Magnesium 2,3,4,5,6,7-Hexahydroxyheptanoate

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:

key study

Justification for type of information:

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
Sodium gluconate and magnesium glucoheptonate are structurally similar sugar-like substances with the same functional groups, whereby gluconate and glucoheptonate anions share similar chemical moiety. They differ only in one carbon segment (HCOH): glucoheptonate is longer (C7) than gluconate (C6). Since biodegradation is not applicable to dissociating metals in aqueous environement, the only organic part of the substance undergoes biodegradation. A metal cation can however influence the stability of metal-chelate complex and therewith can result in different kinetic profiles of biodegradation. Since the stability constant of magnesium glucoheptonate is low, the chelate is a weak complex at normal environmental pH range (4-9). Sodium gluconate is a salt that freely dissociates to sodium cation and gluconate anion in water. Therefore, it is expected that free gluconate and glucoheptonate anions appears in equal amounts from the salt or complex, respectively. Moreover, gluconates and glucoheptonates are believed to be metabolised by the same mechanisms by microorganisms and by other classes of living organisms. Therefore they are expceted to follow the same pattern of biodegradation.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Purity of sodium gluconate is generally above 97 % (OECD SIDS, 2004). The rest is water.
Theorical composition of magnesium glucoheptonate (HGAMg (1:1), if water were extracted, is 78.0-82.4%; other component is Na2SO4: 17.6-21.2%. Sodium is the same originating from Na2SO4 and from the source substance sodium gluconate, thus the only difference in the impurities is sulphate. Sulphate is considered not to impact biodegradation rate of the main component of the target substance because sulfur species are in considerable amounts in living organisms and are used as energy source by microorganisms.

3. ANALOGUE APPROACH JUSTIFICATION
Gluconates and glucoheptonates are naturally occurring substances that are metabolised by pentose phosphate pathway.

4. DATA MATRIX
please refer to the detailled read-across statement attached in section 13.

Reason / purpose for cross-reference:

read-across source

Duration of test (contact time):

d

Key result

Parameter:

other: Theoritical Oxygen Demand

Value:

89

Sampling time:

28 d

Remarks on result:

other: the same degradation rate is assumed for glucoheptonate moiety because hexoses and heptoses are oxidised by the same way by bacteria.

The 89% degradation indicated here relates to the Theoritical Oxygen Demand (ThOD).

Validity criteria fulfilled:

yes

Remarks:

Oxygen depletion in the inoculum blank did not exceed 1.5 mg dissolved oxygen/litre after 28 days.

Interpretation of results:

readily biodegradable

Conclusions:

The source substance sodium gluconate (CAS 527-07-1) is readily biodegradable with 89% degradation (based on ThOD) after 28 days. Conclusively, the target substance is also considered as readily biodegradable because gluconates and glucoheptonates are oxidised by the same way by bacteria.

Executive summary:

The same pattern of biodegradation are expected for gluconate and glucoheptonate anion since they have similar stability constants in aquatic environment and are both intermediates in carbohydrate metabolism.

Reference 2

Endpoint:

biodegradation in water: screening test, other

Type of information:

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

Adequacy of study:

supporting study

Justification for type of information:

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
Glucoheptitol and glucoheptulose are reduced analogues of glucoheptonic acid and therefore they are believed to be metabolised by the same mechanisms by microorganisms and by other classes of living organisms. Therefore they are expceted to follow the same pattern of biodegradation.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
No purity is reported for glucoheptitol.
Theorical composition of magnesium glucoheptonate (HGAMg (1:1), if water were extracted, is 78.0-82.4%; other component is Na2SO4: 17.6-21.2%. Sodium and sulphate are considered not to impact biodegradation rate of the main component of the target substance because sulfur species are in considerable amounts in living organisms and are used as energy source by microorganisms. Sodium is a macroelement.

3. ANALOGUE APPROACH JUSTIFICATION
The carbohydrates are oxidised in the direction: glucoheptitol - glucoheptulose - glucoheptonate and can be considered as different oxidation stages of heptaatomic carbohydrates. They are naturally occurring substances that are metabolised by different classes of bacteria.

4. DATA MATRIX
please refer to the detailled read-across statement attached in section 13.

Reason / purpose for cross-reference:

read-across source

GLP compliance:

no

Parameter:

% degradation (O2 consumption)

Value:

9

Sampling time:

24 h

Remarks on result:

other: is expected to be similar for magnsium glucoheptonate

Parameter:

% degradation (O2 consumption)

Value:

28

Sampling time:

48 h

Remarks on result:

other: is expected to be similar for magnsium glucoheptonate

Parameter:

% degradation (O2 consumption)

Value:

80

Sampling time:

96 h

Remarks on result:

other: is expected to be similar for magnsium glucoheptonate

Parameter:

% degradation (O2 consumption)

Value:

93

Sampling time:

120 h

Remarks on result:

other: is expected to be similar for magnsium glucoheptonate

Parameter:

% degradation (O2 consumption)

Value:

100

Sampling time:

144 h

Remarks on result:

other: is expected to be similar for magnsium glucoheptonate

Validity criteria fulfilled:

not specified

Interpretation of results:

readily biodegradable

Conclusions:

The oxidation of D-Gluco-D-gulo-heptitol to L-glucoheptulose by Acetobacter suboxydans was complete (100 %) within 144 hours. This result shows the biodegradation rates of reduced analogues of glucoheptonic acid. Further oxidative degradation of L-Glucoheptulose to L-gluconic acid is described.

Executive summary:

L-glucoheptulose is an oxidation product of D-gluco-D-guloheptitol that is a reduced analogue of glucoheptonate, the anion of the target substance. Further oxidative degradation of L-glucoheptulose to L-gluconic acid provide evidence of crossing the metabolic pathways of gluconate and glucoheptonate. The results of biodegradation of these reduced analogues is presented here to elucidate biodegradation pattern of the target substance.

Reference 3

Endpoint:

biodegradation in water: screening tests

Type of information:

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

Adequacy of study:

supporting study

Justification for type of information:

1. HYPOTHESIS FOR THE ANALOGUE APPROACH
Sodium gluconate and magnesium glucoheptonate are structurally similar sugar-like substances with the same functional groups, whereby gluconate and glucoheptonate anions share similar chemical moiety. They differ only in one carbon segment (HCOH): glucoheptonate is longer (C7) than gluconate (C6). Since biodegradation is not applicable to dissociating metals in aqueous environement, the only organic part of the substance undergoes biodegradation. A metal cation can however influence the stability of metal-chelate complex and therewith can result in different kinetic profiles of biodegradation. Since the stability constant of magnesium glucoheptonate is low, the chelate is a weak complex at normal environmental pH range (4-9). Sodium gluconate is a salt that freely dissociates to sodium cation and gluconate anion in water. Therefore, it is expected that free gluconate and glucoheptonate anions appears in equal amounts from the salt or complex, respectively. Moreover, gluconates and glucoheptonates are believed to be metabolised by the same mechanisms by microorganisms and by other classes of living organisms. Therefore they are expceted to follow the same pattern of biodegradation.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Purity of sodium gluconate is generally above 97 % (OECD SIDS, 2004). The rest is water.
Theorical composition of magnesium glucoheptonate (HGAMg (1:1), if water were extracted, is 78.0-82.4%; other component is Na2SO4: 17.6-21.2%. Sodium is the same originating from Na2SO4 and from the source substance sodium gluconate, thus the only difference in the impurities is sulphate. Sulphate is considered not to impact biodegradation rate of the main component of the target substance because sulfur species are in considerable amounts in living organisms and are used as energy source by microorganisms.

3. ANALOGUE APPROACH JUSTIFICATION
Gluconates and glucoheptonates are naturally occurring substances that are metabolised by pentose phosphate pathway.

4. DATA MATRIX
please refer to the detailled read-across statement attached in section 13.

Reason / purpose for cross-reference:

read-across source

Duration of test (contact time):

d

Parameter:

% degradation (inorg. C analysis)

Remarks:

also expected for glucoheptonate anion

Value:

100

Sampling time:

35 d

Remarks on result:

other: The percentage biodegradation is calculated from the total carbon transformed to biogas and dissolved ionorganic carbon (DIC) and the measured or calculated amount of carbon added as test item.

Validity criteria fulfilled:

not specified

Interpretation of results:

other: The test item is ultimately biodegradable under anaerob test conditions.

Conclusions:

The source substance Sodium gluconate (CAS 527-07-1) is ultimately biodegradable under anaerobic test conditions. Conclusively, the target substance is also considered as readily biodegradable because gluconates and glucoheptonates are oxidised by the same way by bacteria.

Executive summary:

The same pattern of biodegradation are expected for gluconate and glucoheptonate anion since they have similar stability constants in aquatic environment and are both intermediates in carbohydrate metabolism.

Description of key information

Sodium gluconate_EU Method C.4-E: 89 % degradation after 28 days
Sodium gluconate_DIN EN ISO 11734: 100 % after 35 days (anaerobic)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Two experimental study reports are cited in the OECD SIDS Report (2004) on Gluconic Acid and its Derivatives. Both studies refer to the read-across substance Sodium gluconate (CAS 527 -07 -01). Actual data on the target substance Magnesium glucoheptonate is not available for this endpoint. Nevertheless, conclusions drawn on the read-across substance are assignable for the target substance as well (please refer to read-across statement).

Referring to the key study, the biodegradation of sodium gluconate (CAS 527-07-1) was investigated according to EU Method C.4-E (Closed bottle test) in compliance with GLP (Hydrotox GmbH, 2001; as cited in OECD SIDS, 2004).

All in all, 16 test bottles with a test item concentration of 3 mg/L with 4 mL/L inoculum (secondary effluent of a municipal sewage plant) were filled bubble-free and incubated in the dark at 20°C for 28 days. On days 3, 7, 10, 14, 21 and 28, at least duplicate bottles were removed for determination of dissolved oxygen and pH. At the end of the test, dissolved oxygen concentration in all remaining bottles was measured. Reference item bottles containing sodium acetate stock solution (concentration= 4 mg/L) with 0.4 mL/L inoculum were also filled and incubated in the dark at 20°C. A blank was also prepared without any stock solution.

Referring to the test substance and based on the ThOD, 61.13% degradation were reported after 3 days, followed by 74.35% after 7 days, 66.09% after 14 days, 71.94% after 21 days and 88.88% after 28 days. With regard to the reference substance, 67.15% degradation were measured after 3 days and 80.93% after 28 days – both based on the ThOD.

With regard to the supporting information, the biodegradation of sodium gluconate (CAS 527-07-1) was investigated according to DIN EN ISO 11734 in compliance with GLP (Hydrotox GmbH, 2001; as cited in OECD SIDS, 2004).

Washed digested sludge containing very low amounts of inorganic carbon (IC) was diluted to 1-3 g/L total solids concentration and incubated in the absence of oxygen at 35 +/-2°C in sealed vessels with the test item (303 mg/L) at a concentration of 20-200 mg/L total organic carbon (TOC) for 35 days. As reference substance, sodium benzoate (0.069 g/400 mL) has been used. The percentage biodegradation is calculated from the total carbon transformed to biogas and DIC and the measured or calculated amount of carbon added as test item.

Referring to the test substance, 8% degradation has been determined after 1 day, followed by 51% after 8 days, 57% after 15 days, 61% after 22 days and 100% after 35 days. With regard to the reference substance, 6% degradation was determined after 8 days and 100% after 35 days.

In supporting studies, oxidation of glucoheptitol through glucoheptulose to gluconic acid was reported (Hann et al., 1938; Maclay et al., 1942; Richtmeyer and Hudson, 1942). These hepta-carbohydrates are reduced analogues of glucoheptonic acid. L-glucoheptulose was obtained through the biochemical oxidation of D-gluco-D-guloheptitol (alpha-glucoheptitol) by Acetobacter suboxydans (Hann et al., 1938; Maclay et al., 1942). Subsamples were analyzed for reducing value at the expiration of 24, 48, 96, 120 and 144 hours and the analyses indicated that the oxidation was 9, 28, 80, 93 and 100% complete at these periods. The L-glucoheptulose was obtained in a yield of 88%.

In a follow up study, oxidative degradation of L-Glucoheptulose to L-gluconic acid is described (Richtmyer and Hudson, 1942). The transformation of D-glucose to L-glucose by the step involving the degradation of L-glucoheptulose to Lgluconic acid is postulated. The oxidative degradation of L-glucoheptulose to L-gluconic acid provide evidence of crossing the metabolic pathways of gluconate and glucoheptonate. The results of biodegradation of these reduced analogues is presented here to elucidate biodegradation pattern of the target substance.