Paraquat-dichloride

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Mar 1992 to Apr 1992

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Qualifier:

equivalent or similar to guideline

Guideline:

other: Domsch KH, Jagnow G and Anderson JH (1983), An Ecological Concept for the Assessment of Side-Effects of Agrochemicals on Soil Microorganisms, Residue Reviews, 86, 65-105.

Qualifier:

equivalent or similar to guideline

Guideline:

other: Anderson JPE, Dijk H van, Domsch KH, Greaves MP, Poole NJ, Sommerville L and Verstraete W (1985), Recommended Tests for Assessing the Side-Effects of Pesticides on the Soil Microflora. Proceedings of the 3rd International Workshop, Cambridge, UK.

Principles of method if other than guideline:

In a laboratory study, a sandy loam and a sandy clay loam soil were treated with the test substance in formulation (a 100 g/L SL formulation) at rates of 4.0 and 0.8 mg a.i./kg soil, approximately equivalent to 3.0 and 0.6 kg a.i./ha incorporated into soil to a depth of 5 cm. The effects of the test substance on ammonification/nitrification and the CO2 respiration were determined.

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on preparation and application of test substrate:

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

Test organisms (inoculum):

soil

Total exposure duration:

28 d

Test temperature:

20 ± 1 °C

Moisture:

All experiments were performed at 18.3% moisture content in soil #1 and 24.7% moisture content in soil #2. These contents correspond to 40% of their moisture holding capacities at zero suction.

Details on test conditions:

TEST DESIGN
A detailed description of the methodology is presented in 'Any other information on materials and methods incl. tables'.

SOURCE AND PROPERTIES OF SUBSTRATE SOIL #1
- Name: Frensham soil
- Geographical reference of sampling site: A sandy loam taken from a site on Wishanger Farm, Churt, Near Frensham, Surrey.
- History of site: The site has been maintained for 18 years
- Vegetation cover: Grass
- Treatments with pesticides or fertilizers: During the 18-year period, Frensham has received one application of fertilizer containing 2,4-D as the dimethyleamine salt at 2.4 kg ai/ha in September 1985 to control Ragwort, two applications of a lime (4500 kg ha·1 in 1983 and 5000 kg ha·1 in 19901 and two applications of a fertilizer in 1982 and 1987).
- Depth of sampling: Soil was removed from the 5 - 15 cm horizon at each site.
- % sand: 67
- % silt: 17
- % clay: 16
- Soil taxonomic classification: Sandy loam
- Soil classification system: USDA
- pH: 7.2
- Organic matter (%): 2.2
- Initial nitrate concentration for nitrogen transformation test (mg nitrate/kg dry weight):
- Moisture holding capacity (at zero suction): 46%
- Cation exchange capacity (mequiv/100g): 8.9
- Storage (condition, duration): The soil was transported back to the laboratory in loosely closed polythene bags (to maintain aerobic conditions). When required, the soil was removed from the bags, processed through a 2 mm mesh sieve, then re-bagged as above and stored until required for use in this study. During the processing/storage period (up to 23 days) the soil was held at 4 ± 1 °C (except when being sampled or sieved) in a moist condition (ie not less than approximately 16 and 12 % moisture content in 18 Acres and Frensham soils, respectively).
- Initial microbial biomass as of total organic C (mg/kg soil): 297

SOURCE AND PROPERTIES OF SUBSTRATE SOIL #2
- Name: 18 Acres soil
- Geographical reference of sampling site: A sandy clay loam taken from a site at Nuptown, Jealott's Hill Research Station, Near Bracknell, Berkshire.
- History of site: The site has been maintained for 14 years
- Vegetation cover: Grass
- Treatments with pesticides or fertilizers: The soil has received two applications of mecoprop (2.8 kg ai/ha) in 1980 and 1983 to control Clover but no lime or fertilisers.
- Accidental contamination:
- Storage conditions: The soil was transported back to the laboratory in loosely closed polythene bags (to maintain aerobic conditions). When required, the soil was removed from the bags, processed through a 2 mm mesh sieve, then re-bagged as above and stored until required for use in this study. During the processing/storage period (up to 23 days) the soil was held at 4 ± 1 °C (except when being sampled or sieved) in a moist condition (ie not less than approximately 16 and 12 % moisture content in 18 Acres and Frensham soils, respectively).
- Depth of sampling: Soil was removed from the 5 - 15 cm horizon at each site.
- % sand: 51
- % silt: 27
- % clay: 22
- Soil taxonomic classification: Sandy clay loam
- Soil classification system: USDA
- pH: 7.6
- Organic matter (%): 3.8
- Initial nitrate concentration for nitrogen transformation test (mg nitrate/kg dry weight):
- Moisture holding capacity (at zero suction): 62
- Cation exchange capacity (mequiv/100g): 16.1
- Storage (condition, duration): The soil was transported back to the laboratory in loosely closed polythene bags (to maintain aerobic conditions). When required, the soil was removed from the bags, processed through a 2 mm mesh sieve, then re-bagged as above and stored until required for use in this study. During the processing/storage period (up to 23 days) the soil was held at 4 ± 1 °C (except when being sampled or sieved) in a moist condition (ie not less than approximately 16 and 12 % moisture content in 18 Acres and Frensham soils, respectively).
- Initial microbial biomass as of total organic C (mg/kg soil): 683

MEASUREMENTS SOIL PROPERTIES
Air dried samples were characterised with respect to; pH, particle size distribution, organic matter content, cation exchange capacity, and moisture holding capacity. The soil was classified according to particle size data using the USDA Soil Survey Triangle method. The size of the active fraction of the soil microbial biomass was determined for each soil using the method of Anderson and Domsch. These determinations were made using results obtained from the control soil at 0 days after treatment

EFFECT PARAMETERS MEASURED: Nitrogen mineralisation and short term respiration

Nominal and measured concentrations:

- Nominal concentrations: 0.6 and 3.0 kg a.i./ha (corresponding to 1x and 5x the maximum field application rate).

Reference substance (positive control):

no

Key result

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

>= 5.5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

other: pure test substance

Basis for effect:

other: nitrate formation and respiration rate

Remarks on result:

other: corresponding to ≥ 3.0 kg a.i./ha soil

Remarks:

recalculated value, expressed as pure substance, see ‘any other information on results incl. tables’ for respective calculation

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

>= 4 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

other: test substance cation species

Basis for effect:

other: nitrate formation rate and respiration rate

Remarks on result:

other: corresponding to ≥ 3.0 kg a.i./ha soil

Remarks:

Original value presented in study

Details on results:

- Nitrogen mineralisation: No statistically significant differences in nitrate or ammonium levels were observed between the control and treated soils in the sandy loam (soil #1; Frensham) or the sandy clay loam (soil #2; 18 Acres).
- Short-term respiration: In both soils no statistically significant differences were observed between control and treated samples in levels of microbial biomass carbon at any stage during the study.
A complete overview of the results is presented in 'Any other information on results incl. tables'.

Reported statistics and error estimates:

All data was analysed by a one way analysis of variance model to obtain a pooled estimate of error variance. This was then used to compare the mean response of the soils treated with each rate of the test substance with the mean response in the control group using Student's t-test (or least significant difference (LSD) at P = 5 % and P = 1 % ). Each step in the statistical analysis described above was carried out on personal computer using "Statgraphics" version 3 statistical analysis and graphics system, STSC, Inc., 2115 East Jefferson Street, Rockville, Maryland 20852.

Tables: Effects on Nitrogen Mineralisation In Lucerne Amended Frensham Soil (Soil #1)

mg Nitrate N/kg soil

Treatment	Days Incubation
	0	14	28
Control	12.8	63.5	76.8
0.60 kg a.i./ha	12.3	61.7	74.8
3.00 kg a.i./ha	12.5	62.5	76.5
LSD 5%	1.5	2.7	3.4
LSD 1%	2.3	4.0	5.1

 

mg Ammonium N/kg soil

Treatment	Days Incubation
	0	14	28
Control	7.0	<0.5	< 0.5
0.60 kg a.i./ha	7.0	<0.5	< 0.5
3.00 kg a.i./ha	7.8	<0.5	< 0.5
LSD 5%	1.2	nd	nd
LSD 1%	1.8	nd	nd

 

mg Nitrite N/kg soil

Treatment	Days Incubation
	0	14	28
Control	< 0.5	< 0.5	< 0.5
0.60 kg a.i./ha	< 0.5	< 0.5	< 0.5
3.00 kg a.i./ha	<0.5	< 0.5	< 0.5
LSD 5%	nd	nd	nd
LSD 1%	nd	nd	nd

 LSD = Least Significant Difference

nd = Not determined

Tables: Effects on Nitrogen Mineralisation In Lucerne Amended 18-Acres Soil (Soil #2)

mg Nitrate N/kg soil

Treatment	Days Incubation
	0	14	28
Control	13.5	54.7	62.7
0.60 kg a.i./ha	11.3	54.7	61.5
3.00 kg a.i./ha	11.2	55.5	62.0
LSD 5%	3.8	3.4	1.3
LSD 1%	5.7	5.2	2.0

 

mg Ammonium N/kg soil

Treatment	Days Incubation
	0	14	28
Control	11.7	< 0.5	< 0.5
0.60 kg a.i./ha	10.7	<0.5	< 0.5
3.00 kg a.i./ha	11.3	<0.5	< 0.5
LSD 5%	3.4	nd	nd
LSD 1%	5.2	nd	nd

 

mg Nitrite N/kg soil

Treatment	Days Incubation
	0	14	28
Control	0.5	< 0.5	< 0.5
0.60 kg a.i./ha	0.3	< 0.5	< 0.5
3.00 kg a.i./ha	0.3	<0.5	< 0.5
LSD 5%	0.7	nd	nd
LSD 1%	1.1	nd	nd

LSD = Least Significant Difference

nd = Not determined

 

Table: Effects on Short Term Respiration in Frensham soil (Soil #1)

Treatment	Days Incubation
	0	14	28
Control	297	270	233
0.60 kg a.i./ha	334	298	259
3.00 kg a.i./ha	304	253	235
LSD 5%	68	63	65
LSD 1%	102	95	99

 

Table: Effects on Short Term Respiration in 18-Acres soil (Soil #2)

Treatment	Days Incubation
	0	14	28
Control	683	656	668
0.60 kg a.i./ha	668	671	646
3.00 kg a.i./ha	667	661	663
LSD 5%	28	16	37
LSD 1%	42	23	56

LSD = Least Significant Difference

 

Table: Summary of Nitrogen Recovery Efficiencies

Soil	Day	Overall % Recovery Efficiency
		NO3-	NO2-	NH4 +
Frensham	0	84.1 ± 1.1	91.7 ± 0.9	94.2 ± 0.5
	14	96.3 ± 0.5	99.6 ± 0.5	92.5 ± 0.5
	28	91.1 ± 0.4	93.3 ± 0.5	93.8 ± 0.6
18-Acres	0	91.3 ± 0.8	94.6 ± 0.7	89.6 ± 0.3
	14	91.5 ± 0.4	96.2 ± 1.0	92.9 ± 0.8
	28	96.8 ± 1.8	89.2 ± 2.0	89.6 ± 0.7

Calculation of key result

The doses of the test substance were expressed in test substance cation (active ingredient), which relates to the cation species in an aqueous solution of the registered substance. The effect levels are already corrected for the amount of water. The key effect levels are calculated by inclusion of the anion species: (100/72.4) x 4.0 mg test substance cation/kg soil dw = 5.5 mg pure test substance/kg soil dw.

Validity criteria fulfilled:

not specified

Conclusions:

The test substance used at rates up to 3.0 kg a.i./ha in soil did not have any adverse effects on nitrogen mineralisation or short-term respiration in soil. Therefore, the NOEC was determined to be ≥ 3.0 kg a.i./ha soil, corresponding to ≥ 4.0 mg a.i./kg soil. The recalculated 28-d NOEC value for the pure substance is ≥ 5.5 mg/kg soil dw.

Executive summary:

In a GLP-compliant toxicity to soil microorganisms study, equivalent or similar to the guidelines laid down by Domsch et al. and Anderson et al., the effects of the test substance on metabolic activity by respiration (as CO2 evolution) and nitrification processes were evaluated over 28 days. The test substance was tested at rates of 0.8 and 4.0 mg ai/kg (equal to 0.6 and 3.0 kg ai/ha respectively, which corresponds to 1x and 5x the maximum field rate application, respectively). An untreated control was also included. Treatments were made by mixing the test item into the soil. Over a four week period, nitrogen mineralization was measured in lucerne-amended soil and short-term respiration was measured following addition of glucose. The test substance had no significant effects on the respiration and nitrification of soil micro-organisms in the two agricultural soils at concentrations up to 4.0 mg ai/kg (or 3.0 kg ai/ha) (the highest concentration tested). Therefore, the 28-d NOEC was determined to be ≥ 4.0 mg a.i./kg soil (corresponding to ≥ 3.0 kg a.i./ha soil). The recalculated 28-d NOEC value for the pure substance is ≥

5.5 mg/kg soil dw.

Description of key information

28-d NOEC ≥ 5.5 mg pure substance/kg soil (recalculated) on CO2-respiration and N-mineralisation according to Domsch et al. and Anderson et al., Jackson 1992

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:

5.5 mg/kg soil dw

Additional information

Table: Overview of available data on the toxicity to soil microorganisms data

Soil type	Guideline / GLP	Endpoint	Effect value	Comment	Reference
Sandy loam soil (Soil #1)	Domsch et al., Anderson et al.	28-d NOEC CO2 respiration 28-d NOEC N-mineralisation	≥ 5.5 mg pure substance/kg soil ≥ 5.5 mg pure substance/kg soil	No effects on CO2 respiration and N-mineralisation were observed in the two soils in the highest test concentration, which corresponds to 5X the maximum application rate)	Jackson, 1992
Sandy clay loam soil (Soil #2)		28-d NOEC CO2 respiration 28-d NOEC N-mineralisation	≥ 5.5 mg pure substance/kg soil ≥ 5.5 mg pure substance/kg soil