Sodium chlorate

Other distribution data

Administrative data

Endpoint:

other distribution data

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP study. No standard protocol was used, but the test method was described in detail.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2005

Report date:

2005

Materials and methods

Principles of method if other than guideline:

Method: other: internal method

Type of study:

other: leaching

Media:

water - soil

Test material

Test material information

Constituent 1

Reference substance name:

Sodium chlorate

EC Number:

231-887-4

EC Name:

Sodium chlorate

Cas Number:

7775-09-9

Molecular formula:

ClHO3.Na

IUPAC Name:

sodium chlorate

Test material form:

solid: crystalline

Applicant's summary and conclusion

Conclusions:

Increases in chloride concentration were found but due to high background levels did not permit mass balance determination. Nitrate was found in
the leachate throughout the test and did not significantly alter in concentration over the study period. For the standard leaching study, analytical
determinations of chlorate in the first study were close to 100% (95-105%) for both replicates of the four Lufa Speyer soils, confirming the
reproductibility of the analytical method and that adsorption of the test substance to soil is very low.
No sodium chlorate was found in the Lufa Speyer soil profiles except for trace amounts in soil 2.2. The field soil profiles percolated more slowly than the Lufa Speyer soils and the study duration had to be increased to two weeks for these soils to collect the whole leachate. One of the field profiles
stopped leaching during the study and results were not used in the calculation. 80.4% of sodium chlorate was recovered in the leachate in the secondcolumn. No sodium chlorate was found in the field soil profile. Based on other experiments loss is expected to be due to biodegradation in the soil. During the extended soil leaching study leachate concentrations were analysed over a period of up to 34 days. Presence of leachate was checked daily and collected and stored in a freezer individually when found. Analysis was performed on each collected sample over the study period.
Two columns continued to leach until day 34 when the study was terminated. The two remaining columns (A and C) stopped leaching and were
terminated on days 25 and 20, respectively, to prevent overlying water overflowing the top of the columns. No sodium chlorate was found in the fieldsoil profiles.

Percentage recovery of sodium chlorate in the leachate (total % recovered of the original dose applied) was as follows:
Column A 13.6,
Column B 33.4
Column C 0.4
Column D 41.7
The two lowest recoveries were obtained from profiles A and C from which leachate stopped percolating during the study. The low recovery
obtained from all columns in the extended experiment is expected to be due to biodegradation of sodium chlorate over the test period. The very
high loss of test substance from columns A and C can be interpreted as being due to anaerobic biodegradation further to the water-logging of the
columns. This result is similar to that found by van Ginkel and van der Togt (2004) during their biodegradation experiment further to water-logging the soil.

Executive summary:

The purpose of this study was to assess the leaching of sodium chlorate through 30 cm deep soil profiles under laboratory conditions based on 200 mm of rainfall over a 48 hour period. As the threshold for leaching was surpassed, a second study was performed to assess leaching of this compound through a soil profile 30 cm deep under laboratory conditions under more realistic, but nonetheless reasonable worst case, conditions of rainfall over a longer period of time.

Methods

The treatment in the two studies were as follows:

1. Initial leaching experiment. Five replicate pairs of columns made of glass were packed with 30 cm soil from four Lufa Speyer soils and one field soil and afterwards saturated and equilibrated with an "artificial rain" solution (deionised water) and allowed to drain in the standard leaching experiment. Then the surface of each soil column was treated with the test substance at the maximum application rate of 250 kg/ha at the recommended concentration in water (15 g/l). Immediately afterwards, 200 mm of "artificial rain" (deionised water) was applied to the soil columns over a 48 h period and the leachate collected. The field soils took longer to leach and for these columns the experiment was extended to 14 days.

2. Extended field soil leaching experiment. Four columns made of glass were packed with field soil profiles of loamy sand soil with a known water saturation value to a depth of 30 cm and allowed to equilibrate to laboratory conditions at a target temperature of 18°C. Within one week the surface of each soil column was treated with the test substance at the maximum application rate of

250 kg/ha at the recommended concentration in water (15 g/l). 24 h after application "artificial rain" was applied at a rate of 10.5 mm every 1.6 d and the columns were allowed to drain. After the studies were terminated, the soil was removed from the columns and sectioned into six segments per profile. Each soil segment and the leachates collected were analysed for chlorate, chloride and nitrate. Results

Increases in chloride concentration were found but due to high background levels did not permit mass balance determination. Nitrate was found in the leachate throughout the test and did not significantly alter in concentration over the study period.

For the standard leaching study, analytical determinations of chlorate in the first study were close to 100% (95-105%) for both replicates of the four Lufa Speyer soils, confirming the reproducibility of the analytical method and that adsorption of the test substance to soil is very low. No sodium chlorate was found in the Lufa Speyer soil profiles except for trace amounts in soil 2.2.

The field soil profiles percolated more slowly than the Lufa Speyer soils and the study duration had to be increased to two weeks for these soils to collect the whole leachate. One of the field profiles stopped leaching during the study and results were not used in the calculation. 80.4% of sodium chlorate was recovered in the leachate in the second column. No sodium chlorate was found in the field soil profile. Based on other experiments loss is expected to be due to biodegradation in the soil.

During the extended soil leaching study leachate concentrations were analysed over a period of up to 34 days. Presence of leachate was checked daily and collected and stored individually when found. Analysis was performed on each collected sample over the study period. Two columns continued to leach until day 34 when the study was terminated. The two remaining columns (AA and CC) stopped leaching and were terminated on days 25 and 20, respectively, to prevent overlying water overflowing the top of the columns. No sodium chlorate was found in the field soil profiles. Percentage recovery of sodium chlorate in the leachate

(total % recovered of the original dose applied) was as follows:

Column AA 13.6

Column BB 33.4

Column CC 0.4

Column DD 41.7

The two lowest recoveries were obtained from profiles AA and CC from which leachate stopped percolating during the study.

The low recovery obtained from all columns in the extended experiment is expected to be due to biodegradation of sodium chlorate over the test period. The very high loss of test substance from columns AA and CC can be interpreted as being due to anaerobic biodegradation further to the waterlogging of the columns. This result is similar to that found by van Ginkel and van der Togt (2004) during their biodegradation experiment further to water-logging the soil.

The validity criteria were respected:

Recoveries ranged range from 70 % to 110 % in the initial leaching study.

N.B. This criterion was not possible during the realistic worst case study as biodegradation of the test material occurred during the study.