Iron manganese trioxide

Endpoint summary

Description of key information

Data are not available on the effects of iron oxides on terrestrial organisms. However, in accordance with section 1 of REACH Annex XI, studies on terrestrial organisms do not need to be conducted, as the members of the category "poorly soluble iron (hydr)oxides" are inert inorganic (hydr)oxides of iron, which resemble naturally occurring iron (hydr)oxides, and based upon the physico-chemical properties and low bioavailability of the substances. The poorly soluble iron oxide category substances are highly insoluble in water, out of toxic response to aquatic organisms and the category members do not have a potential for adsorption. Oxides of iron, manganese, and zinc, derived from natural sources, occur in soils and sediments. Iron, manganese and zinc are essential elements for humans, other animals, plants, and microorganisms. Synthetic iron oxide pigments have no relevant effect on the levels and bioavailabilities of these elements. Even under worst case conditions, an inhibitory effect of poorly soluble iron (hydr)oxides is not likely to be exerted on soil organisms.

Iron (hydr)oxides in powder and nano-form are not classified as harmful, toxic or very toxic to aquatic life or may cause long lasting harmful effects to aquatic life. Iron (hydr)oxides in powder and nano-form is also not an unclassified hazard to the aquatic environment. Based on the poor solubility, bioavailability, lack of a potential for bioaccumulation and toxicity to aquatic organisms and considering ubiquitousness of iron (hydr)oxides in soil and essentiality of iron, iron (hydr)oxides in powder and nano-form are also not considered an unclassified hazard to the soil compartment.

Further, a comprehensive evaluation of whether the relative contributions of anthropogenic iron to the existing natural iron pool in soils and sediments are relevant in terms of added amounts and in terms of toxicity was performed (see "White Paper on exposure based waiving for iron and aluminium in soil and sediments, 2010", attached in IUCLID section 6.0) and concludes as follows: The justification for exposure based waiving of conducting additional soil and sediment tests should be based on information on absence of exposure or in the case of metals on information showing that the contribution of the anthropogenic emissions are overruled by the already present natural background. Exposure based waiving is justified for iron since results indicate that the relative contribution of anthropogenic iron to the already present natural iron pool in soils and sediments is not relevant in terms of added amounts and in terms of toxicity.

Additional information

Ubiquitousness: Iron is a major constituent of the lithosphere, comprising approximately 5.1% and its mean content in soils is estimated with 3.8%. The median total iron content of European soils expressed as Fe (XRF analysis) is 2.45% ranging from 0.11 to 15.60% in topsoil. In primary minerals iron occurs largely as ferromagnesium minerals (Salminen et al. 2005). These minerals dissolve during weathering and released iron precipitates as ferric oxides and hydroxides. The solubility of iron in soils is largely governed by iron (III) oxides whereas redox, soil pH and hydroxide formation, complexation with fluoride, phosphate and sulfate are modifying factors (Lindsay, 1979). Organic matter in soils is stabilised by sorption to iron (hydr)oxides suggesting that iron phases serve as sink for organic carbon involved in its long-term storage and contribute to the global cycles of carbon, oxygen and sulfur.

Manganese belongs to the first-row transition metals and commonly occurs in the upper crust with an average abundance of 600 mg/kg. Manganese is a frequent lithophile element and is found in several minerals including pyrolusite (MnO2), rhodochrosite (MnCO3) and manganite (MnO(OH)). Manganese occurs in five main oxidation states (Mn+2, Mn+3, Mn+4, Mn+6 and Mn+7) and as one natural isotope (55Mn). In addition, it occurs as an accessory element in several rock-forming minerals. In sedimentary rocks the largest portion of manganese is held in secondary Mn4+ oxides, that form concretions and coatings on primary minerals and lithic fragments (Salminen et al. 2005).

The mobility of manganese in the environment depends strongly on the redox potential (Eh), pH and the presence of complexing agents, i.e. organic acids derived from decaying plants. The Mn2+ ion is easily mobilised under anoxic conditions and has only a low affinity for organic ligands. However, under oxidising conditions Mn3+ and Mn4+ ions form insoluble hydrous oxides, which may co-precipitate (Salminen et al. 2005 and references therein).

Iron exposure, bioavailability and uptake from porewater by soil organisms are under environmentally relevant and tolerable conditions (pH and redox) limited by the solubility of naturally occurring ferric (hydr)oxides. Poorly soluble synthetic iron oxides are not expected to influence any soil parameter, including dissolved and bioavailable iron concentrations.

Essentiality: Iron is essential for almost all living organisms as it is involved in a wide variety of important metabolic processes including oxygen and electron transport, gas sensing and DNA repair and replication and regulation of gene expression. Thus, iron is critical to the survival of living organisms, including terrestrial bacteria, plants and invertebrates. Due to its poor solubility under environmentally relevant conditions, iron is not readily available, and soil organisms have developed sophisticated pathways to import, chaperone, sequester, and export iron. Thus, iron is an essential element that is homeostatically controlled by all organisms.

Manganese is ubiquitous in the environment and an essential trace element. Manganese acts as catalytic or structural component of larger molecules, which occupy key roles in essential metabolic pathways of microorganisms, plants, and animals.

Bioaccumulation: The existence of saturable uptake mechanisms, the presence of significant amounts of stored metal in organisms, and the ability of some organisms to regulate bioaccumulated metal within certain ranges are all thought to be responsible for the inverse relationship that has been frequently reported between bioaccumulation factors (BAFs) and metal exposure concentrations. In these cases, higher BAFs are associated with lower exposure concentrations and also can be associated with lower tissue concentrations within a given BAF study. This is contrary to the implicit assumption that higher BAFs indicate higher metal hazard. Nearly all metals, including iron, have BAFs >1000 in natural, healthy ecosystems with aqueous iron concentrations at background. Bioaccumulation factors for metals are clearly inversely related to water, sediment and soil concentrations (Adams, 2011).

For iron and manganese, essential, homeostatically controlled elements, the bioaccumulation potential is considered to be low. Manganese as essential nutrient is actively assimilated and utilized by plants and animals and does not biomagnify. Differences in iron uptake rates are related to essential needs, varying with the species, size, life stage, seasons etc. Iron homeostatic mechanisms are applicable across species with specific processes being active depending on the species, life stages. The available evidence shows the absence of iron biomagnification across the trophic chain both in the aquatic and terrestrial food chains. The existing information suggests that iron does not biomagnify, but rather that it tends to exhibit biodilution. Differences in sensitivity among species are not related to the level in the trophic chain but to the capability of internal homeostasis and detoxification (see "White Paper on waiving for secondary poisoning for Al and Fe compounds, 2010" attached in IUCLID section 6).

 

References:

Adams B, 2011. Bioaccumulation of metal substances by aquatic organisms, OECD meeting, Paris September 7-8, 2011.

Lindsay WL, 1979. Chemical equilibria in soils. The Blackburn Press.

Salminen R et al. 2005. Geochemical Atlas of Europe. Part 1: Background Information, Methodology and Maps. http://weppi.gtk.fi/publ/foregsatlas/index.php.