Registration Dossier
Registration Dossier
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EC number: 231-512-4 | CAS number: 7601-90-3
Adsorption / desorption
Administrative data
Link to relevant study record(s)
Description of key information
Perchloric acid is considered to have a low potential adsorption onto soil and sediment.
Key value for chemical safety assessment
- Koc at 20 °C:
- 43.89
Additional information
Perchloric acid is a strong inorganic acid and therefore it will be under dissociated form in all environmental compartments. Because of the high water solubility of perchlorate salts, perchlorate is unlikely to accumulate via adsorption to irrigated soil. Similarly, concentrations of perchlorate in soil pore water may be assumed to be equal to the concentration in irrigation water.
Due to the inorganic ionic nature of perchlorate, the adsorption coefficient is highly soil dependent. One reliable key study has been selected for the determination of the adsorption/desorption potential. In this study (Urbansky and Brown, 2003), portions of soil medium were dispensed into centrifuge tubes with addition of Aliquot of deionized water and aliquot of stock solutions of perchlorate salts. The tubes were capped and rotated end-over-end for 2-3 or more days, at ambient temperature to permit equilibration. The tubes were centrifuged and the aqueous phase was analysed by ion chromatography. At low level exposure more than 90% of the perchlorate was recovered in the aqueous phase. The authors suggested that the intrasoil perchlorate content is depositional rather than adsorptive. Although this paper suggests a low potential of adsorption onto soil, no adsorption coefficient (Koc) value is reported.
Some monitoring studies show that contamination of soil by perchlorate is observed in some areas. However, it is recognized that this contamination is a result of direct spills of perchlorate solution, which does not happen for the uses of perchloric acid identified and covered in the REACH dossier. Perchlorate salts that are released to the soil in solid form will readily dissolve in whatever moisture is available. If sufficient infiltration occurs, the perchlorate is expected to be completely leached from the soil. In arid regions, crystallized perchlorate salts may accumulate at various horizons in the soil due to evaporation of infiltrating rainfall that leached perchlorate from shallower depths.
As no direct spills of perchloric acid onto soil takes place via the identified uses in the REACH dossier, the Koc value will be used only to assess the potential of adsorption onto soil and sediment from water containing perchlorate. In this frame of transport between environmental compartments, the low adsorption potential onto soil and sediment should be considered for the environmental exposure assessment. So, a Koc value can be calculated by QSAR model. Although inorganic compounds are outside the applicability domain of the EPISUITE model, this model is the most relevant for this endpoint and therefore it is used to estimate a Koc value of perchlorate as reported below.
KOCWIN v2.00 result estimation for:
- perchloric acid (SMILES : O=CL(=O)(=O)O)
- sodium perchlorate (SMILES : O=CL(=O)(=O)O([Na]))
Estimated Koc from MCI = 43.89 L/Kg (LogKoc = 1.6424).
Both substances give to the same estimated value.
This estimated Koc value is consistent with the conclusion of low adsorption onto soil and sediment.
[LogKoc: 1.6424]
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