Iron chloride sulphate

Endpoint summary

Additional information

Under REACH, only the anhydrous forms of the salts have been to be registered, based on Annex V 6. Therefore, the properties of the anhydrous form is generally regarded as key information. The soluble iron salts were evaluated together as they form a meaningful category for the environmental assessment due to their rapid transformation.

Table: The soluble iron salts registered together

Common name	EC number	CAS number
Ferric chloride	231-729-4	7705-08-0
Ferrous chloride	231-843-4	7758-94-3
Ferric sulphate	233-072-9	10028-22-5
Ferrous sulphate	231-753-5	7720-78-7
Ferric chloride sulphate	235-649-0	12410-14-9

Table: Adjustment factors to convert numerical endpoints expressed as Fe concentrations to numerical endpoints for iron compounds

Chemical Species	Molecular Weight [g/mol]	Ratio
Fe	55.8	1.0
FeSO4	151.9	2.72
FeSO4H2O	169.9	3.04
FeSO4.7H2O	278.0	4.98

On one hand the physical and chemical endpoints for most of the individual iron salts cannot be treated as a category (e.g. appearance, melting point, boiling point, density, water solubility, pH and so on). Remarkably the differences between hydrated and anhydrous forms are more or less as significant as the differences between different salts. On the other hand some read across between the different ferric or ferrous salts makes sense as the counter-anions are inert with regard to e.g. oxidizing properties auto flammability or explosiveness. And finally a number of waiving argumentations apply to the whole group. The chosen approach is thus to give an overview on all salts registered together and additionally the available information on the hydrates in every Endpoint Summary.

Available data on physiochemical properties have been reviewed and discussed in the peer-reviewed published SIARs. Ferrous chloride (FeCl2, CAS 7758-94-3) was subject of SIAM 19 (OECD 2004, section 1.3), and 10 iron salts and their hydrates were evaluated in SIAM 24, April 2007 (OECD 2007, section 1.3). The critical information from the SIARs is as follows: “All the iron salts considered have high melting and boiling points, with degradation occurring at very high temperatures. The vapour pressure of the salts is low and in aqueous solution the vapour pressure observed is that of water and is governed by the colligative properties of the salts. All the salts are highly soluble in water (apart from ferric sulphate, which is slowly soluble but rapidly soluble in the presence of a trace of ferrous sulphate). These salts have been known and studied by chemists for a considerable time and much of the data concerning their physico-chemical properties are to be found in tables and compendia of the properties of inorganic chemicals rather than in referenced papers.”

• OECD Organisation for Economic Co-operation and Development (2004). Iron Dichloride CAS N° 7758-94-3. SIDS Initial Assessment Report for SIAM 19. United Nations Environment Programme (UNEP) Publications. Berlin, Germany, 19-22 October 2004. 89 p.
• OECD Organisation for Economic Co-operation and Development (2007). SIDS Initial Assessment Report for SIAM 24. Chemical Category: Iron Salts. Self-published OECD 138 p.

Chemical Category Reporting Format according to ECHA Guidance

The following definition complies with the ECHA (2008, chapter R.6) Guidance on QSARs and grouping of chemicals. It is more comprehensive and more structured and should be used in the discussions of some physical/chemical properties, environmental fate and ecotoxicology. The most similar example in the above mentioned guidance is given in section R.6.2.7 (Case study using phosphonic acid compounds and alkali metal salts, p 126). For the toxicological evaluation a category approach applies as well, but requires different justification. Therefore the soluble iron salt category with regard to the toxicological endpoints is given in the section on toxicokinetics.

Table: Reporting Format for the Chemical Category according to ECHA Guidance R.6.2.6.2

1.	Category definition and its members
1.1.	Category Definition
a.	Category Hypothesis This category covers inorganic ferric and ferrous compounds with counter-ions, which are ubiquitous and non-toxic (all acute LC50 and EC50 > 100 mg/L & chronic NOEC > 1 mg/L) and do not require additional consideration, i.e. the sulphate (CAS 14808-79-8), chloride (CAS 16887-00-6) and hydroxide (CAS 14280-30-9) anions. Accordingly the first main assumption of the category hypothesis is that sulphate, chloride and hydroxide are not significant in respect of all the properties under consideration. The impact of the hydroxide ion (CAS 14280-30-9) is restricted to pH effects. Such effects do not represent actual intrinsic toxicity and were generally excluded in the environmental fate and hazard assessment. In the respective OECD test guidance documents generally the test pH has to be in a range suitable for the test organisms or the test system. During the pH adjustment the hydroxide ion reacts with the protons to water. A salt will in dilute aqueous conditions of defined pH behave no differently to the parent acid, at identical concentration of the particular speciated form present and will be fully dissociated. The second main assumption of the category hypothesis is that with regard to the environmental fate & behaviour and the effects to environmental organisms the category comprises a directly analogous group of Iron III and II (ferric and ferrous) compounds. The formation of a category is justified on the basis of a self-consistent model of the behaviour and properties of these substances. Under normal environmental conditions of pH, ambient temperature and dissolved oxygen, all of the salts will dissociate immediately in aqueous media to the respective anions and ferric (CAS 20074-52-6) and ferrous (CAS 15438-31-0) kations. Then they will be subject to rapid hydrolysis revealing the hydroxides. The following precipitation, change of oxidation state and further speciation will take place according to the geochemical conditions and identically for all category members (salts and hydroxides). Similar processes are likely in pore water of soils or due to the moisture in the atmosphere. The composition of this equilibrium depends on these conditions rather than the ferric or ferrous character or the counter-anions of the originally released iron compounds as the iron species transform readily, aerobic conditions provided. Anaerobic conditions are generally not expected until the equilibrium is reached. Nonetheless it should be noted that iron (II) is stable in anaerobic media and the reduction of iron (III) may be slow. This is important for the interpretation of MEC (Measured Environmental Concentration) data and the establishment of EQS (Environmental Quality Standards), but does not play a role in the hazard assessment as the released species is again not determining the present species unless in case acute release of iron (II) directly in an anaerobic environmental compartment, e.g. the anoxic ocean water layer. Analytical differentiation in environmental samples is challenging. Generally analytical quantification is bases on total iron. Therefore it would even be hardly achievable to treat iron (II) and (III) separately. Consequently the third main assumption of the category hypothesis is that due to the kinetics of the aerobic transformation processes and as the intended uses the category members do not directly reach the environment but after sufficient equilibration time (ca. 12 h or less) under aerobic conditions. Hence some properties (measured or expressed in aqueous media, e.g. ecotoxicity) for a category salt or hydroxide can be directly read-across (with suitable mass correction) to another salt or hydroxide and vice versa.
b.	Applicability Domain of the category The category is applicable to all possible compounds equilibrating under aerobic conditions in comparable time to iron (II) and (III) kations, provided that the related anions can reasonably be considered non-toxic (all acute LC50 and EC50 > 100 mg/L & chronic NOEC > 1 mg/L) to the aquatic life in the relevant concentrations. Therefore e.g. iron carbonates may fit in the category as defined here while nitrite will probably not. Compounds released directly in the environment are generally not covered by the AD.
c.	List of endpoints covered (numbers refer to the IUCLID 5 sections) A) Physical and Chemical Properties of environmental relevance (not true category endpoints as only common waiving applies) 4.6 Vapour pressure 4.7 Partition coefficient 4.10 Surface tension 4.21 Dissociation constant B) Environmental fate and pathways 5.2.1 Biodegradation in water: screening tests 5.2.2 Biodegradation in water and sediment: simulation tests 5.2.3 Biodegradation in soil 5.3.1 Bioaccumulation: aquatic / sediment 5.3.2 Bioaccumulation: terrestrial 5.4.1 Adsorption / desorption 5.4.2 Henry's Law constant 5.4.3 Distribution modelling 5.4.4 Other distribution data 5.5.1 Monitoring data C)Ecotoxicological Information 6.1.1 Short-term toxicity to fish 6.1.2 Long-term toxicity to fish 6.1.3 Short-term toxicity to aquatic invertebrates 6.1.4 Long-term toxicity to aquatic invertebrates 6.1.5 Toxicity to aquatic algae and cyanobacteria 6.1.6 Toxicity to aquatic plants other than algae 6.1.7 Toxicity to microorganisms 6.1.8 Toxicity to other aquatic organisms 6.2 Sediment toxicity 6.3.1 Toxicity to soil macroorganisms except arthropods 6.3.2 Toxicity to terrestrial arthropods 6.3.3 Toxicity to terrestrial plants 6.3.4 Toxicity to soil microorganisms 6.3.5 Toxicity to birds 6.3.6 Additional ecotoxicological information
1.2	Category Members
	Common name			EC number					CAS number
	Ferric chloride			231-729-4					7705-08-0
	Ferrous chloride			231-843-4					7758-94-3
	Ferric sulphate			233-072-9					10028-22-5
	Ferrous sulphate			231-753-5					7720-78-7
	Ferric chloride sulphate			235-649-0					12410-14-9
	Ferric hydroxide			215-166-1					1309-33-7
	Ferrous hydroxide			242-456-5					18624-44-7
	The definition of these salts also covers a number of chemical identities relating to specific hydrates. Under REACH all hydrates are covered by the registration of the anhydrous salt. As the hydrates influence the molecular weight, correction should apply as the hydrate weight is considered in CLP according to ECHA Guidance on the Application of the CLP Criteria Version 2.0 (2012, p 535, Example D). The following hydrates are identified in the public domain though not all are necessarily commercially relevant:
	Chemical name (CAS name)				CAS number			Molecular formula
	Iron chloride (FeCl3), monohydrate (9CI)				60684-13-1			Cl3 Fe . H2O
	Iron chloride (FeCl3), hydrate (2:3) (9CI)				58694-76-1			Cl3 Fe . 3/2 H2O
	Iron chloride (FeCl3), dihydrate (9CI)				54862-84-9			Cl3 Fe . 2 H2O
	Iron chloride (FeCl3), trihydrate (9CI)				58694-75-0			Cl3 Fe . 3 H2O
	Iron chloride (FeCl3), hexahydrate (8CI, 9CI)				10025-77-1			Cl3 Fe . 6 H2O
	Iron chloride (FeCl3), nonahydrate (9CI)				58694-79-4			Cl3 Fe . 9 H2O
	Iron chloride (FeCl3), dodecahydrate (9CI)				58694-80-7			Cl3 Fe . 12 H2O
	Iron chloride (FeCl3), hydrate (8CI, 9CI)				24290-40-2			Cl3 Fe . x H2O
	Iron chloride (FeCl2), hydrate				23838-02-0			Cl2 Fe . x H2O
	Iron chloride (FeCl2), monohydrate				20049-66-5			Cl2 Fe . H2O
	Iron chloride (FeCl2), dihydrate				16399-77-2			Cl2 Fe . 2 H2O
	Iron chloride (FeCl2), tetrahydrate				13478-10-9			Cl2 Fe . 4 H2O
	Iron chloride (FeCl2), hexahydrate				18990-23-3			Cl2 Fe . 6 H2O
	Sulfuric acid, iron(3+) salt (3:2), nonahydrate				13520-56-4			Fe2(SO4)3 . 9H2O
	Sulfuric acid, iron(3+) salt (3:2), hydrate				15244-10-7			Fe2(SO4)3 . xH2O
	Sulfuric acid, iron(3+) salt (3:2), hexahydrate				13761-89-2			Fe . 3/2 H2SO4 . 3 H2O
	Sulfuric acid, iron(3+) salt (3:2), heptahydrate				35139-28-7			Fe . 3/2 H2SO4 . 7/2 H2O
	Sulfuric acid, iron(3+) salt (3:2), tetrahydrate				230310-51-7			Fe . 3/2 H2SO4 . 2 H2O
	Sulfuric acid, iron(2+) salt (1:1), hexahydrate				59261-48-2			Fe . H2SO4 . 6 H2O
	Sulfuric acid, iron(2+) salt (1:1), trihydrate				58694-83-0			Fe . H2SO4 . 3 H2O
	Sulfuric acid, iron(2+) salt (1:1), tetrahydrate				20908-72-9			Fe . H2SO4 . 4 H2O
	Sulfuric acid, iron(2+) salt (1:1), monohydrate				17375-41-6			Fe . H2SO4 . H2O
	Sulfuric acid, iron(2+) salt (1:1), hydrate				13463-43-9			Fe . H2SO4 . x H2O
	Sulfuric acid, iron(2+) salt (1:1), dihydrate				10028-21-4			Fe . H2SO4 . 2 H2O
	Sulfuric acid, iron(2+) salt (1:1), heptahydrate				7782-63-0			Fe . H2SO4 . 7 H2O
1.3	Purity / Impurities Iron itself is not hazardous to the environment and generally only substances with comparable purity or impurity profiles can be assessed together. Technical grade materials may contain relevant quantities of impurities, which exceed the low ecotoxicological effects of the pure compounds comprised in this category. In cases where the sum of the impurities triggers the toxicity, the assessment has to be based on these impurities considering their concentration and the category assessment is restricted to the iron salt components. The purity of the category members is generally > 80 % w/w. Deviations below this purity value would not normally be acceptable since this would suggest that the substance should not be considered as a mono-constituent substance. Impurities comprise salts of other metals up to ≤ 1 % w/w and free acid up to ≤ 2 % w/w.
2.	Category justification Due to their rapid transformation and the formation of insoluble precipitating species the causation in effect studies is complicated. The Hill (1965) criteria for causation can hardly be met. Therefore precise effect measurement under exclusion of fouling effects accompanied by detailed documentation allowing reconstructing is the exemption in the literature and study report. In consequence there are reliable data to compare equimolar iron effects from different compounds are not available and cannot be produced with reasonable efforts. Testing of the individual category members is thus considered technically not feasible and the wide range of published data is likely to represent test artefacts rather than differences in toxicity. Published data differ for even for the same salts, provided that equimolar solute iron concentrations are regarded. Vangheluwe & Versonnen (2004) performed a comprehensive literature search and evaluation of acute and chronic aquatic ecotoxicity data. The authors state that “it should be noted that most of the effects observed are due to the particulate nature of the formed iron hydroxide (ferric form) rather than the toxic properties of the dissolved Fe (II) ion as such. No evidence of systemic toxicity by iron to aquatic organisms has been found. 16 studies on standard test species were found to be reliable. Six studies were performed on iron (II) and 10 studies were performed on iron (III). The results of the fish studies are all in the same order of magnitude. The LC50 values of the acute experiments (96 h) with standard species have a narrow range from 16.6 to > 27.9 mg Fe/L. Chronic LOECs for fish are in the same order of magnitude. For the daphnids, acute survival (24-48 h) results in EC50 values of 1.29-36.9 mg Fe/L. Chronic NOEC, LOEC and EC50 values range from 0.63 to 5.9 mg Fe/L.” Notwithstanding the methodological objections these data support the category hypothesis. Additionally sufficient knowledge on iron chemistry is in the literature available to assume reasonably that comparable exposure to ferric and ferrous kations originate from initially equimolar category member exposure.
3.	Data matrix Notwithstanding the methodological objections the following Acute toxicity data were deemed reliable according to the literature search and evaluation of Vangheluwe & Versonnen (2004, citation see 2. Category justification, above). The values were used in ECHA (2012, Table IV.7.1, p 536, Example D) Guidance on the Application of the CLP Criteria Version 2.0. However the same principal objections apply as well, to algal studies performed by national institutes of South Korea (NIER) and Japan (MOE) were added to present all required trophic levels. The actual toxicity is considered significantly lower and these values should not be used as starting point for PNEC derivation.
	Test substance	Test organism		Duration		Endpoints			L(E)C50 [mg Fe/L]	Reference
	FeCl3.6H2O	Pimephales promelas		96 h		Survival			21.8	Birge et al 1985
		Lepomis macrochirus		96 h		Survival			20.3
	FeSO4.7H2O	Oncorhynchus mykiss		96 h		Survival			16.6	Mattock (2002a)
	Fe2(SO4)3	Oncorhynchus mykiss		96 h		Survival			>27.9	Mattock (2002b)
	FeSO4	Daphnia pulex		24 h		Immobility			36.9	Lilius et al 1995
	FeSO4	Daphnia magna		24 h		Immobility			17	Calleja et al 1994
	FeCl3.6H2O	Daphnia pulex		48 h		Immobility			12.9	Birge et al 1985
	Fe2(SO4)3	Daphnia longispina		48 h		Immobility			11.5	Randall et al 1999
	FeCl3.6H2O	Daphnia magna		48 h		Immobility			9.6	Biesinger & Christensen 1972
	FeSO4	Daphnia magna		24 h		Immobility			5.25	Lilius et al 1995
	FeSO4.7H2O	Daphnia magna		48 h		Immobility			1.29	LISEC 1999
	FeCl2	Pseudokirchnerella subcapitata		72 h		Growth rate			3.04	NIER 2001
	FeSO4.7H2O	Pseudokirchnerella subcapitata		72 h		Growth rate			18.5	MOE 2002
	Notwithstanding the methodological objections the following Chronic toxicity data were deemed reliable according to the literature search and evaluation of Vangheluwe & Versonnen (2004). The values were used in ECHA (2012, Table IV.7.2, p 537, Example D) Guidance on the Application of the CLP Criteria Version 2.0. The actual toxicity is considered significantly lower and these values should not be used as starting point for PNEC derivation.
	Test substance	Test organism		Duration			Endpoints		NOEC / LOEC [mg Fe/L]	Reference
	Fe(OH)3	Salvelinus fontinalis		30 days			Hatching, Growth, Survival		>10.3 >10.3 >10.3	Smith & Sykora 1976
	Fe(OH)3	Oncorhynchus kisuth		30 days			Hatching, Growth, Survival		>10.3 2.81/>10.3 >10.3	Smith & Sykora 1976
	FeCl3.6H2O	Pimephales promelas		33 days			Length, Weight		1.0/1.61 1.61/2.81	Birge et al 1985
	FeCl3.6H2O	Daphnia pulex		21 days			Immobility, Total offspring, Brood size		2.51/5.01 0.63/1.26 1.26/2.51	Birge et al 1985
	FeCl3.6H2O	Daphnia magna		21 days			Immobility, Reproduction		5.9 EC50 4.4 EC16	Biesinger & Christensen 1972
	FeCl2	Pseudokirchnerella subcapitata		72 h			Growth rate		1.06 NOEC	NIER 2001
	FeSO4.7H2O	Pseudokirchnerella subcapitata		72 h			Growth rate		10.2 NOEC	MOE 2002
4.	Conclusions per endpoint for C&L, PBT/vPvB and dose descriptor The category member with lowest molecular weight is ferric hydroxide, which has 89.862 g/mol. This gives the conversion factor of 1.6 to mg Fe/L values. The lowest reported NOEC is in iron basis 0.63 which is still results in a NOEC > 1 mg/L. All acute values are even on the basis of iron > 1 mg/L and thus higher for all category members. As rapid transformation is deemed, no classification is required PBT and vPvB properties can be excluded. There is no starting point for PNEC derivation as the toxicity values given under point 3. (Data matrix) cannot be considered to be threshold values. Given the half-time for oxidation and precipitation being < 12 h, it is anticipated that a significant proportion of any ferrous salts added to oxygenated aqueous test media will have converted to ferric within the timescale of the standard OECD test protocols. The cited LC50, EC50 and NOEC for the substance, expressed in terms of iron concentration, significantly exceed the equilibrium concentrations of dissolved ferric iron given below. In conclusion the solute iron (III) and (II) equilibrium does not exhibit any toxicity up to the limit of its solubility. Calculated maximum solubility of ferric iron in solution for a pH range of 4.0 to 8.0 and a temperature of 20 ºC:
	pH		Fe [mg/L]						[mmol/L]
	4		6.16E-02						1.1E-03
	5		6.16E-05						1.1E-06
	6		6.16E-08						1.1E-09
	7		6.16E-11						1.1E-12
	8		6.16E-14						1.1E-15

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• MOE Ministry of the Environment, Japan (2002). Growth inhibition test of Pseudokirchnerella subcapitata for Sulphuric acid, iron(2+)salt(1:1), heptahydrate. Japan Food Research Laboratories, Tama, Japan. Report Number 13031. Report date 2002-03-29.
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