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Toxicity to soil microorganisms

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Reference
Endpoint:
toxicity to soil microorganisms
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Study generated according to generally valid and internationally accepted testing guideline and performed under GLP.
Principles of method if other than guideline:
Method: other: OECD Guide-line 216 and OECD Guide-line 217
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
-Analyses: Analyses were performed at the same times as the samples for nitrate measurements were taken. The extracts for the nitrate
measurements were assessed for their concentration in sodium chlorate.
Determination of the C-transformation in soils after addition of glucose. Comparison of test item treated soils with a non-treated soil; 3 replicates
per treatment and concentration. The respiration rate was assessed from the oxygen consumed by the glucose amended soil samples, using an
incubation system combined with a manometric oxygen measurement over a period of 12 hours at different sampling intervals.
Sampling scheme: 0, 7 and 14 days and then at 14 or 15-day intervals, subsamples were withdrawn from the bulk batches and subjected to
measurement. Respiration rates were expressed as oxygen consumed (mg oxygen/kg soil/h). Determination of the N-transformation
(NO3-nitrogen production) in soils amended with powdered plant meal. Comparison of test item treated soils with a non-treated soil; 3 replicates
per treatment and concentration. Nitrate concentration was determined by ionic chromatography. Sampling scheme: 0, 7, 14, 21 and 28 days and
then at 14 or 15-day intervals, sub-samples were withdrawn from the bulk batches and subjected to measurement.
Details on preparation and application of test substrate:
- Soil characteristics:
- Sand 48.2%
- Lime 42.8%
- Clay 9.0%
- Total water holding capacity 38.3% dry soil
- pH 6.70
- CEC 7.4 meq/100 g
- TOC 1.41% dry weight
- Nitrogen 0.084% dry weight
- Soil microbial carbon 1.13% TOC
Test temperature:
18.0-21.5 degree C, except for the second week 16.5-17.5 degree C.
Moisture:
Soil moisture: measured at each sampling time and adjusted with demineralized water if necessary.
Details on test conditions:
Type: soil

Reference substance (positive control):
yes
Remarks:
Fumical, 510 g/L metam sodium
Duration:
42 d
Dose descriptor:
other: nitrogen and carbon mineralization
Effect conc.:
0 other: not applicable see details on results
Basis for effect:
other: 02-consumption and NO3-nitrogen production
Details on results:
- Endpoints: Effects on O2-consumption after 100 days of exposure. Effects on NO3 - nitrogen production after 100 days of exposure.

- Nitrogen mineralization test
N-NO3 mg/kg dw (mean of three replicates):
time Control Test conc (g a.i./kg dw) Ref subs
(days) 0.333 1.67
0 12.74 11.42 11.69 12.52
7 4.63 9.26 11.87 11.35
14 12.12 10.79 12.19 11.28
21 27.27 16.26 13.97 12.10
28 33.15 24.19 15.31 13.90
42 47.18 50.21 19.60 77.88
56 56.77 69.79 22.78 61.41
71 66.32 80.97 28.91 74.34
85 81.44 93.73 38.47 86.78
100 79.48 93.00 47.15 85.13

In the Na-chlorate 0.333 g/kg treated group, the production of nitrate was reduced as compared to the control soil until day 28 of the test period.
Then two successive N-NO3- jumps of +26.0 mg/kg and + 20.0 mg/kg were observed between day 28 and day 42, and then between day 42 and day 56 of the test period. Then after the production of nitrate returned to values similar to that in the control (+10-15 mg/kg N-NO3 - per 2-week
interval), but the total concentration of nitrate produced within the test period remained significantly higher than in the control group
(5% confidence level). As it was observed in the control group, the production of nitrate had ceased on day 100 of the incubation period and
represented 120.3% that of the control group. The total production of nitrate was controlled to be significantly higher than in the control group
(5% confidence level). In the Na-chlorate 1.67 g/kg treated group, the production of nitrate remained regular throughout the test period, but was
significantly reduced as compared to that in the control. No N-NO3- jump occurred, and the production of nitrate was still continued on day 100 of
the test period. The total formation of nitrate was only 51.6% that of the control group at the end of the incubation period, and was controlled to be
significantly lower than that of the control group (5% confidence level). Facultative anaerobic bacteria are responsible for that 350 mg/kg were
reduced in the 1.67 g/kg treated group. These bacteria compete with aerobic nitrating bacteria for organic carbon in soil. Thus a possible
explanation for that nitrogen mineralization was lower than in the control, is that the high reducing activity led to exhaustion of the available
organic matter. As a consequence, the activity of the nitrating bacteria was reduced.

- Carbon mineralization test Induced respiration (mg O2/kg dry soil/h), mean of three replicates:
time Control Test conc (g a.i./kg dw) Ref subs
(days) 0.333 1.67
0 17.8 16.2 18.4 13.3
7 7.2 5.1 6.1 7.4
14 5.7 4.5 5.1 11.5
28 5.3 3.8 4.3 9.8
42 7.3 5.4 6.6 12.7
56 8.1 6.4 6.7 9.0
71 9.4 9.3 8.8 11.3
85 14.3 10.4 12.6 12.6
100 6.7 5.5 7.4 6.5

Soon after the treatment application, the induced respiration was considered as similar to the control for both the Na-chlorate 0.333 g/kg and
the 1.67 g/kg treated soils. The induced respiration was significantly decreased by 25.3% in the Fumical treated group. On day 7 of the incubation
period, the phenomenon was reversed: the Fumical treated group exhibited values similar to that of the control when the induced respiration was
significantly reduced for both the Na-chlorate treated groups (-28.6 and -14.3% to the control for the 0.333 and the 1.67 g/kg treated groups
respectively). F-variance analyses at 5% confidence level showed that the deviation to the control was not significant up from day 14 of the
incubation period. It was thus concluded that the adverse effect of Na-chlorate on the induced respiration was only low.

Reported statistics and error estimates:
- F-test at 5% significance level was used to compare the treatments with the control.
Validity criteria fulfilled:
yes
Executive summary:

 Phyto Safe Study number: 01 -27 -066 -ES
 Study: Laboratory assessment of the side-effects of Sodium Chlorate on the soil micro-organisms
 Test item: Sodium Chlorate, CAS nr. 7775 -09 -9 batch nr. 1E121UM
Nominal test concentrations: 1XPEC = 0.333 g/kg dry soil, 5XPEC = 1.67 g/kg dry soil
Test dates: Nitrogen mineralization test: December 22, 2003 to March 31, 2004 Carbon mineralization test: December 22, 2003 to March 31, 2004

 Soil substrate: Sand = 48.2% (See protocol nr.2) Initial soil micrbial carbon = 1.13% of total organic carbon
 Source: Sampling site 1: Mr Castagnède, parcelle Guilhem (40110 Arengosse, France) Plant cover = peas, under agro biological practice. Sampling site 2: Mr Dupouy, parcelle Parille (40500 Coudures, France) Plant cover = triticales, under agro biological practice.
Reference substance: Fumical, 510 g/L metam sodium (nominal value) batch nr. L-10724 -1 (Calliope, 64150 Noguères, France), 1.3 mL/kg dry soil.

 Results        Compared analysis of the process of mineralization tot the water control
   Sodium chlorate0.333 g/kg dry soil Sodium chlorate 1.67 g/kg dry soil Fumical 1.3 mL/kg dry soil 
 Nitrogen mineralization Significantly reduced, then restored on day 42 of the incubation period  Significantly reduced throughout the 100 day incubation period 51.2% that of the control at the end of the test Significantly reduced, then restored on day 42 of the incubation period  
 Carbon mineralization 70.9 to 81.6% that of the control, but statistically similar to the control at 5% confidence level.  81.8 to 110.2% that of the control, but statisticallysimilar to the control at 5% confidence level.  Significantly increased, then restored on day 56 of the incubation period. 
 Content in Na-chlorate Stabilisation from day 7 of the incubation period:Un-amended soil: 75 to 84% of the treatment concentration. Amended soil: 79 to 86% of the treatment concentration.  Stabilisation from day 7 of the incubation period:Un-amended soil: 72 to 84% of the treatment concentration. Amended soil: 87 to 96% of the treatment concentration.   

Description of key information

The carbon mineralization was not significantly reduced by sodium chlorate.

For nitrogen mineralization a NOEC of 0.333 g/kg can be used.

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:
333 mg/kg soil dw

Additional information

One test with soil was found and considered to be valid.

Facultative anaerobic bacteria are responsible for that 350 mg/kg were reduced in the 1.67 g/kg treated group. These bacteria compete with aerobic nitrating bacteria for organic carbon in soil. Thus a possible explanation for that nitrogen mineralization was lower than in the control, is that the high reducing activity led to exhaustion of the available organic matter. As a consequence, the activity of the nitrating bacteria was reduced.

The carbon mineralization was not significantly reduced by sodium chlorate.

For nitrogen mineralization a NOEC of 0.333 g/kg can be used.

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