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Description of key information

Data on aquatic toxicity are not available for tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate and a read-across approach with the corresponding parent acid 2-phosphonobutane-1,2,4-tricarboxylic acid is proposed.

In aqueous media, tetrasodium hydrogen 2-phosphonatobutane-tricarboxylate and 2-phosphono-butane-1,2,4-tricarboxylic acid 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 2-phosphonobutane-1,2,4-tricarboxylic acid 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 tetrasodium hydrogen 2-phosphonatobutane-tricarboxylate and 2-phosphonobutane-1,2,4-tricarboxylic acid is justified.



A 96h-LC50 of >1042 mg/L was concluded from a 14d-NOEC of >/=1042 mg/L found in a prolonged toxicity study in fish (species: Danio rerio), conducted according to the OECD guideline 204, over 14 days. The results refere to measured concentrations, as the test concentrations were confirmed by analytical monitoring using ion chromatography.



A prolonged toxicity study in Daphnia magna (covering to OECD guidelines 202 and 211) was performed over 21 days and the effect on mobility was determined to be 21d-EC 50 (immobilisation) >1071 mg/L. Based on this result, an 48h-EC50 value of > 1071 mg/l was concluded. Other study results refer to effects on reproduction. A 21d-NOEC of 104 mg/l and a 21d-LOEC of 329 mg/l were obtained. The results are expressed in terms of the arithmetic mean of measured concentrations.



In a test, the fresh water alga Desmodesmus subspicatus was exposed to the parent acid 2-phosphonobutane-1,2,4-tricarboxylic acid for 72 hours. The experiment was conducted according to the OECD TG 201. A 72h-ErC50 of > 1081 mg/L; a 72h-NOEC of 17.8 mg/L and an 72h-ErC10 > 33.3 - < 65.5 mg/l, based on measured concentrations was obtained in this test. Analytical monitoring was carried out and stability of the test substance was confirmed during the duration of exposure.



To assess the toxicity of 2-phophonobutane-1,2,4-tricarboxylic acid to microorganisms, a study was conducted in accordance with Council Regulation (EC) No 440/2008, Method C.11 "Activated sludge respiration inhibition" (2008) - equivalent to OECD Guideline 209 (1984). The activated sludge was exposed to a 50.4 % water solution of 2-phophonobutane-1,2,4-tricarboxylic acid (marketed as Bayhibit AM) at different concentrations. The respiration rate of each mixture was determined after aeration periods of 3 hours.

The test item showed 4.3 % respiration inhibition of activated sludge at a test item concentration of 1000 mg/L.

The effect value related to nominal concentration of the aqueous solution, since no analytical monitoring was performed (Neuhahn, 2008). As a worst case the effect concentration might be converted based upon the water content of the test item, resulting in an EC10 and EC50 of 504 mg/L for the anhydrous substance.

2-phophonobutane-1,2,4-tricarboxylic acid is regarded of low toxicity towards microorganisms.

Additional information

A conditional testing proposal according to REACH Annex IX, 9.1.6. ‘Long-term toxicity testing on fish, (unless already provided as part of Annex VIII requirements)’ is included in the dossier. The Fish Early Life Stage (FELS) toxicity test (OECD TG 210) is regarded as the most suitable test guideline for addressing the information requirements  is included in the dossier based on BoA decisions A-010-2018 and A-011-2018.


As the BoA decision A-010-2018 is currently being challenged before the General Court (T-656/20), we respectfully request ECHA to suspend any decision on the testing proposal and to first await the decision of the General Court in the aforementioned case. Vertebrate studies should always be the last resort to generate information.