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Environmental fate & pathways

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A range of BCF and BAF values are available from different species. In general, metals do not biomagnify unless they are present as, or having the potential to be, in an organic form (e.g. methyl mercury). According to ECHA (2008, p 12) „The PBT and vPvB criteria of Annex XIII to the Regulation do not apply to inorganic substances but shall apply to organo-metals.“ This is because some organo-metals are lipid soluble, not metabolized, and efficiently assimilated upon diet borne exposure. McGeer et al (2002) conclude “Overall, the use of BCF and BAF-based criteria for the hazard classification of metals is not useful. In terms of hazard identification, the declining BCF and BAF values at elevated exposures lead to the prediction of reducing impacts as concentration increases, a conclusion that is contrary to all of the toxicological data. Using BCF and BAF for metals and inorganic metal compounds ignores fundamental physicochemical and toxicological properties associated with these substances. Compared with diffusional uptake of neutral organics, metal uptake is complex and includes a diversity of mechanisms, accumulation of both essential and non-essential elements from natural background, homeostatic control of accumulation, as well as internal detoxification, storage and elimination.”

Biologically, iron is an essential trace element for organisms including micro-organisms, plants and animals. Iron plays an important role in biological processes, and iron homeostasis is under strict control. Due the natural occurrence in considerable amounts biota have mechanisms to cope with concentrations of the iron species in equilibrium with the kations constituting the submission item. Thus the criteria for assessing bioaccumulation were replaced by the bioavailability considerations.

The existence of organic molecules containing iron is obvious. Biota use iron to build functional molecules (e.g. haemoglobin, myoglobin, cytochromes, ferredoxins, rubredoxins, catalases, peroxidases, nitrogenase, ferritin, transferrin, haemosiderine). Given the complex anabolism, abiotical spontaneous formation of these molecules seems unlikely. As they are natural constituents of every prey they will be metabolized and used due to adaptation (evolutionary response to local conditions) and if required acclimation (short-term physiological response to challenges) of the predators. As these (macro)molecules are intensively used over a large range of taxonomic groups it seems unlikely that they bioaccumulate.

More organic iron compounds exist in the environmental media as chelated in organic iron complexes are formed abiotically. Hutchins et al (1999) summarize as follows: “Dissolved iron is overwhelmingly (approximately 99 %) bound to organic ligands with a very high affinity for iron (Wu et al 1995, Rue & Bruland 1995, Witter & Luther 1998). The origin, chemical identity and biological availability of this organically complexed iron is largely unknown (Hutchins 1995). The release into sea water of complexes that strongly chelate iron could result from the inducible iron-uptake systems of prokaryotes (siderophore complexes) (Wilhelm 1995, Butler 1998, Granger & Price 1999) or by processes such as zooplankton-mediated degradation and release of intracellular material (porphyrin complexes).” Iron from chelates seems generally less readily bioavailable than free kations. Hutchins et al (1999) conclude on competitive strategies in marine phytoplancton to make iron bound to uses specific complexes. Lis & Shaked (2009) found the bioavailability of iron bound to the model organic ligand desferrioxamine B (CAS 70-51-9, a naturally occurring chelating agent) reduced compared to uncomplexed iron species. While iron shortage is typically for marine waters, the available data on iron concentrations in the environment show that organisms display adaptation to the high background concentrations of iron. Despite its presence no accumulation in wildlife biota is described in the literature. This supports the suggestion of a low potential for bioaccumulation.

Iron is present in all environmental media with large reservoirs in soils and sediments. Iron is the forth-most abundant element in the Earth's crust (4.7 % by mass) occurring naturally as almost as oxide and hydroxide. Although it is widely distributed and present in all environmental media the highest levels were in soil. Comparison of the environmental levels outlined in the discussion on Environmental fate and pathways with the additional release according to the exposure scenario shows clearly that these additional releases contribute insignificantly. This even more as the environmental fate processes will probably carry additional releases to the soil and sediment reservoirs without any lasting increase of the bioavailable species as the equilibrium times are short.

In result the iron species, which would result from the release of the submission item to the environment, are assessed irrelevant with regard to bioaccumulation factor based hazard classification.

In conclusion no effects and thus no hazard are identified with regard to bioaccumulation and/or bioavailability.

Secondary poisoning

In the light of the inverse relationships between water concentration and BCF and/or the biological regulation of uptake and elimination and/or the presence of all submission item constituents in natural background concentrations, a lack of relevant enrichment is assumed. Thus and due to and the low toxicity of the ions and salts, it is not necessary to assess effects on predators by secondary poisoning for these substances and no hazard is assumed.

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  • ECHA European Chemicals Agency (2008). Guidance on information requirements and chemical safety assessment, Chapter R.11: PBT Assessment, section R.11.1.2.1 Definitive criteria, 97 p.
  • Granger J, Price NM (1999). The importance of siderophores in iron nutrition of heterotrophic marine bacteria. Limnol Oceanogr 44.541–55.
  • Hutchins DA (1995) in: Progress in Phycological Research Volume 11 (eds Chapman D. & Round F) 1–49 (Biopress, Bristol).
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  • Lis H, Shaked Y (2009). Probing the bioavailability of organically bound iron: a case study in the Synechococcus-rich waters of the Gulf of Aqaba. DOI: 10.3354/ame01347 Aquat Microb Ecol 56:241–53.
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