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Environmental fate & pathways

Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: screening test, other
Remarks:
Identification of degradation products
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
In dilute aqueous conditions of defined pH, a salt 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. In the present context the effect of the counter-ion will not be significant.

In the environment, the salt form is immaterial and speciation will occur in natural media. Similarly for all environmental related endpoints, use of buffered test media results often reflect a salt speciation relevant for ~pH7 only and it would be impossible to test specific salts associated with high and low pH.

Detaching or attracting a proton does not change the chemical safety assessment of the molecule as long as no other part of the molecular skeleton is changed, because in studies or when there is exposure, the pH will control the identity of the form or forms present.

Almost all natural waters contain more ions than the usual PEC values of the phosphonates.
Reason / purpose:
read-across source
Parameter:
% degradation (DOC removal)
Value:
0
Sampling time:
28 d
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:
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.

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:
under test conditions no biodegradation observed

Additional information

A reliable ready biodegradability study is available (OECD 301E, Douglas and Pell 1984), indicating 0% biodegradation in 28 days based on DOC removal.

A second reliable ready biodegradability study using pre-adapted inoculum (OECD 301D, Cremers and Hamwijk, 2006) indicated 22 -23% 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 reliability 2 SCAS test study is also available (Saeger et al. 1978). However, SCAS tests are generally considered less reliable than ready biodegradability tests. No statistically significant degradation was observed.

A reliable anaerobic biodegradability study (Zeneca Brixham Environmental Laboratory, 1995) indicated a biodegradation rate of 0 - 21% in 28d.

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