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As there is no data available for tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate ("PBTCNa4") a read-across approach with the corresponding parent acid 2-phosphonobutane-1,2,4-tricarboxylic acid ("PBTC") is proposed.

In aqueous media, PBTCNa4 and PBTC dissociate into the corresponding anion (2-phosphonatobutane-tricarboxylate ion) and the sodium ion and hydrogen ion (proton), respectively. Fate, behavior and the ecotoxicological properties of PBTC and its tetrasodium salt are thought to be an effect of the phosphonato-carboxylate ion rather than of the sodium ion or the hydrogen ion (proton), which are normal constituents in environmental systems and have no relevant ecotoxic properties in low concentrations.

Therefore a read-across between PBTCNa4 and PBTC acid is justified.

Concerning terrestrial toxicity, there is only one study available which is conducted with soil as substrate using a 39.7% aqueous solution of PBTC as test substance. In this study, different concentrations (1 -1000 mg) of the test item, thoroughly mixed in artificial soil, were tested for toxicity of earthworms according to OECD TG 207. After 14 days of exposure to the test material, no significant difference was observed in mortality rate and in weight in any of the different concentration groups that were examined compare to the control group. The LC50 (14 days) was determined as > 1000 mg/kg dry weight substrate. Thus, the no-observed-effect concentration (NOEC) was 1000 mg/kg dry weight substrate, the lowest-observed-effect concentration (LOEC) and the lowest tested concentration with mortality (LLC) was > 1000 mg/kg dry weight substrate. Referring the results to the purity of PBTC in the anhydrous form of the substance, the highest nominal test concentration showing no effect is converted based upon the water content resulting in a 14d-LC50 and LLC > 397 mg/kg dry weight substrate and a NOEC of 397 mg/kg dry weight substrate.The substance is not harmful to earthworms at concentration lower or equal to 397 mg/kg dry weight substrate.

Based on the read-across approach the substance falls into Soil Hazard Category 1 (ECHA Guidance R.7c, table R.7.11-2). Risk to soil organisms exposed to the substance is therfore acceptably assessed based on the PNECsoil calculated using the Equilibrium Partitioning Method, with additional support by a confirmatory short-term terrestrial toxicity study. The worst-case derivation from the study results in a PNECsoil of 0.397 mg/kg dwt. The equilibrium method results in the lowest PNECsoil of 0.08856 mg/kg dwt. Therefore, the PNECsoil derived by the Equilibrium Partitioning Method represents a worst-case approach. As the CSA demonstrates PEC/PNEC values of < 1 towards the environment in all cases, no hazard towards the environment is indicated. In conclusion, according to ECHA Guidance R.7c (Figure R.7.11—3 Scheme B: Integrated testing strategy (Annex IX and Annex X substances)) no further testing is required.