(1-hydroxyethylidene)bisphosphonic acid, potassium salt

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

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.

Qualifier:

no guideline followed

Principles of method if other than guideline:

Soil CO2 evolution test. Degradation chamber consisted of modified 60 ml Buchner-type funnel. 20g soil in each of 12 funnels. Test substance added as aqueous solution to give 10µg/g.

GLP compliance:

no

Test type:

laboratory

Radiolabelling:

yes

Year:

1976

Soil no.:

#1

Soil type:

other: Iowa Farm Soil

% Org. C:

3.31

pH:

5.6

Soil no.:

#2

Soil type:

other: Olivette Garden Soil

% Org. C:

3.03

pH:

7.65

Soil no.:

#3

Soil type:

other: St Charles Ray-Silt Loam

% Org. C:

0.56

pH:

7.05

Soil no.:

#4

Soil type:

other: Meramec River Bank Soil

% Org. C:

0.7

pH:

7.7

Details on soil characteristics:

SOIL COLLECTION AND STORAGE

- Storage conditions: sealed polyethylene bags

- Soil preparation (e.g., 2 mm sieved; air dried etc.): 2 mm sieved

PROPERTIES OF THE SOILS (in addition to defined fields)

Water content (gH2O/g soil): Soil #1: 0.20, Soil #2: 0.23, Soil #3: 0.14, Soil #4: 0.06.

Water holding capacity (gH20/g soil): Soil #1: 0.50, Soil #2: 0.45, Soil #3: 0.45, Soil #4: 0.39.

Duration:

119 d

Initial conc.:

10 mg/kg soil d.w.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on experimental conditions:

1. PRELIMINARY EXPERIMENTS: none reported

2. EXPERIMENTAL DESIGN
- Soil (g/replicate): 20g

- Control conditions, if used (present differences from other treatments, i.e., sterile/non-sterile, experimental conditions): approximation of a sterile control acheived by addition of sodium azide to selected soil samples at the 0.1% level (1mg/g soil)

- No. of replication controls, if used: Samples of Iowa Farm Soil and of Meramec River Bank Soil were prepared as sterile controls.

- No. of replication treatments: 5

- Test apparatus (Type/material/volume): Degradation chamber: modified 60ml Buchner-type funnel (pyrex with coarse frit)

- Details of traps for CO2 and organic volatile, if any: radiolbelled carbon dioxide given off was trapped in scrubbers containing 5ml ethanolamine-ethylene glycol monoethyl ether, 1:7 solution.

Test material application
- Volume of test solution used/treatment: one ml of aqueous solution (200µg/ml)

Any indication of the test material adsorbing to the walls of the test apparatus: none reported

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: soil was continuously purged with air saturated with water and free of carbon dioxide at a rate of 10ml/min.

Other details, if any:

3. OXYGEN CONDITIONS (delete elements as appropriate)
- Methods used to create the an/aerobic conditions: soil was continuously purged with air saturated with water and free of carbon dioxide at a rate of 10ml/min.
- Evidence that an/aerobic conditions were maintained during the experiment (e.g. redox potential): none reported

4. SUPPLEMENTARY EXPERIMENTS: none reported

5. SAMPLING DETAILS
- Sampling intervals: 5, 7, 9, 12, 16, 21, 28, 35, 42, 49, 63, 77, 91, 105, 119 days

- Sampling method: Periodically the first scrubber was removed, the second scrubber moved to position one and replaced with a fresh scrubber. The 14CO2 evolved was then measured by liquid scintillation counting. Duplicate 1 ml aliquots of the monoethanolamine-ethylene glycol solution were pipetted into glass liquid scintillation counting vials and 19 ml of LSC cocktail (9/1, methanol/Fluoralloy TM by volume) added. The vials were then capped, mixed, and equilibrated at 10°C prior to counting. Each sample vial was counted in triplicate for a 20 minute period with a Mark III Liquid Scintillation Spectrometer (Model 6880, Searle Analytic, Inc.) using the preset isotope quench corrected program 3 ( l4C, low activity) mode. 14C counting efficiencies were determined via the external standard pulse method using a certified set of 8 sealed 14C quench standards (Amersham/Searle, cat#180060). All CPM values were automatically converted to DPM values via the Mark III DPM calculation accessory. The percent theoretical 14CO2 evolved was then calculated from these DPM values.

- Sampling intervals/times for:
> Sterility check, if sterile controls are used: 5, 7, 9, 12, 16, 21, 28, 35, 42, 49, 63, 77, 91, 105, 119 days

Soil No.:

#1

% Degr.:

6.7

Parameter:

CO2 evolution

Sampling time:

119 d

Soil No.:

#2

% Degr.:

25.2

Parameter:

CO2 evolution

Sampling time:

119 d

Soil No.:

#3

% Degr.:

28.2

Parameter:

CO2 evolution

Sampling time:

119 d

Soil No.:

#4

% Degr.:

26

Parameter:

CO2 evolution

Sampling time:

119 d

Transformation products:

not measured

Details on results:

The Iowa Farm soil (Soil #1) shows the least activity; this may be related to its low pH. The two soils with the lowest organic carbon content (Soil #3 & #4) were the most active.

Results with reference substance:

The sterile controls evolved no significant 14CO2 (Soil #1(NaN3 treated): 3.29%, Soil #4(NaN3 treated): 3.75% . However, the results indicate that there was probably an incomplete sterilisation of the soil.

Table 1: Soil Biodegradation (Cumulative ¹⁴CO₂ Evolution - % of theory)

Days of Exposure	5	7	9	12	16	21	28	35	42	49	63	77	91	105	119
Soil #1	0.22	0.40	0.60	0.71	0.82	1.42	2.14	2.80	3.38	3.96	4.32	5.07	5.72	5.98	6.68
Soil #2	1.20	2.04	2.90	3.37	3.88	6.54	9.64	12.34	14.66	16.25	17.99	21.04	22.93	23.75	25.16
Soil #3	4.04	6.00	7.45	9.15	10.15	12.26	14.58	16.67	18.64	20.68	22.89	24.31	25.86	26.55	28.16
Soil #4	1.00	1.50	1.96	2.43	3.41	6.80	9.32	10.99	14.88	17.66	19.96	22.08	23.55	24.30	25.98
Soil #1 (NaN­3treated)	0.42	0.55	0.67	0.76	0.86	1.06	1.32	1.69	2.07	2.47	2.61	2.80	2.99	3.07	3.29
Soil #4 (NaN3treated)	0.88	1.19	1.41	1.53	1.65	1.96	2.23	2.43	2.58	2.68	2.90	3.07	3.24	3.38	3.75

Conclusions:

Soil biodegradation rates of between 6.7 and 28.2% over 119d in four soils were determined in a reliable study conducted according to generally accepted scientific principles.

Reference 2

Endpoint:

biodegradation in soil: simulation testing

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 between members of the HEDP category.

Reason / purpose for cross-reference:

read-across source

Soil No.:

#1

% Degr.:

6.7

Parameter:

CO2 evolution

Sampling time:

119 d

Soil No.:

#2

% Degr.:

25.2

Parameter:

CO2 evolution

Sampling time:

119 d

Soil No.:

#3

% Degr.:

28.2

Parameter:

CO2 evolution

Sampling time:

119 d

Soil No.:

#4

% Degr.:

26

Parameter:

CO2 evolution

Sampling time:

119 d

Transformation products:

not measured

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.

Description of key information

Although biodegradation in soil has not been demonstrated for HEDP-H and its salts, the role of abiotic removal processes is significant. The key data for soil 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) in river and lake water microcosms (Saeger, 1979; cited by Gledhill and Feijtel, 1992, see IUCLID Section 5.2.2). 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 in the regional and continental scales. This abiotic removal rate is used for the soil half-life in the chemical safety assessment of HEDP-H and its salts.

Key value for chemical safety assessment

Half-life in soil:

10 d

at the temperature of:

12 °C

Additional information

Two reliable studies of biodegradation in soil are available. Soil biodegradation rates of between 6.7 and 28.2% over 119 days in four soils were determined for HEDP-H (Saeger et al., 1977). A soil biodegradation rate of 47% over 148 days in silt-loam soil was determined for HEDP-H (Saeger 1978).

Three supporting studies with HEDP (2-3Na) indicate low rates of biodegradation in soil. 0.4-4.8% biodegradation was observed in two soil types after 79 days (Henkel, 1979), 4.8% biodegradation of HEDP (2-3Na) was observed after 80 days (Steber and Wierich, 1986a), and 0.4% biodegradation of HEDP (2-3Na) was observed after 80 days (Steber and Wierich, 1986b) in defined soil types. These studies are reliability 4 due to a lack of documentation.

Two supporting studies indicate HEDP-H degraded 6.7 -28.2% in soil after 119 days and 47.5% in soil after 148 days (Monsanto, 1976 and 1977).

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.