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Effects to aquatic organisms

The effects of ferric or ferrous salts on aquatic organisms in reliable short-term tests as collected in the existing reviews (Vangheluwe & Versonnen 2004, Johnson et al. 2007 and OECD 2007) were observed at nominal exposure concentrations in the range 1 – 1000 mg/L salt with the majority being in the range 10 – 100 mg/L. Effects arising from reliable long-term exposures are observed at nominal concentrations > 1 mg/L.

Given the half-time for oxidation and precipitation detailed in the section on Stability 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 available LC50, EC50 and NOEC for the substance, expressed in terms of iron concentration, significantly exceed the equilibrium concentrations of dissolved ferrous and ferric iron, given in the section on Hydrolysis as these kations are in equilibrium with other hydrolysis products. In any case the molarity of elemental iron cannot exceed the low solubility of the ferric kation (see section on Hydrolysis) under aerobic conditions unless precipitation/flocculation occurs, which causes secondary effects rather than intrinsic toxicity. None of the available and reliable studies from the literature searches (Vangheluwe & Versonnen 2004, Johnson et al 2007 and OECD 2007) report effects at such low levels. The necessary conditions for harmful effects (of the more soluble and thus more toxic ferrous kation) to be expressed are very specific (low pH and low dissolved oxygen) and are, in themselves, intrinsically unfavourable to many aquatic species and the results of any such tests would not be a suitable basis for setting regulatory parameters for hazard and risk assessment for ecosystems under normal environmental conditions.

Were the effects observed in the tests to have arisen from exposure to the presence of the dissolved ferric iron this would have placed the substance on a par with some of the most toxic substances that are known. This is unrealistic given that iron is an essential trace element for plants and animals that is widely distributed and abundant in nature.

In view of the low equilibrium concentrations of dissolved ferric iron it can therefore be expected that most of the iron to which test organisms are exposed will be present as undissolved and precipitated ferric hydroxide. Effects arising from exposure to undissolved iron, such smothering or clogging of the gills or respiratory membranes in fish and invertebrates and restriction of plant growth by impairment of photosynthesis or nutrient chelation (in particular phosphorous), are not toxic effects and should not be used as the basis for deriving a PNEC.

Iron salts may present only a hazard to environmental species but only under very specific geochemical conditions and as a consequence of release to iron deficient areas.

  • Johnson I, Sorokin N, Atkinson C, Rule K, Hope S-J (2007). Proposed EQS for Water Framework Directive Annex VIII substances: iron (total dissolved). ISBN: 978-1-84432-660-0. Science Report: SC040038/SR9. SNIFFER Report: WFD52(ix). Product Code SCHO0407BLWB-E-E. Self-published by Environment Agency, Almondsbury, Bristol BS32 4UD, U.K. 65 p.
  • Vangheluwe M, Versonnen B (2004). Critical review on acute and chronic aquatic ecotoxicity data to be used for classification purposes of iron sulfate. Commissioned by ARCELOR SA, CEFIC, EUROFER, RIO TINTO plc. Final report - 25 August 2004. Prepared by EURAS, Rijvisschestraat 118, box 3. B-9052 Gent, Belgium. 76 p.
  • OECD Organisation for Economic Co-operation and Development (2007). SIDS Initial Assessment Report for SIAM 24. Chemical Category: Iron Salts. Self-published, Paris, France, 17-20 April. 138 p.

Notwithstanding the methodological objections expressed in the waiving argumentations the following toxicity data were deemed “reliable“ according to the literature search and evaluation of Vangheluwe & Versonnen (2004, table 6, p 24). Because 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 overview of these data is given here for completeness. It must be emphasized that the actual toxicity is considered significantly lower and these values should not be used as starting point for PNEC derivation. Nonetheless the overview demonstrated that even in case these data would be used for classification the conclusion must be that soluble iron salts are not classifiable.

Table: By the authors for the purpose of classification selected acute and chronic ecotoxity data on Fe from the EURAS critical review (Vangheluwe & Versonnen 2004)

Test substance

pH

Test organism

Test
duration

Effect [mg Fe/L]

Reference

FISH

Short-term exposure

FeCl3.6H2O

6.3

Lepomis macrochirus

acute 96h

LC50 = 20.3 (M)

Birge et al. 1985

FeCl3.6H2O

6.7

Pimephales promelas

acute 96h

LC50 = 21.8 (M)

Birge et al. 1985

FeSO4.7H2O

7.35

Oncorhynchus mykiss

acute 96h

LC50 = 16.6

Mattock 2002

Long-term exposure

FeCl3.6H2O

7.7

Pimephales promelas

chronic 33d

LOEC = 1.61 (M)

Birge et al. 1985

DAPHNIDS AND OTHER INVERTEBRATES

Short-term exposure

FeCl3.6H2O

6.1

Daphnia pulex

acute 48h

EC50 = 12.9 (M)

Birge et al. 1985

FeSO4.7H2O

6.25

Daphnia magna

acute 48h

EC50 = 1.29

LISEC study no. WE-01-225. Draft

FeSO4

7.6

Daphnia magna

acute 24h

EC50 = 5.25

Lilius et al. 1995

FeSO4

7.6

Daphnia pulex

acute 24h

EC50 = 36.9

Lilius et al. 1995

FeCl3.6H2O

7.7

Daphnia magna

acute 48h

EC50 = 9.6

Biesinger & Christensen 1972

FeSO4

n.r.

Daphnia magna

acute 24h

EC50 = 17

Calleja et al. 1994

FeSO4

n.r.

Brachionus calyciflorus

acute 24h

EC50 = 12

Calleja et al. 1994

Long-tern exposure

FeCl3.6H2O

7.6

Daphnia pulex

chronic 21d

LOEC = 1.26

Birge et al. 1985

FeCl3.6H2O

7.7

Daphnia magna

chronic 21d

LOEC = 5.2

Biesinger & Christensen 1972

BACTERIA

FeSO4

n.r.

Vibrio fischeri

acute 15min

EC50 = 40

Calleja et al. 1994

n.r. not reported; M: calculated as total measured mg Fe/L

The information is summarized by the authors (Vangheluwe & Versonnen 2004)) as follows: “The range of reliable acute L(E)C50 values is 1.29 – 40 mg Fe/L, chronic LOECs range from 1.26 – 5.2 mg Fe/L. For acute fish tests the reported LC50 values are very similar. On average fish and invertebrates appear to be equally sensitive towards Fe. There is no clear explanation for Daphnia pulex being 7 times less sensitive towards Fe than D. magna in Lilius et al. (1995). The range for invertebrate acute EC50 values is 1.29 - 17 mg Fe/L. Some of the differences reported for daphnids might well be due to differences in the test media (pH, hardness). The least sensitive species was the bacterium Vibrio fischeri. No clear pH related shifts in toxicity are noted.

Compared with the data reliable with restrictions, effect concentrations of the reliable data are in the same order of magnitude, albeit somewhat higher for the fish. Compared with nonstandard test species, standard species appear to be more sensitive.

In conclusion the authors state: “However, 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.

  • Biesinger KE, Christensen GM (1972). Effects of various metals on survival, growth, reproduction and metabolism of Daphnia magna. Journal of Fisheries Research Board of Canada 29: 1691-1700.
  • Birge WJ, Black JA, Westerman AG, Short TM, Taylor SB, Bruser DM, Wallingford ED (1985). Recommendations on numerical values for regulating iron and chloride concentrations for the purpose of protecting warmwater species of aquatic life in the Commonwealth of Kentucky. Memorandum of Agreement No. 5429, Kentucky Natural Resources and Environmental Protection Cabinet.
  • Calleja MC, Persoone G, Geladi P (1994). Human acute toxicity prediction of the first 50 MEIC chemicals by a battery of ecotoxicological tests and physicochemical properties. Food Chemistry and Toxicology 32:173-187.
  • Lilius H, Hästbacka T, Isomaa B (1995). A comparison of the toxicity of 30 reference chemicals to Daphnia magna and Daphnia pulex. Environmental Toxicology and Chemistry 14:2085-8.
  • LISEC 1999. Acute toxicity of FeSO4.7H2O. LISEC study no. WE-01-225. Draft report.
  • Mattock S (2002). Iron sulphate heptahydrate: acute toxicity to Oncorhynchus mykiss. Covance report number 1934/1 D2149.