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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

No relevant effects

Key value for chemical safety assessment

Additional information

This endpoint is covered by the category approach for soluble iron salts (please see the section on physical and chemical properties for the category justification/report format). Testing for this endpoint has been waived in accordance with column 2 and Annex XI, part 1 and 2, restrictions.

Information from Literature Searches and earlier Assessment Approaches

The literature reviews of Vangheluwe & Versonnen (2004), Johnson et al. (2007) and OECD (2007) revealed some data. The results of the studies, selected as “reliable” by the respective authors are listed in the following tables. Nonetheless the experiments must be rated “not reliable” (Klimisch 3) according to the Klimisch et al. (1997) scale due to methodological objections against testing of aquatic organisms as concluded in the beginning of this chapter (section „Ecotoxicological information“). True, intrinsic toxicity of iron kations in aerobic aquatic test organisms cannot be determined in studies when the solubility of the dissolved ferric kation (as the ferrous form will readily be oxidized to ferric species) is exceeded. None of the experiments found effects at such low levels (depend on pH, section “water solubility”). Notwithstanding the methodological objections formally expressed in the waiving argument for the standard aquatic test organisms, the following data are mentioned for completeness.

Table: Data from the EURAS critical review (Vangheluwe & Versonnen 2004, table 3, p 13)


Test organism

Test medium


Nominal / Measured



L(E)C50 [mg/L]




Vibrio fischeri

Reconstituted water



15 min



Calleja et al. 1994


N: Nominal concentration

R1: Reliable without restriction according to the scheme of the authors (set out in chapter 3.2 of their publication), corrected to Klimisch 3 “not reliable” as discussed above

SOP: Toxkit standard operation procedure

Table: Data according to Johnson et al. (2007, table 2.7, p 24)

Scientific name

Common name



Test duration [h]

Concentration [mg/L] #


Toxicant analysis

Comments (Author's Reliability)


Tetrahymena pyriformis








As FeCl3 (R3)

Sauvant et al. 1995

R3: Not reliable according to the authors (set out in Annex 1, p 56 of their publication)

Exposure: s = static

Toxicant analysis: n = not measured.

An overview on the evaluated literature toxicity data is given in OECD (2007) as follows: “In acute toxicity studies in micro-organisms, an IC50 result for ferrous sulfate of 40 mg Fe/L in a reliable study using luminescent bacteria (Vibrio fischeri) is available. (Calleja et al. 1994) It is supported by results (“acute toxicity”, endpoint and duration not stated, and one EC0 value; it is not stated whether the results are as mg Fe/L or mg salt/L.) in the range of 100-183 mg/L in studies of uncertain reliability using Pseudomonas putida, P. fluorescens and Photobacterium phosphoreum). Several IC50 values (1-10 mg/L) have been measured for Fe(Cl)3 using 14 micro-organism species, in studies of uncertain reliability. Available data on test conditions is minimal but in some cases the acidic pH (4-5) was noted. The observed effects may be associated with the intrinsic acidity of Fe (III) salts.

Effects on aquatic micro-organisms appear to be related to the pH of the test medium, which decreases as more iron is added. Inhibition of cellular respiration in activated sludge biomass was observed, with an IC50 of ca. 500 mg FeCl3/L (equivalent to ca. 170 mg Fe(III)/L) (Broglio 1987).

Table: Data from the OECD (2007) assessment (table 24, p 68)

Test substance

Test organism

Test duration


LC50 [mg Fe/L]


Author’s Reliability


Vibrio fischeri

15 min


40 (n.t)

Calleja et al. 1994


n.t = nominal total Fe

R2 = Rating by the authors (OECD 2007) referring to the Klimisch et al. (1997) scale, corrected to Klimisch 3 “not reliable” as discussed above.

Soluble iron (III) salts are commonly used as flocculating agent and for phosphate removal in sewage water treatment plants (SWTP. The range of loading rate varies between ca. 1 – 100 g Fe/m³ waste water. The reported typical overall average usage (15 g Fe/m³ waste water) is reported to result in concentrations of 200-500 mg Fe/L in activated sludge (Kronos, Phosphate elimination by simultaneous precipitation pamphlet). Higher levels have been reported but this may be a seasonal or occasional effect; loading rates of iron vary significantly for different applications at different stages of the wastewater treatment processing, and the maximum concentration to which activated sludges are regularly exposed could easily be much higher than this.

At these levels the soluble iron salt loadings have no detrimental effects on the functioning of SWTP. On the contrary the intention of the procedure is to increase the capacity of SWTP, which is confirmed by the professional practice. Thus is can be concluded the soluble iron salts are not toxic to sewage micro-organisms.

  • Broglio P (1987). Toxicity of Ferric Chloride. Inquinamento 29(3):112-4
  • 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 32:173-87.
  • 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.
  • Klimisch H-J, Andreae M, Tillmann U (1997). A systematic approach for evaluating the quality of experimental toxicological and ecotoxicological data. Regul Toxicol Pharm 25:1-7.
  • 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.
  • Sauvant MP, Pepin D, Bohatier J, Groliere CA (1995). Microplate technique for screening and assessing cytotoxicity of xenobiotics with Tetrahymena pyriformis. Ecotoxicology and Environmental Safety 32(2):159–65.
  • 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.