Iron-fortified water: a new approach for reducing iron deficiency anemia in resource-constrained settings

A new approach for fortification of drinking water is presented for combating iron deficiency anemia (IDA) worldwide. The idea is to leach Fe from a bed containing granular metallic iron (Fe0), primarily using ascorbic acid (AA). AA forms very stable and bioavailable complexes with ferrous iron (FeII). Calculated amounts of the FeII-AA solution can be added daily to the drinking water of households or day-care centers for children and adults (e.g. hospitals, kindergartens/schools, refugee camps) to cover the Fe needs of the populations. Granular Fe0 (e.g., sponge iron) in filters is regarded as a locally available Fe carrier in low-income settings, and, AA is also considered to be affordable in low-income countries. The primary idea of this concept is to stabilize FeII from the Fe0 filter by using an appropriate AA solution. An experiment showed that up to 12 mg Fe can be daily leached from 1.0 g of a commercial sponge iron using a 2 mM AA solution. Fe fortification of safe drinking water is a practicable, affordable and efficient method for reducing IDA in low-income communities.


Background of the Fe II -AA concept
The ability to improve iron status in populations largely depends on the understanding of the biochemistry and absorption of Fe in the human body 2,7,17,28 .There are two types of iron: heme (found in red meat) and non-heme (found in plant-based foods) iron.Iron absorption in the gastrointestinal tract is lower for non-heme sources of iron.The literature contains many contradictory findings regarding parameters pertinent to the effective absorption of Fe by humans 3,5,17 .It seems established that ferrous salts are better than heme iron in combatting IDA, however, some newer iron formulations have claimed the opposite 30,31 .Fortunately, it is unequivocally reported that a combination of ascorbic acid (AA) and Fe-bearing diets improves the iron status in populations 7,30 .Being a weak acid, AA is a strong reducing agent for Fe III and an excellent complexing agent for Fe II7,28,29 .This means that, where necessary, AA reduces aqueous Fe III -Fe II and builds the very stable Fe-AA complex which is available for the human body (Fact 1: AA reduces aqueous Fe III and builds stable Fe-AA complex).Therefore, Fe-AA complexes are bio-available in the human body 7 .
People living in a high-iron groundwater setting have demonstrated better iron status or suffer less from IDA [32][33][34][35][36][37][38] .The rationale for this finding is that Fe-rich groundwater contains Fe II which is oxidized to Fe III upon contact with air (20% O 2 ) 39 .This implies that the amount of bioavailable Fe II also depends on the duration of storage.Upon oxidation Fe III precipitates as Fe hydroxides/oxides or is complexed to less/non bioavailable species.Fe-rich groundwater contains bioavailable Fe II .Whenever clean Fe-rich groundwater is available as a drinking water source, it suffices to stabilize Fe II , for example by addition of AA or lemon juice, to improve the Fe status of the population 25,40,41 .
Taken together, supplying populations with drinking water containing Fe stabilized in the ferrous form (Fe II ) is sufficient (Fact 1).This idea is not new, as it has been successfully applied in rural Brazil for the last three decades 7,[21][22][23][24]26 . In ts original form, each family was required to have an earthen pot with about 10 L capacity for storing drinking water.Families received a concentrated iron solution (l0 g/L) in the form of ferrous sulfate (FeSO 4 ) and L-ascorbic acid in the molar ratio Fe II :AA = 1:3, dispensed in l0 mL bottles 21 .The success of this approach has motivated its extension to day-care institutions 7,24 .The present work seeks to leach Fe II from metallic iron (Fe 0 ).Thus, commercial ferrous sulfate is replaced by a more affordable granular Fe 0 , which is additionally readily available, for example as iron filings, iron wire, scrap iron, sponge iron (direct reduced iron), or steel wool.Fe 0 sources to be considered in this context should not contain any toxic alloying elements.Sponge iron is certainly the best material fulfilling this prerequisite.The typical mineralogical composition (in %) of sponge iron is 42,43 : Fe (total): 92-95; Fe 0 : 85-90; C: 1.0-1.5;S: 0.005-0.015;P: 0.02-0.09,SiO 2 : 1.0-2.0,and balanced by The typical mass density of sponge iron is 1600 kg m −3 and its apparent density is 3200 kg m −342 . Maerials selected herein for use in the Fe fortification unit are known to be effective for producing stable soluble Fe II solutions under environmental conditions.Availability and cost are also considered in the selection process because substantial quantities would be required for decentralized production. UsedFe 0 particles should not contain toxic alloying elements (e.g.Cr, Ni). Frtunately, this is the case for many readily available Fe 0 materials such as cast iron and low alloyed steel.For example, Lufingo et al. 29 analyzed nine commercial steel wool for their elemental composition and found that the Fe 0 content was constantly higher than 99%, while the (Cr + Ni) level was lower than 0.7% in all the specimens.These data suggest that a solution containing some 10 mg/L of Fe would contain non-detectable levels of (Cr + Ni). Hwever, ideally, used Fe 0 specimens should be free of Cr, Ni and Pb.Therefore, there is a need to (1) determine the chemical composition of potential Fe 0 materials, and (2) test them with regard to the leaching ability of relevant toxic elements before their use for drinking water fortification.The next section presents a proof of concept, limited to illustrating the Fe leaching capability of a 0.02 M AA solution (pH = 3.5) from four selected Fe 0 specimens, in five parallel experiments.

Current use of Fe 0 for IDA control
Fe 0 is currently considered an adventitious source of bioavailable iron with both adverse and beneficial effects on human health (Tables 1, 2) [44][45][46][47][48][49][50] .On the one hand, excessive Fe intake (e.g.Fe overload or iron poisoning) is attributed to metallic poisoning derived from foods and drinks prepared in Fe 0 -based vessels 2,[18][19][20]44,45 . On th other hand, Fe leached from Fe 0 -based cooking utensils is recommended to prevent and cure IDA [18][19][20]40,49,50 .Where Fe 0 cooking utensils are not available, not affordable, or not socially accepted, reusable Fe 0 ingots have been used [51][52][53][54][55] , for example in Al-based cooking utensils (Fig. 1). Figure 2 shows the photograph of a fish-shaped iron ingot as used for in-situ food fortification in Cambodia as well as a leaf-shaped iron ingot as used in India 55,56 .Table 2. Overview on the status of current approach to exploit metallic iron (Fe 0 ) to controlling iron deficiency anemia (IDA).

Tool Status References
Leaching Fe from cooking pots Field applications 57 Placing Fe 0 in drinking water containers Experimental Fe 0 in the form of iron powders has also been widely used in food fortification 14,17,56 .In this context, Fe absorption is governed by the extent of the dissolution of used Fe 0 powders in the gastric fluid 17 .The extent of Fe absorption thus depends on the intrinsic reactivity of the used Fe 0 in the human gastric fluid.The lack of characterization of the Fe 0 intrinsic reactivity seems to be a major shortcoming as many different Fe 0 types have been tested and used without appropriate quality control 58 .A proper quality control would characterize the relative Fe bioavailability from used Fe 0 powders.For example, H-reduced Fe 0 powders for fortifying cereal flours have been largely used, while the WHO recommends only electrolytic iron powder 14 .The WHO recommendation is based on field evidence from Fe absorption in efficacy studies.However, it would have been better to develop an operational parameter (e.g. a dissolution index) to assess the Fe 0 dissolution trend under different physiological conditions (in the gastrointestinal tract).
Food fortification is largely considered the best strategy to increase iron intake of a population, especially for children and pregnant women 2,[14][15][16]55 . TheWHO has recognized food fortification as a potential universal tool for defeating IDA worldwide 11 .However, there are several concerns to be named: (1) by solving one problem (IDA) in some people, universal fortification exacerbates Fe intoxication for other people (questioned universality), and iron poisoning is as severe as IDA 2 , (2) because of low income, a large fraction of the population has only restricted access to commercial fortified foods (questioned affordability), and (3) it is not known which fraction of Fe 0 in food is effectively solubilized during digestion and which proportion is absorbed by the body of each individual person 2,7,17,23 .
With the objective of solving the three named problems this communication suggests a solution that is beneficial to the segment of the population (potentially) suffering from IDA.This solution is called 'semi-universal' fortification 2 and uses water as a vehicle 7 .Moreover, only drinking water is fortified and is considered affordable or at least more affordable than commercial fortified foods.Concerning the bioavailability, Fe is leached from granular Fe 0 by ascorbic acid and is long-term stable and bioavailable 7,[21][22][23][24]26,28 .
Fe 0 leaching with ascorbic acid: proof of concept Fundamental aspects.The present study presents a concept to extract Fe II from Fe 0 specimens, using ascorbic acid (AA) as leaching agent or lixiviant.Previously, AA has been used to leach and extract metals from natural metal oxides (e.g.marine MnO 2 ) by reductive dissolution [63][64][65][66] .In this context, AA is a reduction and leaching (chelating) agent for ore processing at ambient temperature and under normal pressure.A key lesson from this hydrometallurgical process is that AA leaching has good dynamic characteristics, high reaction kinetics, and requires simple equipment.In this paper, AA is used to sustain the oxidative dissolution of Fe 0 specimens.Fe 0 is oxidized by water (H + ) (oxidative dissolution) (Eq. 1) and the resulting Fe 2+ is stabilized by chelation with AA (Eq.2).In the absence of AA, Fe 2+ would have been further oxidized to Fe 3+ by oxygen present in air (Eq.3) and precipitated as Fe(OH) 3 (Eq.4) 58,[67][68][69][70] .From Eq. ( 1), a tool to increase the extent of Fe 2+ leaching is to lower the pH value (H + addition).
Once Fe(AA) 2+ complexes are formed (Eq.2), they remain stable even when the pH increases to values as high as 8.0 71,72 .In particular, Conrad and Schade 71 demonstrated that, adding NaOH to a (FeCl 3 + AA) solution results in a soluble iron chelate, while adding AA to a (FeCl 3 + NaOH) mixture results in an insoluble Fe(OH) 3 .
Organic acids (e.g.acetic acid, citric acid, oxalic acid) and other chelating agents (e.g.ethylenediaminetetraacetic acid-EDTA) can be used as effective lixiviants for fly ash and minerals 73,74 .Organic acid mixtures are currently tested to recover valuable metals from spent Li-batteries 75 .For example, the process described by Chen et al. 74 , used iminodiacetic acid and maleic acid to quantitatively recover Li + and Co 3+ at 60 °C.AA then converts Co 3+ -Co 2+ and enables selective recovery of Co.The present work uses AA to sustain Fe 0 dissolution (Eq.1).Comparable approaches are efforts from our research group using two organic chelates (EDTA and 1,10-Phenanthrolin) to characterize the intrinsic reactivity of Fe 0 specimens 29,58,76 .Moreover, our research group has been routinely using a 0.1 M AA as a washing solution to free glassware from Fe III oxides after Fe 0 decontamination experiments.
Experimental procedure.This section is adapted from Ndé-Tchoupé et al. 76 who characterized the reactivity of twelve Fe 0 materials for H 2 evolution in H 2 SO 4 .The four tested herein were included, and depicted significant different reactivity.This result was recently confirmed using a newly developed test for Fe 0 screening: the ascorbic acid test 58 .
Solutions.The working solution was prepared from a L-ascorbic acid powder (Merk, Darmstadt, Germany).The used 1,10-Phenanthroline, sodium ascorbate, and the iron standard (1000 mgL −1 ) were also from Merck (Darmstadt, Germany).All chemicals were of analytical grade.
Iron materials.Four selected Fe 0 materials were used.Two of them were commercially available materials for groundwater remediation termed as: (1) "sponge iron", and (2) "iPuTec".Sponge iron is Eisenschwamm from ISPAT GmbH, Hamburg; while iPuTec is Graugußeisengranulat from iPutec GmbH & Co. KG, Rheinfelden; both in Germany.The other two materials were scrap iron materials from a metal recycling company (Metallaufbereitung Zwickau) termed as: "S15" and "S69".S15 was a mixture of mild steels from various origins, while S69 was a similar mixture of cast irons.Apart from sponge iron, Fe 0 materials were used in their typical state and form (i.e., "as received" state).Sponge iron was crushed into small pieces, sieved and the particles with sizes ranging between 1.0 and 1.6 mm were used, without any further pre-treatment.
Table 2 summarizes the elemental compositions of the materials based on analyses made using X-Ray fluorescence spectrometry.It can be clearly seen that the materials primarily differ in their carbon (C) and silicon (Si) contents.Thus, based on the C content, the tested materials can be divided into three classes: (1) iPuTec and S69 containing more than 3% C (cast irons), (2) S15 containing less than 2% C (mild steel), and (3) sponge iron (1.9% C), belonging to the third class, characterized by a specific manufacturing technology, which yielded porous materials 42,43 .All these materials were irregular in shape (filings and shavings) with rough surfaces.Sponge iron had a very rough surface and was even porous.iPutec and the two scrap irons (S15 and S69) were visibly covered with rust.
Experimental methods.1.0 g of each Fe 0 material was placed in a chromatographic column containing sand in its lower third and the 0.02 M AA solution in its upper two thirds (Fig. 3).Fe 0 was leached daily for five consecutive days (Monday-Friday) every week with about 180 mL of a 0.02 M ascorbic acid solution (pH = 3.5), at constant temperature of 23 ± 2 °C.At each leaching event, the exact volume of the leachate was monitored and its iron concentration was determined.The experiment was ended after 55 leaching events.This corresponds to a leaching rate of 53% for sponge iron (the most reactive material).An accompanying experiment with 2.0 g of iPuTec was performed to enable the assessment of the impact of the Fe 0 mass on the extent of Fe leaching by AA.
Analytical methods.Analysis for iron was performed using the Phenanthroline method.Although Fe(AA) was already Fe(II), reduction was performed to follow the analytical protocol which include calibrating the standard solutions.Iron concentrations were determined by a Cary 50 UV-Visible Spectrophotometer (Cary instruments, LabMakelaar Benelux B.V., Zevenhuizen, The Netherlands) at a wavelength of 510.0 nm using 1.0 cm glass cells.The pH values were measured by combined glass electrodes (WTW Co., Weinheim, Germany).
(1)  3 that sponge iron exhibited the highest extent of Fe leaching with 529.5 mg or 53% of the initial 1.0 g after 55 leaching events over 129 days.The increasing order of Fe 0 reactivity with respect to the extent of Fe leaching in 0.02 M AA is: S15 < iPuTec < S69 < sponge iron.The high reactivity of sponge iron is attributed to its higher porosity and the corresponding surface area in comparison to other materials.The same order of reactivity was reported in related works 58,76 .Another important feature from Table 4 is the fact that using twice the amount of Fe 0 (2.0 g for iPuTec) did not double the extent of Fe leaching.In fact, when doubling the initial Fe 0 mass, the daily leached mass of Fe increased by only 24.4%, from 8.6 to 11.4%.This observation is consistent with the non-linear kinetics of Fe 0 dissolution 57 .Figure 4a shows that the daily dose of 2-12 mg of Fe could be leached from each column containing 1 g of Fe 0 .For each material, the leached amount was high at the start of the experiment, then it decreased progressively with increasing leaching events (elapsed time) until about 70 days.It then increased again to values comparable to initial values for all Fe 0 specimens except S15 until day 110 (Table After day 110, a new decrease of the leached Fe level started.The trend was the same for all Fe 0 specimens including S15, with only differences in magnitude.Interestingly, around day 70, sponge iron exhibited the lowest extent of Fe leaching.Figure 4b depicts the cumulative extent of Fe leaching and shows clearly that sponge iron is the best material over the 129 leaching events. A combination of (1) non-constant kinetics of iron corrosion for individual materials, and (2) different laws of the variation kinetics amount materials, make any prediction of the leaching extent challenging (Table 5).Table 5 shows that for the first 10 leaching events, the increasing order of reactivity was iPuTec < sponge iron < S15 < S69.After this initial period, S15 was the least reactive material until t = 112 d, corresponding to the 52nd leaching event.Between the 10th leaching event and the 52nd there is also no uniform trend in the variation of the extent of Fe leaching from the three other materials.However, it is certain that various amounts of Fe(AA) 2+ can be obtained to prepare diluted solutions to prevent or combat IDA by varying the following factors: (1) the Fe 0 mass (e.g.1.0 g, 2.0 g), (2) the Fe 0 type (e.g.sponge iron, iPuTec), (3) the AA concentration (e.g.0.02 M, 0.2 M), and eventually (4) acidifying the solution.Fe 0 can first be leached by EDTA and the resulting solution (Fe III EDTA) reduced and stabilized to Fe(AA) 2+ .In fact, preliminary experiments (results not shown) have demonstrated that EDTA is a far better lixiviant than AA.The ability of AA to reduce Fe III EDTA is documented and used in analytical chemistry 29,58 .
This experiment has unequivocally shown that using two columns containing the same amount of a Fe 0 specimen (m) will yield a larger leaching Fe level than a single column containing 2 times the same materials (2 * m).This is due to extreme complexity of the phenomena associated with aqueous iron corrosion (Table 1) 29,57 .Summarized, these results prove that Fe 0 leaching using AA is a promising approach to generate stable Fe II solutions to improve the iron status of humans.

Designing a Fe II -bearing unit
The conceptual design of a Fe II -AA production unit involves two components: (1) a reactive source of metallic iron (Fe 0 ), and (2) an ascorbic acid (AA) solution.In principle, batch and column leaching operations are possible.However, column operations are preferred herein mainly because they can run for several months with limited labor input ("Fe0 0 leaching with ascorbic acid: proof of concept" section)."Fe 0 leaching with ascorbic acid: proof of concept" section and available data on Fe 0 leaching by ethylenediaminetetraacetic acid (EDTA) 29 suggest that it is possible to leach constant amounts of Fe from Fe 0 filling, sponge iron, and steel wool placed in a glass column for several weeks 77 (Fig. 5).The Fe concentration in the effluent (C 0 ) depends mainly on the intrinsic reactivity of used Fe 0 , the Fe 0 mass used, the flow velocity of the AA solution, and the AA concentration.The C 0 value (Eq.5) is selected such that a certain volume of the effluent (V 0 ) is added to a water reservoir (V 1 ) to obtain the desired concentration of Fe in the fortified drinking water (C 1 ).
Assuming that available safe drinking water is iron free, the mass balance of Fe implies that C 0 V 0 = C 1 V 1 (Eq.1).If 1 m 3 Fe II -AA fortified water (V 1 = 1000 L) containing 2 mg/L Fe II (C 1 ) is to be daily produced, and 1.0 L (V 0 ) of the effluent should be used, then the C 0 value should be 2000 mg/L or 2.0 g/L (C 0 = 2000 mg/L).The challenge is to find the best combination of Fe 0 materials (e.g.iron filings, sponge iron), Fe 0 mass, AA concentration, ( 5) Daily Fe leached mass (mg) from 1.0 g of the tested Fe 0 specimens at 8 selected events.The Fe 0 specimens are ordered from left to right in the order of increasing value of m after the second leaching event, corresponding to day 2 of the experiment.www.nature.com/scientificreports/and flow velocity of the AA solution, yielding 1 L of a 2.0 g/L Fe II effluent.In case 2.0 g/L Fe is not realistic, one should rather seek to have 10 L of the effluent with 0.2 g/L Fe II (C 0 = 200 mg/L).Figure 5 shows an operational device for the production of the Fe II -AA effluent for dilution.For the realization of this concept, common affordable laboratory devices for weighing (Fe 0 , AA) and analytically determining Fe are needed.This means that for the development of the Fe II -AA method, a small chemical laboratory or Fe II sensor is necessary.However, once the method is established, a laboratory is no longer necessary, and trained personnel can build columns to leach Fe 0 and perform dilution in water tanks.Calculations are made herein for 1 m 3 .For larger populations, the 1 m 3 water device can be used as a module, and as many modules as necessary can be used to cover the needs.The operational C 1 value of 2 mg/L is purely arbitrarily considered.More relevant values should be selected for testing.
A survey of the literature reveals that various Fe doses have been administered to persons in individual studies.For example, Ginanjar et al. 25 discussed the results of some previous studies using oral supplements of a 0 mg (placebo) to 100 mg (therapy) Fe dose in 200 mL water.Fe was added either as FeSO 4 or NaFeEDTA and was administered to test persons after at least eight hours of fasting.In other words, up to 100 mg of Fe represents the daily dose to prevent and/or cure IDA.On the other hand, Rakanita et al. 13 reported that women need 30-60 mg Fe/day.The World Health Organization recommends up to 30 mg Fe/day for children under five 11,54 .Table 6 summarizes the masses of FeSO 4 , Fe II fumarate, Fe II gluconate, and NaFeEDTA necessary to obtain 1 kg of elemental iron (Fe).It is seen that (1) 3.0 to 8.0 kg of salts are needed where just 1 kg of Fe 0 suffices, (2) FeSO 4 is more than 50 times the price of iron nails (Fe 0 ).However, the (bio)availability of Fe from Fe 0 is primarily uncertain.To design an appropriate Fe II -AA production unit, Eq. 5 is used.The system is operated such that three liters of the drinking water (C 1 ) bring the needed daily Fe dose for IDA prevention.For curative issues, (up to 100 mg/d), appropriate designs can be developed on the same basis.
Fe leaching as used herein is extensively employed in extractive metallurgy and in reclamation of mining media [79][80][81][82] .The operational parameters impacting the effectiveness of the leaching process include concentration of the AA solution, duration of the leaching operation (long-term corrosion rate), Fe 0 grain size, Fe 0 intrinsic reactivity, flow velocity of the AA solution (contact time), and leaching temperature.Given that the kinetics of iron corrosion are neither constant nor linear (see "Fe 0 leaching with ascorbic acid: proof of concept" Section) 29,[82][83][84] the service life of each Fe II -AA production unit (Fig. 5) cannot be predetermined.In other words, the question on when to recharge a Fe 0 /sand column with fresh Fe 0 can only be answered by testing.

IDA and safe drinking water provision: killing two birds with one stone?
The presentation until here has revealed that many low-income settings are still seeking for reliable ways out of the iron deficiency crisis.Past Fe 0 -based attempts to overcome this problem include: (1) using iron cookwares, (2) adding iron ingots while cooking with aluminum cookwares, and (3) consuming food fortified with Fe 0 powders.The latter is not suitable because of limited access to commercial fortified foods especially for low-income and vulnerable households.All three tools suffer from the natural time-dependent decrease of the kinetics of iron corrosion (decreased corrosion rate or "reactivity loss") 29,[82][83][84][85][86][87] .On the other hand, limited access to medical care and other costly iron supplements make other available tools for improving iron status less suitable for generalized use in low-income communities.
During the past three decades, a substantial body of evidence has demonstrated that iron intake from drinking water is a powerful weapon against IDA 7,31,39 .In this context, Fe II is either naturally available, for example from groundwater 30,31,34,35 , or artificially added, for example as ferrous sulfate (FeSO 4 ) 21 .FeSO 4 is reported to be the best water-soluble and cheapest iron salt available (Table 6) 7 .Dutra-de-Oliveira et al. 21used 10 mg of FeSO 4 and 100 mg of ascorbic acid (AA) per litre of drinking water.10 mg of FeSO 4 contains 3.7 mg of Fe, 2.1 mg of S and 4.2 mg of O.This implies that just 3.7 mg Fe is needed for 1 L or some 4.0 g for 1 m 3 of water.In other words, 1 kg of Fe 0 will produce more than 250 m 3 of Fe fortified drinking water.The price of 1 kg of Fe 0 (3.00 Euro) 78 is far less than that of 1 kg of FeSO 4 (Table 6), and Fe 0 is readily available, for instance as iron nails or sponge iron 77,88,89 .The advantage of water as a vehicle for Fe is summarized by Dutra-de-Oliveira et al. 7 as follows: "Water is consumed daily, everywhere by all ages", including children, pregnant women, and adults of all ages.In other words, Dutra-de-Oliveira et al. 7,90,91 have already demonstrated the success of iron-fortified drinking water to improve the iron status of low-income populations mainly consuming low iron (Fe II ) vegetable diet and daily drinking local water [90][91][92][93][94][95][96] .Consequently, provided local water is of drinking quality, a universal solution to defeat IDA is made more accessible and affordable by using the Fe II -AA method presented herein ("Current Table 6.Common iron salts used for food and water fortification and their corresponding mass to obtain 1 kg of elemental iron.'x (−)' is the mass ratio of Fe in the salt.The given kg prices of the salts (chemicals) are from Fisher Scientific (https:// www.fishe rsci.com/ -Acces ses 26/09/2022).The given Fe 0 price corresponds to commercial iron nails 78 .www.nature.com/scientificreports/use of Fe 0 for IDA control" section).AA for Fe 0 leaching is readily, commercially available.For example, in July 2023, 2.5 kg ascorbic acid (vitamin C), food grade can be purchased from Amazon Germany (www.amazon.de) for just 33 Euro.
The past two decades have witnessed the development of affordable solutions for safe drinking supply [97][98][99][100][101][102] .From these technologies, one is based on filtration on Fe 0 /sand beds 97,100,[103][104][105][106][107] .In principle, it is possible to design a Fe 0 filter capable of releasing about 2 mg/L Fe II in the effluent.In such a case, it suffices to add a diluted solution of ascorbic acid to stabilize Fe II and make it available to the human body.Research is needed to achieve the proverbial notion of "killing two birds with one stone": (1) safe drinking water, and (2) iron-fortified water, in a decentralized manner.The problem of clean drinking water supply and IDA co-occur or are juxtaposed in low-income countries 108 .This points to the novelty of coupling clean drinking water supply based on Fe 0 filter systems to the fortification of drinking water to overcome IDA.

Concluding remarks
There are three main approaches to control IDA: (1) supplementation with iron and folic acid tablets, (2) fortification with iron salts, metal iron and dissolved iron, and (3) natural food-based approaches.Efforts for wide implementation of the first two approaches have not really been successful in combating IDA over the past three decades 14,15,[109][110][111][112] .The third approach is attractive as it focuses on dietary diversification and enrichment of diets with naturally iron-rich foods, but it is difficult to bring it to scale.Thus, more affordable and applicable tools are still needed.
The Fe II -AA approach is an improved version of a 30-year-old method using commercially available highly soluble Fe II salts 7 .Home iron fortification of water supplies bioavailable iron to rural and urban populations and is optimal for mass supply in schools and other institutions.Systematic research is needed to develop scalable Fe II -AA producing units.Well-designed experiments are needed to determine the practicality of several potential Fe 0 materials to serve as reliable Fe sources and to combat IDA.

Figure 1 .
Figure 1.Photograph of an aluminum cooking pot on the fire in Bamena (rural Cameroon).Photograph taken by Serge Ndokou-Nana, October 2021.

Figure 2 .
Figure 2. Photograph of a Lucky Iron Fish and a Lucky Iron Leaf.Photograph taken by Gerhard Hundertmark, November 2021.

Figure 3 .Figure 4 .
Figure 3. Column experimental set-up for Fe 0 leaching by ascorbic acid (2 mM).The photograph was made at the end of the experiments.The spout of the third column was broken during the experiments but this has no incidence on the performance of the system.

Figure 5 .
Figure 5. Schematic representation of the process of generating the Fe II -AA solution (V 0 ) and adding it to a safe drinking water storage tank (V 1 ).Fe 0 is a reactive iron source.Sand is used as a filling material.

Table 1 .
Characteristics of the three main sources of iron for controlling iron deficiency anemia.The most readily available iron sources are selected with two per state of oxidation (oxidation state-OS).RBA stands for the relative bioavailability, RBA is related to the solubility in 0.1 N HCl (Harrison et al. (1976) cited by Kumari and Chauhan 4 ).The gange is the residual unreduced oxides, mainly comprising of Al 2 O 3 , CaO, FeO, MgO, MnO, and SiO 2 .

Table 4 .
Summary of the extent of Fe leaching from the tested Fe 0 specimens after 55 leaching events.The daily leaching is the sum of the leaching mass divided by 55, 'iPuTec (2)' corresponds to the experiment using 2.0 g of Fe 0 .