Tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate

Endpoint summary

Additional information

In cases where no data are available for the substance, tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate ("PBTCNa4"), results of the parent acid, 2-phosphonobutane-1,2,4-tricarboxylic acid ("PBTC"), are taken into account and a read-across approach is proposed with PBTC. 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 is justified.

 

(1) Stability

Hydrolysis

With regard to its chemical structure PBTCNa4 does not contain hydrolysable functional groups and is therefore not expected to hydrolyses under environmental conditions.

In line with this, no indication for a hydrolysis after 5 days at 50 °C can be found and no half-life times and hydrolysis rates were determined for PBTCNa4 (Holzaht-Grimme, 2021). 

 

Phototransformation in water

As there is no data on photodegradation available for PBTCNa4, results of the parent acid PBTC are taken into account for this endpoint. The results of modelling based on the irradiation of PBTC in buffer pH 9 and in presence of FeCl3 indicated that the mean photolysis half-life should range from 2-3 days in summer to 15-65 days in winter. The results of modelling based on the irradiation of PBTC in pure water and stored in brown glass prior to irradiation indicated that the mean photolysis half-lives should range from 0.2-0.3 days in summer to 1-10 days in winter.

 

(2) Biodegradation

Biodegradation in water

Follwing the EU Method C.4-B (Determination of the "Ready" Biodegradability - Modified OECD Screening Test) a degradation rate of 4 % within 28 days was determined for PBTCNa4, indicating that PBTCNa4 is "Not Readily Biodegradable". Inherent biodegradability of PBTCNa4 was assessed according to the OECD TG 203 B, showing 17% degradation after 28 days. Based on this result PBTCNa4 is considered to be not inherently biodegradable. Anaerobic biodegradation was determined with a method equivalent or similar to EPA OTS 796.3140 (Anaerobic Biodegradability of Organic Chemicals). As no degradation was observed within 56 days PBTCNa4 is regarded as not biodegradable under anaerobic conditions.

Biodegradation in water and sediment

Results of the parent acid, PBTC are taken into account for this endpoint, as no data are available for PBTCNa4. Opposed to OECD guideline 308, not a water-sediment system but the inocula gained from river water and river sediment were separately tested for their ability to degrade PBTC. The study has shown that biodegradation of PBTC in river water and river sediment under environmental conditions primarily depends on the presence of an alternative carbon source and could be optimized certain strains that can easily be enriched and isolated from these both compartments.

Biodegradation in soil

For PBTCNa4 no data on biodegradation in soil are available and results of the parent acid, PBTC are taken into account for this endpoint. The degradability of [3,4-14C]PBTC was investigated in three agricultural soils following the OECD guideline 304A. It was shown that PBTC is moderately degradable and is thoroughly metabolised to CO2 in soil. However, with a worst-case DT50 of 142 d the substance must be classified as persistant (P).

 

(3) Bioaccumulation

The QSAR determination of the logarithmic octanol-water partition coefficient for tetrasodium hydrogen 2-phosphonatobutane-1,2,4-tricarboxylate using the model KOWWIN included in the Estimation Program Interface (EPI) Suite v4.10 revealed a value of -5.45 of the dissociated form of the substance (Ranz, 2012).

Therefore, based on the physical-chemical properties for PBTCNa4 and its parent acid, PBTC, the substance is considered not likely to bioaccumulate.

 

(4) Transport and distribution

Adsorption / desorption

The QSAR determination of the carbon partition coefficient for PBTCNa4 using the model KOCWIN included in the Estimation Program Interface (EPI) Suite v4.10 revealed values of 0.001756 L/kg (logKow method) and 25.38 L/kg (MCI method). Both predicted values indicate no adsorption/desorption potential for PBTCNa4.

Henry's Law constant

The Henry's Law Constant (HLC) for PBTCNa4 was predicted using the QSAR calculation of the Estimation Program Interface (EPI) Suite v4.10. Based on the Bond contribution methodology the HLC was estimated to be 1.21E-21 Pa*m³/mol indicating that PBTCNa4 is essentially non-volatile from water.