[ethane-1,2-diylbis[nitrilobis(methylene)]]tetrakisphosphonic acid

Endpoint summary

Additional information

In the natural environment the fate and behaviour of EDTMP and its ions are dominated by abiotic dissociation / complexing, irreversible adsorption to surfaces, and less by degradation processes. The most important properties are summarised below.

While some biodegradation has been observed, the results for EDTMP acid and its salts do not show significant biodegradation in the short term, and they are not readily or inherently biodegradable, based on several reliable studies (OECD 301E, Huntingdon Research Centre, 1984; SCAS test, Saeger, 1978; anaerobic screening test, Saeger, 1978; Modified Screening (ready test) and modified SCAS (inherent test), Horstmann and Grohmann (1988); for further details, please refer to IUCLID Section 5.2). However, photodegradation in the presence of common metal ions has been observed (Lesueur et al., 2005, Brandenburg University of Technology, 2010, and Saeger, 1979a; for further details, please refer to Section 5.1). Based on evidence from the data summarised in this section, members of this group are considered to be partially degradable over short time periods, and with evidence of mineralisation, particularly in the light, over longer periods. Oxidation may also play a role in the longer term environmental fate of EDTMP, based on evidence of oxidation of structurally analogous phosphonates in the form of manganese complexes (Nowack and Stone, 2003).

Removal from the aqueous phase occurs principally by irreversible adsorption to substrates present (minerals), and to a lesser extent removal by photodegradation, oxidation in the presence of iron(III) and limited biodegradation. The significant role of adsorption is discussed later in this section with relevant data across the analogue group presented in Section 5.4. For EDTMP Ksolids-water (sediment) up to 1500 l/kg (soft water), up to 1900 l/kg (hard water) is available. The degradation processes operate most rapidly in combination as abiotic breakdown products are more susceptible to biodegradation than the starting material. Bioavailability from solution is extremely low due to the highly unfavourable hydrophilicity (reliable measured BCF <100, supported by log Kow<-4 under environmental conditions).

In soil and sediments, removal is expected to occur by the same partitioning mechanisms. Bioavailability from interstitial water present in soils and sediments is extremely low due to both the very strong adsorption and unfavourable bioconcentration properties, even if the phosphonate were to be ingested in an adsorbed state in the soil or sediment constituents.

The properties of EDTMP and its salts are profoundly affected by their ionisation behaviour.

EDTMP can ionise by loss of a hydrogen ion up to eight times and protonation of the amines up to two times. As a consequence it is a strong complexing agent, and is highly hydrophilic. Because ionisation is a rapid and reversible process, salts such as sodium salts will dissolve readily in water to give a speciation state dictated by the pH of the medium.

The available weight of evidence shows that removal from solution to a non-bioavailable bound form, and abiotic mechanisms, are important in the environmental exposure and risk assessment. Specific deficiencies in the available studies of biodegradability are not significant compared to the other fate and distribution mechanisms.