[nitrilotris(methylene)]trisphosphonic acid, ammonium salt

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: The study was conducted according to an appropriate OECD test guideline and in compliance with GLP.

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 E (Ready biodegradability: Modified OECD Screening Test)

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Activated sludge from HRC sewage treatment plant. The nature of the influent to this treatment plant is not known. Filtered through Whatman No. 1 paper (first 200 ml discarded).

- Storage conditions: Filtrate kept aerated until used

Duration of test (contact time):

28 d

Details on study design:

TEST CONDITIONS
- Composition of medium: The carbon content of each sample was calculated from the empirical formula and sufficient added to 2 litre medium to give a nominal carbon content of 40 mg/l. The solution was then spli into two 1 litre replicates and inoculated. Inoculum usage rate: 0.5 ml/l

- Test temperature: 22 °C nominal. Temperatures were recorded daily and evaporative losses made up with distilled water.

- Continuous darkness: yes



TEST SYSTEM
- Culturing apparatus: 1 litre glass beakers. Agitation; by magnetic stirrer. Colling; by cold finger condenser.


SAMPLING
- Sampling frequency: 0, 7, 14, 21, 27, 28 d.

- Sampling method: Samples (25-30 ml) were withdrawn from each test vessel and filtered through millipore GS 0.22 µm disposable filters, discarding the first 15-20 ml. The 10 ml samples were stored frozen if not analysed imediately.

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (DOC removal)

Value:

0

Sampling time:

28 d

Table 1: Dissolved organic carbon levels (mg/l) and calculated % bioelimination

Type of suspension		Day 0	Day 7	Day 14	Day 21	Day 27	Day 28
Test Sample	DOC (mg/l)	44	44	42	45	52	51
Test Sample	Bioelimination (%)	-	0	5	0	0	0
Reference substance	DOC (mg/l)	33	7	5	1	2	1
Reference substance	Bioelimination (%)	-	79	85	97	94	97

Conclusions:

A ready biodegradation rate of 0% in 28d was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Please refer to Annex 3 of the CSR and IUCLID Section 13 for justification of read-across within the ATMP category.

Reason / purpose for cross-reference:

read-across source

Parameter:

% degradation (DOC removal)

Value:

0

Sampling time:

28 d

Identification of degradation products:

The registrants consider that the possible benefits to the CSA of conducting further studies of the formation of degradation products are not significant in comparison with the foreseeable difficulties to conduct and interpret the study.

Isolating and identifying degradation products presents a significant analytical challenge. There is substantial evidence across most types of phosphonates of rapid and irreversible binding to solids, particularly inorganic substrates (please refer to Section 4.2.1 of the CSR). It is difficult to envisage an analytical system suitable for extracting and analysing the substances which could not be affected by this. Secondly, the relevance of the data must be considered. Whilst there is limited degradation in the environment, it is not extensive or rapid under standard conditions. Removal processes from natural waters are attributed to the typically rapid, irreversible adsorption to solid matrices. As such the chemical safety assessment for the environment focuses on the parent substance. There are no unacceptable risks (please refer to CSR Chapter 10). The substance is not classified for environmental hazard, and is not PBT or vPvB. The organophosphonate impurities are predicted to have the same properties as DTPMP and not be of higher toxicity. Inorganic impurities present are not biodegradable.

Description of key information

ATMP and its salts are not readily biodegradable, based on 0 - 23% degradation in 28 days in reliable ready biodegradability studies.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Additional information

A reliable ready biodegradability study is available (OECD 301E, Douglas and Pell 1984), indicating 0% biodegradation of ATMP-xNa in 28 days based on DOC removal. This study is reliability 1 and is selected as the key study.

A second reliable ready biodegradability study (reliability 2) using pre-adapted inoculum (OECD 301D, Cremers and Hamwijk, 2006) indicated 22 -23% biodegradation of ATMP-H in 28 days based on O2 consumption. (Note: This is a standard study with some acceptable deviations: pre-adapted inoculum was used and inorganic phosphate was omitted from the nutrient medium. In addition, solutions of test substance stock solution were made in natural seawater).

 

A reliability 2 SCAS test study is also available for ATMP-H (Saeger et al. 1978). However, SCAS tests are generally considered less reliable than ready biodegradability tests. No statistically significant degradation was observed.

 

In a modified SCAS test, 15-35% degradation was observed after 126 days and ca. 5% degradation was observed after 28 days in a modified OECD ready screening test, reported in the same study (Horstmann and Grohmann, 1988). The results are variable, but were determined to be reliable and indicate that ATMP-H is not readily biodegradable (reliability 2).

A reliable anaerobic biodegradability study (Zeneca Brixham Environmental Laboratory, 1995) indicated a biodegradation rate of 0 - 21% in 56d for ATMP-H.

 

Furthermore, the results of three biodegradability in seawater studies conducted with ATMP-H (Drake, 2005, Rowlands, 2005 and Hamwijk and Cremers, 2005) (refer to IUCLID Section 5.2.2) support the conclusion that the substance is not expected to be readily biodegradable.

An OECD 306 study is available for ATMP-xNa, which reports 8% and 11% degradation in 28 days based on oxygen consumption relative to theoretical and chemical oxygen demand, respectively (Muttzall and Hanstveit, 1996, see IUCLID section 5.2.2). 56-day degradation values of 18 and 23% degradation based on oxygen consumption relative to theoretical and chemical oxygen demand, respectively (reliability 1).

The ammonium ion upon release into the environment would enter natural nitrogen cycles in air, soil and water.

The acid, sodium, potassium and ammonium salts in the ATMP category are freely soluble in water. The ATMP anion can be considered fully dissociated from its sodium, potassium or ammonium cations when in dilute solution. Under any given conditions, the degree of ionisation of the ATMP species is determined by the pH of the solution. At a specific pH, the degree of ionisation is the same regardless of whether the starting material was ATMP-H, ATMP.4Na, ATMP.7K or another salt of ATMP.

 

Therefore, when a salt of ATMP is introduced into test media or the environment, the following is present (separately):

1. ATMP is present as ATMP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the media and not whether ATMP (3-5K) salt, ATMP (3-5Na) salt, ATMP-H (acid form), or another salt was used for dosing.
2. Disassociated potassium, sodium or ammonium cations. The amount of potassium or sodium present depends on which salt was dosed.
3. It should also be noted that divalent and trivalent cations would preferentially replace the sodium or potassium ions. These would include calcium (Ca²⁺), magnesium (Mg²⁺) and iron (Fe³⁺). These cations are more strongly bound by ATMP than potassium, sodium and ammonium. This could result in ATMP-dication (e.g. ATMP-Ca, ATMP-Mg) and ATMP-trication (e.g. ATMP-Fe) complexes being present in solution.

In this context, for the purpose of this assessment, read-across of data within the ATMP Category is considered to be valid.