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

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to aquatic algae and cyanobacteria

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). Gluconates and glucoheptonates are expected to dissociate from their respective salt or complex, releasing metal cations at physiological pHs. So, to address the toxicity of free of metal glucoheptonate anion to aquatic algae and cyanobacteria, the data on gluconate is presented here. Furthermore, gluconate or glucoheptonate anion is fully protonated at low pH values and are not able to participate in complexation of metal cations (Alekseev et al., 1998; please refer to the read-across statement). 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, the toxicity of gluconate and glucoheptonate salts or complexes is driven by the supplied metal cation that can affect mineral balance of the body, while no toxicity is attributed to gluconate or glucoheptonate moiety up to considerable amounts. Additionally, gluconates and glucoheptonates are believed to be metabolised by the same mechanisms by microorganisms and by other classes of living organisms. Therefore their toxicity to aquatic algae and cyanobacteria is expected to be similar.

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 toxicity of magnesium glucoheptonate to aquatic algae and cyanobacteria to a significant extent because sulfur species are in considerable amounts in living organisms.

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

Reason / purpose for cross-reference:

reference to other study

Test organisms (species):

Desmodesmus subspicatus (previous name: Scenedesmus subspicatus)

Reference substance (positive control):

not required

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

100 mg/L

Nominal / measured:

estimated

Conc. based on:

other: correpsonding amounts of glucoheptonate anion and magnesium moiety

Basis for effect:

growth rate

Remarks on result:

other: calculated for magnesium glucoheptonate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

estimated

Conc. based on:

other: corresponding glucoheptonate and magnesium moieties

Basis for effect:

growth rate

Remarks on result:

other: calculated for magnesium glucoheptonate

Details on results:

No details reported.

Results with reference substance (positive control):

Not applicable.

Reported statistics and error estimates:

No details reported.

Calculation of corresponding effect/hazard levels for glucoheptonate anion:

Molecular weight of magnesium glucoheptonate (1:1): 266.6 g/mol

Molecular weight of sodium gluconate: 218.14 g/mol

Molecular weight of sodium: 22.99 g/mol

Molecular weight of glucoheptonate anion: 242.29 g/mol

Provided that 1 mol of gluconate and glucoheptonate anions bind metals as 1:1, the weight of 1 mol of glucoheptonate is more than the weight of 1 mol of gluconate anion. Thus, the corresponding weight of 1 mol magmesium glucoheptonate is more than that of sodium gluconate.

The hazard values EC50 and NOEC (72 h) are greater than 100 mg/L or equal to 100 mg/L for sodium gluconate, respectively. Then the corresponding values for glucoheptonate anion originating from magnesium glucoheptonate would be as follows:

1) 10.5 mg sodium is contained in 100 mg sodium gluconate: (100 x 22.99) / 218.14; and 100 - 105.39 = 89.5 mg gluconate anion.

2) If 89.5 mg was glucoheptonate anion, it would correspond to 98.5 mg of magnesium glucoheptonate (89.5 x 266.6) / 242.29;

3) On the other hand, if 100 mg was magnesium glucoheptonate, the weight of glucoheptonate moiety would be (100 x 242.29) / 266.6 = 90.9 mg.

Comparing the weight of gluconate vs glucoheptonate moieties in 100 mg: 89.5 mg vs. 90.9 mg, the values are close to each other. Therefore, it is expected that the hazard from glucoheptonate anion would not be higher than that from gluconate anion.

Estimation of hazard values for magnesium glucoheptonate:

In respect to cation moiety, the corresponding amount of magnesium containing in 100 mg of magnesium glucoheptonate is: 100- 90.9 = 9.1 mg /L. This amount is lower than the lowest hazard value (EC50 of 62.2 mg Mg moiety/L, established for Raphidocelis subcapitata (Bosnir et al., 2013; please refer to cross references in this section).

Therefore, a toxicity of magnesium glucoheptonate to Desmodesmus subspicatus is not expected at EC50 (72 h) > 100 mg/L and NOEC (72 h) of 100 mg/L established for sodium gluconate.

Validity criteria fulfilled:

not applicable

Conclusions:

EC50 (72 h) of > 100 mg/L and a NOEC (72 h) of 100 mg/L are calculated for magnesium glucoheptonate based on molecular weights and taking into account the lowest hazard value for magnesium established for aquatic algae and cyanobacteria.

Executive summary:

Summary from the source record:

"The toxicity of the read-across substance Sodium gluconate (CAS 527-07-1) towards algae has been determined according to OECD Guideline 201 in compliance with GLP. Two tests have been performed. In the first test, 1000 mg/L of the test item have been tested. However, a decrease of the test item concentration was observed and therefore the test could not meet the stability requirements. Conclusively, a second test with 100 and 1000 mg/L test concentration was performed. Desmodesmus subspicatus CHODAT (strain No 86.81 SAG) was used as test organism. An initial cell density of 10 x 10E4 algae/mL was applied. For the second test, 3 flasks with 100 mg/L, 3 flasks with 1000 mg/L and 6 flasks without test item were used. The common OECD procedure has been modified by covering the test vessels with glass petri dishes to prevent contamination by micro-organisms. After 24, 48 and 72 hours, cell concentration was determined using a microscope with a counter chamber (8 fields counted). No cell growth inhibition at 100 mg/L was determined. At 1000 mg/L, 70% cell growth inhibition was observed. For the average specific growth rate, no inhibition at 100 mg/L but 42% inhibition at 1000 mg/L was determined. The cell concentrations in controls increased by a factor of 65.9 after 72 h. As final results and based on growth rate, an EC50 (72 h) of > 100 mg/L and a NOEC (72 h) of 100 mg/L were derived."

The data on sorce substance is presented here to cover toxicity of organic part of the molecule - glucoheptonate anion.

Since gluconate and glucoheptonate anions are naturally occurring substances and are both intermediates in the carbohydrate metabolism, their toxicity to aquatic environment is expected to be similar. Therefore, the EC50/NOEC (72 h) value of greater than 100 mg/L is also applicable for corresponding amounts of glucoheptonate anion originating from magnesium glucoheptonate. Additionally, since according to the read-across hypothesis, the toxicity to aquatic life is driven more by the applied metal cation and not by glucoheptonate anion, the toxicity of the corresponding amounts of magnesium originating from 100 mg/l of magnesium glucoheptonate, if the target substance was tested, were compared to the known hazard values established for magnesium moiety from inorganic salts.

In respect to cation moiety, the corresponding amount of magnesium containing in 100 mg of magnesium glucoheptonate is: 100 - 90.9 = 9.1 mg /L. This amount is lower than the lowest hazard value (EC50 of 62.2 mg Mg moiety/L, established for Raphidocelis subcapitata (Bosnir et al., 2013; please refer to cross references in this section).Therefore, toxicity of magnesium glucoheptonate to Desmodesmus subspicatus is not expected at EC50 (72 h) > 100 mg/L and NOEC (72 h) of 100 mg/L established for sodium gluconate.

Reference 2

Endpoint:

toxicity to aquatic algae and cyanobacteria

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
The toxicity of glucoheptonate complexes is driven by the supplied metal cation that can affect mineral balance of the body, while no toxicity is attributed to the organic part of the molecule - glucoheptonate moiety - up to considerable amounts. Magnesium glucoheptonate is expected to dissociate from its complex, releasing metal cation - magneisum - at physiological pHs. So, glucoheptonate anion is fully protonated at low pH values and is not able to participate in complexation of metal cations: the stability constant of magnesium glucoheptonate is low, the chelate is a weak complex at normal environmental pH range (4-9) (Alekseev et al., 1998; please refer to the read-across statement). Therefore, the released equimolar amount of magnesium from magnesium glucoheptonate is expected to determine its toxicity to aquatic algae and cyanobacteria. In this regard, the toxicity of magnesium originated from another magnesium compound could provide an additional information on toxicity of magnesium glucoheptonate. Therefore, the data on magnesium food supplements is presented here as source of data for the target substance magnesium glucoheptonate to address the toxicity of metal cation.

2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES)
Different food supplements containing Mg were analyzed. The level of Mg in study samples ranged from 133 mg to 250 mg.
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 a macroelement containing in considerable amounts in surface waters and in living organisms. Sulfur species including sulphate are also in considerable amounts in living organisms. Thus, these cation and anion are considered not to impact the toxicity to aquatic algae and cyanobacteria of magnesium.

3. ANALOGUE APPROACH JUSTIFICATION
As announced in the hypothesis for the read-across, magnesium glucoheptonate is expected to dissociate in aquatic environments (at normal pH range 4-9). Magnesium sulphate is a salt that fully dissociates in water too. However, the amount of magnesium released from magnesium glucoheptonate and from magnesium sulphate is different because the molecular masses of these compound are different . Also the proportion of magnesium to glucoheptonate or to sulphate anions will be different. As a result, more magnesium will be released from the salt magnesium sulphate than from magnesium glucoheptonate. Thus, the data on magnesium sulphate represent worst case for magnesium glucoheptonate.

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

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

read-across source

Details on sampling:

none provided

Test organisms (species):

Pseudokirchneriella subcapitata (previous names: Raphidocelis subcapitata, Selenastrum capricornutum)

Reference substance (positive control):

not specified

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

62.6 mg/L

Nominal / measured:

not specified

Conc. based on:

element

Remarks:

magnesium

Basis for effect:

growth rate

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

1 020 mg/L

Nominal / measured:

estimated

Conc. based on:

element (total fraction)

Remarks:

magnesium (6.1 %) in magnesium glucoheptonate

Basis for effect:

growth rate

Remarks on result:

other: calculated for magnesium glucoheptonate

Calculation of corresponding effect/hazard levels for mahnesium glucoheptonate:

Molecular weight of magnesium glucoheptonate (1:1): 266.6 g/mol

Molecular weight of magnesium: 24.31 g/mol

Molecular weight of glucoheptonate anion: 242.29 g/mol

According to molecular formulas, 1 mol magnesium moiety is contained in 1 mol magnesium glucoheptonate.

The EC50 (72 h) of 62.2 mg/L was established for magnesium (element) in Raphidocelis subcapitata.

The corresponding amounts of magnesium glucoheptonate is:

(62.2 x 266.6) / 24.31 = 682.12 mg/L.

Estimation of hazard values for magnesium glucoheptonate based on total magnesium content in magnesium glucoheptonate :

The target substance Magnesium glucoheptonate contains 6.1 % Magnesium, which leads to the following conversion:

 

LC50 = 62.2 mg/L x 100 % / 6.1 % = 1020 mg/L

Although this values is higher than the value 682.1 mg/L calculated based on molecular weight, it is more realistic because the total content of metal in the product is the driving factor of toxicity.

Validity criteria fulfilled:

not applicable

Conclusions:

EC50 (72 h) of 682 and 1020 mg Mg glucoheptonate /L are calculated for Raphidocelius subcapitata based on molecular weight and total magnesium content (6.1 %) in magnesium glucoheptonate.

Executive summary:

The aim of this study was to determine the effect of uncontrolled environmental disposal of food supplements containing magnesium (Mg), chromium (Cr), iron (Fe) and zinc (Zn) on selected aquatic organisms including freshwater algae Scenedesmus subspicatus and Raphidocelis subcapitata, water flea Daphnia magna and duckweed Lemna minor.

Thirty different food supplements containing Mg, Cr, Fe and Zn were analysed. Results were expressed as effective concentration 50 (EC50), i.e. growth inhibiting Mg, Cr, Fe and Zn (mg/L) concentration immobilizing 50% of treated organisms.

Particular metal EC50 differed significantly (p<0.001) among study organisms. Referring to the effective concentrations of magnesium determined for algae, the following results were obtained:

Scenedesmus subspicatus: EC50 (72 h) = 73.0 mg Mg/L

Raphidocelis subcapitata: EC50 (72 h) = 62.2 mg Mg/L

Uncontrolled environmental disposal of food supplements containing Mg, Cr, Fe and Zn exerts adverse effects on aquatic organisms. Therefore, legal provisions should regulate both the utilization and disposal of food supplements into the environment.

Based on the read-across hypothesis, metal is the driving factor of toxicity. Therefore, EC50 value has been adapted taking into account molecular formula of magnesium glucoheptonate. The corresponding amounts of magnesium glucoheptonate have been calculated also based on total fraction of magnesium (6.1 %) in the target substance:

The corresponding amounts of magnesium glucoheptonate is:

(62.2 x 266.6) / 24.31 = 682.12 mg/L.

Estimation of hazard values for magnesium glucoheptonate based on total magnesium content in magnesium glucoheptonate :

The target substance Magnesium glucoheptonate contains 6.1 % Magnesium, which leads to the following conversion:

 

LC50 = 62.2 mg/L x 100 % / 6.1 % = 1020 mg/L

Although this values is higher than the value 682.1 mg/L calculated based on molecular weight, it is more realistic because the total content of metal in the product is the driving factor of toxicity.

Description of key information

OECD SIDS, 2004_OECD 201_Desmodesmus subspicatus: ErC (72 h) > 100 mg/L and NOErC (72 h) = 100 mg/L [Sodium gluconate]
Bosnir et al., 2013_WoE_Raphidocelis subcapitata_ EC50 (72 h) = 62.2 mg Mg/L [Magnesium]; EC50 (72 h) = 1020 mg/L [Magnesium glucoheptonate]

The studies with the lowest hazard values for gluconate and magnesium have been chosen for the calculation of an equivalent exposure concentration for the target substance magnesium glucoheptonate.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC10 or NOEC for freshwater algae:

100 mg/L

Additional information

There is no data available for the target substance Magnesium glucoheptonate (CAS 1821694-26 -1) on acute toxicity towards algae. However, there is data available for the source substances Sodium gluconate (CAS 527-07-01), Gluconic acid (CAS 526-95-4), Magnesium chloride (CAS 7786-30-3) and Magnesium sulphate (CAS 7487-88-9).

Data on sodium gluconate and gluconic acid

Referring to the key study, the toxicity of the read-across substance Sodium gluconate (CAS 527-07-1) towards algae has been determined according to OECD Guideline 201 in compliance with GLP (OECD SIDS, 2004). Two tests have been performed. In the first test, 1000 mg/L of the test item have been tested. However, a decrease of the test item concentration was observed and therefore the test could not meet the stability requirements. Conclusively, a second test with 100 and 1000 mg/L test concentration was performed. Desmodesmus subspicatus CHODAT (strain No 86.81 SAG) was used as test organism. An initial cell density of 10 x 10E4 algae/mL was applied. For the second test, 3 flasks with 100 mg/L, 3 flasks with 1000 mg/L and 6 flasks without test item were used. The common OECD procedure has been modified by covering the test vessels with glass petri dishes to prevent contamination by micro-organisms. After 24, 48 and 72 hours, cell concentration was determined using a microscope with a counter chamber (8 fields counted). No cell growth inhibition at 100 mg/L was determined. At 1000 mg/L, 70% cell growth inhibition was observed. For the average specific growth rate, no inhibition at 100 mg/L but 42% inhibition at 1000 mg/L was determined. The cell concentrations in controls increased by a factor of 65.9 after 72 h. As final results and based on growth rate, an EC50 (72 h) of > 100 mg/L and a NOEC (72 h) of 100 mg/L were derived.

As supporting information, the acute toxicity of the read-across substance Sodium gluconate (CAS 527-07-1) towards algae was determined according to OECD Guideline 201 in compliance with GLP (OECD SIDS, 2004). A range-finding test was conducted prior to the definitive test to enable the following concentrations in the definitive test: 0 (control), 100, 180, 320, 560, 1000 mg/L (nominal concentrations). Measured concentrations of the test substance in the test solutions at the beginning of exposure were +/-20 % of the nominal concentrations. As test organism, Pseudokirchneriella subcapitata has been used (Biomass loading: 1 x 10 E04 cells/mL).As final results, the EC50 (72 h) was determined to be > 1000 mg/L while the NOEC (72 h) was set to 560 mg/L based on the growth rate (nominal concentration).

With regard to the second supporting study, acute toxicity of four relatively new chelating agents and their equimolar manganese and cadmium complexes was studied (Silanpää et al., 2003). The chelating agents studied were gluconic acid (GA),β-alaninediacetic acid (ADA), diethylenetriaminepentakismethylenephosphonic acid (DTPMP), and nitrilotriacetic acid (NTA).The bioassay with R. subcapitata using gluconic acid was performed according to a Finnish standard SFS 5072 (1986, Toxicity test with pure culture of algae). At the time of an inoculation, the alga was in its exponential growth phase. During the test, the flasks were shaken in every 24 h. The volume in all tests was 10 mL and illumination intensity was set to 5000 lx. Temperature was maintained at 22 ± 1°C throughout the 72-h test. Two simultaneous experiments were performed for each test concentration and the highest concentration of chelating agents was 1000 mg/L. The growth was estimated with in vivo fluorescence of chlorophyll (Labsystems, Fluoroskan Ascent) and the results obtained from the bioassay are expressed as 72-h EC50 values with 95% confidence interval. The EC50 (72 h) value for gluconic acid is reported as 76 mg/L. R. subcapitata proved the most sensitive to these compounds compared to Daphnia magna and Photobacterium phosphoreum.

Data on magnesium salts

Since aquatic toxicity of magnesium glucoheptonate is considered to be driven by magnesium, aquatic toxicity data on magnesium salts have been taken into account to address the toxicity of metal cation magnesium.

The aquatic toxicity of the source substance magnesium chloride (CAS 7786-30-3) towards Desmodesmus subspicatus

was investigated (EC ECB IUCLID, 1994). The test duration amounts to 72 hours. Further information on applied test guidelines and tested concentrations is not available. An EC50 value (72 h) of 562 mg Mg/L is reported for the metal ion, based on biomass.

Furthermore, the aquatic toxicity of the source substance magnesium chloride (CAS 7786 -30 -3) towards Desmodesmus subspicatus

was investigated in another study (EC ECB IUCLID, unknown). The test duration amounts to 24 hours. Further information on applied test guidelines and tested concentrations is not available.An EC50 value (24 h) of 1195mg Mg/L is reported for the metal ion.

In another study, comparisons were made of the growth patterns of Chlorella vulgaris when cultured in nutrient solutions containing glucose and differing in magnesium concentration (Finkle and Appleman, 1952). The amounts of magnesium used were such that symptoms of magnesium deficiency were produced at the lower concentrations. Growth was measured primarily in terms of increase in the cell population and increase in the volume of packed cells per unit volume of culture, the latter being an expression of the synthesis of cellular material. In the full-magnesium cultures (49 ppm Mg) cell population increased and the synthesis of cell material proceeded rapidly, being limited finally by conditions other than magnesium deficiency in the medium. The cells decreased greatly in size during the period of rapid growth and then remained at the same small size for the duration of the experiments. Symptoms of magnesium deficiency appeared in the cultures initially containing 0.2, 0.5, and 1.0 ppm Mg, while only some of these deficiency effects were apparent in the cultures with 2.8 ppm Mg. Magnesium deficiency interrupted cell multiplication at cell populations proportional to the original magnesium concentrations of the various media. The synthesis of cell material was not arrested hence cell size increased greatly, some of the cultures deficient in magnesium giving average cell sizes more than 20-fold larger in volume than the cultures with sufficient magnesium. These increases in cell size were paralleled by proportional increases in nitrogen content and dry weight. It appears that cell multiplication and synthesis of cell material are independent processes in cultures of Chlorella vulgaris and that the process of multiplication requires a larger concentration of magnesium in the medium than does the production of cell material. Anatomical observations suggest that cell division (mitosis) was possibly taking place in the magnesium deficient cultures but was not apparent owing to lack of cell separation. The limiting role of magnesium in the growth processes is discussed.

In an additional study (Bosnir et al., 2013), the effect of uncontrolled environmental disposal of food supplements containing magnesium (Mg), chromium (Cr), iron (Fe) and zinc (Zn) on selected aquatic organisms including freshwater algae Scenedesmus subspicatus and Raphidocelis subcapitata was investigated. Thirty different food supplements containing Mg, Cr, Fe and Zn were analysed. Results were expressed as effective concentration 50 (EC50), i.e. growth inhibiting Mg, Cr, Fe and Zn (mg/L) concentration immobilizing 50% of treated organisms.

Particular metal EC50 differed significantly (p<0.001) among study organisms. Referring to the effective concentrations of magnesium determined for algae, the following results were obtained:

Scenedesmus subspicatus:EC50 (72 h) =73.0 mg Mg/L

Raphidocelis subcapitata:EC50 (72 h) = 62.2 mg Mg/L

Derivation of effective concentrations for Magnesium glucoheptonate (CAS 1821694-26-1)

There are two key study defined for the source substances Sodium gluconate (CAS 527-07-1) and magnesium from food supplements (Bosnir et al., 2013). Data on the source substances magnesium chloride (CAS 7786-30-3) and magnesium sulphate (CAS 7487-88-9) are shown in a weight of evidence approach. Although it is expected that toxicity of the target substance is rather triggered by the magnesium cation, data on a gluconate are also considered for the Chemical Safety Assessment.

 

An EC50 (72 h) of > 100 mg/L and a NOEC (72 h) of 100 mg/L were determined for the substance Sodium gluconate (OECD SIDS, 2004).

 

The most critical effect concentration for magnesium has been determined by Bosnir et al. (2013). An EC50 value (72 h) of 62.2 mg Mg/L is reported for Raphidocelis subcapitata.

 

The target substance Magnesium glucoheptonate contains 6.1 % Magnesium, which leads to the following conversion.

 

62.2 mg/L x 100 % / 6.1 % = 1020 mg/L

 

The calculated EC50 (72 h) value of 1020 mg/L for the target substance is higher than the EC50/NOEC determined for Sodium gluconate (CAS 527-07-1). Thus, the EC50 (72 h) of > 100 mg/L and NOEC (72 h) of 100 mg/L will be used for the Chemical Safety Assessment.