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Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Additional information

Some experimental data are reported for several organism groups, but none of the experiments used an equilibrated, aged iron species mixture as it will be formed resulting exposure of soils due to the supported use of the submission item soluble iron salts. The limited data that are available describing the effects of iron salts on soil-dwelling organisms show either:

  • an absence of toxic effects in soil invertebrates at high soil loadings,
  • a positive effect on plants resulting from improved soil fertility or,
  • an adverse effect on plants that can be attributed to complexation by the iron of phosphorous, an important plant nutrient, or
  • an adverse effect on plants that might have resulted from co-exposure to toxic aluminium under conditions of low pH and
  • high levels for acute bird toxicity.

It is therefore unlikely that exposure to iron salts under oxygenated and physiologically tolerable pH conditions will result in toxic concentrations of iron in the soil compartment. To place a proper perspective on the assessment of iron in soils we quote the Summary of the U.S. EPA (2007) Eco-SSL assessment: “Iron is a commonly occurring metallic element, comprising 4.6 % of igneous rocks and 4.4 % of sedimentary rocks (Morel & Hering 1993). The typical iron concentrations in soils range from 0.2 % to 55 % (20 to 550 g/kg) (Bodek et al 1988), and concentrations can vary significantly, even within localized areas, due to soil types and the presence of other sources.

Iron can occur in either the divalent (ferrous or Fe (+2)) or trivalent (ferric or Fe (+3)) states under typical environmental conditions. The valence state is determined by the pH and Eh (redox potential) of the system, and the iron compound is dependent upon the availability of other chemicals (e.g. sulphur is required to produce FeS2 or pyrite).

Iron is essential for plant growth and is generally considered to be a micronutrient (Thompson & Troeh 1973). Iron is considered the key metal in energy transformations needed for syntheses and other life processes of the cells. Consequently, plants regulate iron uptake. Ferrous iron is more soluble and bioavailable to plants than ferric iron. Iron occurs predominantly as Fe (+3) oxides in soils (Bodek et al 1988). Goethite (α-FeOOH) is the predominant mineral form (Kabata-Pendias & Pendias 1984). The divalent state (or ferrous state) can be oxidized to the trivalent state (or ferric state), where it may form oxide or hydroxide precipitates, and become unavailable to plants as a micronutrient (Thompson & Troeh 1973).

The general rule governing the mobilization and fixation of iron are that oxidizing and alkaline conditions promote the precipitation of insoluble iron Fe (+3) oxides, whereas acidic and reducing conditions promote the solution of ferrous (+2) compounds. The availability of ferrous versus ferric iron is also dependent on the soil-water status of a particular environment. For example, reduced environments (which include lowland or waterlogged soils) promote the availability of ferrous iron to plants, while oxidized environments (upland or well-aerated soils) promote the precipitation of ferric-oxide compounds, which are not available to plants for uptake. If excess ferrous iron occurs, iron toxicity may occur in plants, but this is highly dependent upon plant species. Likewise, if ferrous iron is not available in soils due to precipitation of ferric iron compounds, iron deficiency or chlorosis may occur. Proper soil management can help control the pH and soil-water status and allow optimal concentrations of bioavailable ferrous iron to plants.

Currently, identifying a specific benchmark for iron in soils is difficult since iron’s bioavailability to plants and resulting toxicity are dependent upon site-specific soil conditions (pH, Eh, soil-water conditions).

To evaluate site-specific conditions and potential toxicity of iron to plants, it is recommended that the site-specific measured pH and Eh (collected concurrently in the field) be used to determine the expected valence state of the iron and associated chemical compound and resulting bioavailability and toxicity in the environmental setting. In well-aerated soils between pH 5 and 8, the iron demand of plants is higher than the amount available (Römheld & Marschner 1986). Because of this limitation, plants have evolved various mechanisms to enhance iron uptake (Marschner 1986). Under these soil conditions, iron is not expected to be toxic to plants.”

In conclusion it is assessed that due to the significantly high natural presence of iron in soils and due to the generation of bioavailable and potentially toxic iron species by pH, Eh, and soil-water conditions rather than additional amounts of anthropogenic iron an emission of the submission item to terrestrial environmental compartments would have no relevance with regard to ecological iron hazards. In studies the addition of iron is generally done using aqueous solutions without an aging/weathering period, which constitutes an artificial bioavailability of potentially toxic iron species. As this constitutes a testing artefact the derived results of such test are of little evidence for the environmental hazard assessment and have to be disregarded.

Thus the submission item is considered not to contribute to any soil toxicity.

  • Bodek I, Lyman WJ, Reehl WF, Rosenblatt DH (1988). Environmental Inorganic Chemistry: Properties, Processes, and stimation Methods. SETAC Special Series, Walton BT, Conway RA, eds. New York, NY, U.S.A. Pergamon Press.
  • Kabata-Pendias A, Pendias H (1984). Trace elements in soils and plants. ISBN 0849366399, 9780849366390. CRC Press, Boca Raton, FL, U.S.A. 315 p.
  • Marschner H (1986). Mineral nutrition of plants. New York, NY, U.S.A. Academic Press
  • Morel FMM (1983). Principles of aquatic chemistry. ISBN 0-471-08683-5, 9780471086833. John Wiley and Sons, New York, U.S.A. 446 p.
  • Römheld V, Marschner H (1986). Mobilization of iron in the rhizosphere of different plant species. In: Advances in Plant Nutrition, Volume 2, Tinker B, Läuchli A, editors. New York, NY, U.S.A. Praeger Scientific. p 155-204.
  • Thompson LM, Troeh FR (1973). Soils and Soil Fertility, third ed. McGraw-Hill Book Company.
  • U.S. EPA United States Environmental Protection Agency (2003). Ecological Soil Screening Levels for Iron Interim Final OSWER Directive 9285.7-69. Self-published by U.S. EPA Office of Solid Waste and Emergency Response, Washington, DC, U.S.A in November. 44 p.

Absence of toxicity to aquatic species and EPM

The assessment on aquatic effects indicates no relevant toxicity of the submission item category member soluble iron salts to the aquatic life in the foreseen uses. Therefore and due to the assigned ready biodegradability the submission category belongs to the lowest “soil hazard category 1” (according to ECHA 2008, Chapter R.7c, Table R.7.11-2, p 131) and thus the straight forward application of the EPM according to the TGD (ECB 2003, part II, p 112) is possible to derive PNECs for soils, but as no aquatic PNECs were derived this is obsolete.

  • ECB European Chemicals Bureau (2003). Technical Guidance Document in support of Commission Directive 93/67/EEC on Risk Assessment for new notified substances, Commission Regulation (EC) No 1488/94 on Risk Assessment for existing substances and Directive 98/8/EC of the European Parliament and of the Council concerning the placing of biocidal products on the market. Parts I to IV. Self-published, Ispra, Italy.
  • ECHA European Chemicals Agency (2008). Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance. Self-published, Helsinki, Finland, May 2008. 235 p.

Exposure considerations

Iron compounds may represent about 2 % mass of the soil dry weight (see section on Environmental fate and pathways). It can therefore be assumed that the contribution of additional iron species due to human activity will be low compared to these levels. Moreover the iron species are involved in intense readily transformation to different species and any additional release would probably not result in an increase of bioavailable species but contribute to the anyhow large sediment sinks/reservoirs.

Straightforward testing technically not feasible, existing data not relevant/adequate

Furthermore, although effects can be observed in some studies with soil organisms, the lowest concentrations at which they have been found to occur are well below natural background concentrations, to which natural soil organisms are adapted. Laboratory test data indicating effects at concentrations below background therefore have no practical significance for setting PNECs. The chemical species reaching environmental soils as consequence of the supported uses of the submission item will be equilibrated to the naturally occurring almost insoluble and biounavailable forms. Testing of soil freshly spiked with soluble iron salts would not reflect relevant environmental exposure. Exposure to iron-amended soil via ingestion might result in additional uptake of iron as a consequence of the conditions prevailing in the gut of the organism. Therefore and due to the secondary effects of speciation such as oxygen consumption due to oxidation from ferric to ferrous forms and fouling the results from such experiments cannot show intrinsic toxicity. This is a violation of Hill criterion 3 (Specificity, see section on Ecotoxicological information) and no mono-causation of the observed effects is assured. Therefore the existing data are of little relevance for the assessment of intrinsic toxicity. Nonetheless the use of aged, equilibrated test item could be performed, but regarding the significant high natural background concentrations this will not be insightful.

Anoxic and low pH conditions in soils may result in higher concentrations of the more toxic ferrous iron forms, but such conditions are only conducive to supporting specialist species. Experiments with test organisms that are adapted to conditions of low pH and anoxia might be justified but only to investigate specific exposure scenarios.