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Key value for chemical safety assessment

Additional information

Substance specific information on acute oral toxicty are not available for diammonium hydrogen citrate. Hence, a read-across concept was developed:

Read-across - diammonium hydrogen citrate:

The target substancediammonium hydrogen citrate(CAS # 221-146-3, EC # 221-146-3) is a mono-constituent substance that consists of two monovalent ammonium cation and a divalent hydrogencitrate anion, designated as inorganic salt (IUPAC 2005). Upon dissolution,diammonium hydrogen citrateliberates ammonium cations and (depending on pH) citrate anions, which represent the sub-categories. In the following, “citrate anions” represents the anions citrate, hydrogencitrate and dihydrogencitrate as well as citric acid.Citrate, hydrogencitrate, dihydrogencitrate and citric acid are considered as common anion based on theequilibrium between those anions in aqueous solutions under physiological/environmental conditions depending on pH value which is clearly described in published literature and summarised in the following equations:

Diammonium hydrogen citrate consists of two ammonium [NH4]+ ions and one hydrogen citrate ion [C6H6O7]2-. Based on the solubility of diammonium hydrogen citrate in water (1,000 g/L at 20°C), a complete dissociation of diammonium hydrogen citrate, resulting in ammonium (NH4+) and (hydrogen) citrate, may be assumed.


Depending on solution pH, citrate anions exist as citrate, hydrogencitrate, dihydrogencitrate and citric acid  species in aqueous solutions under physiologically/environmentally relevant conditions as summarised in the following equations:


C6H8O7+ H2O <->(C6H7O7)- + H3O+                       [pka1: 3.13; citric acid             <->dihydrogencitrate]

(C6H7O7)- + H2O <-> H3O++(C6H6O7)2-                 [pKa2: 4.76;dihydrogencitrate <-> hydrogencitrate]

(C6H6O7)2-+ H2O <->(C6H5O7)3-+H3O+                [pKa3:6.40; hydrogencitrate    <->citrate]

Ammonium cations are formed by an acid-base reaction of e.g. H2O (or other, stronger aids) and NH3as follows:

NH4++ OH-<->NH3+ H2O                                        [pka:9.25; ammonium            <-> ammonia] 

NH4+and NH3coexist in aqueous solution in adynamic pH-dependent equilibrium. Under basic conditions (pH >10), ammonia (NH3) redominates whereas theammoniumion (NH4+) is the dominant species in weakly basic to neutral (environmental) conditions. With decreasing pH, the ammonium cation becomes the only species. A Hägg-graph representing the described equilibrium in solution is provided in Section 13 (Read-across assessment report) using the above given pka[1]value at 25°C

[1]Weast, R.C. (ed.) (1974) CRC Handbook of Chemistry and Physics, 55th ed. CRC Press.

Since the target substance and the source substance release the (eco-)toxicological relevant units under environmental/physiological relevant conditions, the overall ecotoxicity/toxicity of the dissociated diammonium hydrogen citrate can be interpolated by assessing the (eco-)toxicity of the individual moieties. The category hypothesis, i.e. release of the common (eco-)toxicological units, applies to the target substance and the source substances.Thus, the category consists of ammonium salts for which the (eco-)toxicity is either governed by the ammonium cation (sub-category 1) or the citric acid anion (sub-category 2).

Acute oral toxicity of ammonium:

Ammonium chloride has been tested for acute toxicity in several species. A single gavage dose of303 mg ammonium/kg b.w. induced mortality in guinea pigs, with pulmonary oedema beingestablished as the cause of death (ATSDR, 2004). According to WHO/IPCS (1986) this effect was notsecondary to metabolic acidosis and was observed with other ammonium salts and in other species atsimilar concentrations by the same research group. However, pulmonary oedema following gavageexposure to ammonium salts was not reproduced in other species at comparable ammonium chloridedoses and pulmonary effects were considered secondary to metabolic acidosis by ATSDR (2004).In more recent studies, rats and mice did not show pulmonary effects following acute exposure toammonium chloride by gavage. Following a single exposure to aqueous solutions of ammoniumchloride by gavage, LD50values of 1630 mg/kg b.w. (equivalent to 548 mg ammonium/kg b.w.) and 1220 mg/kg b.w. (equivalent to 410 mg ammonium/kg b.w.) were observed in male and female rats,respectively (OECD, 2003). An LD50 of 1300 mg/kg b.w. (equivalent to 437 mg ammonium/kg b.w.)was established in male mice after a single gavage dose of ammonium chloride in water (OECD, 2003). Oral LD50values for ammonium sulphate range from 2000 mg/kg b.w. to 4250 mg/kg b.w.(544-1156 mg ammonium/kg b.w.) (OECD, 2004).

Recalculation of the above stated LD50 values (assuming the worst case and consider LD50 of most sensitive sex) to diammonium hydrogen citrate results in a LD50 of ca. 2590 mg/kg bw ammonium chloride) and 3430 mg/kg bw (ammonium sulfate).


ATSDR (Agency for Toxic Substances and Disease Registry), 2004. Toxicological profile for

ammonia. U.S. Department of Health and Human Services, Atlanta, Georgia, 269 pp.

WHO/IPCS (World Health Organization/International Programme on Chemical Safety), 1986.

Ammonia. Environmental Health Criteria 54, World Health Organization, Geneva, Switzerland.

Available from


OECD (Organisation for Economic Co-operation and Development), 2003. Ammonium chloride –

CAS N°: 12125-02-9. Screening Information DataSet (SIDS). Available from

OECD (Organisation for Economic Co-operation and Development), 2004.Ammonium sulfate – CAS

N°: 7783-20-2. Screening Information DataSet (SIDS). Available from

Acute oral toxicity - citric acid/citrates:

Two publications could be identified that investigated the acute oral toxicity of citric acid using rabbits, rats and/or mice and are described below:

Weiss et al. (1923) evaluated the potential of acute oral toxicity of citric acid anhydrate in rabbits. Female rabbits were administered the substance at dose levels of 3800, 4600, 5100, 6500 and 7000 mg/kg bw via gavage. One rabbit was dosed at each dose level and the animals were observed at least once an hour for 24 hours. Clinical signs and mortality were recorded. The estimated initial minimum fatal dose was found to be 7000 mg/kg bw.

Yokotani et al. (1971) investigated the potential of acute oral toxicity of citric acid monohydrate in rats and mice. Groups of six male SD-JCL rats or six male ICR-JCL mice

were given citric acid monohydrate at different dose levels (rats: at least at 10420, 12500 and 18000 mg/kg; mice: at least at 4820, 5790 and 7000 mg/kg) via oral administration. After administration the animals were observed for 7 days and behaviour and mortality were recorded. Furthermore, an autopsy was conducted. The LD50 was determined to be 11700 mg/kg (equivalent to 10647 mg citric acid anhydrate/kg) and 5790 mg/kg (equivalent to 5268.9 mg citric acid anhydrate/kg) for male rats and male mice, respectively.

Although these studies had some experimental and reporting deficiencies (e.g. number of animals per dose level too low; dose levels not clearly defined; observation period too short; body weight measurements missing), combined these studies enable to conclude on the acute oral toxicity potential of citric acid. The minimum fatal dose or LD50 values were all far above the limit dose level of 2000 mg/kg bw as foreseen by the OECD guidelines for acute oral toxicity testing. Furthermore, all animals that died in the studies were found dead early in the observation period, which lets assume that the observation period was long enough to determine the toxicity of the substance.

Furthermore, citric acid is known for being an intermediate metabolite in the Krebs cycle (tricarboxylic acid cycle) in almost all organisms. It is well-absorbed, fully metabolised and used as an energy source by organisms (EFSA (2006); CIR (2012)). As stated by CIR (2012), "approximately 2 kg of citric acid are formed and metabolized every day in humans". Source of citric acid in human food consumption are vegetables, fruits, beverages and food products (HERA (2005); EFSA (2006)). For these reasons, it can be safely assumed that citirc acid should be of no concern regarding acute oral toxicity.


- EFSA (2006) Opinion of the Scientific Panel on Food Additives, Flavourings, Processing Aids and Materials in Contact with Food on a request from the commission related to magnesium potassium citrate as a source of magnesium and potassiun in food for particular nutritional uses, food supplements and foods intended for the general population. The EFSA Journal 392: 1 - 6.

- Hera (2005) Substance:Citric acid and salts (CAS# 77 -92 -9; 5949 -29 -1; 6132 -04 -3) Edition 1.0 - April 2005. p. 1- 6.

- CIR (2012) Final Report: On the safety assessment of citric acid, inorganic citrate salts, and alkyl citrate esters as used in cosmetics. 1 - 36.


Justification for classification or non-classification

Acute oral toxicity:

Based on the given read-across information the substance diammonium hydrogen citrate does not require classification according to

Regulation (EC) No 1272/2008 and subsequent adaptations.