(1-hydroxyethylidene)bisphosphonic acid, potassium salt

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: simulation testing on ultimate degradation in surface water

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

Please refer to Annex 3 of the CSR and IUCLID Section 13 for justification of read-across between members of the HEDP category.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

% Degr.:

5 - 10

Parameter:

radiochem. meas.

Sampling time:

42 d

Remarks on result:

other: Saeger 1979

Remarks:

natural water-sediment microcosms

% Degr.:

1.2

Parameter:

radiochem. meas.

Remarks:

14CO2 evolution

Sampling time:

38 d

Remarks on result:

other: Henkel 1979a

Remarks:

sewage treatment plant

% Degr.:

0.3

Parameter:

radiochem. meas.

Remarks:

14CO2 evolution

Sampling time:

14 wk

Remarks on result:

other: Henkel 1979b

Remarks:

sewage treatment plant

% Degr.:

3.5

Parameter:

radiochem. meas.

Remarks:

14CO2 evolution

Sampling time:

70 d

Remarks on result:

other: Henkel 1979c

Remarks:

surface water

Transformation products:

not specified

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 Category 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. This CSR discusses the environmental fate of HEDP and other analogous phosphonates. 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 HEDP and not be of higher toxicity. Inorganic impurities present are not biodegradable.

Reference 2

Endpoint:

biodegradation in water: sewage treatment simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The study was well documented and meets generally accepted scientific principles, but was not conducted in compliance with GLP.

Principles of method if other than guideline:

Method: other: Screening Test / radioactive substance

GLP compliance:

not specified

Oxygen conditions:

aerobic

Inoculum or test system:

other: sewage treatment plant effluent/biological stage

Initial conc.:

0.14 mg/L

% Degr.:

1.2

Parameter:

radiochem. meas.

Remarks:

14CO2 evolution

Sampling time:

38 d

Transformation products:

not measured

Nicht signifikant abbaubar

Conclusions:

other: poorly biodegradable under pertaining test conditions

Reference 3

Endpoint:

biodegradation in water: sewage treatment simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The study was well documented and meets generally accepted scientific principles, but was not conducted in compliance with GLP.

Principles of method if other than guideline:

other: 14C-sewage treatment plant simulation test

GLP compliance:

not specified

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic (adaptation not specified)

Initial conc.:

1.3 mg/L

Based on:

other: active substance

Parameter followed for biodegradation estimation:

radiochem. meas.

% Degr.:

0.3

Parameter:

radiochem. meas.

Remarks:

14CO2 evolution

Sampling time:

14 wk

Transformation products:

not measured

Conclusions:

poorly biodegradable under pertaining test conditions

Reference 4

Endpoint:

biodegradation in water: simulation testing on ultimate degradation in surface water

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The study was well documented and meets generally accepted scientific principles, but was not conducted in compliance with GLP.

Principles of method if other than guideline:

Method: other: Screening Test / radioactive substance

GLP compliance:

not specified

Oxygen conditions:

aerobic

Inoculum or test system:

other: adapted inoculum

Initial conc.:

0.3 mg/L

% Degr.:

3.5

Parameter:

radiochem. meas.

Remarks:

14CO2 evolution

Sampling time:

70 d

Transformation products:

not measured

Nicht signifikant abbaubar

Conclusions:

other: poorly biodegradable under pertaining test conditions

Reference 5

Endpoint:

biodegradation in water: sediment simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The study was well documented and meets generally accepted scientific principles, but was not conducted in compliance with GLP.

Principles of method if other than guideline:

Natural water - sediment microcosms. C14 labelled.

GLP compliance:

not specified

Oxygen conditions:

aerobic

Inoculum or test system:

natural water / sediment: freshwater

Details on study design:

Microcosms simulating a natural water environment were constructed using 10-gallon aquaria and a core-chamber technique. In the early phase of this study, water and sediment were collected from the littoral region of a spring fed freshwater lake (Lake 34). The sediment was screened through a steel screen (0.5 in mesh) to remove large particulates. 8 litres sediment; 22 litres water. Microcosms were allowed to stabilise for periods ranging fom one month to four months, with gentle aeration and a 16/8 hr light/dark cycle. Microcosms were allowed to stabilize for periods ranging from one to four months with gentle aeration and a 16/8 hour light/dark cycle using 300ft-candle Daylight fluorescent lamps. The pHs of the Lake 34 aquaria were in the 8.4 to 8.6 range with a conductivity of 420 to 460 µmhos. Dissolved oxygen levels were in the 6.5 to 7.5 range before coring.

At the end of stabilization period, core chambers were created by inserting sterile glass cylinders (3.8 x 30 cm) through the water column and sediment onto silicone stoppers. Each chanber contained 150 -175 ml water and 20 - 60 g sediment (dwt). Gas manifolds supplied either CO2 -free air or oxygen-free nitrogen about 5cm above the sediment surface. Gas flow in the Lake 34 microcosms were regulated by means of aquarium vales. Exhaust gas was passed through a resin trap to remove volatilised organics and then through a CO2 scubbing system containing 10ml of 2-methoxyethanol : monoethanolamine solution (7:1, V:V). The maintenance of sterile conditions was monitored using a 1ml water column sample and Millipore Total-Count water tester. Core chambers were removed from the aquaria, water and sediment were separately autoclaved and recombined. One ml of sodium azide aqueous solution (20 mg/ml) was then added.
C14 labelled test substance was added to each core chamber as an aqueous solution to achieve the desired concentration and activity. For the lake 34 microcosms, 1000 ppb concentrations were used. Samples of the water column were removed at day 0 and periodically thereafter and analyzed for C14 activity.
Ethanolamine traps were replaced according to the same schedule and the scrubber solutions were assayed for radioactivity. Tenax traps were removed at the end of each study and eluted with two 10ml portions of acetone. Eluates were assayed for radioactivity.

At the conclusion of each test, core chambers were removed from the aquaria. Teh water column remaining was carefully removed from each chamber and its volume determined. The sediment cores were transferred to tared evaporating dishes and the wet weight determined. The sediments were then air-dried. After determining the dry weight of each sediment, portions were subjected to extractive procedures or burned in an oxidiser to determine C14 activity.
15g dried sediment were extracted successively with 75ml and 50ml aliquots of of acidified acetone (5ml concentrated HCl per liter of acetone) using a homogenizer. Combined extracts were dried by passage through sodium chloride and anhydrous sodium sulfate and concentrated to 5ml in an evaporative concentrator. Portions of the extracts were then burned in an oxidiser to determine radioactivity.

C14 radioactivity analyses were carried out by liquid scintillation counting. Each sample was counted for three ten-minute cycles with a Liquid scintillation spectrometer using the preset isotope quench corrected program. C14 counting efficiencies were determined via the external standard pulse method using a certified set of 8 sealed quench standards. Correction for reagents of control blanks were made for all test samples.

For the water-column samples single one ml samples were added to 15ml of Packard insta-gel scintillation cocktail. 10ml of insta-gel was added to each ethanolamine scrubber prior to counting.
Sediment sampels were burned before and after extraction with an oxidiser. Triplicate 0.1g samples of each sediment were burned. The oxidiser samples were then counted in the manner previously described.

Acetone extracts of the sediments, because of their high quenching characteristics were assayed by burning 0.2ml of a 10:1 dilution of the concentrated extract.

Each aquaria had two controls with no test substance to monitor C14 activity. Single or duplicate cores were set up to monitor non-biological losses.

Key result

% Degr.:

5 - 10

Parameter:

radiochem. meas.

Sampling time:

42 d

Transformation products:

no

>90% decrease in water column C14 activity after 10d. >97% decrease was observed after 42 days (with the exception of 74% in the sterile, nitrogen purge, light condition). Microcosm variables: aeration vs nitrogen purge; light vs dark; active vs sterile, did not seem to significantly affect the rate of removal from the water column. This is indicative that a non-degradative mechanism dominates removal from water column. Autoclaving sodium azide treatment was not adequate for sterilisation.

In active, aerated systems, CO2 evolution ranged from 5 to 10%. In active nitrogen purged system, the CO2 evolution ranged from 3 to 5%. In sediment, C14 activity was not extracted to any significant degree with acidified acetone (unextracted and extracted had similar % of theory, and extract had low %). The percentage of C14 activity extracted varied from 0.5% to 2.2%. No significant C14 activity was found in the eluate from the Tenax resin traps, indicating that volatilised organics were not significant. The distribution of C14 activity after a 42 day study clearly demonstrated the majority of the C-14 activity was in the sediment, not in the water column.

Conclusions:

A degradation rate in a water-sediment microcosm of 5 - 10 % after 42 days (3 - 5% under anaerobic conditions) was determined in a reliable study conducted according to generally accepted scientific principles.

Description of key information

A number of simulation studies are available for HEDP-H and its salts and provide a consistent weight of evidence for a lack of significant biodegradation under STP and aquatic simulation conditions in the absence of other factors.

Although biodegradation in sediment has not been demonstrated for HEDP-H and its salts, the role of abiotic removal processes is significant. The key data for sediment adsorption are from the study with HEDP-H by Michael (1979) (refer to Section 5.4.1 for further information about this test). There is no evidence for desorption occurring in this sediment adsorption study. Effectively irreversible binding is entirely consistent with the known behaviour of complexation and binding within crystal lattices. The high levels of adsorption which occur are therefore a form of removal from the environment. In river and lake water microcosms, after approximately 40-50 days, the phosphonate is >95% bound to sediment with only 5% extractable by ultrasonication and use of 0.25N HCl-xylene solvent (based on radiolabelling) (Saeger, 1979; cited by Gledhill and Feijtel, 1992). 66-80% removal (binding) is seen after 11 days in the same test. In the context of the exposure assessment, largely irreversible binding is interpreted as a removal process; 5% remaining after 40 - 50 days is equivalent to a half-life of 10 days which is significant for the environmental exposure assessment on the regional and continental scales. Thisabioticremoval rate is used for freshwater/marine water and freshwater/marine sediment half-lives in the chemical safety assessment of HEDP-H and its salts.

Key value for chemical safety assessment

Half-life in freshwater:

10 d

at the temperature of:

12 °C

Half-life in marine water:

10 d

at the temperature of:

12 °C

Half-life in freshwater sediment:

10 d

at the temperature of:

12 °C

Half-life in marine water sediment:

10 d

at the temperature of:

12 °C

Additional information

Three weight-of-evidence studies for HEDP (2-3Na) indicate a low amount of biodegradation in sewage treatment simulation and water studies: 1.2%, 0.3% and 3.5% biodegradation was observed in 38-day, 14-week and 70-day sampling times, respectively, based on radiochemical measurements/14CO₂ evolution (Henkel, 1979a-c). These studies were well documented, met the generally accepted scientific principles, but were not conducted in compliance with GLP. Therefore, these studies were assigned reliability ratings of 2. Another weight-of-evidence study (reliability 2) indicated 5 -10% degradation of HEDP-H in natural water-sediment microcosms after 42 days, based on C14 radioactivity analysis via liquid scintillation counting (Saeger, 1979).

Additionally, <1% degradation was reported after 91 days of continuous administration of 14C-labelled HEDP (2-3Na) with synthetic sewage in a sewage treatment plant simulation study, under aerobic conditions (Steber and Wierich, 1986a and b). However, the documentation of the study was insufficient for assessment and it was assigned a reliability rating of 4. Another reliability 4 study indicated 50% degradation of HEDP-H based on DOC in a sewage treatment plant simulation study (Schoberl and Huber, 1988).

The acid, sodium and potassium salts in the HEDP category are freely soluble in water and, therefore, the HEDP anion is fully dissociated from its sodium or potassium cations when in solution. Under any given conditions, the degree of ionisation of the HEDP 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 HEDP-H, HEDP (1-2Na), HEDP (2-3Na), HEDP-4Na, HEDP-xK or another salt of HEDP.

 

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

1. HEDP is present as HEDP-H or one of its ionised forms. The degree of ionisation depends upon the pH of the system and not whether HEDP (1-2Na), HEDP (2-3Na), HEDP-4Na, HEDP-xK salts, HEDP-H or another salt was added.
2. Disassociated sodium/potassium cations. The amount of sodium/potassium present depends on which salt was added.
3. Divalent and trivalent cations have much higher stability constants for binding with HEDP than the sodium or potassium 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 HEDP-dication (e.g. HEDP-Ca, HEDP-Mg) and HEDP-trication (e.g. HEDP-Fe) complexes in solution, irrespective of the starting substance/test material.

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

Gledhill and Feijtel (1992) Environmental properties and safety assessment of organic phosphonates used for detergent and water treatment applications. The Handbook of Environmental Chemistry, Vol. 3, Part F, (Ed.: Hutzinger, O.), Springer-Verlag, Berlin.