ZnO nanoforms - REACH substance evaluation: environmental aspects

ein weißes Pulver in einer schwarzen DoseClick to enlarge
Zinc oxide is used in a wide variety of products.
Source: tankist276 / Adobe Stock

Together with the Federal Office for Chemicals and the Federal Institute for Risk Assessment, the German Environment Agency (UBA) has been carrying out a REACH substance evaluation on the registered nanoforms of zinc oxide since 2017. The assessment of the data on the environmental behaviour and effects of the registered zinc oxide nanoforms is now concluded.

Based on the studies submitted by the registrants, the UBA concludes that the tested nanoforms have a comparable aquatic toxicity to other zinc compounds and that the harmonised classification in Annex VI of the ⁠CLP⁠ Regulation as acute and chronic aquatic toxicity category 1 also applies to the tested nanoforms. However, it cannot be excluded that a nanoparticle specific effect contributes to the overall toxicity of the tested zinc oxide nanoforms. There are also slight differences in toxicity both between the different nanoforms and between the nanoforms and the easily soluble zinc chloride tested as a control.

The studies presented by the registrants clearly show that the registered nanoforms differ not only in size and geometry, but also in their surface properties, as well as solubility and dispersion stability over time.

As part of the substance evaluation, the solubility of all registered zinc oxide nanoforms was determined using the screening test according to the OECD's "Transformation/Dissolution Protocol" and the dispersion stability according to OECD Test Guideline 318. Based on these results, the registrants selected three nanoforms for which the long-term toxicity to algae and daphnia was examined according to OECD Test Guidelines 201 and 211.

According to the ⁠REACH⁠ Regulation, it is the responsibility of the registrants to ensure that the available information is sufficient to assess the risks of all forms covered by the registration. The verification of the fulfilment of this obligation is not part of the substance evaluation, but may be subject to random checks by ECHA as part of a dossier evaluation.

Zinc oxide is a basic chemical that is used for the manufacturing of a wide variety of products. Large quantities of pigmentary and microscale zinc oxide are used worldwide as a white pigment in wall paints, as an additive for vulcanising rubber or as an additive to cement. Nanoparticulate zinc oxide has special physical-chemical properties due to its small size and large specific surface area. These include catalytic, optical and electronic properties. These properties enable further applications for zinc oxide, e.g. as a UV filter in sunscreens, in textiles, in clear varnish or for transparent plastics.

Substance evaluation is an instrument of the REACH Regulation used by the competent authorities of the EU Member States to clarify whether the manufacture or use of a substance registered in the EU poses a risk to human health and/or the environment. To assess the risk of the substance, both the data provided when the substance was registered and all other available sources of information are consulted. If the available data do not allow a clear assessment of the risk, the national authorities may request further information from the registrants of the evaluated substance. If the concern cannot be dispelled or if the suspicion of risk is confirmed, EU-wide risk management measures, such as restrictions on the substance, identification as a substance of very high concern or other measures, such as harmonised classification in accordance with the CLP Regulation, may be taken as a consequence of a substance evaluation.

The substance evaluation of zinc oxide by the German competent authorities focuses on the nanoforms contained in the registration dossier. Nanoforms of a substance are the forms of a chemical substance that correspond to the EU's definition recommendation on nanomaterials.

The UBA is solely responsible for the environmental aspects of the substance evaluation of zinc oxide. The aspects relating to human health are the responsibility of the Federal Institute for Risk Assessment.