DuPont study No. 35135) study from cleavage of the parent molecule into two portions contained within these degradates. Under irradiated conditions, IN-F4106 appeared to be somewhat stable and was therefore observed in similar amounts in light as well as dark soil.

On the other hand, IN-QEK31 degraded under irradiated conditions and was therefore, only observed in dark soil. Extensive degradation of IN-QEK31 in the IP-Label samples to small volatile molecules presumably resulted in less than quantitative mass balance in day 12 and 15 samples.

The DT50 and DT90 values of [14C]-DPX-Q8U80 were calculated using a simple first-order (SFO) model. The DT50 and DT90 values for DPX-Q8U80 in the irradiated system were 16.57 days and 55.06 days, respectively. In non-irradiated (dark control) samples the DT50 and DT90 values were similar to those in irradiated samples, and calculated as 18.85 days and 62.61 days, respectively. The DT50 values in irradiated and in dark soil were within experimental error leading to the conclusion that there was no significant degradation due to light on soil surface. Incidentally, observed DT50 is nearly identical to the DT50 observed in Sassafras soil in aerobic soil metabolism study [DuPont-35135, DT50 of 12.5 days]. Adjusting the degradation in the presence of light with the degradation rate in the dark led to DT50 and DT90 values of 137.53 days and 456.86 days, respectively for continuous irradiation of DPX-Q8U80 in moist soil. These DT50 data are clearly extrapolated well beyond the study duration and therefore adjusted soil photolysis DT50 is not reliable. Further adjustment for light dark cycles will essentially double the photodegradation rate.

The DT50 and DT90 values for photolysis (after excluding aerobic soil degradation) of DPX-Q8U80 in moist soil, not adjusted for light/dark cycle, were 137.53 days and 456.86 days, respectively.

It can be concluded from the results of this experiment that DPX-Q8U80 does not degrade photolytically on moist soil when exposed to artificial sunlight under laboratory conditions. Degradation observed is primarily due to microbes with little influence from sunlight. Soil metabolite IN-QEK31 will however degrade readily on moist soil surface in the presence of light.