Dichlobenil

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

18 April 2002 to 25 November 2003

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

according to guideline

Guideline:

other: SETAC Document 'Procedures for Assessing the Environmental Fate and Ecotoxicology of Pesticides (March 1995)'

Deviations:

no

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

other: BS 3882

Year:

1994

Soil no.:

#1

Soil type:

clay loam

% Org. C:

3.9

pH:

7.6

CEC:

35.5 meq/100 g soil d.w.

Soil no.:

#2

Soil type:

silty clay loam

% Org. C:

3.6

pH:

6.1

CEC:

29.5 meq/100 g soil d.w.

Soil no.:

#3

Soil type:

loamy sand

% Org. C:

1.1

pH:

5.9

CEC:

10.5 meq/100 g soil d.w.

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Land Research Associates (Derby, UK) and LandLook (Leamington Spa, UK)
- Pesticide use history at the collection site: none within the previous 5 years
- Storage conditions: under aerobic conditions at approximately 4 °C

Soil No.:

#1

Duration:

273 d

Soil No.:

#2

Duration:

273 d

Soil No.:

#3

Duration:

273 d

Soil No.:

#1

Initial conc.:

8.1 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#2

Initial conc.:

8.1 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#3

Initial conc.:

8.1 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Soil No.:

#1

Temp.:

20 ± 2 ºC

Microbial biomass:

89.4 mg C/100g

Soil No.:

#2

Temp.:

20 ± 2 ºC

Microbial biomass:

46 mg C/100g

Soil No.:

#3

Temp.:

20 ± 2 ºC

Microbial biomass:

24.6 mg C/100g

Details on experimental conditions:

1. PRELIMINARY EXPERIMENTS:
Performed using same procedure as main study.

2. EXPERIMENTAL DESIGN
- Soil preincubation conditions: 9 days under aerobic conditions and continuous aeration in the dark at 20 ± 2 ºC.
- Soil condition: fresh
- Soil (g/replicate): 50
- No. of replication controls, if used: 7 prior and 7 termination control soil samples
- No. of replication treatments: 10 per soil
- Test apparatus (Type/material/volume): 250 mL Erlenmeyer flasks
- Details of traps for CO2 and organic volatile, if any: sodium hydroxide traps and expanded polyurethane for volatile [14C]-dichlobenil

Test material application
- Volume of test solution used/treatment: 100 µL
- Application method: applied on surface

Any indication of the test material adsorbing to the walls of the test apparatus: No

Experimental conditions (in addition to defined fields)
- Continuous darkness: Yes

3. OXYGEN CONDITIONS (delete elements as appropriate)
- Methods used to create the an/aerobic conditions: moist, CO2 free-air applied twice weekly for 15 minutes at approximately 20-25 mL/min.

4. SAMPLING DETAILS
- Sampling intervals: 0, 14, 28, 56, 84, 112, 182 and 273 days after application.
- Sampling method for soil samples: removal of incubation flask.
- Method of collection of CO2 and volatile organic compounds: sodium hydroxide traps and expanded polyurethane for volatile [14C]-dichlobenil,

Soil No.:

#1

% Recovery:

110.67

Remarks on result:

other: Day 273

Soil No.:

#2

% Recovery:

103.49

Remarks on result:

other: Day 273

Soil No.:

#3

% Recovery:

94.63

Remarks on result:

other: Day 273

Key result

Soil No.:

#1

DT50:

77.9 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Rate of degradation

Key result

Soil No.:

#1

DT50:

75.3 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Rate of dissipation (including volatilisation)

Key result

Soil No.:

#2

DT50:

70.7 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Rate of degradation

Key result

Soil No.:

#2

DT50:

65.4 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Rate of dissipation (including volatilisation)

Key result

Soil No.:

#3

DT50:

100.5 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Rate of degradation

Key result

Soil No.:

#3

DT50:

79.7 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: Rate of dissipation (including volatilisation)

Transformation products:

yes

No.:

#1

Evaporation of parent compound:

yes

Volatile metabolites:

not specified

Residues:

no

Details on results:

Quantitative recoveries of applied radioactivity (approximately 95-111 %) were obtained at all sampling time-points. The recovery of applied radioactivity in methanol extracts of the loamy sand, clay loam and silty clay loam soils decreased from quantitative values at Day 0 to approximately 54, 76 and 57 % respectively at Day 273. Significant volatilisation of [14C]dichlobenil occurred, and at Day 273 volatile [14C]dichlobenil accounted for approximately 50, 13 and 18 % of the applied radioactivity in the loamy sand, clay loam and silty clay loam respectively. Insignificant amounts of 14CO2 were recovered from each of the soil types.

Chromatographic analysis of soil extracts revealed two components. [14C]dichlobenil accounted for between approximately 5 to 100 % of applied radioactivity over the period of the study and 2,6-dichlorobenzamide accounted for up to 47, 69 and 63 % in loamy sand, clay loam and silty clay loam soils respectively.

Chromatographic analysis of polyurethane plug extracts revealed only one component, [14C]dichlobenil.

The DT50 and DT90 values in loamy sand, based on the degradation (excluding volatilisation) of [14C]dichlobenil, were 100.5 and 333.7 days respectively. The corresponding values in the clay loam and silty clay loam soil were slightly lower at 77.9 and 258.7 days and 70.7 and 235.0 days respectively. The DT50 and DT90 values, based on degradation and dissipation, were 79.7 and 264.7 days, 75.3 and 250.3 days and 65.4 and 217.2 days, for loamy sand, clay loam and silty clay loam soil, respectively. The DT50 and DT90 values for the 3 soils (excluding volatilisation as well as including volatilisation) are tabulated below.

The rate of degradation was decreasing towards the end of the study. This was likely to be due to a decrease in microbial activity, and as a consequence, it is probable that the rate of degradation in the environment would be greater than that determined in this study.

The distribution patterns of the applied radioactivity can be found in the attached Figures.

Conclusions:

Under the conditions of the test, the DT50 values for the test material range from 70.7 to 100.5 days (excluding volatilisation) and from 65.4 to 79.7 days including volatilisation. The only major metabolite observed in all three soils was 2,6-dichlorobenzamide.

Executive summary:

In a GLP compliant aerobic degradation study conducted in line with sound scientific principles (and to guideline SETAC Document 'Procedures for Assessing the Environmental Fate and Ecotoxicology of Pesticides (March 1995)'), the aerobic degradation of the test material was determined. [¹⁴C]dichlobenil was added to samples of loamy sand, clay loam and silty clay loam at 8.1 mg/kg and the samples were incubated at 24 ºC in the dark. After 0, 14, 28, 56, 84, 112, 182 and 273 days, a soil sample was analysed. The DT50 values were determined to be 70.7-100.5 days (excluding volatilisation) and 65.4-79.7 days (including volatilisation). The only major metabolite observed in all three soils was 2,6-dichlorobenzamide.

Reference 2

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

October 1988 to 21 December 1989

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: EPA Guideline 162-1

Deviations:

no

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

sandy loam

% Clay:

4.8

% Silt:

20.2

% Sand:

75

% Org. C:

1.5

pH:

5.3

CEC:

5.3 meq/100 g soil d.w.

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Udenhout, The Netherlands

PROPERTIES OF THE SOILS (in addition to defined fields)
- Moisture at 1/3 atm (%): 12.3 %

Soil No.:

#1

Duration:

50 wk

Soil No.:

#1

Initial conc.:

2.1 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

other: Measurement of 2,6-dichlorobenzamide in KOH solution (necessary due to volatility of test material).

Details on experimental conditions:

1. EXPERIMENTAL DESIGN
- Soil preincubation conditions (duration, temperature if applicable): 24 ºC for 15 days
- Soil (g/replicate): 42.8 g
- No. of replication treatments: 27
- Test apparatus (Type/material/volume): biometer flasks
- Details of traps for CO2 and organic volatile, if any: absorption tube

Test material application
- Volume of test solution used/treatment: 1 mL

Experimental conditions (in addition to defined fields)
- Continuous darkness: Yes

Other
- 25 mL KOH was added to each flask at the same time as the test substance was added and refreshed (in remaining flasks) every 5 weeks

2. SAMPLING DETAILS
- Sampling intervals: 0, 2, 501, 10, 20, 30, 40 and 50 weeks (3 flasks each week)

Key result

Soil No.:

#1

DT50:

13 wk

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: considering metabolism as well as evaporation

Key result

Soil No.:

#1

DT50:

46.3 wk

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: considering metabolism only

Transformation products:

yes

No.:

#1

Details on transformation products:

- Description of biotransformation pathway:
- Figure attached: Yes

Evaporation of parent compound:

yes

Volatile metabolites:

yes

Residues:

yes

Details on results:

The results of the determination of the amount of trapped volatiles, extractable and soil bound radioactivity and the amount of test material, 2,6-dichlorobenzannide and other metabolites present in the soil extracts are represented as percentage of the applied dose can be found in Table 1.

Assunning first order kinetics, the following equation can be calculated fronn these data: In(DBN) = 4.46 - 0.043 t. The correlation coefficient (r) of this equation was calculated to be -0.991.

The metabolism of the dichlobenil in sandy loam soil during 50 weeks resulted in the formation of two metabolites. The major metabolite was 2,6-dichlorobenzamide (BAM), present for 13% of the initially added amount. A minor metabolite, which could not be identified, accounted for at most 1.2% of the initially added amount of radioactivity. The postulated pathway of dichlobenil degradation in soil is provided in Figure 1.

Table 1: Mean recovery (percentage of applied [¹⁴C]-dichlobenil) of trapped volatiles, extractables and soil-bound radioactivity in sandy loam after treatment with [¹⁴C]-dichlobenil

	Trapped volatiles			Extractable
Incubation time in weeks	Total [^14C]	CO2	DBN	Total [^14C]	DBN	BAM	METAB	TBR	Total recovery
0	-	-	-	101	101	<0.1	<0.1	<0.2	101
2	14.8	0.1	13.3	80.7	80.3	0.4	<0.1	22	97.8
5	19.0	0.7	18.0	74.2	71.7	0.8	0.5	5.1	98.2
10	39.2	0.7	37.2	52.9	49.8	1.3	<0.1	5.8	97.8
20	46.0	1.9	41.9	44.4	35.6	7.3	1.2	8.2	98.5
30	63.9	1.5	61.0	26.8	20.6	5.2	0.6	8.2	98.9
40	62.3	2.7	58.5	26.1	16.2	8.4	0.5	8.0	96.4
50	61.0	2.3	56.8	26.7	11.6	13.1	0.7	10.2	97.9

Conclusions:

Under the conditions of the test, the half-life of the test material in sandy loam was calculated to be 13 weeks when metabolism and evaporation were taken into account. When considering metabolism on its own, the half-life of the test material was calculated to be 46.3 weeks.

Executive summary:

In a GLP compliant aerobic soil metabolism study conducted in line with standardised guideline EPA 162-1, the aerobic soil metabolism of the test material was determined. [¹⁴C]dichlobenil was added to samples of sandy loam at 2.1 mg/kg and the samples were incubated at 24 ºC in the dark. After 0, 2, 5, 10, 20, 30, 40 and 50 weeks each, three soil samples were analysed. The metabolism of the test material in sandy loam resulted in the formation of two metabolites, 2,6-dichlorobenzamide (13 % of radioactivity) and an unidentified metabolite (1.2 % of radioactivity). The half-life of the test material in sandy loam was calculated to be 13 weeks when metabolism and evaporation were taken into account. When considering metabolism on its own, the half-life was calculated to be 46.3 weeks.

Description of key information

The half-life of the test material was determined to be 46.3 weeks according to a study performed in line with EPA Guideline 162-1.

The half-life of the test material was determined to be 70.7-100.5 days (excluding volatilisation) and 65.4-79.7 days (including volatilisation) according to a study performed in line with sound scientific principles.

Additional information

See 'Environmental Fate and Pathways' endpoint summary.