Registration Dossier
Registration Dossier
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EC number: 201-069-1 | CAS number: 77-92-9
Adsorption / desorption
Administrative data
Link to relevant study record(s)
Description of key information
Key value for chemical safety assessment
Additional information
The adsorption/desorption study required in REACH guidance, Annex IX (Section 9.3.3) does not need to be conducted as the substance is readily biodegradable.
Citric acid has a low log Kow value of <0. It is however recognised that molecules with ability to complex with metals may adsorb more strongly than log Kow would suggest.
Citrate forms stable complexes with metal ions due to its multiple-binding capacities; the pH will affect the number of binding sites by altering the ionisation state of the substance. The log Koc value of citric acid may be read across from EDTA on the principle that they are both complexing agents, containing multiple carboxylic acid groups. EDTA has four carboxylic acid group on an ethylenediamine backbone; citric acid has three carboxylic acids on a propan-2-ol backbone. EDTA is a stronger complexing agent than citric acid and so the read-across represents a worst-case scenario.
The Koc value of citric acid was determined from the Kp-susp of Ethylene Diamine Tetra Acetic Acid (EDTA) by the following equations
Kp-susp = 75 (EC 2004)
Kp-susp = Foc * Koc= 0.05 *Koc
75 = 0.05 *Koc => Koc= 1500
The Koc and Kp-susp values of 1500 and 75 were used for the exposure calculation of citric acid respectively.
Where:
Kp-susp = partition coefficient solid-water in suspended matter
Foc = weight fraction of organic carbon in water compartment
0.05 = weight fraction organic carbon sediment solids
In addition, a measured study (O'Connor and Mullee 2006, reported inthe CLH consultation on citric acid) conducted according to OECD 106 and in compliance with GLP, the Koc/Kd of citric acid was studied using 5 different soil types with test substance purity of 99.5%. Equilibrium time was reduced to 30 minutes in order to reduce biological degradation. In this study mean Kd and Koc values of 8.68 to 22.9 and 76.2 to 1530 were obtained for citric acid. The upper Koc result of 1530 is in agreement with that calculated above and the results indicate that citric acid is moderately to slightly mobile in soils. Access to the report has not been purchased, for details please refer to CLH consultation here https://echa.europa.eu/documents/10162/c721decb-298f-92a3-b425-55cbf9c6cc9b [accessed January 2019].
Any remaining uncertainty the Koc value of citric acid is insignificant to the outcome of the Chemical Safety Assessment (CSA).
References:
EC (2004). Edetic Acid (EDTA). CAS No. 60-00-4, EINECS No: 200-449-4 Summary Risk Assessment Report. Special Publication I.04.279. European Commission Joint Research Centre. Germany 2004
O’Connor B and Mullee D 2006, Determination of Adsorption Coefficient, Safepharm laboratories, 2089-008.
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