Trisodium nitrilotriacetate

Endpoint summary

Additional information

In Annex X of Regulation (EC) No 1907/2006, it is stated that long-term toxicity to terrestrial organisms shall be proposed by the registrant if the chemical safety assessment indicates the need to investigate further the effects of the substance and/or relevant degradation products on terrestrial organisms. Column 2 of Annex X states that studies do not need to be conducted if direct and indirect exposure of the soil compartment is unlikely. There are no ecotoxicity studies for terrestrial organisms relating to trisodium nitrilotriacetate (Na₃NTA) and the requirement for terrestrial data is waived based on the low adsorption, low bioaccumulation potential, very low toxicity to aquatic organisms (extrapolated to terrestrial organisms), ready biodegradability and unlikely exposure to Na₃NTA in soil.

 

Adsorption

It is not expected thatNa₃NTA will adsorb onto the organic fraction of soils, sediments or suspended solids, due to the ionic structure of the substance though interaction with the mineral phase may occur. This assumption is supported by the studies conducted by Dunlapet al.,(1971) and Boltonet al.,(1993) who demonstrated that Na₃NTA is neither strongly adsorbed by loam, clay-loam and sandy soils or marine surface sediments (Kp sediment-water = 1.6 L/kg). In addition, Na₃NTA is a highly water-soluble organic substance with an aqueous solubility of 457 g/L.

Bioaccumulation

The partitioning behaviour of Na₃NTA was estimated using the speciation model ChemEQL based on the assumption that Na₃NTA completely dissociates upon dissolution in water and that the presence of the sodium ions does not appreciably influence the equilibrium behaviour of NTA. It was determined that the partitioning behaviour of Na₃NTA is pH-dependent and the estimated Log Kow for the different NTA species is highest at pH 1.4, with a value of -4.14; at pH 7, the log Kow reduces to -13.2. At pH 14, the estimated log Kow is -31.2. The substance’s high hydrophilicity is demonstrated by the very low log octanol-water partition coefficient (Log Kow) of -13.2 at a neutral pH. These low distribution coefficients and Log Kow indicate the substance has a low adsorptive and bioaccumulative potential.

 

Biodegradability

Evidence for ready and inherent biodegradability is also provided; reliable tests resulted in 75 -100 % degradation after lag phases ranging between 1 and 16 days and the substance is regarded as readily biodegradable. The Canadian Ministry of the Environment (CCME, 2010) provides additional evidence of the rapid degradation of NTA and products where it was reported that NTA is readily biodegraded in all environmental compartments even at low environmental temperatures. Therefore, biodegradation can be considered to be an important removal process of NTA in soil, sediment, surface water, and water treatment plants.

 

Toxicity

Furthermore, it is reasonable to assume that trends seen in aquatic toxicity are likely to be observed in terrestrial organisms. Reliable toxicity data are available for freshwater species representing fish, invertebrates and a mollusc. Short-term (acute) exposures of Na₃NTA to fish ranged from 103 to 125 mg/L and invertebrate data ranged from 80 to 115 mg/L. All trophic levels of aquatic organisms revealed similar sensitivities to Na₃NTA. Long-term exposures to invertebrates and fish were reported as NOECs of 9.3 and >54 mg/L, respectively. These short- and long-term data, when considered with bioaccumulative and degradation information, result in Na₃NTA being non-classified and considered to be practically non-toxic to aquatic organisms. It is reasonable to assume that Na₃NTA will also be non-toxic to soil organisms.

Exposure

There are no identified uses of the substance which involve direct application to soil. The CSR uses default environmental release fractions in accordance with technical guidance for CSR preparation.  Release of the substance to soil as a result of application of Na₃NTA in any of the identified uses is not intentional; the fraction release to soil is therefore a worst case scenario and can be considered very conservative.  Moreover, due to the high solubility, ready biodegradability and low octanol-water partition coefficient of Na₃NTA, this substance will not sorb to or persist in aerobic soils when used as directed under environmental conditions.  The environmental concentrations of Na₃NTA in soil predicted by EUSES2.1 may therefore be considered conservative because (i) default release factors to soil are higher than expected for identified uses and (ii) environmental fate and partitioning will tend to over-predict concentration in soil.

The regional and highest local PEC for soil are 0.000474 mg.kg dw^-1(industrial) and 0.06 mg/kg wwt^-1(manufacture), respectively.  Accordingly, exposure to soils, as predicted by EUSES with conservative release and distribution assumptions, is considered de minimis, and no further data is required.

 

In summary, based on the evidence of low adsorption, low bioaccumulative potential, very low toxicity to aquatic organisms (extrapolated to terrestrial organisms), ready biodegradability and no potential for exposure, the requirement for terrestrial data is waived.