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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 PBTC as test substance. In this study, different concentrations (1 -1000 mg) of PBTC, 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 for PBTC 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. PBTC is not harmful to earthworms at concentration lower or equal to 1000 mg/kg dry weight substrate.

However, in case of only one test result is available, the risk assessment should be performed both on this test result and on the basis of the outcome of the aquatic toxicity data. Therefore the equilibrium partitioning method with the PNEC for aquatic organisms is also taken into account for assessment.