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Sediment toxicity

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Description of key information

Na3NTA is readily biodegradable within the STP process. Furthermore, Na3NTA is expected not to accumulate relevantly in sediment, even when emitted directly to surface water. Therefore, Na3NTA poses no hazard to sediment-dwelling organisms, and sediment-dwelling organisms will not be exposed to Na3NTA, regardless of its use. In accordance with column 2 of REACH Annex X, testing does not need to be conducted.

Key value for chemical safety assessment

Additional information

In Annex X of Regulation (EC) No 1907/2006, it is stated that long-term toxicity to sediment 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 sediment organisms. Column 2 of Annex X states that studies do not need to be conducted if direct and indirect exposure of the sediment compartment is unlikely. There are no reliable ecotoxicity studies for sediment organisms relating to trisodium nitrilotriacetate (Na3NTA)and the requirement for sediment data is waived based on the low adsorption, low bioaccumulation potential, very low toxicity to aquatic organisms (extrapolated to sediment organisms), ready biodegradability and unlikely exposure to Na3NTA in sediment.

Adsorption

It is not expected that Na3NTA will adsorb onto the organic fraction of soils, sediments or suspended solids due to the ionic structure of the substance. However, interaction with the mineral phase may be possible. This assumption is supported by the studies conducted by Dunlapet al.,(1971) andBolton et al.,(1993)who demonstrated thatNa3NTAis 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.

There are no identified uses of the substance which involve direct application to sediment. Indirect exposure of sediment organisms, for example via sewage sludge disposal to land or release of residual quantities of dilute Na3NTA to sediment, is unlikely as the substance is readily biodegradable and has a very low sorption potential.

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 sediment organisms.

Exposure

There are no identified uses of the substance which involve direct application to sediment. The CSR uses default environmental release fractions in accordance with technical guidance for CSR preparation.  Release of the substance to sediment as a result of application of Na3NTA in any of the identified uses is not intentional; the fraction release to sediment 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 sediment when used as directed under environmental conditions.  The environmental concentrations of Na3NTA in freshwater and marine sediments predicted by EUSES2.1 may therefore be considered conservative because (i) default release factors to sediment are higher than expected for identified uses and (ii) environmental fate and partitioning will tend to over-predict concentration in sediment.

The highest local PEC for freshwater sediment and marine sediment is 0.59 mg/kg wwt-1(manufacture) and 0.059 mg/kg wwt-1(manufacture), respectively. Accordingly, exposure to sediments, 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 sediment organisms) and ready biodegradability, no tests on sediment organisms are required.