reaction mass of neodymium carbonate and praseodymium carbonate

Adsorption / desorption

Administrative data

Endpoint:

adsorption / desorption: screening

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Study period:

08-JAN-2013 to 15-APR-2013

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The study was performed according to OECD guideline 106 and in compliance with GLP. However, as the data are used in a read-across approach, the maximal reliability score was decreased from 1 to 2, according to Practical Guide n°6.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2013

Report date:

2013

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EU Method C.18 (Adsorption / Desorption Using a Batch Equilibrium Method)

Deviations:

no

Principles of method if other than guideline:

With the exception of the acidic soil type 7, definitive results of distribution coefficients (Kd) and organic carbon normalised adsorption coefficients (Koc) were calculated from the initial sampling time-point, employing an adsorption equilibration period of 2 hours, at which the recovery of the dissolved neodymium content of soil-less control solutions was maximised. This was concluded not to impact on the validity of the distribution coefficient and adsorption coefficient values obtained. With reference to the European Commission Health and Consumer Protection Directorate guidance document SCP/KOC/002, a batch equilibrium method with a reduced equilibrium time was detailed as the preferred method for substances shown to generate unstable aqueous solutions. The guidance document states that a large fraction of the adsorption onto the soil phase occurs within the first 30 minutes, and therefore any underestimation of the adsorption coefficient values by an amended procedure using a 30 minute incubation period to be less than a factor of two, i.e. negligible when considered in the more common logarithmic scale. Any systematic error would therefore be further reduced by the use of at least a 2 hour incubation period, as used in calculation of the adsorption characteristics of this test material.

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Test material

Test material information

Constituent 1

Reference substance name:

Dineodymium tricarbonate

EC Number:

227-579-4

EC Name:

Dineodymium tricarbonate

Cas Number:

5895-46-5

Molecular formula:

CH2O3.2/3Nd

IUPAC Name:

dineodymium tricarbonate

Test material form:

solid: particulate/powder

Remarks:

migrated information: powder

Radiolabelling:

no

Study design

Test temperature:

25 ± 2°C

Batch equilibrium or other method

Analytical monitoring:

yes

Details on sampling:

- Concentrations: Saturated solution in 0.01 M calcium chloride solution
- Sampling interval: 2, 5, 24 and 48 hours

Details on matrix:

All soils were stored air dried, in the dark, at ambient temperature. Organic carbon content, CEC and pH were re-analysed at least every 3 years.

SOIL TYPE 2
- USDA soil class: Loam
- Particle size: 50 µm to 2 mm: 35.9 %; 2 to 50 µm: 37.1 %; <2 µm: 27.0 %
- pH, 1:5 soil to 0.01 M CaCl2 ratio: 7.3
- Cation exchange capacity (meq/100 g): 34.7
- Organic carbon content (%): 4.10
- Total nitrogen content (%): 0.44
- Moisture content (% w/w): 18.0
- Geographical location: South Witham, Lincolnshire, UK, SK 921191
- Land usage: Undisturbed, previously arable land, adjacent to quarry. No pesticide use since at least 1995.
- Date of sampling: 28/10/2008
- Depth of sampling: 5 to 20 cm

SOIL TYPE 3
- USDA soil class: Silt loam
- Particle size: 50 µm to 2 mm: 12.3 %; 2 to 50 µm: 68.1 %; <2 µm: 19.6 %
- pH, 1:5 soil to 0.01 M CaCl2 ratio: 6.2
- Cation exchange capacity (meq/100 g): 15.1
- Organic carbon content (%): 2.47
- Total nitrogen content (%): 0.27
- Moisture content (% w/w): 4.84
- Geographical location: Chelmorton, Derbyshire, UK, SK 104691
- Land usage: Permanent dairy pasture. Localised pesticide spraying, but not to the sampling site.
- Date of sampling: 13/06/2003
- Depth of sampling: 10 to 20 cm

SOIL TYPE 4
- USDA soil class: Silt loam
- Particle size: 50 µm to 2 mm: 28.4 %; 2 to 50 µm: 51.8 %; <2 µm: 19.8 %
- pH, 1:5 soil to 0.01 M CaCl2 ratio: 5.1
- Cation exchange capacity (meq/100 g): 14.2
- Organic carbon content (%): 3.89
- Total nitrogen content (%): 0.36
- Moisture content (% w/w): 4.26
- Geographical location: Middleton, Derbyshire, UK, SK 179618
- Land usage: Permanent dairy pasture. No pesticide application.
- Date of sampling: 11/01/2011
- Depth of sampling: 10 to 20 cm

SOIL TYPE 5
- USDA soil class: Loamy sand
- Particle size: 50 µm to 2 mm: 81.8 %; 2 to 50 µm: 11.4 %; <2 µm: 6.8 %
- pH, 1:5 soil to 0.01 M CaCl2 ratio: 5.8
- Cation exchange capacity (meq/100 g): 9.2
- Organic carbon content (%): 1.01
- Total nitrogen content (%): 0.13
- Moisture content (% w/w): 1.46
- Geographical location: Ingleby, Derbyshire, UK, SK 34636 26943
- Land usage: Permanent pasture. No pesticide application to sampling site.
- Date of sampling: 06/06/2008
- Depth of sampling: 15 to 20 cm

SOIL TYPE 7
- USDA soil class: Loamy sand
- Particle size: 50 µm to 2 mm: 85 %*; 2 to 50 µm: 10 %*; <2 µm: 5 %*
- pH, 1:5 soil to 0.01 M CaCl2 ratio: 3.1
- Cation exchange capacity (meq/100 g): 49.8
- Organic carbon content (%): 22.7
- Total nitrogen content (%): 0.59
- Moisture content (% w/w): 17.1
- Geographical location: Lindholme, South Yorkshire, UK, SE 674064
- Land usage: Topsoil stock pile from former quarry works. No pesticide application.
- Date of sampling: 01/07/2003
- Depth of sampling: 0 to 20 cm

* No definitive experimental determination was possible due to the high humus content of the soil. Therefore the values presented are typical, historic values.

Details on test conditions:

The optimal soil to solution ratio was identified through preliminary testing at nominal soil to solution ratios of 1:5, 1:25 and 1:100. This indicated that testing would be optimised at a nominal ratio of 1:100, whilst remaining within the recommendations of the method guidelines. Due to limited aqueous solubility of the test material and the irrelevance of organic co-solvents to inorganic test materials, stock solutions were prepared by shaking saturated solutions of test material in 0.01 M calcium chloride solution overnight, at ambient laboratory temperature.

PROCEDURE
Aliquots of soil and 0.01 M calcium chloride solution were taken in FEP/ETFE centrifuge tubes. Aliquots of 0.01 M calcium chloride solution required for soil-less blanks and soil-less controls were also taken in these test vessels. Due to the capacity of the available apparatus, the procedure was initially performed using soil type 2, soil type 3 and soil type 4. The procedure was then completed on a separate occasion using soil type 5 and soil type 7.

PREPARATION OF STOCK SOLUTIONS
An aliquot of test material (0.2546 g for testing of soil type 2, soil type 3 and soil type 4, and 0.2554 g for testing of soil type 5 and soil type 7) was diluted with 500 mL of 0.01 M calcium chloride solution. Each solution was shaken overnight on a flatbed shaker, at ambient temperature, to saturate. Following saturation, each stock solution was filtered through 0.45 µm filters to eliminate undissolved test material prior to use.

ADDITION OF TEST MATERIAL INTO SAMPLES
Relevant stock solution (2 mL) was added to all soil samples and all soil-less control solutions. An aliquot (2 mL) of 0.01 M calcium chloride solution was added to all soil blanks and all soil-less blanks. The addition of 2 mL to the existing 25 mL already present resulted in a stock solution addition of 7.4 % v/v.

ADSORPTION PROCEDURE
Each sample and soil-less control was agitated at 25 ± 2 °C, in the dark, for the relevant adsorption period.
All soil-less blanks and soil blanks were removed after 48 hours agitation to provide maximum opportunity for interfering species to leach out into solution.

DATA HANDLINGADSORPTION DATA
The percentage of neodymium adsorbed (A) was calculated using the following equation:
A = [(Ccont - Ceq) / Ccont] x 100
where:
Ccont = mean soil-less control neodymium concentration (mg/L)
Ceq = neodymium concentration remaining in solution on analysis after completion of equilibration period (mg/L)

The distribution coefficient (Kd) was calculated using the following equation:
Kd = [Aeq / (100 - Aeq)] x (Vo / m-soil)
where:
Kd = distribution coefficient (cm³/g)
Aeq = percentage of test material adsorbed (%)
Vo = volume of the aqueous phase in contact with the soil (cm³)
m-soil = quantity of the soil phase, expressed in dry mass of soil (g)

The organic carbon normalised adsorption coefficient (Koc) was calculated using the following equation:
Koc = Kd x (100 / %oc)
where:
Koc = organic carbon normalised adsorption coefficient (cm³/g)
%oc = percentage of organic carbon in the soil type (%)

Results and discussion

Adsorption coefficient

Adsorption coefficient 1

Type:

Kd

Value:

1 380 - 6 100

Temp.:

25 °C

Remarks on result:

other: The overall Kd range was 1380 to at least 6100 at 25 ± 2°C

Adsorption coefficient 2

Type:

Koc

Value:

1 330 - 239 000

Temp.:

25 °C

Remarks on result:

other: The overall Koc range was 1330 to at least 239000 at 25 ± 2°C

Adsorption coefficient 3

Type:

log Koc

Value:

4.12 - 5.38

Temp.:

25 °C

Remarks on result:

other: The overall log10 Koc range was 4.12 to at least 5.38 at 25 ± 2°C

Results: Batch equilibrium or other method

Adsorption and desorption constants:

The mean Kd values (cm³/g) were as follows:
- Soil type 2: 6.10 x 10³
- Soil type 3: ≥5.90 x 10³
- Soil type 4: 3.25 x 10³
- Soil type 5: 1.38 x 10³
- Soil type 7: 3.01 x 10³

The mean Koc values (cm³/g) were as follows:
- Soil type 2: 1.49 x 10⁵
- Soil type 3: ≥2.39 x 10⁵
- Soil type 4: 8.35 x 10⁴
- Soil type 5: 1.37 x 10⁵
- Soil type 7: 1.33 x 10⁴

Details on results (Batch equilibrium method):

The neodymium concentration (mg/L) of test material analysed in each solution, the solution pH and the percentage of test material adsorbed are shown in table 1. For soil type 2, 3, 4 and 5, the percentage of test material adsorbed has been calculated with respect to the relevant adsorption period mean soil-less control concentration. For soil type 7, the percentage of test material adsorbed has been calculated with respect to the theoretical dosed concentration, confirmed from analysis of the relevant stock solution.

The data required for the calculation of the distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) are shown in Table 2. Calculations have been completed from data generated at the 2 hour adsorption period time-point for soil type 2, 3, 4 and 5, and from the 5 hour adsorption period time-point for soil type 7.

The calculated distribution coefficients (Kd) and organic carbon normalised adsorption coefficients (Koc) for the neodymium content of the test material at 25 ± 2 °C, including the mean for each soil type, are shown in Table 3.

DISCUSSION
On analysis of the total dissolved neodymium concentration of the soil-less control solutions, the percentage recoveries with respect to the theoretical dosed concentration (from stock solution analysis) were low and declined with time. It could not be confirmed if losses were through adsorption to the test vessels, which were already optimised for low adsorption properties, or through precipitation followed by sedimentation on centrifugation; the control solutions being treated identically to the sample solutions.
However, irrespective of the fate of the decrease in neodymium concentration within the soil-less control solutions, the total dissolved neodymium concentration of the soil containing sample solutions decreased much more significantly and rapidly, such that this loss could be attributed confidently to interaction with the soil present.

Percentage adsorption calculations have been performed using the respective mean analysed soil-less control concentration at the 2 hour time-point. This therefore assumed the same degree of vessel adsorption and/or precipitation within the soil containing samples as for the soil-less controls. However, the strong affinity the test material has demonstrated for soils may have resulted in the soil active sites outcompeting any other underlying mechanism to strip the neodymium from solution and as such underestimated the actual adsorption onto the soils. To assess for the potential impact of this scenario on the study outcome, the distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) were recalculated against the theoretical dosed sample solution (calculated from stock solution analysis). This therefore assumed all decreases in the neodymium concentration of the sample solutions was due to soil adsorption alone. The results are summarised in Table 4.

This confirmed that the maximum possible deviation originating from the use of analysed soil-less control concentrations in calculation was equivalent to only 0.2 units as log10 Koc. Therefore, the decreases observed in the 2 hour soil-less control solutions on analysis did not impact significantly on the validity of the study, nor significantly skew the resulting quantified adsorption characterisation values obtained for soil types 2, 3, 4 and 5.
For the soil type 7, potentially due to the acidic nature of the soil/solution mixture promoting aqueous solubility, equilibrium was not evident at 2 hours. However consistent replicates were obtained following 5 hours equilibration and therefore these data were used for calculation of the distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) values. In addition, again due to the acidic pH promoting solubility of the neodymium content of the test material, for soil type 7 only, adsorption calculations have been performed from the theoretical dosed concentration confirmed from analysis of the relevant stock solution. This was since losses from the approximately neutral pH soil-less control solutions, attributed to adsorption and/or precipitation over time, were expected to be greatly reduced at an acidic pH. Therefore ( for the case of this soil type only) all reductions in the neodymium concentration of the aqueous phase on analysis have been attributed to adsorption on to the soil phase.On analysis of the un-dosed soil blanks, low background concentrations of neodymium were detected. Due to the high percentage adsorption observed for the test material in the presence of all soil types, these blank concentrations were subsequently considered significant. Therefore prior to calculation of adsorption data, all sample solution concentrations were corrected for the relevant mean analysed soil blank concentration. The mean analysed soil blank neodymium concentrations were 6.0 x 10E-4 mg/L, 1.64 x 10E-3 mg/L, 1.04 x 10E-3 mg/L, 2.54 x 10E-3 mg/L and 8.16 x 10E-3 mg/L for soil types 2, 3, 4, 5 and 7 respectively. No significant neodymium concentration was detected in the matrix blanks or soil-less (solvent) blanks on analysis.

For soil type 3, 2 hour replicate B, and soil type 7, 48 hour replicates A and B, no detectable concentration of neodymium remained in the aqueous phase on analysis. These three samples have therefore been reported as greater than 99.0 % adsorption.

It was evident from the data generated that organic carbon normalised adsorption coefficient (Koc) values should be used with caution in any further environmental modelling of this test material. The adsorption properties (as distribution coefficients) observed for the dissolved neodymium content of the sample solutions showed no significant correlation to the organic carbon content of the soils evaluated.From the soil type 7 results obtained, pH was evidently a very significant soil/solution criterion for the behaviour of this inorganic ion in soil. Even though soil type 7 presented both the highest organic carbon content and cation exchange capacity of the five soils investigated (22.7 % and 49.8 meq/100 g, respectively), the resultant distribution coefficient (Kd) value was the second lowest of the five soils investigated. Such a result was inversely proportional to the expectations of the methodology, predominantly aimed at organic compounds, as the acidic nature of this soil promoted aqueous solubility of the metal cation and therefore reduced the proportion partitioning on to the soil phase. Only soil type 5 resulted in a lower distribution coefficient (Kd) value. Soil type 5 presented both the lowest organic carbon content and cation exchange capacity of the five soils investigated (1.01 % and 9.2 meq/100 g, respectively). Therefore on comparison of soil type 5 and soil type 7, it can be observed that both the influence of an approximately 20 fold increase in organic carbon content and an approximately 5 fold increase in cation exchange capacity were negated by the decrease in the aqueous phase solution pH.

Any other information on results incl. tables

Table 1: Neodymium Concentration, pH and Percentage Adsorption

Soil Type	Solution	Nd Concentration (mg/L)*	Solution pH	Percentage Adsorption (%)	Mean Percentage Adsorption (%)
2	2 hour, Sample A	2.49E-03	6.4	98.4	98.0
	2 hour, Sample B	3.91E-03	6.4	97.5
	5 hour, Sample A	3.78E-03	6.4	96.9	97.5
	5 hour, Sample B	2.28E-03	6.6	98.1
	24 hour, Sample A	2.64E-03	6.4	95.3	93.0
	24 hour, Sample B	5.24E-03	6.5	90.7
	48 hour, Sample A	2.74E-03	6.4	95.9	96.1
	48 hour, Sample B	2.41E-03	6.3	96.4
3	2 hour, Sample A	2.75E-03	5.6	98.3	≥98.3
	2 hour, Sample B	None detected	5.7	>99.0
	5 hour, Sample A	2.28E-03	6.1	98.1	97.9
	5 hour, Sample B	2.72E-03	6.2	97.8
	24 hour, Sample A	1.03E-03	6.2	98.2	97.0
	24 hour, Sample B	2.40E-03	6.2	95.7
	48 hour, Sample A	1.21E-03	6.1	98.2	98.6
	48 hour, Sample B	5.91E-04	6.3	99.1
4	2 hour, Sample A	4.57E-03	5.8	97.1	96.9
	2 hour, Sample B	5.17E-03	5.4	96.7
	5 hour, Sample A	4.56E-03	5.5	96.2	95.7
	5 hour, Sample B	5.80E-03	5.3	95.2
	24 hour, Sample A	2.42E-03	5.2	95.7	95.6
	24 hour, Sample B	2.53E-03	5.2	95.5
	48 hour, Sample A	4.20E-03	5.3	93.7	95.3
	48 hour, Sample B	2.01E-03	5.4	97.0
5	2 hour, Sample A	8.41E-03	6.1	92.2	93.1
	2 hour, Sample B	6.51E-03	6.0	94.0
	5 hour, Sample A	6.20E-03	6.4	87.1	83.2
	5 hour, Sample B	9.92E-03	6.0	79.3
	24 hour, Sample A	4.51E-03	6.5	94.5	94.7
	24 hour, Sample B	4.26E-03	6.5	94.8
	48 hour, Sample A	2.44E-03	6.2	95.5	96.3
	48 hour, Sample B	1.57E-03	6.3	97.1
7	2 hour, Sample A	9.22E-03	3.3	94.4	92.0
	2 hour, Sample B	1.72E-02	3.3	89.6
	5 hour, Sample A	7.45E-03	3.2	95.5	96.1
	5 hour, Sample B	5.41E-03	3.2	96.7
	24 hour, Sample A	1.06E-02	3.5	93.6	96.2
	24 hour, Sample B	1.87E-03	3.5	98.9
	48 hour, Sample A	None detected	3.4	>99.0	>99.0
	48 hour, Sample B	None detected	3.4	>99.0

* Corrected for mean soil blank concentration on analysis

 

Table 2: Data Required for the Calculation of the Distribution Coefficient (Kd) and the Organic Carbon Normalised Adsorption Coefficient (Koc)

Soil Type	Sample Identity	Dry Mass of Soil (g)	Volume of Aqueous Phase (cm³)	Percentage Adsorption at Equilibrium (%)
2	A	0.2268	27	98.4
	B	0.2273	27	97.5
3	A	0.2601	27	98.3
	B	0.2593	27	>99.0
4	A	0.2647	27	97.1
	B	0.2626	27	96.7
5	A	0.2641	27	96.2
	B	0.2712	27	94.0
7	A	0.2306	27	95.5
	B	0.2252	27	96.7

 

Table 3 : Distribution Coefficient (Kd) and Organic Carbon Normalised Adsorption Coefficient (Koc) Values

Soil Type	Sample Identity	Kd (cm³/g)	Mean / Overall Kd (cm³/g)	Koc (cm³/g)	Mean / Overall Koc (cm³/g)
2	A	7.48 x 10³	6.10 x 10³	1.83 x 10⁵	1.49 x 10⁵
	B	4.71 x 10³		1.15 x 10⁵
3	A	5.90 x 10³	≥5.90 x 10³	2.39 x 10⁵	≥2.39 x 10⁵
	B	>1.03 x 10⁴		>4.17 x 10⁵
4	A	3.44 x 10³	3.25 x 10³	8.85 x 10⁴	8.35 x 10⁴
	B	3.05 x 10³		7.85 x 10⁴
5	A	1.21 x 10³	1.38 x 10³	1.20 x 10⁵	1.37 x 10⁵
	B	1.56 x 10³		1.54 x 10⁵
7	A	2.48 x 10³	3.01 x 10³	1.09 x 10⁴	1.33 x 10⁴
	B	3.54 x 10³		1.56 x 10⁴

 

Table 4: Distribution Coefficient (Kd) and Organic Carbon Normalised Adsorption Coefficient (Koc) Values Derived from Analysed and Theoretical Soil-less Control Concentrations

Soil Type	Mean / Overall Kd (cm³/g)		Mean / Overall Koc (cm³/g)
	Calculated from Analysed Control Concentrations	Calculated from Theoretical Dosed Concentration	Calculated from Analysed Control Concentrations	Calculated from Theoretical Dosed Concentration
2	6.10 x 10³	7.85 x 10³	1.49 x 10⁵	1.92 x 10⁵
3	≥5.90 x 10³	≥7.59 x 10³	≥2.39 x 10⁵	≥3.07 x 10⁵
4	3.25 x 10³	4.19 x 10³	8.35 x 10⁴	1.08 x 10⁵
5	1.38 x 10³	2.17 x 10³	1.37 x 10⁵	2.15 x 10⁵

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of this study, the overall Kd range was 1.38 x 10³ to at least 6.10 x 10³, the overall Koc range was 1.33 x 10⁴ to at least 2.39 x 10⁵ and the overall log10 Koc range was 4.12 to at least 5.38.

Executive summary:

The adsorption characteristics of the test material were determined using a batch equilibrium method in accordance with the standardised guidelines OECD 106 and EU Method C.18 under GLP conditions.

The distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) for the neodymium content of the test material were determined for five soil types at 25 ± 2 °C. The soils were: soil type 2, loam (pH 7.3); soil type 3, silt loam (pH 6.2); soil type 4, silt loam (pH 5.1); soil type 5, loamy sand (pH 5.8); and soil type 7, loamy sand (pH 3).

Due to limited aqueous solubility of the test material and the irrelevance of organic co-solvents to inorganic test materials, stock solutions were prepared by shaking saturated solutions of test material in 0.01 M calcium chloride solution overnight, at ambient laboratory temperature.

With the exception of the acidic soil type 7, definitive results were calculated from the initial sampling time-point, employing an adsorption equilibration period of 2 hours, due to an inherent instability of the dissolved neodymium content of the soil-less control solutions as a function of time. For the soil type 7, potentially due to the acidic nature of the soil/solution mixture promoting aqueous solubility, equilibrium was not evident at 2 hours. However consistent replicates were obtained following 5 hours equilibration and therefore this data were used for calculation of the distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) values.

 

The adsorption properties (as distribution coefficients) observed for the dissolved neodymium content of the sample solutions showed no significant correlation to the organic carbon content of the soils evaluated.

From the soil type 7 results obtained, pH was evidently a very significant soil/solution criterion for the behaviour of this inorganic ion in soil. Even though soil type 7 presented both the highest organic carbon content and cation exchange capacity of the five soils investigated (22.7 % and 49.8 meq/100 g, respectively), the resultant distribution coefficient (Kd) value was the second lowest of the five soils investigated. Such a result was inversely proportional to the expectations of the methodology, predominantly aimed at organic compounds, as the acidic nature of this soil promoted aqueous solubility of the metal cation and therefore reduced the proportion partitioning on to the soil phase. Only soil type 5 resulted in a lower distribution coefficient (Kd) value. Soil type 5 presented both the lowest organic carbon content and cation exchange capacity of the five soils investigated (1.01 % and 9.2 meq/100 g, respectively). Therefore on comparison of soil type 5 and soil type 7, it can be observed that both the influence of an approximately 20 fold increase in organic carbon content and an approximately 5 fold in cation exchange capacity were negated by the decrease in the aqueous phase solution pH.

 

Under the conditions of this study, the overall Kd range was 1.38 x 10³ to at least 6.10 x 10³, the overall Koc range was 1.33 x 10⁴ to at least 2.39 x 10⁵ and the overall log10 Koc range was 4.12 to at least 5.38.