Reaction mass of aluminium chloride, iron dichloride, magnesium chloride and manganese dichloride

Endpoint summary

Additional information

For inorganic metal salts the concept of biodegradation is not applicable in general (OECD 2001 Series on testing and assessment number 27). Nonetheless biota can play a role in the fate of metals in the environment as they may influence the speciation.

Iron

The environmental factors which rule degradation/transformation processes of water soluble iron salts in the environment is covered in the IUCLID 5 Endpoint Summaries 5.1.2 Hydolysis, 5.1.3 Phototransformation in water, and 5.4 Transport and distribution, which correspond to the chapters 4.1.1.1. Hydrolysis, 4.1.1.2.2. Phototransformation in water, and 4.2 Environmental distribution in the CSR (Chemical Safety Report) and Sections 2.2.3, 2.2.2, and 2.2.4 of the SIAR respectively.

Available data on biodegradation have been reviewed and discussed in peer-reviewed published SIAR for iron salts (SIDS Initial Assessment Report for SIAM 24, Paris, France, 17-20 April 2007), Section 2.2.5.

Since iron is an essential element, it is also subjected to biological activity and control. Organometallic complexes play an important role in biota as haemoglobin contains iron. Due to their essentiality iron chemistry in biota controlled and readily biodegradation for the recoupment of the iron applies. Bacterial transformations of iron are extensively studied and basically well known processes. Iron is abundant in the environment from natural mineral sources and iron transformations and the whole iron cycle in the environment is a combination of abiotic and biological processes.

Two papers demonstrate the importance of natural bacteria. Chen et al (2003) studied ferric iron reduction kinetics and capacity by three fractionated NOM subcomponents in the presence or absence of metal reducing bacteria (Shewanella putrefaciens), strain CN32. which are generally associated with aquatic or marine environments. Results indicate that natural organic matter (NOM) was able to reduce ferric iron abiotically; the reduction was pH-dependent and varied greatly with different fractions of NOM. The polyphenolic-rich fraction (NOM-PP) exhibited the highest reactivity and oxidation capacity at a low pH (<4) as compared with the carbohydrate-rich fraction (NOM-CH) and a soil humic acid (soil HA) in reducing ferric iron. However, at a pH >4, soil HA showed a relatively high oxidation capacity. In the presence of the bacteria, all NOM fractions were found to enhance the microbial reduction of ferric iron under anaerobic, neutral pH conditions.

A further level of complication was demonstrated in a study by Straub et al (2001). Numerous ferric iron-reducing bacteria have been isolated from a great diversity of anoxic environments, including sediments, soils, deep terrestrial subsurfaces, and hot springs. In contrast, only few ferrous iron-oxidizing bacteria are known so far. At neutral pH, iron minerals are barely soluble, and the mechanisms of electron transfer to or from iron minerals are still only poorly understood. In natural habitats, humic substances may act as electron carriers for ferric iron-reducing bacteria. Anaerobic ferrous iron-oxidizing phototrophic bacteria, on the other hand, appear to excrete complexing agents to prevent precipitation of ferric iron oxides at their cell surfaces. This finding is an illustration of the extent of adaptation of the environment to iron ions.

In natural systems, bacteria interact with the humic redox system. Kappler et al (2004) suggest that microbial reduction of humic acids and subsequent chemical reduction of poorly soluble Fe(III) minerals by the reduced humic acids represents an important path of electron flow in anoxic natural environments such as freshwater sediments as well as soil. Natural organic matter NOM can act as an electron acceptor for microbial respiration by iron-reducing bacteria.

• Chen J, Gu B, Royer RA, Burgos WD (2003). The roles of natural organic matter in chemical and microbial reduction of ferric iron, Science of the Total Environment 307(1-3):167-78
• Kappler A, Benz M, Schink B, Brune A (2004). Electron shuttling via humic acids in microbial iron(III) reduction in a freshwater sediment, FEMS Microbiology Ecology 47(1):85-92.
• Straub KL, Benz M, Schink B (2001). Iron metabolism in anoxic environments at near neutral pH, FEMS Microbiology Ecology 34(3):181-6.

Manganese

Two manganese forms exist in aquatic environments, i.e. Mn(II) and Mn(IV). The transformation by oxidation and reduction can be effected abiotically or microbially. Microorganisms are believed to play an important role in the cycling of manganese in aquatic environments (Heal 2001, Nealson 1983, Stein et al 2001, Thamdrup et al 2000, WHO 2004).

Micro-organisms can change the oxidation state in soils and sediments (Geering et al 1969; Francis 1985). Geering et al (1969) observed oxidation leading to precipitation of manganese minerals. Johnston & Kipphut (1988) observed in the summer Manganese (II) oxidation in a lake. After application of a microbial poison this reaction was inhibited. Altomare et al (1999) report that the sparingly soluble manganese dioxide was solubilised by a fungus (Trichoderma harzianum). The microbial metabolism of manganese is presumed to be a function of pH, temperature, and other factors, but no data were located on this (ATSDR 2008).

• Altomare C, Norvell WA, Björkman T, Harman GE (1999). Solubilization of phosphates and micronutrients by the plantgrowth-promoting and biocontrol fungus Trichoderma harzianum Rifai 1295-22. Applied Environmental Microbiology, 65:2926–33.
• ATSDR Agency for Toxic Substances and Disease Registry (2008). Draft Toxicological Profile for Manganese. U.S. Department of Health and Human Services, Public Health Service, Atlanta, Georgia, U.S.A. 593 p
• Geering HR, Hodgson JF, Sdano C (1969). Micronutrient cation complexes in soil soluti on. IV. The chemical state of manganese in soil solution. Soil Science Society of America Proceedings 33:81–5.
• Heal KV (2001) Manganese and land-use in upland catchments in Scotland. Science of the Total Environment, 265(1 –3):169–79.
• Nealson KH (1983). The microbial manganese cycle. IN: Krumbein WE (Ed) Microbial geochemistry. Oxford, Blackwell, 191–221.
• Stein LY, La Duc MT, Grundl TJ, Nealson KH (2001). Bacterial and archeal populations associated with freshwater ferromanganous micronodules and sediments. Environmental Microbiology 3(1):10–8.
• Thamdrup B, Rossello-Mora R, Amann R (2000). Microbial manganese and sulfate reduction in Black Sea shelf sediments. Applied and Environmental Microbiology 66(7):2888–97.
• WHO World Health Organization (2004 and 2005). Manganese and its Compounds: Environmental Aspects. Concise International Chemical Assessment Document 63, Corrigenda published by 12 April 2005 have been incorporated. Self-published, Geneva, Switzerland

Aluminium

For inorganic substance like aluminium salts for which the chemical assessment is based on the elemental concentration (i. e., pooling all inorganic speciation forms together), biotic degradation is an irrelevant process, regardless of the environmental compartment that is under consideration: biotic processes may alter the speciation form of an element, but it will not eliminate the element from the aquatic compartment by degradation or transformation. This elemental-based assessment (pooling all speciation forms together) can be considered as a worst-case assumption for the chemical assessment.