Mecoprop

Phototransformation in soil

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

key study

Study period:

13 May 1986 to 08 September 1986

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

high-performance liquid chromatography

Details on soil:

PROPERTIES
- Soil classification system and year: Fox No. 2. Sandy loam soil as determined by the University of Wisconsin-Extension Soil and Forage Laboratory, Madison, Wisconsin.
- Soil texture: Sandy loam
- % sand: 56 %
- % silt: 34 %
- % clay: 10 %
- pH: 7.6
- Organic carbon (%): 23 ton/ acre
- CEC (meq/100 g): 9
- Water holding capacity: Field moisture capacity was 15. 2 % (determined by HLA).

PREPARATION OF SOIL
- Air dried / fresh: Air dried
- Sterile / non-sterile: The soil was not sterilised before study initiation.

Light source:

other: Artificial sunlight

Details on light source:

At approximately 1.9 cm from the chroma 50 lamps, the light intensity was measured using a Blak-Ray UV meter, Model No. J221. The infrared light intensity was 30 μW/cm^2. The UV light intensity was 30 μW/cm^2.
When measured on a partly cloudy day while the sun was shining with the same meter, the natural sunlight had an infrared light intensity of 1 560 μW/cm^2 and a UV light intensity of 2 346 μW/cm^2.

Details on test conditions:

Preliminary Investigation I
Using approximately 1 g of sieved, air-dried Fox No. 2 sandy loam soil and approximately 2 mL of water, a slurry was made in each of six petri dishes. The petri dishes were allowed to air-dry overnight to yield a firm, uniform surface.
Each petri dish was then fortified with 250 µL of a methanol solution of radioactive and nonradioactive test material, formulated to contain approximately 0.5 μCi and 10 μg/ 250 μL test material. The solvent was allowed to air-dry, and the dishes were placed in their respective test locations.
Three petri dishes, selected at random, were placed in an enclosed chamber and kept in a dark room maintained at 25 ± 2 °C. A Dickson Minicorder was used to monitor the temperature. Three other petri dishes were placed in an enclosed chamber on a water-jacketed platform, and exposed to artificial sunlight by positioning them below two Chroma 50 lamps. The soil temperature was maintained at 20 ° to 30 °C by circulating the water in the platform. A single dark control dish was removed from the chamber and analysed immediately to serve as a Day 0 time point for both sample types.
Following the extraction scheme and sample analysis procedures one dish was taken from each of the dark control and exposed chambers on Days 3 and 7 for analysis. One dish was taken from the exposed chamber on Day 1 for analysis.
In this preliminary study, low total recoveries were obtained, which indicated the possible production of a volatile metabolite. In an attempt to trap this metabolite, two additional preliminary investigations were done on samples exposed to artificial sunlight.

Preliminary Investigation II
Two soil petri dishes were prepared as outlined for Preliminary Investigation I. One of these dishes was then fortified with 200 µL of the test material solution used for Preliminary Investigation I. Analysis completed prior to fortification indicated that 200 μL of the solution contained about 0.5 µCi and 10 µg of radioactive and nonradioactive test material. The second petri dish remained unfortified.
Both petri dishes were placed in a single enclosed chamber similar to the one described for Preliminary Investigation I. In this case, however, a trapping apparatus intended to capture volatiles was also used. The apparatus consisted of a bent glass tube that was positioned over the fortified dish and extended to a trap containing 90 mL of mineral spirits with glass beads. Air was drawn through this apparatus by a pump. Silastic tubing was used to connect the glass tubing as needed. An identical, but separate, trapping apparatus was used for the unfortified dish and served as a control to ensure that no radioactive residue remained in the chamber from the previous preliminary study.
The fortified petri dish was extracted after 7 days of exposure.
Low recoveries indicated that a volatile metabolite was possibly being formed. Thus, a third preliminary study using a more elaborate trapping system was done.

Preliminary Investigation III
Seven petri dishes were prepared as outlined previously. Six of the dishes were then fortified with 250 μL of a recently prepared methanol solution of radioactive and nonradioactive test material, formulated to contain approximately 0.5 µCi and 10 μg/ 250 µL test material. The seventh petri dish was unfortified.
After the solvent evaporated, all seven petri dishes were placed in an enclosed chamber similar to the one used in Preliminary Investigation I, except that it had a trapping apparatus.
The traps used in Preliminary Study III were, in order of position from the chamber, ethylene glycol (100 mL), mineral spirits (75 mL) with glass beads, and ethanolamine: 2-ethoxyethanol (1:1, v/v, 100 mL). The traps were connected to a vacuum line to provide a more constant airflow rate. Glass tubing was bent, fitted over each petri dish, and connected to the vacuum line. Silastic tubing was used to connect the glass tubing as necessary. An identical, but separate, trapping apparatus was used for the unfortified dish. This served as a control similar to that used in Preliminary Investigation II.
Following the extraction scheme and sample analysis procedures, one dish was taken for analysis on Days 4, 7, 14, and 20. Due to the results, two fortified dishes were not taken for analysis.
Low total recoveries were also obtained with this trapping system and again indicated that the volatile metabolites, if present, were not being adequately captured by this trapping system.
These preliminary investigations were made to familiarise the analyst with the chromatographic behaviour of the test material, its possible photolysis products, and its rate of degradation. The data obtained were used to determine the test material's extractability from soil and its relative material balance. The data were also used to aid in selecting sampling times in the definitive study, as well as optimum extraction conditions.

TEST SYSTEM
- Type, material and volume of test apparatus or thin layers: Using approximately 1 g of sieved, air-dried Fox No. 2 sandy loam soil and approximately 2 mL of water, a slurry was made in each of 26 petri dishes. The petri dishes were allowed to air-dry overnight to yield a firm, uniform surface.
- Application procedure: An admixture of radioactive (5.62 x 10^10 dpm, 139.2 µg) and nonradioactive (289.6 µg) test material was prepared in 10.0 mL of methanol. Each petri dish was then fortified with 1.40 x 10^6 dpm (0.63 µCi) equivalent to 3.48 and 7.24 µg of radioactive and nonradioactive test material, respectively, as determined by liquid scintillation counting (LSC) analysis of 250 µL aliquots of the fortification solution taken before, during, and after fortification. Thus, the total test material applied to the soil in each petri dish was approximately 10.7 ppm (µg/g).
- Details of traps for volatile, if any: The chamber was connected in series with three traps, one that contained approximately 125 mL of 10 % sodium hydroxide for trapping volatiles, one that contained approximately 100 mL of ethanolamine: 2-ethoxyethanol (1:1, v/v) for trapping carbon dioxide, and one that contained water (which was not sampled) to keep the vacuum nozzle from becoming fouled or clogged and to trap any other possibly harmful solvent vapours. Air was pulled through the system at a rate of at least 50 mL/minute by a vacuum line.
A custom-made glass tube having 12 ports, one located above each petri dish, was placed between the two Chroma 50 lamps and attached in series with the traps in an attempt to capture all the volatile products. The chamber was tinted to exclude extraneous light. This chamber was also connected in series to a custom-made glass tube and three traps that contained 10 % sodium hydroxide, ethanolamine: 2-ethoxyethanol, and water. Air was pulled through the system at a rate of at least 50 mL/minute by a vacuum line. Two of the dark control dishes were set aside for extraction immediately after the fortification solution evaporated, thus serving as a Day 0 time point for both the exposed and dark control samples.

PREPARATION OF THIN-LAYER PLATES:
- Aliquots of organic fractions (the only matrix that contained more than 10 % of the applied radioactivity), as well as the nonradioactive test material standard, were applied to TLC plates before development.
- All TLC plates used for rate determinations were developed in chloroform: cyclohexane: acetic acid (80:20:10), which was prepared just before use. The plates were removed from the solvent system and dried. A profile of the radioactivity was made using autoradiography as well as a linear analyser. TLC plate scraping was used to quantitate the bands of radioactivity. The radioactivity in the test material band on the TLC plate was quantitated by dividing the total radioactivity measured on the test material band by the total radioactivity measured on the strip by LSC analysis. The standard was visualised by fluorescent quenching while viewed under UV light. To validate the TLC procedure, the TLC plates of samples exposed to artificial sunlight on Days 14, 21, and 32 were scraped, and 5 mL of water and 10 mL of Insta-Gel LSC cocktail were added to the scrapings. The mixture was analysed by LSC for 14C content to determine a material balance for the TLC procedure.
- Validation of Test Material. Because no organosoluble photoproducts were seen in quantities greater than 10 %, no attempt was made to isolate any products from the soil extracts. The identity of the test material at all time points for both exposed and dark control samples was validated by use of one-dimensional TLC (in two solvent systems provided by the Sponsor) and co-chromatography with an authentic nonradioactive standard. Chloroform: cyclohexane: acetic acid (80:20:10) and toluene: methanol: acetic acid (90:16:8) were used as the developing systems. The plates were all autoradiographed to visualise the bands. The test material was identified on the TLC plate by matching the fluorescent quench of the nonradioactive band with the band revealed by autoradiography. Greater than 10 % of the applied activity never remained at the origin; thus, further TLC analysis was not pursued.

REPLICATION
- No. of replicates (dark): The remaining 14 dishes were used as dark controls. These dishes were placed in a similar chamber, but were kept in a room maintained at 25 °C ± 2 °C in the dark.

MAINTENANCE OF TEST CONDITIONS SPECIFIED UNDER "DURATION"
- Temperature maintenance method: A Dickson Minicorder was used to continuously monitor the temperature.

OTHER
- Sampling: At 4, 7, 14, 21, and 32 days after fortification, duplicate dishes exposed to artificial sunlight and dark controls were removed from their respective chambers and analysed as described below. At 0 days after fortification, only duplicate dark control dishes were analysed. Each time dishes were removed, the traps were sampled and assayed for 14C content as described below, and the trapping materials were replaced. A computer-generated randomisation scheme was used to determine which dishes were sampled at each time point. All sampling times were selected and scheduled on a master calendar based on results of the previous analyses, preliminary investigations, or both.
- Extraction Procedure: The soil from duplicate petri dishes was transferred to 20 mL scintillation vials. A 10 mL portion of 20 % aqueous acetonitrile with 2 % glacial acetic acid was used to rinse each petri dish, and the rinse was added to the corresponding vial. The mixture was stirred mechanically with a magnetic stir bar for 1 hour and centrifuged for 15 minutes. The supernatant was decanted to separatory funnels. The rinse, stir, centrifuge, and decant procedures were repeated two more times using fresh extraction solvent, but with a 30-minute stir time. A 20 mL portion of extraction solvent was used the third time to ensure that the dish was thoroughly rinsed. The extracts were combined in the separatory funnels, mixed by swirling, and monitored by removing duplicate aliquots of about 0.5 g each for LSC. The combined extracts were partitioned twice with a double portion of chloroform. The organic fractions were combined, and duplicate aliquots of about 1.0 g each were removed for LSC. The organic fractions were then rotary-evaporated to near dryness and transferred to scintillation vials with 10.0 mL of methanol. Duplicate aliquots of about 0.5 or 1.0 g each were taken for LSC. The aqueous fractions were combined and monitored by removing duplicate aliquots of about 1.0 g each for LSC.
- Sample storage: All test material and any extract and extracted soil sample that contained greater than 10 % of the applied activity were stored in a freezer.
- When the solvent evaporated, the 12 dishes to be exposed to artificial sunlight were placed in an enclosed chamber on a water-jacketed platform. The temperature of the soil was measured using a thermocouple embedded in unfortified soil at a depth approximating that in the petri dishes. Using a Blak Ray UV meter, the intensity of the two Chroma 50 lamps was measured at a distance of approximately 1.9 cm below the source, the same distance the dishes were from the lamps when the water-jacketed platform was in place.
- Determination of Volatile Products: Radioactivity in the traps was measured by LSC using 1.0 mL aliquots in 9 mL of water and 10 mL of lnsta-Gel cocktail.
- Validation of Carbon Dioxide Traps: The carbon dioxide trapping efficiency of 2-ethoxyethanol: ethanolamine (1:1) in a gas washing bottle was measured. A gas line from the Harvey biological oxidiser was used to successively oxidise five measured quantities of Spec-Chec-14C. The carbon dioxide combustion product was bubbled through the washing bottle at a flow rate of 270 mL/minute. A cumulative total of approximately 500 dpm/mLwas trapped at five intervals ranging from 80 to 132 dpm/mL in approximately 190 mL of trapping solution. Cumulative recoveries averaged 92.7 % with a coefficient of variation of 5.3 %.
- Determination of Non-extractable Residues: Soil-bound radioactivity was quantified by combustion analysis of approximately 0.1 g aliquots from the extracted soil samples.
- Validation of Soil Oxidation: Aliquots of untreated soil were fortified with known amounts of 14C test material solution. The samples were oxidised and the oxidation recovery was determined. Because the recovery was greater than 95 %, no correction was made for oxidised test material recovery.
- Sample Oxidiser Quality Control: At the start of each day's sample oxidation, the performance of the sample oxidiser was verified by oxidising known amounts of Spec-Chec-14C. A blank (no radiotracer) was first burned to determine normal background. Another blank was burned, and the vial was spiked with, 20 µL of Spec-Chec-14C to represent total counts. The same volume of standard was oxidised, and the oxidiser recovery was determined. Finally, another blank was burned to determine the residual radiotracer from the previous burning. Recoveries of greater than 90 % indicated that the oxidiser was operating properly.
- Calculations: The half-life of the parent compound was determined by multiplying the percent of the applied activity found in the organic fraction by the percent of the parent compound in the organic fraction (determined by TLC plate scraping). This calculation yielded the percent of applied activity that remained as parent compound, whose log when plotted versus time (as a linear regression) gave the first-order rate constant needed to determine the half-life.
A second half-life was calculated for the exposed samples, which corrected for the degradation that occurred in the dark controls. The dark control first-order rate constant was subtracted from the exposed sample rate constant to yield a corrected first-order rate constant. This corrected rate constant was then used to calculate the corrected exposed sample half-life.

Duration:

32 d

Reference substance:

no

Dark controls:

yes

Preliminary study:

The extraction scheme was demonstrated in Preliminary Investigation I to be an effective procedure for removing the test material from soil. The TLC analysis showed no organosoluble photoproducts. Total recoveries at Day 7 were low for exposed samples, indicating possible formation of one or more volatile metabolites.
Preliminary Investigation II, and subsequently Preliminary Investigation III, were conducted to design a trapping system that would collect the suspected volatile metabolite(s). Only exposed samples, with unspiked controls, were used in these investigations. Day 7 total recoveries in Preliminary Investigation II remained low despite a small amount of radioactivity being collected by the mineral spirits trap. Based on these results, an ethylene glycol, mineral spirits, and ethanolamine: 2-ethoxyethanol (1:1) trap series was devised for Preliminary Investigation III. This system, however, also failed to significantly raise total recoveries by the time the study was completed. The TLC analysis showed no organosoluble photoproducts in either the second or third investigation. Despite the material balance difficulties being unresolved, it was decided to proceed with the definitive study using a different trapping system [10 % aqueous sodium hydroxide followed by ethanolamine: 2-ethoxyethanol (1:1)] based on the results of the preliminary investigations. The sodium hydroxide trap was chosen because it was believed that a possibly volatile metabolite, such as 2-methyl-4-chlorophenol, could be formed from the degradation of the test material, and that sodium hydroxide would be an effective trapping medium for it.

Key result

DT50:

50 d

Test condition:

Artificial light

Transformation products:

not measured

Details on results:

Organosoluble Fraction. The percent of the total applied radioactivity found in the organic fraction of the exposed soil samples decreased from 93.8 % (mean value at Day 0) to 60.8 % (mean value at Day 32). The activity found in the dark control organic fractions consistently remained above 92 % throughout the study.
Aqueous Fraction. The total activity found in the aqueous fractions of the exposed samples showed a slight increase from 0.1 % at Day 0 to 1.8 % at Day 32. The activity in the dark control aqueous layers remained at 0.1 % of the total applied dose throughout the study.
Volatile Products. The total activity found in the ethanolamine: 2-ethoxyethanol trap increased from 0.1 % at Day 4 to 2.5 % at Day 32 in the exposed soil samples. No activity was found in the ethanolamine: 2-ethoxyethanol trap of the dark control samples. The sodium hydroxide traps of both exposed and dark control samples showed no activity.
Non-extractable Residue. The soil-bound radioactivity in the exposed samples increased from a mean value of 0.8 % at Day 0 to a mean value of 7.8 % at Day 32. A slight increase in bound residues was also seen in the dark control samples. Mean values rose from 0.8 % at Day 0 to 1.2 % at Day 32.
Photodegradation. The presence or absence of photodegradation was determined by comparing the exposed and dark control samples.
Parent compound Half-life. The calculated half-life of the parent compound for expose samples was 44 days, as compared with 381 days for dark control samples. The corrected calculated half-life of the test material for exposed samples was 50 days.
Identification of Photoproducts. The TLC of exposed sample organic extracts from Day 32 showed that no organosoluble photoproducts were formed during the 32 days of exposure to artificial sunlight. However, the gradual decrease in the material balance for the exposed samples over the duration of the study (recoveries fell from a mean value of 94.7 % at Day 0 to a mean value of 73.0 % at Day 32) suggests the existence of a volatile photoproduct that was not collected by the trapping apparatus.

Typical Half-life Calculation

Half-life (t½) is defined as the time it takes for one-half of the parent compound to degrade. The calculated results depend on the model that is used to describe the degradation process. The data from this experiment were fitted to the model equation by a least squares regression using an IBM-PC or a 100 % IBM-compatible computer, and Symphony® Version 1.1 software.

For this study the process of photodegradation was assumed to be well represented by first-order kinetics. The equation used was:

 

P(t) = Pi 10^-kt

 

where: P(t) = The percent of parent compound that remained at any time, t. As a percent value, P(t) is dimensionless.

t = The time of exposure in days.

Pi = The initial percent of parent compound that remained.

The theoretical value of Pi is the value that is observed at t=0.

k = The proportionality constant between change in P(t) and t. The units of k are reciprocal days; -k itself is equal to the slope of the log of the percent of parent compound that remained versus time.

The parameters of the selected equation that best fits the data are used to calculate the half-life. Substituting Pi/2 for P(t) and solving for t yields:

 

t½ = t = (Log 2)/ -k

 

For example, in the calculations of the artificial sunlight exposures, the fitted equation has parameters of:

Pi = 88.7

-k = -6.80 E-3

Hence, the estimated half-life is:

(Log 2)/k) = 0.301 / (6.80 E-3) = 44 days

 

Summary of Observed Temperatures for Exposed Soil Dishes: Definitive Study

Day	Temperature (°C)
0	24.5
1	24.3
4	25.0
5	25.8
6	24.6
7	25.4
8	25.1
11	25.4
12	25.3
13	24.7
14	24.4
15	24.6
18	24.4
19	24.4
20	24.4
21	24.6
22	24.8
23	25.6
24	25.4
25	25.4
26	24.8
27	24.4
28	24.6
29	24.8
32	24.8

 

Representative Material Balance for TLC Procedure

Duration (Days)*	Dish	Total Applied (DPM)	Total Recovered (DPM)	Total Percent Recovery**
14	5U	35 997	35 969	99.9
14	9U	40 167	40 028	99.7
14	10U	18 149	16 361	90.1
14	7T	15 238	14 521	25.3
21	6T	9 660	7 982	92.2
21	9T	12 585	11 552	91.8
21	6U	13 458	12 590	93.6
21	3U	13 734	13 523	98.5
32	2U	10 584	10 260	96.9
32	8T	7 828	7 346	93.8
32	1QT	14 454	12 358	85.8
32	2T	7 302	6 842	93.7

U: Untreated (dark control) sample

T: Treated (exposed) sample

*These tome points were selected only to demonstrate that the amount of 14C applied from extracts to TLC plates could be accounted for when the plates were scraped.

**Total percent recovery values are based on total dpm recovered divided by total dpm applied and have been rounded to the nearest 0.1 %.

 

Rd Values of Standards in the Solvent Systems

Solvent System	Rf*
	Test Material	4-Chloro-2-methylphenol
I [Chloroform: cyclohexane: acetic acid (80:20:10)]	0.60	0.63
I [Toluene: methanol: acetic acid (90:16:8)]	0.40	0.46

*Rf values are from a typical TLC plate and may vary from plate to plate.

 

Mean Material Balance for Exposed Soil Samples (%)

Exposure Time (Days)	Organic Fraction	Aqueous Fraction	Soil Fraction	Ethanolamine: 2-Ethoxyethanol Trap*	Sodium Hydroxide Trap*	Mean of Total Recoveries
0	93.8	0.1	0.8	ND	ND	94.7
4	80.6	0.38	4.2	0.1	ND	85.6
7	89.8	0.4	4.7	0.3	ND	95.2
14	76.2	1.2	6.4	0.5	ND	84.3
21	64.4	1.5	6.4	0.7	ND	73.0
32	60.8	1.8	7.8	2.5	ND	73.3

Number are expressed as average percentages of the total recovery.

*Recovery is expressed as a cumulative total.

ND: Nondetectable (levels below 0.05 %)

 

Mean Material Balance for Dark Control Soil Samples (%)

Exposure Time (Days)	Organic Fraction	Aqueous Fraction	Soil Fraction	Ethanolamine: 2-Ethoxyethanol Trap*	Sodium Hydroxide Trap*	Mean of Total Recoveries
0	93.8	0.1	0.8	ND	ND	94.7
4	99.6	0.1	1.2	ND	ND	100.9
7	98.3	0.1	1.0	ND	ND	99.4
14	99.6	0.1	1.	ND	ND	100.6
21	95.0	0.1	1.1	ND	ND	96.2
32	92.2	0.1	1.2	ND	ND	93.4

Number are expressed as average percentages of the total radioactivity.

*Recovery is expressed as a cumulative total.

ND: Nondetectable (levels below 0.05 %)

 

Data Used to Determine Half-Life for Exposed Samples (%)

Exposure Time (Days)	Applied Activity in Organic Fraction	Percent Compound in Organic Fraction*	Parent Compound Remaining
0	96.1	99.2	95.3
	91.6	99.3	91.0
4	73.2	97.8	71.6
	88.1	98.1	86.4
7	97.3	97.7	95.3
	92.2	97.8	90.2
14	74.1	95.7	70.9
	78.3	97.0	76.0
21	59.3	95.0	56.3
	69.5	95.6	66.4
32	60.7	92.6	56.2
	60.9	94.0	57.2

*Determined by TLC plate scraping

 

Data Used to Determine Half-Life for Dark Control Samples (%)

Exposure Time (Days)	Applied Activity in Organic Fraction	Percent Compound in Organic Fraction*	Parent Compound Remaining
0	96.1	99.2	95.3
	91.6	99.3	91.0
4	100.8	99.5	100.3
	98.4	98.5	96.9
7	102.6	99.0	101.6
	94.0	99.3	93.3
14	101.8	99.4	101.2
	97.3	99.1	96.3
21	93.4	98.8	92.3
	96.5	99.1	95.6
32	101.2	99.5	100.7
	83.1	97.9	81.4

*Determined by TLC plate scraping.

Validity criteria fulfilled:

not specified

Conclusions:

Under the conditions of the study the corrected half-life of the test material in soil was 50 days.

Executive summary:

The photodegradation of the test material was assessed according to Section 161-3, Subdivision N of Environmental Protection Agency (EPA) Pesticide Assessment Guidelines and in compliance with GLP.

Radiolabelled test material was added to Fox No. 2 sandy loam soil in petri dishes. Degradation was studied during exposure to artificial sunlight. Two Chroma 50- lamps, which have a spectral energy distribution similar to natural sunlight, were used as the artificial sunlight source. Following exposure, the soil was extracted, and a radioactivity distribution was determined. The calculated half-life of the test material in artificial sunlight was 44 days. The total activity remaining in the organic, aqueous, and non-extractable fractions was 60.8 %, 1.8 %, and 7.8 %, respectively, after 32 days of exposure. The calculated half-life of the test material in the dark was 381 days. The total remaining in the organic, aqueous, and non-extractable fractions after 32 days was 92.2 %, 0.1 %, and 1.2 %, respectively. Due to the observed degradation of the dark control samples, a corrected half-life of the test material in artificial sunlight was calculated; it was 50 days.

Under the conditions of the study the corrected half-life of the test material in soil was 50 days.

Description of key information

Key Study: Obrist (1986)

Under the conditions of the study the corrected half-life of the test material in soil was 50 days.

Key value for chemical safety assessment

Half-life in soil:

50 d

Additional information

Key Study: Obrist (1986)

The photodegradation of the test material was assessed according to Section 161-3, Subdivision N of Environmental Protection Agency (EPA) Pesticide Assessment Guidelines and in compliance with GLP. The study was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997).

Radiolabelled test material was added to Fox No. 2 sandy loam soil in petri dishes. Degradation was studied during exposure to artificial sunlight. Two Chroma 50- lamps, which have a spectral energy distribution similar to natural sunlight, were used as the artificial sunlight source. Following exposure, the soil was extracted, and a radioactivity distribution was determined. The calculated half-life of the test material in artificial sunlight was 44 days. The total activity remaining in the organic, aqueous, and non-extractable fractions was 60.8 %, 1.8 %, and 7.8 %, respectively, after 32 days of exposure. The calculated half-life of the test material in the dark was 381 days. The total remaining in the organic, aqueous, and non-extractable fractions after 32 days was 92.2 %, 0.1 %, and 1.2 %, respectively. Due to the observed degradation of the dark control samples, a corrected half-life of the test material in artificial sunlight was calculated; it was 50 days.

Under the conditions of the study the corrected half-life of the test material in soil was 50 days.