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

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

REPORTING FORMAT FOR THE ANALOGUE APPROACH
The category hypothesis is that all the members are various ionised forms of the same parent acid. This category covers various sodium and sodium/calcium salts of ethylene diamine tetra(methylene phosphonic acid). The different salts are prepared by neutralising the acid to a specific pH and accordingly the constituents proportions and degree of ionisation are comparable between substances under similar conditions (in vivo and in the environment). All category members are based on the EDTMP structure. Data are available for the acid form and some salts. EDTMP category members are marketed as neutralized and acid aqueous solutions, and the acid is available as a solid. The properties of the members of the category are consistent across all endpoints.

Contributing effect of counter-ions
The approach assumes in general that alkaline and alkaline earth metal (sodium and calcium) counter-ions are not significant in respect of all the properties under consideration.
In an environmental context, the speciation will be controlled by the prevailing conditions and ions present, and will be the same regardless of the starting form. In dilute aqueous conditions of defined pH and mineral composition, a salt or complex introduced into this medium will behave no differently to the parent acid, at identical concentration of the particular speciated form present and will be fully dissociated. Hence some properties (measured or expressed in aqueous media, e.g. ecotoxicity) for a salt can be directly read-across (with suitable mass correction) to the parent acid and vice versa, and from one salt to another.
Where data are available across different salt forms of EDTMP, this approach is supported.

Reason / purpose for cross-reference:

read-across source

Parameter:

% degradation (DOC removal)

Value:

0

Sampling time:

21 d

Reference 2

Endpoint:

biodegradation in water: inherent biodegradability

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

EU Method C.12 (Biodegradation: Modified SCAS Test)

GLP compliance:

no

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Duration of test (contact time):

220 d

Details on study design:

TEST DETAILS: Mixed liquor was taken (activated sludge and supernatant) from a domestic STP at  a nominal suspended solid concentration of 2500 mg/l. At the beginning of each cycle (24 hours per day, 72 hours at the weekend), 5 mg of radiolabelled Dequest 2041 (equivalent to 2.5 mg active acid) in 2 ml water was added to the mixed liquor along with synthetic sewage sludge. Aeration was maintained until the end of each cycle, at which time the sludge was settled and 1 litre of supernatant liquid removed. The cycle was then re-initiated by  the addition of tap water, sewage and a further aliquot of test material solution. The pH and settled sludge volume were monitored for each cycle and the suspended solids concentration weekly. Testing was carried out over a 7-month period.

Reference substance:

not required

Parameter:

% degradation (radiochem. meas.)

Remarks:

(mean value)

Value:

1.85

Sampling time:

24 h

Remarks on result:

other: ± 0.98 % (95% confidence limits). Results for 24h cycle

Parameter:

% degradation (radiochem. meas.)

Remarks:

(mean value)

Value:

6.67

Sampling time:

72 h

Remarks on result:

other: ± 1.83 % (95% confidence limits). for 72-hour cycle.

Details on results:

The length of time the SCAS unit was acclimated to the test material had no significant effect on the observed degradation rates. A higher percent degradation would typically be observed over the longer time cycle.

Interpretation of results:

not inherently biodegradable

Conclusions:

The inherent biodegradability of the test substance was examined in a reliable SCAS test. The results suggest that significant removal of Dequest 2041 by biodegradation is not to be expected in a secondary sewage treatment plant.

Reference 3

Endpoint:

biodegradation in water: screening tests

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The study was conducted according to a test protocol that is comparable to the appropriate OECD test guideline/EU test method. It was not compliant with GLP.

Qualifier:

equivalent or similar to guideline

Guideline:

other: OECD Modified Screening (ready test); modified SCAS (inherent test)

GLP compliance:

not specified

Inoculum or test system:

activated sludge, non-adapted

Duration of test (contact time):

ca. 140 d

Value:

75 - 90

Sampling time:

126 d

Remarks on result:

other: SCAS test.

Value:

ca. 5 - ca. 10

Sampling time:

28 d

Remarks on result:

other: ready test. Removal level taken from graph

Details on results:

High degrees of variation are seen in the DOC removals throughout the duration of the test, for all phosphonates. This is ascribed to removal by adsorption mechanisms.

The kinetics seen in the ready test are unusual with apparently declining DOC-elimination (from ca +5% DOC elimination at day 7 to ca -30% DOC elimination late in the test) implying increasing DOC concentrations throughout most of the duration of the test. This finding is not discussed and given that EDTMP is soluble in aqueous media at the concentrations used, and given that the text states that the EDTMP test media were confirmed to be pH-neutral, the finding is not easily explicable.

Conclusions:

Biodegradability in ready and inherent test conditions was tested in a reliable study conducted according to appropriate test protocols. The results are variable but indicate that the phosphonates are not readily biodegradable.

Reference 4

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2010

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Guideline study but without GLP.

Qualifier:

equivalent or similar to guideline

Guideline:

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

Qualifier:

according to guideline

Guideline:

ISO DIS 9408 (Ultimate Aerobic Biodegradability - Method by Determining the Oxygen Demand in a Closed Respirometer)

GLP compliance:

no

Remarks:

The study was not conducted for REACH compliance purposes.

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

- Source of inoculum: activated sludge from Cottbus treatment plant

Duration of test (contact time):

28 d

Initial conc.:

80 mg/L

Parameter followed for biodegradation estimation:

O2 consumption

Reference substance:

acetic acid, sodium salt

Parameter:

% degradation (O2 consumption)

Remarks:

28 day BOD to COD ratio

Value:

ca. 30

Sampling time:

28 d

Results with reference substance:

Na Acetate used; results not stated

The test results have been proved by analyzing the production of inorganic phosphate and ammonia.

About 50% of the phosphorus was split off during the biodegradation process. The elimination of ammonia for EDTMP was 50%.

From the results the study authors concluded that the primary attack occurred always in the P-N region of the molecules resulting in the cleavage of 2 phosphate groups each. Thereafter, ammonia can be eliminated also, but with lower efficiency. However, it seems that only one carbon atom is eliminated. A further degradation of the remaining intermediates has not been observed. This implies that the remaining intermediates are persistent, at least under aerobic conditions.

Interpretation of results:

other: not readily biodegradable

Reference 5

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

1984

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

The study was conducted according to the appropriate OECD test guideline, and in compliance with GLP.

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, 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

Initial conc.:

40 other: mg C/l

Based on:

DOC

Parameter followed for biodegradation estimation:

DOC removal

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (DOC removal)

Value:

0

Sampling time:

21 d

Remarks on result:

other: Data for days 27-28 of the test period were not recorded due to contamination by a broken pipe.

Details on results:

Briquest 422-25S attained 0% degradation after 21 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%

Validity criteria fulfilled:

yes

Interpretation of results:

under test conditions no biodegradation observed

Description of key information

EDTMP acid and its salts are considered not readily biodegradable and not inherently biodegradable. Low but recordable levels of biodegradation were seen in two ready and two inherent tests. A high degree (75-90%) of removal was recorded in the longer term (extended SCAS test over 126 days; Horstmann and Grohmann, 1988).

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

Two reliable tests of ready biodegradation (similar to modified OECD screening test method) and two reliable tests of inherent biodegradation (semi-continuous activated sludge) are available for EDTMP-H. All available results are consistent with very low levels of biodegradation in the short term (28-day) time window. The levels of removal observed were ca. 30% in 28 d (Martienssen, 2010, modified OECD test of ready biodegradation); ca. 5 to ca. 10% in 28 d (Horstmann and Grohmann, 1988, modified OECD test of ready biodegradation), 1.85 and 6.67% in 24-h and 72-h cycles respectively in a 220-day test (Saeger, 1978, extended SCAS test) and 75-90% in 126 d (Horstmann and Grohmann, 1988, extended SCAS test).

One reliable test of ready biodegradation is available for EDTMP-xNa. This showed 0% biodegradation in 28 d (OECD 301E; Huntingdon Research Centre, 1984). The conclusion may be validly read across to EDTMP-H within the EDTMP Category.