Di(µ-2,2´,2´´-nitrilotris(ethanol)-diperchlorato)dinatrium

Adsorption / desorption

Description of key information

Koc (triethanolamine, MCI method) = 10 l/kg

Log Koc (triethanolamine, MCI method) = 1 l/kg.

Key value for chemical safety assessment

Koc at 20 °C:

10

Additional information

The physicochemical properties of the substance indicate that it is expected to have a low potential for adsorption; the test is therefore not necessary. The substance is very soluble in water and has a LogPow value that is much lower of the cut-off value of 3 (Chapter R.7a, Guidance on Information Requirements and Chemical Safety Assessment., ECHA, 2016). The substance is furthemore readily biodegradable (in only 19 days) which indicates that it remains in water for a limited time; the possibility of adsorpion to soil or sediment is limited. In addition, in the biodegradation test, an additional flask was used to assess the adsorption potential of the substance through the test duration. Based on the results, the decrease of DOC in the adsorption control was only 7 mg/l in 19 days, while the decrease due to biodegradation was much more (49 mg/l) suggesting that the adsorption potential of the substance is not important.

The substance dissociates in water into triethanolamine and sodium perchlorate. Since no data on the substance are available, data on the dissociation substances are more appropriate and they are used for the assessment of the adsorption potential of the substance. Justification for Read Across is given in Section 13 of IUCLID.

Sodium perchlorate

The adsorption coefficient (Koc) was calculated by using KOCWIN V.2.00, an application contained in the EpiSuite 4.1, by two different methods: MCI method and Kow method. The values of Koc calculated were 43.89 l/kg and 5.862.10 E-7 l/kg by MCI method and Kow method respectively. However, the LogKow of the substance is outside the Kow range of the training set (limits of training set: log Kow = -2.11 to 9.10; log Kow of test substance: -7.81) and thus the result should be taken with caution. The definite values may not be fully reliable.

In water perchlorate salts are rapidly dissociate into the perchlorate anion and the corresponding cation. Given that perchlorates dissociate at environmentally significant concentrations, their cations are spectators in the aqueous fate of perchlorates. Therefore the environmental fate of the perchlorate salts is dominated by perchorate anion while the cations do no participate in, nor do they substantially influence its fate. Perchlorates are water soluble and the anion does not typically form insoluble metal complexes in solution (1). Since the perchlorate ion is only weakly adsorbed to mineral surfaces in solutions of moderate ionic strength, its movement through soil is not retarded (2). These two properties indicate that perchlorate will travel rapidly over soil with surface water runoff or be transported through soil with infiltration. Therefore, if released to soil, perchlorates are expected to be highly mobile and travel to groundwater and surface water receptors. This is consistent with surface water and groundwater monitoring data that indicate that perchlorates have been found far from known sites of their release to soil.

Other data available for perchlorate support the lack of adsorption in soil (3) studied the adsorption and release of perchlorate in a variety of soils, minerals and other media when the solid media were exposed to low (3.4 μg/g perchlorate-to-soil ratio) and high aqueous solutions of perchlorate salts. At the low level of exposure, more than 90 % of the perchlorate was recovered in the aqueous phase. In some cases more than 99 % of the perchlorate remained in the aqueous phase. The forced perchlorate anion exchange capacities (PAECs) were studied by soaking triplicate portions of the solid media in 0.20 M sodium perchlorate (NaClO₄) followed by repeated deionized water rinses (overnight soaks with mixing) until perchlorate concentrations fell below 20 ng/ml in the rinse solutions. The dried residual were leached with 0.10 M sodium hydroxide. The leachates were analyzed by ion chromatography and the perchlorate concentrations thus found were subsequently used to calculate the PAECs. The measurable PAECs of the insoluble and settleable residual ranged from 4 to 150 nmol/g (μmol/kg), with most in the 20–50 nmol/g range. In some soils or minerals, no sorption was detectable. Overall, the findings support the widely accepted idea that perchlorate does not appreciably sorb to soils and that its mobility and fate are largely influenced by hydrologic and biologic factors. They also generally support the idea that intrasoil perchlorate content is depositional rather than sorptive. On the other hand, sorption (anion replacement) of perchlorate appears to occur in some soils. Many soils would be expected to show higher anion exchange capacities at lower pH due to protonation of various oxo (oxide) and hydroxo (hydroxide) moieties, and perchlorate sorption in variable charge soils has been reported (4).

Brown G.M. and Gu B. (5) studied the chemistry of perchlorate in the environment and reviewed its fate in the environment. Perchlorate is stable and non reactive in aqueous systems; the high stability of ClO4- in water is due to its large kinetic barrier to reduction as well as its reductance to bind to surfaces (pure nucleophilic, poor coordinating ability). It is poorly retained or sorbed by sedimental minerals in the subsurface because of its negative charge and its noncomplexing nature with metal ions. Its large ionic size and low charge density reduce its affinity for metal cations and make it highly soluble and thus exceedingly mobile in natural aqueous systems. As such, perchlorate sorption to soils and sediments has not been widely observed nor extensively studied. Sorption of perchlorate appears to occur in soils with appreciable anion-exchange capacities (AEC).

Triethanolamine

The adsorption coefficient (Koc) was calculated by using KOCWIN V.2.00, an application contained in the EpiSuite 4.1, by two different methods: MCI method and Kow method. The values of Koc calculated were 10 l/kg and 0.3046 l/kg by MCI method and Kow method respectively.

Review of the adsoprtion potential of triethanolamine is available in literature; Koc values mentioned are also estimated and not experimentally measured. If released to soil, triethanolamine is expected to biodegrate fairly rapidly following acclimation (half-life on the order of days to weeks). Residual triethanolamine may leach into ground water. Volatilization from soil surfaces is not expected to be an important fate process (6). A soil adsorption coefficient of 3 (LogKoc = 0.477) was estimated based on a log Kow of -1.59. This Koc value and the complete solubility of triethanolamine in water suggests that this compound would be extremely mobile in soil and would not adsorb appreciably to suspended solids and sediments in water (7), (8). Further data on adsorption were found in a report for the assessment of triethanolamine; regression equations were used to estimate the LogKoc which was found to be equal to 0.19. This indicates that triethanolamine has a high mobility in soil.

Conclusion

The substance is not expected to adsorb to soil since it is very soluble in water, has a logPow much lower than 3 and it is readily biodegradable. Therefore it is expected to be found in water rather than the soil, in which it is not expected to remain for a long period since it biodegrades readily (in 19 days). Furthermore, since the substance dissociates in water, into triethanolamine and sodium perchlorate, the adsorption potential of these dissociation substances was also evaluated. Both substances are water soluble with a low logPow. The available data support the idea of their great mobility in soil and thus they are expected to be found in the water environment. Taking in consideration all the data, the substance is not expected to adsorb in soil therefore is expected to have a low adsorption coefficient. For the evaluation of risk assessment the adsorption coefficient of triethanolamine instead of the one of perchlorate is taken into consideration even if perchlorate's value indicates a higher adsorption potential (worst case senario). The Koc value of sodium perchlorate is not reliable since its estimation does not fall in the model's application domain. However the review of adsorption potential of perchlorate available in literature suggests that the perchlorate is not expected to be present in soil but rather is expected to be found in water. The Koc of triethanolamine found by MCI method is used as the MCI methodology is somewhat more accurate than the Log Kow methodology, although both methods yield good results.

(1) Cotton FA, Wilkinson G. 1980. Advanced inorganic chemistry. New York, NY: John Wiley & Sons, 560.

(2) Logan BE. 2001. Assessing the outlook for perchlorate remediation. Environ Sci Technol 35(23):482A-487A

(3) Urbansky E.T. and Brown S.K. J. Perchlorate retention and mobility in soils. Environ. Monit., 2003, 5, 455–462

(4) G. Ji and X. Kong, Adsorption of chloride, nitrate and perchlorate by variable charge soils. Pedosphere, 1992, 2, 317 -326.

(5) Brown, G. M.; Gu, B. The Chemistry of Perchlorate in the Environment. In Perchlorate: Environmental Occurrence, Interactions and Treatment; Gu, B.; Coates, J. D., Eds.; Springer US: Boston, MA, 2006; pp 17−47.

(6) Howard PH. Handbook of environmental fate and exposure data for organic compounds. Lewis publishers 1990

(7) Hansch V, Leao AJ, Medchem. Project Issue No. 26, Claremont, C.A., Pomona College, (1985)

(8) Lyman WJ et al, Handbook of Chemical Property Estimation Methods, NY: McGraw-Hill, 4-9, (1982)

[LogKoc: 1.0]