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Environmental fate & pathways

Adsorption / desorption

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adsorption / desorption, other
Type of information:
experimental study
Adequacy of study:
supporting study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Meets generally accepted scientific standards, well documented and acceptable for assessment, however data is not sufficient to determine a Kd value for risk assessment.
Reason / purpose for cross-reference:
reference to same study

Data source

Reference Type:
Hydrolysis and sorption reactions of orthophosphate, pyrophosphate, tripolyphosphate and trimetaphosphate anions added to an elliot soil
Blanchar RW and Hossner LR
Bibliographic source:
Soil sci. soc. Amer. Proc. 33: 141-144

Materials and methods

Test guideline
no guideline available
Principles of method if other than guideline:
An estimation of sorption onto soil was determined by shaking 30 ml of phosphate solutions with 3 g oven dried soil for given periods of time. At the end of the specified time period, the soil to water ratio was adjusted, the flasks shaken and centrifuged and the total P and tripolyphosphate content determined
GLP compliance:
Type of method:

Test material

Constituent 1
Chemical structure
Reference substance name:
Pentasodium triphosphate
EC Number:
EC Name:
Pentasodium triphosphate
Cas Number:
Molecular formula:
Na5P3O10 H5-xP3O10Nax (where x is approximately 5) 6H2O.Na5P3O10
Pentasodium triphosphate
Details on test material:
- Name of test material (as cited in study report): Sodium Tripolyphosphate
- Analytical purity: 96.9%
- Impurities (identity and concentrations): 2.7% Pyrophosphate, 0.4% Orthophosphate

- Name of test material (as cited in study report): Sodium Orthophosphate
- Analytical purity: 100%

- Name of test material (as cited in study report): Sodium Pyrophosphate
- Analytical purity: 97.4%
- Impurities (identity and concentrations): 2.6% Orthophosphate

- Name of test material (as cited in study report): Sodium Trimetaphosphate
- Analytical purity: 96.7%
- Impurities (identity and concentrations): 2.3% Tripolyphosphate, 1% Orthophosphate

Results and discussion

Any other information on results incl. tables

The relationship between P added and solution content of P for all the tested phosphates follows the Freundlich equation prediction very closely. The data show that sodium phosphates were strongly adsorbed. An estimate of the extent of hydrolysis during the sorption study was made by determining the phosphate content of the solution phase of the most concentrate sample. The sample was 46% orthophosphate, 19% pyrophosphate and 35% tripolyphosphate.

Although considerable hydrolysis of the phosphates had taken place, an approximation of the sorption capacities were determined from the Langmuir adsorption isotherm.

The sorption capacity was 462, 965 and 706 µg P/g soil for orthophosphate, pyrophosphate and tripolyphosphate respectively.

Applicant's summary and conclusion

The sorption capacity is equal to the amount of test substance (µg) absorbed / amount of sorbent (g) at equilibrium. In this study it was determined to be 706 µg P/g . Despite the paper stating that the Freundlich equation is observed to be followed by the results of the study, it is not considered to be scientifically valid to calculate a Koc for an inorganic substance following this method. The concept of the Koc doesn't work with the Langmuir adsorption isotherm (detailed in the publication).
In addition, the study does not determine a Kd (partition coefficient value).