Sodium salts of [[(phosphonomethyl)imino]bis[ethane-2,1-diylnitrilobis(methylene)]]tetrakisphosphonic acid (5-7 Na:1)

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

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:

test procedure in accordance with national standard methods

Remarks:

Study was conducted in accordance with a recognized scientific procedure for determining biodegradability. Study was conducted in compliance with GLP. The study meets national and international scientific methods and provides sufficient information to support the conclusion.

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, non-adapted

Details on inoculum:

 Activated sludge from the HRC sewage treatment plant. The nature of the influent to this treatment plant is not known. The activated sludge was filtered through Whatman No 1 paper (first 200 ml discarded) and the filtrate was kept aerated until used. 

Duration of test (contact time):

28 d

Parameter followed for biodegradation estimation:

DOC removal

Details on study design:

The carbon content of the test substance was calculated from the empirical formula and sufficient added to 2 litres of culture medium to give a nominal carbon content of 40 mg C/l. The solution was then split into two 1 litre replicates and inoculated with activated sludge at a rate of 0.5 ml/l. Duplicate negative controls were also prepared. The test was conducted in  darkness. Vessels were stirred using a magnetic stirrer. The test solutions were maintained at a nominal temperature of 22 °C, with cooling by cold-finger condenser. Evaporative losses were made up with distilled water.  Samples were taken for analysis on days 0, 7, 14, 21, 27 and 28.  

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (DOC removal)

Value:

0

Sampling time:

28 d

Details on results:

The test substance attained 0% degradation after 28 days and was not considered readily biodegradable under OECD Guideline No. 301-E. The control substance attained 85% degradation after 14 days and 97% after 28 days, confirming suitability of the inoculum and culture conditions. Degradation products: no

Results with reference substance:

Day 7: 79%
Day 14: 85%
Day 28: 97%

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

The test substance achieve 0% biodegradation in 28 days using a relevant test method. The result is considered to be reliable.

Description of key information

The substance is not readily or inherently biodegradable, based on several reliable studies (0% biodegradation in 28 days)

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

A reliable ready biodegradability study is available using DTPMP(5-7Na) (OECD 301E, Huntingdon, 1984), indicating 0% biodegradation in 28 days based on DOC removal. This study is assigned as the key study because it represents the lowest observed biodegradation value across the available data.

A second reliable ready biodegradability study using pre-adapted inoculum (OECD 301D, TNO, 2006, using DTPMP-xNa) indicated 7% biodegradation 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 reliable inherent biodegradation test study using DTPMP(1-3Na) (Safepharm 1999) indicated 0% biodegradation in 28 days.

A reliable SCAS test using DTPMP-H (Saeger, 1978) indicated 3.5% biodegradation in a 24 h cycle.

A reliable anaerobic biodegradability study using DTPMP(1-3Na) (Zeneca, 1995) indicated 6 - 8% biodegradation in 56 days.

Furthermore, the results of a reliable biodegradability in seawater study using DTPMP(5-7Na) (TNO, 1996) (refer to IUCLID Section 5.2.2) supports the conclusion that the substance is not expected to be readily biodegradable.

The acid and salts in the DTPMP category are freely soluble in water and, therefore, the DTPMP anion is fully dissociated from its cations when in solution. Under any given conditions, the degree of ionisation of the DTPMP 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 DTPMP-H, DTPMP (1-3Na), DTPMP (5-7Na), DTPMP-xK, DTPMP (xNH4) or another salt of DTPMP.

 

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

1. DTPMP is present as DTPMP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the media and not whether DTPMP-H, DTPMP (1-3Na), DTPMP (5-7Na), DTPMP-xK, DTPMP (xNH4), or another salt was used for testing.

2. Disassociated ammonium, potassium or sodium cations. The amount of ammonium, potassium or sodium present depends on which salt was added.

3. Divalent and trivalent cations have much higher stability constants for binding with DTPMP than the sodium, potassium or ammonium ions so would preferentially replace them. These ions include calcium (Ca²⁺), magnesium (Mg²⁺) and iron (Fe³⁺). Therefore, the presence of these in the environment or in biological fluids or from dietary sources would result in the formation of DTPMP-dication (e.g. DTPMP-Ca, DTPMP-Mg) and DTPMP-trication (e.g. DTPMP-Fe) complexes in solution, irrespective of the starting substance/test material.