Reaction products of sodium glucoheptonate with iron sulfate and ammonium hydroxide

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to microorganisms, other

Remarks:

TOXcontrol® assay (MicroLAN BV, The Netherlands)

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: well described bioassay based on scientific principles; read-across

Qualifier:

no guideline followed

Principles of method if other than guideline:

TOXcontrol® (MicroLAN BV, The Netherlands) based on the measurement of Vibrio fischeri bioluminescence inhibition (ISO 11348). TOXcontrol® is an advanced automatic on-line water toxicity monitor based on the use of luminescent bacteria (V. fischeri) to give an indication of the toxicity of the contaminants in water as a function of the emitted light.
The equipment works on the same basis as the certified methodology for the analysis of toxicity with V. fischeri (ISO 11348-3) but adapted to automatic equipment.

GLP compliance:

not specified

Specific details on test material used for the study:

No details reported.

Analytical monitoring:

not required

Details on sampling:

No details reported.

Vehicle:

no

Details on test solutions:

Stock solutions were obtained by dissolving metal salts in HPLC water. The pH of solutions was not adjusted but it was monitored and no sudden changes of pH were reported.

Test organisms (species):

Vibrio fisheri

Details on inoculum:

- Strain: NRRL B-11177
- Source: Microlan B.V., Waaljik

Test type:

static

Water media type:

not specified

Limit test:

no

Total exposure duration:

15 min

Post exposure observation period:

No details reported.

Hardness:

No details reported.

Test temperature:

kept constant at 15 °C during incubation time

pH:

No details reported.

Dissolved oxygen:

No details reported.

Salinity:

No details reported.

Nominal and measured concentrations:

No details reported.

Details on test conditions:

TEST SYSTEM
- Series of five concentrations of each test solution were prepared and the measures were performed in triplicate. A quality control of the performance of the tests was executed.
Positive and negative controls of the measurements were done before and after each series of measurement. Negative control was done using reference water. Measurement was accepted if toxicity value was between −3 and 3%. Positive control used zinc sulphate (2500 mg/L). If toxicity is over 60%, the series of measurement are accepted. If the negative or positive control is out of range, the series of measurements are excluded and the test repeated.

OTHER TEST CONDITIONS
- Adjustment of pH: no (The pH of solutions was not adjusted but it was monitored and no sudden changes of pH were reported.)

TEST CONCENTRATIONS
- Test concentrations: Different concentrations of the same compound were tested automatically to obtain the curve concentration– response that will show information for the EC50 calculation. For Fe (III), the standard solution contained 624 mg/L. The concentration range of the working solution is between 20 and 80 mg/L.

Reference substance (positive control):

yes

Remarks:

zinc sulphate (2500 mg/L)

Duration:

15 min

Dose descriptor:

EC50

Effect conc.:

52.08 mg/L

Nominal / measured:

not specified

Conc. based on:

element

Remarks:

Fe (III)

Basis for effect:

other: bioluminescence

Remarks on result:

other: SD of 5.4 mg/L

Details on results:

No details provided.

Results with reference substance (positive control):

Not reported.

Reported statistics and error estimates:

EC50 values have been calculated according to “dilution series procedure” of TOXcontrol® instrument for each target compound. The sigmoidal inhibition curves were calculated with the help of the Prism 4 software (GraphPad Software Inc.).

Validity criteria fulfilled:

not applicable

Conclusions:

EC50 (15 min) = 52.08 mg Fe(III)/L

Executive summary:

The toxicity of the read-across substance Iron (III) sulfate hydrate (CAS 15244-10-7) towards aquatic microorganisms was determined by using TOXcontrol® assay (MicroLAN BV, The Netherlands). The equipment works on the same basis as the certified methodology for the analysis of toxicity with Vibrio fisheri (ISO 11348-3; strain used: NRRL B-11177) but adapted to automatic equipment. TOXcontrol® is an advanced automatic on-line water toxicity monitor which gives an indication of the toxicity of the contaminants in water as a function of the emitted light. Series of five concentrations of each test solution were prepared and the measures were performed in triplicate. As positive control, zinc sulphate (2500 mg/L) has been used. For Fe (III), the standard solution contained 624 mg/L. The concentration range of the working solution is between 20 and 80 mg/L. Positive and negative controls of the measurements were done before and after each series of measurement.

As final result, the EC50 (15 min) amounts to 52.08 mg Fe(III)/L.

Reference 2

Endpoint:

toxicity to microorganisms, other

Remarks:

Photobacterium phosphoreum Microtox test

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

other: scientific method which is not conform to OECD standard

Qualifier:

no guideline followed

Principles of method if other than guideline:

Photobacterium phosphoreum Microtox test

GLP compliance:

no

Specific details on test material used for the study:

No details given.

Analytical monitoring:

not specified

Details on sampling:

Not applicable.

Vehicle:

not specified

Details on test solutions:

No details given.

Test organisms (species):

other: Photobacterium phosphoreum

Details on inoculum:

No details given.

Test type:

not specified

Water media type:

not specified

Limit test:

no

Total exposure duration:

15 min

Post exposure observation period:

No details provided.

Hardness:

No details provided.

Test temperature:

No details provided.

pH:

No details provided.

Dissolved oxygen:

No details provided.

Salinity:

No details provided.

Nominal and measured concentrations:

No details provided.

Details on test conditions:

No details provided.

Reference substance (positive control):

not specified

Duration:

15 min

Dose descriptor:

EC50

Effect conc.:

118.7 mg/L

Nominal / measured:

not specified

Conc. based on:

test mat.

Basis for effect:

other: bioluminescence

Details on results:

L(E)C50 for ferrous sulfate reported as 182 µmol/L.

Conversion from µmol to mg/L by considering molecular weight for ferrous sulfate (151.9 g/mol):
782 µmol/L = 0.000782 mol/L
0.000782 mol/L x 151.9 g/mol = 118.7 mg/L

Results with reference substance (positive control):

No details provided.

Reported statistics and error estimates:

The 5- and 15-min EC50s of the Microtox ® test were obtained by the linear regression package provided by the Microbics Corporation (Microbics
1989).

Validity criteria fulfilled:

not specified

Conclusions:

Test concentrations unknown, pH was not adjusted after added iron and no dose-response curve was available. Toxicity of ferrous sulfate to microorganisms is limited (EC50 (15 min) = 118.7 mg/L for Ferrous sulfate).

Executive summary:

The aquatic toxicity of the read-across substance Ferrous sulfate (CAS 7720 -78 -7) was determined using a Photobacterium phosphoreum Microtox test. Exact test conditions such as substance concentrations are not mentioned. As final result, an EC50 (15 min) of 782 µmol/L (equals 118.7 mg/L) for Ferrous sulfate is reported.

Reference 3

Endpoint:

toxicity to microorganisms

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: basic scientific principles met

Qualifier:

no guideline required

Principles of method if other than guideline:

SCAS reactors; feeding with synthetic influent dosed with different iron and/or nitrogen compounds

GLP compliance:

no

Specific details on test material used for the study:

None reported.

Analytical monitoring:

yes

Details on sampling:

Not reported.

Vehicle:

not specified

Details on test solutions:

No details reported.

Test organisms (species):

activated sludge, domestic

Details on inoculum:

- Source: Bourgoyen-Ossemeersen, Gent, Belgium

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

12 d

Post exposure observation period:

After period I (Day 0-12) including exposure to iron/nitrogen compounds, the second experimental phase (period II) was initiated.

Hardness:

not reported

Test temperature:

28°C

pH:

at the end of the batch period: 7.0 - 8.2

Dissolved oxygen:

not reported

Salinity:

not applicable

Nominal and measured concentrations:

112 mg Fe/L,

Details on test conditions:

TEST SYSTEM
- Test vessel: erlenmeyers
- Aeration: yes, continuous shaking at 120 rpm

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: skimmed mild powder dissolved in tap water

TEST CONCENTRATIONS
- Test concentrations: 112 mg Fe/L

Reference substance (positive control):

not required

Remarks on result:

other: see 'Remarks'

Remarks:

Addition of iron salts appeared toxic towards the microbial population.

Details on results:

No details provided.

Results with reference substance (positive control):

not applicable

Reported statistics and error estimates:

Please refer to the attached backgroud material for standard deviations etc. of the achieved test results.

Physical mixed liquor characteristics

Visual observation of the ML supernatant showed differences in color and turbidity. The supernatant of the control, the NO2(-) and NO3(-) reactors was more or less clear and colorless during the entire experiment. From day 4 on, the iron-dosed reactors manifested yellowish to brown, at times extremely turbid effluents (up to 243 NTU). After ending the iron and oxidized nitrogen additions, the effluents of all reactors regained low turbidity (21.6 ±8.8 NTU, averaged over all reactors in period II).

Immediately after the combined addition of ferric iron ions and nitrite (Fe(IIl) + NO2(-)), and to a lesser extent after addition of Fe(III) alone, settleability severely decreased (results not shown). Fe(III) + NO3(-) and Fe(II) + NO3(-) demonstrated slightly higher settleability, i.e. lower SVI than the control throughout the experiment. Both ferrous and ferric iron alone resulted in an increased CST, up to 35 CST-s (results not shown). After ending the iron salt addition (period II), dewaterability seemed initially to recover, but, especially in the Fe(III) treated reactor, soon worsened again (>60 CST-s). Adding nitrite or nitrate in combination with ferric iron had also a negative effect on the dewaterability. The CST values of the other reactors (NO2(-), NO3(-), Fe(II) + NO2(-), Fe(II) + NO3(-)) remained approximately constant (16 ± 2 CST-s) during the whole experiment.

The sludge of the different reactors was also examined under the microscope. The treatment history, namely the type of iron and oxidized nitrogen additions during period I, was still influencing the appearance of the sludge flocs and the presence of protozoa on day 23, e.g. 12 days after ending the different additions. The control sludge formed greyish, sufficiently large, mostly compact flocs. Free-swimming protozoa were present in quite large numbers. The sludge of the NO2(-) and NO3(-) SCAS reactors did not differ much from the sludge in the control reactor. As for the iron-dosed reactors, large differences could be observed depending on the form of the iron, and combination with nitrite or nitrate. The sludge with a history of ferrous iron appeared as vast, dark orange/brown colored flocs, which were larger than in the control, and with only occasionally filaments sticking out. Almost no protozoa could be found. Fe(II) + NO2(-) and Fe(II) + NO3(-) produced more or less similar sludge. Addition of Fe(III) had a totally opposite effect. Sludge flocs had fallen apart into small, loose and irregularly shaped flocs. No filaments could be observed. Remarkable however was the abundant presence of stalked protozoa, presumably Vorticella. In Fe(III) + NO2(-) and Fe(III) + NO3(-), these stalked protozoa could not be observed. The floc structure of the sludge in the Fe(III) + NO2(-) reactor was similar to the Fe(III) sludge, whereas the sludge from Fe(III) + NO3(-) had a better structure.

Nutrient removal efficiencies

To avoid crowded graphs, the concentrations of COD, TAN and TON (=NO2(-)-N + NO3(-)-N) were drawn in two separate graphs (Fig. 1, see attached background material). The control has been plotted on both graphs for easier comparison. Ferric iron alone (Fe(III)) or combined with nitrite (Fe(III) + NO2(-)) resulted in rapid increase in residual COD (Fig. 1). After one week of operation the sludge seemed to adapt to the additions, seen by the decrease in residual COD. In this experiment, a similar course was followed by Fe(II) and Fe(II)+NO2(-). Repeating the test with new sludge however resulted in lower COD peaks for the latter reactors. In contrast to these iron and nitrite dosed reactors, no increased COD concentrations were found in Fe(II) + NO3(-) and Fe(III) + NO3(-). Despite the relative peak concentrations, COD removal efficiencies were above 90% for all reactors during the entire experiment (Fig. 2, see attached background material). In contrast to the COD removal, total nitrogen removal was highly influenced by the received treatment (Fig. 2).

Regarding the residual TAN (Fig. 1) or Kjeldahl nitrogen (results not shown), similar observations to the COD can be made. Again the addition of iron salt alone or combined with nitrite caused increased effluent concentrations, followed by a recovery in period II. In this case, nitrite even intensified the inhibitory effect of the ferrous and ferric iron. The effluent TON concentrations of the control NO2(-), NO3(-), Fe(II) + NO3(-) and Fe(III) + NO3(-) reactors were comparable. For these reactors, TON was almost entirely nitrate (nitrite concentrations were throughout the experiment lower than 1 mgN/1; results not shown). In contrast to the latter reactors, the reactors treated with ferrous or ferric iron, with or without NO2(-) additions, demonstrated a steep decrease in TON. Moreover, a large fraction of the TON was nitrite.

The increased TAN concentrations during period I in Fe(II), Fe(II) + NO2(-), Fe(III) and Fe(III) + NO2(-) indicated that nitrification, more specifically the ammonia oxidation, was negatively affected. Fig. 3 (see attached background material) clearly shows that an inhibitory effect was exerted on the ammonia oxidation for these reactors. This inhibition of the ammonia oxidation appeared to be reversible, as values for the nitrification efficiency increased in period II.

The high NO2(-)/TON ratio in the Fe(II), Fe(III), Fe(ll) + NO2(-) and Fe(III) + NO2(-) reactors (60 -80%) seems to indicate that the nitrite oxidation, i.e. the second step of nitrification, was even more severely inhibited than the ammonia oxidation. Moreover, the nitrite oxidation remained inhibited even in period II, shown by the NO2(-)/TON values in period II (data not given).

The low TON concentrations in the effluent of Fe(II), Fe(II) + NO2(-), Fe(III) and Fe(III) + NO2(-) (Fig. 1) (period I) could be explained by the inhibition of nitrification, but eventually also by increased denitrification of the available nitrogen. The efficiency of denitrification (Fig. 3) of the available TON is for these reactors indeed higher than for the other SCAS.

Activity of the activated sludge ( OUR)

On day 12 respirometric measurements were performed on the activated sludge. OUR measurements form a useful technique to evaluate biomass inhibition or stimulation. By using ATU as a selective inhibitor of nitrification, both total activity and nitrifying activity could be assessed (Fig. 4, see attaches background material). It is striking that both nitrite and nitrate had a negative effect on oxygen uptake after repeated addition. Adding iron more severely influenced the activity of the biomass. Total respiration activity fell back to 28% for Fe(II) and 23% for Fe(III) of the activity of the control. The decrease is even higher in case of the nitrifying activity: after addition of ferrous iron, only 7% of the nitrifying activity remained, while ferric iron completely inhibited nitrifying activity. The results further indicate that NO2(-) enhanced the toxicity of the Fe(III). NO3(-) seemed to counteract some of the toxicity of the iron ions.

Short term effect of iron salts and nitrogen oxides on respirometric activity

In an additional test with analogous SCAS reactors, activity was assessed within the hour after the different additions. The addition of iron salts, both ferric and ferrous, induced a decrease in both total and nitrifying activity, 1 h after their addition (results not shown). Nitrite hereby increased the effect of the iron salts. Measurements of the residual nitrite and nitrate concentrations in the ML after the 1 h period on the shaker (Fig. 5, see attached background material), illustrate that in the Fe(II) + NO2(-) and Fe(III) + NO3(-) vessels the nitrite was partly transformed to nitrate, and that a large amount of nitrogen had disappeared. In the Fe(II) + NO3(-) and Fe(III) + NO3(-) vessels, almost all of the nitrate could be recovered. Parallel test with water resulted in similar changes in nitrogen concentrations. Moreover, the observed nitrogen deficit increased in time. Qualitative analyses of the air above the liquid surface with Gastec tubes indicated trace productions of NO and NO2 for the flasks containing Fe(II) + NO2(-) and Fe(III) + NO2(-).

Evolution of pH

Being an important factor for microbial activity and the removal efficiencies of activated sludge, pH was measured in the ML at the end of each batch period. The pH at the end of the batch period was in the range of 7.0-8.2 for all treatments during the whole experiment. Measurement of the evolution of the pH during a batch period (Fig. 6, see attached background material) however showed that although pH at the end of the batch period was comparable for all treatments, the different additions induced particular changes in pH. Addition of ferric iron led almost immediately to a large pH drop, followed by a recovery during the remainder of the batch period. Fe(IIl) - NO2(-) and Fe(III) + NO3(-) experienced the same decrease in pH, but in these reactors the pH recovery was faster and larger. Similar observations could be made for ferrous iron, although with a much smaller decrease in pH.

Supplementing additional phosphate

The milkfeed of the SCAS contained already 20 mg P/L. From the SCAS experiments, it was found that addition of iron salts to activated sludge had a strong negative effect on nitrification. To verify whether this nitrification failure was due to shortage in phosphorous, extra phosphate (25 mg PO4(3 -)-P/L) was added together with the feed to SCAS reactors that were further operated in the same way as in the first experiment, Calculation of the reactor performance from the results of the effluent analyses (Table 1) indicates that supplementing the sludge with extra phosphorus did not prevent the inhibition of the nitrification.

Table 1. Averaged (over 15 days) removal (COD and total nitrogen) and conversion (nitrification and denitrification) efficiencies in the SCAS reactors with or without additional phosphate addition (+P = +25 mgPO4(3-) -P/L)

SCAS	Removal (%)		Conversion (%)
	COD	Ntot	Nitrification	Denitrification
Control	98.3 ± 0.4	60.7 ±16.3	98.3 ± 1.2	61.3 ± 16.0
Control + P	98.3 ± 0.4	60.6 ± 16.1	97.3 ± 1.2	62.0 ± 16.3
Fe(II)	97.7 ± 0.8	50.3 ± 20.7	75.8 ± 16.4	60.6 ± 22.3
Fe(II) + P	97.6 ± 0.8	51.5 ± 21.9	76.8 ± 17.1	62.3 ± 23.2
Fe(III)	97.1 ± 1.6	66.3 ± 14.2	67.2 ± 34.9*	81.5 ± 17.7
Fe(IlI) + P	97.5 ± 0.9	54.1 ± 15.7	65.3 ± 19.7*	76.4 ± 19.3

Values are mean ± standard deviation (n = 6).

*Significantly different from control reactor.

Validity criteria fulfilled:

not applicable

Conclusions:

Addition of iron salts appeared toxic towards the microbial population.

Executive summary:

The impact of iron salts on activated sludge and interaction with nitrite or nitrate was experimentally investigated and gives additional information referring to the evaluation of iron toxicity towards microorganisms.

The influence of addition of Fe(II) or Fe(III), alone or together with NO2(-) or NO3(-) on bench-scale activated sludge reactors was examined. Large differences were established between the distinct treatments, regarding reactor performance, sludge characteristics as well as microbial community. Ferric iron was more detrimental than ferrous iron. In some cases, nitrite was found to enhance inhibitory effects of the added iron, whereas nitrate had more a neutralizing effect. It was found that precipitation of phosphate by the iron was not responsible for the observed inhibition. Decrease in pH upon formation of iron hydroxides and the impairment of the floc structure could partially explain the toxicity of the iron dosages.

Reference 4

Endpoint:

toxicity to microorganisms, other

Remarks:

DIN 38412, part 8 (Pseudomonas Zellvermehrungshemm-Test)

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: basic scientific principles are met; read-across

Qualifier:

according to guideline

Guideline:

DIN 38412-8 (Pseudomonas Zellvermehrungshemmtest)

Deviations:

not specified

GLP compliance:

not specified

Specific details on test material used for the study:

No details provided.

Analytical monitoring:

not specified

Details on sampling:

No details provided.

Vehicle:

not specified

Details on test solutions:

No details provided.

Test organisms (species):

Pseudomonas putida

Details on inoculum:

No details provided.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

16 h

Post exposure observation period:

No details reported.

Hardness:

No details provided.

Test temperature:

21°C

pH:

No details provided.

Dissolved oxygen:

No details provided.

Salinity:

Not applicable.

Nominal and measured concentrations:

No details provided.

Details on test conditions:

TEST CONCENTRATIONS
- Test concentrations: 3 range of concentration tested: 0-40 mg/L; 80-5000 mg/L; > 5000 mg/L

Reference substance (positive control):

not specified

Duration:

16 h

Dose descriptor:

EC0

Effect conc.:

> 5 000 mg/L

Nominal / measured:

not specified

Conc. based on:

test mat.

Basis for effect:

growth inhibition

Details on results:

0-40 mg/L: no effect
80-5000 mg/L: stimulation of growth
> 5000 mg/L: no stimulation of growth but not toxic

Results with reference substance (positive control):

No details given.

Reported statistics and error estimates:

No details given.

Validity criteria fulfilled:

not specified

Remarks:

Only limited information available.

Conclusions:

EC0 (16 h) > 5000 mg/L

Executive summary:

The toxicity of the read-across substance Sodium gluconate (CAS 527-07-1) was tested according to the German standard procedure DIN 38412, part 8 (Pseudomonas Zellvermehrungshemm-Test). As test organism, Pseudomonas putida has been used. Three different concentration ranges were tested: 0 -40 mg/L, 80 -5000 mg/L and > 5000 mg/L. It was reported that in the 0 -40 mg/L concentration range, no effect were observed. In the 80 -5000 mg/L concentration range, growth was stimulated. For the range of > 5000 mg/L, neither stimulation of growth nor toxic effects were observed. As final result, the EC0 (16 h) amounts to > 5000 mg/L.

Description of key information

There is no data available for the target substance iron glucoheptonate (CAS 23351 -51 -1) on toxicity towards microorganisms. However, there is data available for the read-across substances sodium gluconate, iron sulphate and iron salts. This data is used within a frame of a weight-of-evidence approach to assess the toxicity of iron glucoheptonate.

In a TOXcontrol® assay (MicroLAN BV, The Netherlands; Lopez-Roldan et al., 2012) with Vibrio fisheri an EC50 (15 min) value of 52.08 mg Fe(III)/L was measured with the test substance Iron (III) sulfate hydrate. Converted to the target substance FeGHA, the EC50 (15 min) value is 369.14 mg FeGHA/L.

Key value for chemical safety assessment

EC50 for microorganisms:

369.14 mg/L

Additional information

There is no data available for the target substance Iron glucoheptonate (CAS 23351-51-1) on toxicity towards microorganisms. However, there is data available for the read-across substances Sodium gluconate (CAS 527-07-01), Iron sulphate (CAS 7720-78-7) and Iron (III) sulphate hydrate (CAS 15244-10-7) which is evaluated in a weight of evidence approach. All in all, four different studies are available which are briefly summarised as follows.

 

The toxicity of the read-across substance Sodium gluconate (CAS 527-07-1) was tested according to the German standard procedure DIN 38412, part 8 (Pseudomonas Zellvermehrungshemm-Test; OECD SIDS, 2004). As test organism, Pseudomonas putida has been used. Three different concentration ranges were tested: 0 -40 mg/L, 80 -5000 mg/L and > 5000 mg/L. It was reported that in the 0 -40 mg/L concentration range, no effect were observed. In the 80 -5000 mg/L concentration range, growth was stimulated. For the range of > 5000 mg/L, neither stimulation of growth nor toxic effects were observed. As final result, the EC0 (16 h) amounts to > 5000 mg/L.

The aquatic toxicity of the read-across substance Ferrous sulfate (CAS 7720 -78 -7) was determined using a Photobacterium phosphoreum Microtox test (Calleja et al., 1994). Exact test conditions such as substance concentrations are not mentioned. As final result, an EC50 (15 min) of 782 µmol/L (equals 118.7 mg/L) for Ferrous sulfate is reported.

 

The toxicity of the read-across substance Iron (III) sulfate hydrate (CAS 15244-10-7) towards aquatic microorganisms was determined by using TOXcontrol® assay (MicroLAN BV, The Netherlands; Roldan et al., 2012). The equipment works on the same basis as the certified methodology for the analysis of toxicity with Vibrio fisheri (ISO 11348-3; strain used: NRRL B-11177) but adapted to automatic equipment. TOXcontrol® is an advanced automatic on-line water toxicity monitor which gives an indication of the toxicity of the contaminants in water as a function of the emitted light. Series of five concentrations of each test solution were prepared and the measures were performed in triplicate. As positive control, zinc sulphate (2500 mg/L) has been used. For Fe (III), the standard solution contained 624 mg/L. The concentration range of the working solution is between 20 and 80 mg/L. Positive and negative controls of the measurements were done before and after each series of measurement. As final result, the EC50 (15 min) amounts to 52.08 mg Fe(III)/L.

The impact of iron salts on activated sludge and interaction with nitrite or nitrate was experimentally investigated and gives additional information referring to the evaluation of iron toxicity towards microorganisms (Philips et al., 2003). The influence of addition of Fe(II) or Fe(III), alone or together with NO2(-) or NO3(-) on bench-scale activated sludge reactors was examined. Large differences were established between the distinct treatments, regarding reactor performance, sludge characteristics as well as microbial community. Ferric iron was more detrimental than ferrous iron. In some cases, nitrite was found to enhance inhibitory effects of the added iron, whereas nitrate had more a neutralizing effect. It was found that precipitation of phosphate by the iron was not responsible for the observed inhibition. Decrease in pH upon formation of iron hydroxides and the impairment of the floc structure could partially explain the toxicity of the iron dosages.

 

Derivation of (non)-effective concentrations for Iron glucoheptonate (CAS 23351-51-1)

There are four studies available for different read-across substances. Since it is expected that toxicity of the target substance is rather triggered by the iron cation, data on the metal salt are considered for the Chemical Safety Assessment.

 

An EC0 (16 h) of > 5000 mg/L was determined for the substance Sodium gluconate (OECD SIDS, 2004). By consideration of the molecular weights of the read-across substance Sodium gluconate (MW = 218.14 g/mol) and the target substance Iron glucoheptonate (MW = 354.8 g/mol; trihydrated form), the EC0 value for the read-across substance can be converted in order to account for the target substance.

5000 mg/L x 354.8 g/mol / 218.14 g/mol = 8132 mg/L

The calculated EC0 (16 h) value of 8132 mg/L for the target substance will be used for the Chemical Safety Assessment.

 

The EC50 (15 min) value for Ferrous sulphate was determined to be 118.7 mg/L (Calleja et al., 1994). Since this value refers to the compound itself and not only to the metal ion, a conversion is necessary. By consideration of the molecular weights of Ferrous sulphate (151.9 g/ mol) and Iron (55.84 g/mol), the LC50 value for Iron is calculated as follows.

118.7 mg/L x 55.84 g/mol / 151.91 g/mol = 43.92 mg Fe/L

The EC50 (15 min) is converted to the target substance FeGHA with regard to the molecular weight using the following equation

EC (Fe) in source = 43.92 mg/L

EC (FeGHA) in target = 43.92 / 55.84 x 300.8 = 236.58 mg/L

Purity: 76 %

236.58 / 0.76 = 311.29 mg/L

The calculated EC50 (15 min) value of 311.29 mg/L for the target substance will not be used for the Chemical Safety Assessment since the publication is assessed with Klimisch 3.

  

The EC50 (15 min) value for Iron (III) sulfate hydrate was determined to be 52.08 mg Fe/L (Roldan et al., 2012).

The EC50 (15 min) is converted to the target substance FeGHA with regard to the molecular weight using the following equation

EC50 (Fe) in source = 52.08 mg/L

EC50 (FeGHA) in target = 52.08 / 55.84 x 300.8 = 280.55 mg/L

Purity: 76 %

280.55 / 0.76 = 369.14 mg/L

The calculated EC50 (15 min) value of 369.14 mg/L for the target substance will be used for the Chemical Safety Assessment

.