Mill scale (ferrous metal)

Toxicity to aquatic algae and cyanobacteria

Administrative data

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Mill scale is mainly and primarily composed of high-purity iron oxides (on average above 65%, i.e. FeO, Fe2O3, Fe3O4). Besides, other metal oxides and spinels, elements, and trace compounds such as oil residues <1% for all the uses except for batteries and Melting charge for which <3% can be found in the mill scale. More information on the justification of read across can be found in the attached document in the endpoint summaries of section 5 and 6.

Materials and methods

Test material

Test material information

Constituent 1

Reference substance name:

Iron

EC Number:

231-096-4

EC Name:

Iron

Cas Number:

7439-89-6

IUPAC Name:

iron(2+)

Applicant's summary and conclusion

Conclusions:

Literary studies have extensively used test solutions with iron concentrations above that of its solubility limit. Results of these studies are therefore meaningless for the investigation of intrinsic toxicity. Available data do suggest that iron salts are relatively non toxic and this was sufficient for the EU Classification and Labelling Committee to determine that there was no need for classification of iron salts. It was also concluded that there is no need to perform additional aquatic hazard tests for iron massive and sparingly soluble forms of iron (like iron oxides) for REACH as these substances are highly insoluble and non-hazardous. Iron ions released to surface waters quickly form insoluble iron hydroxides in mixing zones.
These positively charged iron (III) colloids will react with the negatively charge mucus that lines the fish gill. This accumulation of iron on the fish gill results in physical effects. Iron has a complex redox chemistry. Ongoing investigations were performed to investigate whether intrinsic iron toxicity at low pH and high dissolved organic carbon concentration exists. In very special conditions transient iron species can be formed that cause toxicity. These conditions however are not typical of most ambient conditions and are more representative of specific mixing zones. In ambient conditions, the dissolved natural background concentrations of iron, in most cases, are at equilibrium therefore an addition of iron would lead to the precipitation of iron compounds from solution. Intrinsic toxicity would therefore not be observed. More information can be found in the attached position paper ('Position Paper Iron.pdf' and 'WCA - Iron Chemistry Environment Freshwater Background Report.pdf).