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EC number: 233-899-5 | CAS number: 10421-48-4
It is considered that there are sufficient hazard data available for the required SIDS endpoints for these iron salts when considered as a chemical category. The results of acute laboratory toxicity tests conducted with aquatic species indicate that effects of the salts are observed at nominal exposure concentrations as the salt in the range 1 – 1000 mg/l, with the majority being in the range 10 – 100 mg/l. Chronic effects on aquatic organisms are also observed at nominal concentrations in the range 1 – 1000 mg/l for each individual salt with the majority of the results being > 10 mg/l.
Given the half-life for oxidation and precipitation detailed in section 4.1 it is anticipated that a significant proportion of any ferrous salts added to aqueous test media would have converted to ferric within the timescale of the standard OECD test protocols. The cited LC50, EC50 and NOEC values for all the iron salts significantly exceed the equilibrium concentrations of dissolved ferric iron given in Table 7.2, which are very low values. It is important to note that were these equilibrium concentrations to truly reflect the toxicity of iron in solution they would place it alongside, or more toxic than, some of the most potent toxic chemicals that are known. Such a view could clearly not be sustained given the ubiquity of iron in all its various forms in the environment, in loadings that would yield these apparently toxic concentrations.
It is therefore reasonable to assume that a small proportion of the added iron in the tests will have been present in the form of dissolved iron – the majority being present as precipitated ferric hydroxide. Secondary effects arising from the presence of the precipitate together with possible pH reduction and phosphate precipitation (relevant to plant tests only) are likely to have contributed significantly to the effects observed in the tests. This assumption is substantiated by observations noted in some of the test reports.
Iron salts may present a toxic hazard to environmental species under specific conditions. For example, it is possible that ferrous iron salts could have toxic effects in circumstances where the following conditions apply and persist:
Such conditions would need to result in dissolved iron concentrations in the order of 1 to 10 mg/l and would not be expected to arise from the industrial production and use patterns for these iron salts that are described in Section 2.
Iron species are naturally common throughout the environment. Measured background concentrations and Regulatory Standards for iron provide a useful context for considering the results of this assessment:
The higher background concentrations for surface waters overlap the effect concentrations determined in this assessment. However the standards are protective against those effects occurring.
The physical fouling phenomena, that are believed to be the explanation for the majority of the effects observed in laboratory tests, are still a genuine hazard. They are more likely to occur in the environment under circumstances where significant loads of iron are added. In many natural waters suspended sediments (high in iron content) are already present and resident organisms are adapted to tolerate such conditions. The extent to which organisms will be affected by further additions of iron will be determined by their ecology and physiology – some organisms can tolerate elevated levels of suspended material and surface sediment, others cannot. Responses arising from physical phenomena would not be indicative of a significant chronic hazard.
Responses to effects arising from other secondary factors such as lowered pH and nutrient complexation will also be dependent upon the susceptibility of resident organisms to perturbations in these parameters and the characteristics of the receiving environment (e.g. buffering capacity and background nutrient concentrations). The results of the laboratory tests and the published EQS values again suggest that it would be necessary for dissolved iron concentrations to exceed 1 mg/l before significant effects could be anticipated. Such concentrations are only likely to occur and persist under conditions of low dissolved oxygen concentration and low pH.
Even if the test results reported in this assessment are taken at face value as indicative of toxic effects, it was considered in a recent EU classification of ferrous sulfate heptahydrate and monohydrate that the majority of acute toxicity end points had values > 10 mg/l iron salt and that the reduction of soluble iron concentrations below measured chronic NOECs could be considered as equivalent to ‘rapid degradability’ leading to a ‘no environmental hazard’ classification decision. The GHS proposals would lead to a similar conclusion.
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