cyproconazole (ISO); (2RS,3RS;2RS,3SR)-2-(4-chlorophenyl)-3-cyclopropyl-1-(1H-1,2,4-triazol-1-yl)butan-2-ol

Phototransformation in soil

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

25 Mar 1999 to 31 May 1999

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-3 (Photodegradation Studies on Soil)

Version / remarks:

October 18, 1982

Deviations:

yes

Remarks:

See deviations in 'Any other information on materials and methods incl. tables'

Qualifier:

according to guideline

Guideline:

other: Agriculture Canada: Environmental Chemistry and Fate. Guidelines for Registration of Pesticides in Canada

Version / remarks:

July 15, 1987

Deviations:

yes

Remarks:

See deviations in 'Any other information on materials and methods incl. tables'

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

high-performance liquid chromatography

other: Thin-Layer Chromatography (TLC); Liquid Scintillation Counters

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 300 - <= 400

Duration:

30 d

% Moisture:

75

Temp.:

19.5 °C

Initial conc. measured:

0.09 kg/ha d.w.

Dark controls:

yes

% Degr.:

5

Sampling time:

30 d

Test condition:

Irradiated

% Degr.:

0

Sampling time:

30 d

Test condition:

Darkness

DT50:

296.2 d

Test condition:

irradiated (12 hours light/dark cycle)

Transformation products:

yes

Remarks:

M5 and M6

No.:

#1

No.:

#2

RECOVERY AND DISTRIBUTION OF RADIOACTIVITY

The artificial light source was normalised to natural summer sunlight conditions of 30-50 °N (NSS), thus 30 days of continuous irradiation, corresponded to 20 days (12 hours light/dark cycle). This was achieved by measuring the intensity of light (W/m2) irradiated onto the samples (300-400 nm) for all positions in the Suntest apparatus before and after the exposure. The measured values were related to the sunlight intensity (67 W/m2 at 30-50 °N, 300-400 nm) present at midsummer latitude 30 to 50 °N using the following equation: d=hr/(12*0.75). Where r is the ratio of light intensities of artificial source (mean value of all positions) to natural midsummer sunlight at latitude 30-50 °N (67 W/m2), h is the duration (in hours) of the irradiation period in the Suntest apparatus. 0.75 is a correction factor for diurnal variation of natural sunlight. 12 is used to convert hours of experimental time to 12 hours light/dark cycle. Light in the range of 300-400 nm was utilised in this analysis, as this is the most significant for photodegradation of chemicals in nature.

The overall recovery for the whole study averaged 100.1 ± 1.0 %. It ranged from 98.1 to 101.1 % for irradiated samples and from 99.3 to 102.6 % for the dark controls.

The extractable amount of radioactivity in irradiated samples decreased from 100.4 % at day 0 to 96.3 % after 30 days. In the dark controls the amount of extractable radioactivity decreased to 98.9 % at the same time.

In light exposed samples the non-extractable radioactivity increased from < 0.1 % at day 0 to 3.3 % at day 30 of the study. In the dark control samples the highest amount of the non-extractable radioactivity was 0.8 % after 30 days.

The mineralisation rate of the test substance after 30 days accounted for 1.0 % and 0.1 % of the applied radioactivity for light exposed samples and dark controls, respectively. The radioactivity trapped in the NaOH solution was quantitatively precipitated by addition of BaCl2. The loss of radioactivity was considered as proof for 14C02.

 

Table 1. Average (trials) distribution and characterisation of applied radioactivity (%) in irradiated (mean values) Gartenacker loam/silt loam soil treated with radiolabelled test substance. 

Irradiation time (suntest)/ Day (12 hr dark-light cycle)	Exposure time at Summer sunlight/days  (30 to 50 °N)	Amount of radioactivity extractable from soil samples	Characterisation of extractable radioactivity				Non extractable Residues	14CO2	Recovery
			Test substance	M5	M6	Unknown
0	0	100.4	100.4	< LOD	0.3		< 0.1	< LOD	100.4
3	2.0	100.2	99.6	< LOD	0.6	0.6	0.8	< 0.1	100.9
7	4.7	97.3	96.7	0.3	0.5	0.5	1.1	0.2	98.6
9	6.0	97.9	97.4	< LOD	0.5	0.5	1.4	0.3	99.5
15	10.0	97.2	96.4	0.5	0.4	0.4	1.7	0.5	99.4
22	14.7	96.9	95.3	0.7	0.4	0.4	2.5	0.7	100.1
30	20.0	96.3	95.3	0.6	0.4	0.4	3.3	1.0	100.6

 

Table 2. Characterisation of applied radioactivity (%) in Gartenacker loam soil, which was treated with radiolabelled test substance and kept in the dark

Actual Irradiation time Time/day	Amount of radioactivity extractable from soil samples	Characterisation of radioactivity in the soil samples	Non extractable Residues	14CO2	Recovery
		Test substance
0	110.4	100.4	<0.1	< LOD	100.4
7	101.0	100.3	0.5	< 0.1	101.5
15	99.6	99.6	0.6	0.1	100.3
30	98.9	98.9	0.8	0.1	99.8

DEGRADATION

In the irradiated samples ~5 % of the test substance was degraded during the course of the incubation period. In concurrent control experiments up to 2 % degradation was observed.

Two minor photoproducts formed in quantities less than 1% were identified as M5 and M6 using co-chromatography (HLPC and TLC analysis).

In the dark control samples, no degradation products were observed after 30 days. The degradation times for the test substance were estimated using pseudo first order reaction kinetics.

 

Table 3. Test substance degradation times under irradiated conditions.

Test substance	DT50 Xe arc lamp	DT90 Xe arc light	DT50 30 - 50 °N	DT90 30 - 50 °N
Irradiated	5,331.9 hr	17,712.2 hr	296.2 days	984.0 days

Validity criteria fulfilled:

not specified

Conclusions:

In a soil photolysis study conducted according to EPA 161-3 and Canada national standard guidelines, the DT50 of the test substance was determined to be 296.2 days at 30°N - 50°N summer sunlight in a silt loam soil. No significant evolution of CO2 was observed from irradiated or dark control systems (maximum of 1.0 %). Minor amounts of photo-products (< 1 %) identified as M5 and M6 were observed. Exposure of the test substance to sunlight at a soil surface is expected to slightly accelerate its degradation in the environment.

Executive summary:

A photolytic degradation study in soil was conducted according to EPA 161-3 and Canada national standard guidelines and following GLP. The 14C-Phenyl labelled test substance was applied at a rate of 0.09 kg/ha onto the surface of moist (75 % field capacity) Gartenacker soil (loam/silt loam) and irradiated with xenon arc light (300 – 400 nm wavelength) for 30 days. Dark control was included in the study as well. The mean temperature of the soil layers was kept at 19.5 ± 0.1 °C. The duration of the experimental light exposure was converted to the corresponding light exposure at latitude 30 °N to 50 °N.

The overall recovery of radioactivity ranged between 98.1 and 101.1 % for irradiated samples and between 99.3 and 102.6 % for the dark controls. Under irradiation (12 hours light/ dark cycle), the extractable radioactivity decreased from 100.4 to 96.3 % after 30 days (i.e. 20 days summer sunlight at 30 °N - 50 °N). Correspondingly, non-extractable radioactivity increased from < 0.1 % at day 0 up to 3.3 % at 30 days. In the irradiated samples, only about 5 % of the test substance were degraded during the experiment. Two minor photoproducts formed in quantities ≤ 0.9 % of the applied radioactivity (AR) were identified as M5 and M6 by co-chromatography using HPLC and TLC analysis. In the dark control samples, no degradation of the compound was observed after 30 days. The decline of the extractable test substance from 100.4 to 98.9 % at the end of the study was mainly due to formation of 14CO2 and bound residues, which accounted for 0.1 % and 0.8 % AR, respectively.

Based on the findings, the DT50 of the test substance was determined to be 296.2 days at 30°N - 50°N summer sunlight.

Description of key information

DT50 = 296.2 days, irradiation with 12 hours light-dark cycle by Xenon arc lamp (300 – 400 nm wavelength) for 30 days, 30 °N - 50 °N/ summer, EPA 161-3 and Canada national standard guidelines, Adam 2000

Key value for chemical safety assessment

Half-life in soil:

296.2 d

Additional information

One study is available for this endpoint. The 14C-Phenyl labelled test substance was applied at a rate of 0.09 kg/ha onto the surface of moist (75 % field capacity) Gartenacker soil (loam/ silt loam) and irradiated with xenon arc light (300–400 nm wavelength) for 30 days (Adam 2000, Reliability 2). Dark control was included in the study as well. The mean temperature of the soil layers was kept at 19.5 ± 0.1 °C. The duration of the experimental light exposure was converted to the corresponding light exposure at latitude 30 °N to 50 °N. In the irradiated samples, only about 5 % of the test substance were degraded during the experiment. Two minor photoproducts formed in quantities ≤ 0.9 % of the applied radioactivity (AR). They were identified as M5 and M6 by co-chromatography using HPLC and TLC analysis. In the dark control samples, no degradation of the compound was observed after 30 days. Based on the findings, the DT50 of the test substance was determined to be 296.2 days at 30°N - 50°N summer sunlight.