reaction mass of neodymium carbonate and praseodymium carbonate

Endpoint summary

Additional information

Hydrolysis:

Due to the low solubility of the reaction mass of neodymium carbonate and praseodymium carbonate (3.93 mg/L at 20°C), the hydrolysis study does not need to be conducted (column 2 adaptation of REACh Annex VIII).

 

Biodegradation:

Due to the inorganic nature of the reaction mass of neodymium carbonate and praseodymium carbonate, biodegradation studies do not need to be conducted (column 2 adaptation of REACh Annex VII).

 

Adsorption/desorption:

Adsorption/desorption tests allow to determine a distribution coefficient, which is the ratio of equilibrium concentrations of a dissolved substance in two-phase system consisting of a sorbent (typically soil or sewage sludge) and an aqueous phase. Hence, suitable methods must be available to determine the substance concentrations in both phases. In a first step, the HPLC method (OECD 121, EU C.19) may be used as a screening. However, such a method is not suitable for inorganic compounds as the reaction mass of neodymium carbonate and praseodymium carbonate. Batch equilibrium method (OECD 106, EU C.18) may be considered in a more definitive step. 

 

As data on a reaction mass constituent (i.e. dineodymium tricarbonate) and on a constituent analogue (i.e. dicerium tricarbonate) were available, a weight-of-evidence approach was carried out to conclude on the distribution coefficient of the reaction mass of neodymium carbonate and praseodymium carbonate. Both studies were performed according to OECD guideline 106 and in compliance with GLP. However, the maximal reliability score was decreased from 1 to 2, since used as read-across (according to Practical Guide n°6) and the studies were flagged as weight of evidence.

The adsorption characteristics of dineodymium tricarbonate were determined using a batch equilibrium method (O’Connor B.J., 2013). The distribution coefficient (Kd) and the organic carbon normalised adsorption coefficient (Koc) for the neodymium content of the test material were determined for five soil types at 25 ± 2 °C. The soils were: soil type 2, loam (pH 7.3); soil type 3, silt loam (pH 6.2); soil type 4, silt loam (pH 5.1); soil type 5, loamy sand (pH 5.8); and soil type 7, loamy sand (pH 3). Due to the instability of the dissolved neodymium content, adsorption equilibration periods were shortened (from 2 to 5 hours). This observation did not have any effect on Kd and Koc data experimentally determined in the study. The overall Kd range was 1.38 x 10³ to at least 6.10 x 10³, the overall Koc range was 1.33 x 10⁴ to at least 2.39 x 10⁵ and the overall log10 Koc range was 4.12 to at least 5.38. These values demonstrated the high absorption of dineodymium tricarbonate to soils. This result was consistent with the slight water solubility of dineodynium tricarbonate (i.e. 3.65 mg/L at 20°C) which suggested that the substance might mainly adsorb to soil.

The adsorption/desorption behaviour of dicerium tricarbonate on soil was determined using three soils and the batch equilibrium method (Völkel W., 2008). The soils chosen represented a range of soil properties that were most important for adsorption, i.e. organic carbon content, clay content, soil texture and the pH value. Different soil types must be used in order to cover as widely as possible the interactions of a given item with naturally occurring soils. The soils were: Soil SI: Loamy sand (pH 5.6), Soil SII: Silt loam (pH 7.4), Soli SIII: Clay (pH 7.0). The adsorption on soils of the dicerium tricarbonate has been high only after 2 hours (95 to 100%). In contrary, desorption of dicerium tricarboante was negligible (maximum after 48 hours: 2%). The mass balance results confirmed the strong adsorption of dicerium tricarbonate to soil. The following adsorption/desorption distribution coefficients were obtained for the soils at 20 ± 2°C: mean Koc value of 3940404 and mean Koc des value of 7556699. These values demonstrated that the high absorption of dicerium tricarbonate to soils. This result was consistent with the slight water solubility of dicerium tricarbonate (i.e. 3.95 mg/L at 20°C) which suggested that the substance might mainly adsorb to soil.

 

Data on the insoluble dineodymium tricarbonate and the slightly soluble dicerium tricarbonate showed that both substances strongly adsorbed to soil. As a consequence, by analogy with dineodymium tricarbonate and dicerium tricarbonate, the reaction mass of neodymium carbonate and praseodymium carbonate is expected to adsorb to soil.