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Environmental fate & pathways

Adsorption / desorption

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Administrative data

Endpoint:
adsorption / desorption
Remarks:
adsorption
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Meets generally accepted scientific standards, well documented and acceptable for assessment, however data is not sufficient to determine a Kd value for risk assessment.

Data source

Reference
Reference Type:
publication
Title:
Hydrolysis and sorption reactions of orthophosphate, pyrophosphate, tripolyphosphate and trimetaphosphate anions added to an elliot soil
Author:
Blanchar RW and Hossner LR
Year:
1969
Bibliographic source:
Soil sci. soc. Amer. Proc. 33: 141-144

Materials and methods

Test guideline
Qualifier:
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 of oven dried soil for given periods of time. At the end of the specified time period, the soil to water ratio was adjusted to 1:10, the flasks were shaken for 15 secs and centrifuged. The total phosphate and orthophosphate content of the solution phase were determined.
GLP compliance:
no
Type of method:
other: Sorption study
Media:
soil

Test material

Reference
Name:
Unnamed
Type:
Constituent
Type:
Constituent
Type:
Constituent
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report): sodium orthophosphate
- Molecular formula (if other than submission substance): NaH2PO4.H2O
- Analytical purity: 100%

Study design

Test temperature:
No data

Batch equilibrium or other method

Analytical monitoring:
not specified
Details on matrix:
COLLECTION AND STORAGE
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): Air dried and screened to pass 8 mesh.

PROPERTIES:
- pH: 1 part soil to 1 part water mix = 5.6
- Extractable Cations (Ca, Mg, Na, K, H) (MEQ/100 g):
exchangeable Ca: 19.1
Mg: 5.8
K: 0.4
H: 6.1
-Water content: 24% at 1/3 atm
Details on test conditions:
No data

Results and discussion

Any other information on results incl. tables

The relationship between P added and solution content of P for sodium orthophosphate follows the Freundlich equation prediction very closely. The data shows that sodium orthophosphate was strongly absorbed. An estimate of the hydrolysis during the sorption study was made by determining phosphate content of the solution phase of the most concentrated sample.

The sorption capacity was found to be 462 µg/ P/g soil.

Applicant's summary and conclusion

Validity criteria fulfilled:
not specified
Conclusions:
The sorption capacity is equal to the amount of test substance (µg) absorbed / amount of sorbent (g) at equilibrium. In this study is was determined to be 462 µg. 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).