Registration Dossier
Registration Dossier
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EC number: 228-601-5 | CAS number: 6303-21-5
Adsorption / desorption
Administrative data
Link to relevant study record(s)
Description of key information
One key study is available for the sodium phosphinate salt by read across. Independent of the soil characteristics, phosphinate adsorption was low, with Kd and Koc values ranging from 0.11-0.3 mL/g and 3.7-15 mL/g, respectively. The highest value of Koc equal to 15 mL/g corresponding to the strongest adsorption observed and measured in an acidic slit loam soil with a pH of 5.3 was retained as key value for assessment.
Based on these results, the potential of adsorption/desorption of phosphinic acid is low and therefore no further information according to Annex IX is not necessary.
Key value for chemical safety assessment
- Koc at 20 °C:
- 15
Additional information
One key study is available on sodium phosphinate according to the OECD guideline 106 and under GLP compliance.
Phosphinic acid is commercially prepared as the result of pH adjustement of the sodium phosphinate. Both are highly soluble in water and release the phosphinate anion. The phosphinate anion is expected to play the most significant role for determining toxicity hence at comparable concentration and defined pH, the adsorption/desorption potential of the phosphinic acid hydrolysis can be read across from the sodium phosphinate salt.
Five soils were tested for this batch equilibrium method showing a range of textures and pHs [5.32; 7.47]. After two preliminary tests, the adsorption/desorption kinetics of the phosphinate anion was determined in the five soils after 24h, 48h and seven days of agitation using a soil-to-solution ratio of 1:1 and a phosphinate concentration of 10 µg/mL.
No consistent adsorption was seen for soil I at any time and for the other soils, a plateau was reached after 24-48 h, with no further increase for the seven day time point. After 48 hours of agitation, adsorption represented 24%, 13%, 10% and 14% for soils II to V, respectively. The Kd values amounted to 0.31, 0.15, 0.11 and 0.16 mL/g for soils II to V, respectively, with corresponding Koc values of 15, 11, 11 and 3.7 mL/g. The adsorption was strongest in soil II, an acidic slit loam with a pH of 5.3.
Due to the overall low adsorption of phosphinate, Freundlich isotherms were not determined. Desorption was investigated and could only be measured in soil II, where 24% of the adsorbed amount could be recovered after 48 h of desorption. Thus, adsorption was at least partially reversible in this soil.
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