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Environmental fate & pathways

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Additional information

Stability of Na3NTA the environment:

No data are available for trisodium nitrilotriacetate (Na3NTA) with regard to the endpoints phototransformation in air, water, and soil, and hydrolysis.

In accordance with Annex X of the Regulation (EC) No 1907/2006 REACH concerning the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), information regarding phototransformation in air, as well as in water and soil, is not mandatory.

In Annex VIII column 2 of the REACH Regulation, it is suggested, that a study on the "Hydrolysis as function of pH" does not need to be conducted if the "substance is readily biodegradable". Therefore, a study on the "Hydrolysis as function of pH" does not have to be conducted for trisodium nitrilotriacetate.

 

Biodegradation of Na3NTA:

Trisodium nitrilotriacetate was tested for ready biodegradability according to OECD 301 E (BASF, 1983b,c), OECD 301 F (in addition to a combined CO2/DOC test, see Strotmann et al., 1995), and Sturm Test (BASF, 1983d), and in a die away test (Takahashi et al, 1997) as well as for inherent biodegradability according to OECD 302 B (BASF, 1983a). These tests resulted in 75 -100 % degradation after 7 to 28 days with lag phases ranging between 1 and 16 days. According to results from ready biodegradation tests, Na3NTA can be regarded as readily biodegradable. 

Based on reliable results from simulation tests it was demonstrated that Na3NTA is readily degraded under aerobic conditions in fresh waters (Larson & Davidson, 1982; Shannon et al., 1974) and freshwater sediments (McFeters et al., 1990). Biodegradation is enhanced by increased temperature, although was still found to occur even at low temperatures, albeit at a slower rate (Shannon et al., 1974). Acclimation of bacteria to Na3NTA was demonstrated even at low test concentrations. In saline/estuarine conditions, Na3NTA degradation was found to be rapid over a range of salinities (up to 19%, see Larson & Ventullo, 1986), however the rate of Na3NTA removal decreases at higher salinities and the effect of high salinity was found to be compounded under high Na3NTA dose conditions (Hunter et al., 1986). This suggests that the role of microbes in degradation of Na3NTA may be limited in marine conditions if initial doses are high; dilution and other degradation processes may be dominant in the marine system. Data relating to anaerobic sediments is limited, however Na3NTA was shown to be degraded in anaerobic sludges and waterlogged soils (Tabatabei & Bremner, 1975), which have been acclimatised, as such this is considered to be an important factor. Na3NTA degradation rates in aerobic sludge are found to be reduced at low temperature; demonstrated in field rather than laboratory conditions.

Microbial degradation of Na3NTA leads to intermediates such as iminodiacetate (IDA), glyoxylate, glycine and ammonia, with final metabolic end products including ammonia, nitrates, and carbon dioxide (Egli, 1992).

Study results for biodegradation in soil indicate that Na3NTA is readily decomposed by soil microorganisms under aerobic conditions in previously adapted soils (Tabatabei & Bremner, 1975; Dunlap et al., 1971; Tiedje & Mason, 1974; Shimp et al., 1994), but may be limited under anaerobic conditions (Dunlap et al., 1971) and in unadapted soils. Analogue to biodegradation in surface waters, iminodiacetate is a possible degradation intermediate of Na3NTA soil biodegradation (Tiedje & Mason, 1974). Biodegradation rates of the test substance did not correlate with pH, drainage, texture, or plant cover (Tiedje & Mason, 1974). Na3NTA was found to be degraded also at low temperatures (2 °C) in previously acclimatized soils. At room temperature degradation rates were highest in soils receiving sewage effluent and in muck soils (Tiedje & Mason, 1974) as well as in soil and sediment samples taken near tile fields (half-lives: ≥ 1 – 3.5 days), while reduced biodegradation rates in mineral surface soils ranging from 4.6 to 55.5 days could be observed. Therefore, it can be assumed that adaption is a key process in Na3NTA biodegradation (Shimp et al., 1994).

The reported results demonstrate that Na3NTA is readily biodegraded in all environmental compartments even at low environmental temperatures. Therefore, biodegradation can be considered to be an important removal process of Na3NTA in soil, sediment, surface water, and treatment plants.

 

Bioaccumulation of Na3NTA:

In accordance with column 2 of REACH Annex IX, trisodium nitrilotriacetate (Na3NTA) has a log octanol-water partition coefficient of -13.2 at pH 7, is highly water-soluble, and is unlikely, due to its polar nature, to be taken up by fish gills or across other biological membranes. Therefore, there is no need to newly perform a (fish) bioaccumulation study according to current guidelines, especially as secondary references are available which indicate that only a low accumulation of NTA occurs in the hydrosphere.

 

Transport and distribution of Na3NTA:

Due to the ionic structure of the substance a relevant adsorption of trisodium nitrilotriacetate (Na3NTA) onto the oragnic fraction of soils, sediments or suspended solids is not expected. However, interaction with the mineral phase may be possible. This assumption is in line with available study results (Dunlap et al., 1971; Bolton et al., 1993) which demonstrate that Na3NTA is neither strongly sorbed by loam, clay-loam and sand soils or marine surface sediments (Kp sediment-water = 1.6 l/kg).

Sorption of Na3NTA to soil particles does not appear to be sufficient to reduce the movement of the substance through the soil column. However, by retarding this movement the residence time in regions with high microbial activity can be increased. Therefore, sorption may play a secondary role in the removal of Na3NTA from infiltrating waters by microbial degradation (Dunlap et al., 1971).

 

Environmental data of Na3NTA:

Monitoring data are available for primary effluents of the Glatt sewage treatment plant near Zürich (Alder et al., 1990). The influent concentration of Na3NTA ranged between 300 and 1500 µg/l. In summer as well in winter the substance was biologically degraded up to 97%.

In a field study (Shannon et al. 1974) the degradation of Na3NTA in the natural river environment downstream of a wastewater treatment was assessed in winter and summer. Removal of the substance by the treatment works was > 95 % at 13 - 14 ºC (aeration tank temperature) compared to < 45 % at 10 ºC. There was evidence of in-stream biodegradation even at the lower temperatures. 

From these studies it can be concluded that Na3NTA is removed in municipal treatment plants with rates generally above 95% under normal operation conditions, having in mind that in harsh winters the NTA releases can be increased. 

 

Additional information on Na3NTA – laboratory/pilot scale activated sludge units

The available studies demonstrate that Na3NTA is substantially complete biodegraded after acclimation (Stephenson et al., 1983a) and can serve as serve as the sole source of organic carbon for activated sludge (Swisher et al., 1967). Even at levels from 20 to 500 mg/l no upsets of normal functioning of the sludge units could be observed (Swisher et al., 1967).

Besides, Na3NTA can be degraded under anaerobic conditions with sludge previously aerobically acclimatised to the substance (Moore & Barth, 1976).

The removal rate can be affected at decreasing temperatures in combination with higher heavy metal concentrations typical for industrial sewage: the removal was 95.2 %, 92.9 %, and 79 % at 17.5 °C, 10 °C, and 6 °C, respectively (Stephenson et al., 1983b).

 

 

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