Guidance on testing health effects of nanomaterials

The applicability of the OECD Test Guidelines for testing manufactured nanomaterials has been reviewed by the OECD WPMN.3 This review found that, in general, the guidelines are applicable for investigating the health effects of nanomaterials, although in some cases there is a need to further modify the guidelines—particularly with studies using the inhalation route and with toxicokinetic studies. The table below summarises the key points from the WPMN's review.

For each test, you must report an adequate characterisation of the nanomaterial tested out-of-the-bottle and describe the sample preparation. Where feasible, provide the characterisation of the nanomaterial in the dosing medium (that is, particle size distribution, agglomeration and aggregation state).

Summary of preliminary review of OECD test guidelines for their applicability to manufactured nanomaterials

OECD test guideline/s

Test

Notes

417

Toxicokinetics (Administration-Distribution-Metabolism-Excretion)

The guideline is very general. Although being updated at time of writing, it is questionable if modifications will be sufficient for investigating nanomaterials.

It is likely that specific studies on the absorption and distribution of nanomaterials will need to be designed case-by-case. In particular, due to the likely property of nanoparticles to translocate whatever the exposure conditions, studies tracking the distribution of labelled nanomaterials in vivo at realistic exposure scenarios will be necessary.

The main issues associated with absorption, distribution, metabolism and excretion studies with nanomaterials are ensuring the (product) label:
(1) remains with the nanoparticles following route of entry into the body; and (2) does not alter the biological activity of the nanoparticle, particularly since the changes in surface chemistry of the nanoparticle can significantly influence its physicochemical properties and, as a consequence, its toxicity.

Preliminary studies should therefore be undertaken to certify that both issues are covered before undertaking a toxicokinetic study.

427

Skin absorption in vivo

No comments.

428

Skin absorption in vitro

The use has been questioned for nanomaterials since it has been claimed that mechanical aspects such as flexing may be important and some further development of this assay may be needed for nanomaterials.

420, 423, 425

Acute oral

Would be appropriate for initial investigation. It should be recognised that the extent of pathology at autopsy is limited.

403

Acute inhalation

Includes only very limited histological examination at autopsy. Detailed examination of the respiratory tract would be appropriate with consideration of the addition of broncho-alveolar lavage and possibly pulmonary cell proliferation endpoints.The methodology for this test should not be confused with intratracheal instillation, commonly used to assess the pulmonary toxicity of nanomaterials. Intratracheal instillation in rats can cause misleading artefactual effects associated with doses that overload respiratory clearance mechanisms.

This guideline is being updated, but the update is not taking into account nanomaterial assessment. Further revision should be planned or a separate guideline developed.

402

Acute dermal

Only requires minimal pathology; would be desirable to have enhanced pathology when investigating nanomaterials.

430, 431, 435

In vitro methods for investigating skin corrosion

May be used, but noting that measurement of cell viability using MTT (or other metabolically converted vital dye) may not be appropriate due to marker inactivation.

404, 405

Skin and eye irritation

Appropriate for investigating the irritancy of nanomaterials.

406

Skin sensitisation—guinea pig models

Should not be considered for nanomaterials.
TG 429 is the preferred method.

429

Skin sensitisation—local lymph node assay

Appears to be the most appropriate method for investigating the skin sensitisation potential of nanomaterials. The test permits an estimation of the potency of the sensitisation reaction.

432

Phototoxicity—in vitro assay

Mainly used for cosmetics—ultra violet filters in sunscreens for phototoxicity.

407,  409

28-day and 90-day repeat dose oral studies

Appropriate for investigating the repeated dose toxicity of nanomaterials by the oral route. Consideration needs to be given to enhancing the ability of this method to detect adverse effects that are a particular concern with some nanoparticles (for example, cardiovascular effects with nanoparticles).

Has been updated to enhance their ability to detect neurotoxic and immunotoxic effects and also effects on the reproductive system. TG 407 is being updated to give enhanced ability to detect effects on the endocrine system.

412 and 413

14 to 28-day and 90-day repeat dose inhalation

Both guidelines need to be enhanced with respect to neurotoxicity and immunotoxicity when investigating nanomaterials. TG 412 has very limited pathology. Detailed histological examination of the entire respiratory tract would be expected when investigating the effect of nanomaterials following repeated exposure by inhalation.

Consideration needs to be given to enhancing the ability of these methods to detect adverse effects that are a particular concern with some nanoparticles.

410, 411

21, 28 or 90-day repeat dose dermal studies

Little use for chemicals in general.

It is likely that any testing of nanomaterials by the dermal route would be limited to acute toxicity and investigation of the extent of absorption through skin.

471


473


476

In vitro genotoxicity tests

Bacterial reverse mutation assay

In vitro mammalian cell gene mutation test

In vitro mammalian cell gene mutation assay, with the mouse lymphoma assay being the preferred assay

Appropriate for an initial investigation of the mutagenic potential of nanomaterials. However it has been recognised that treatment of mammalian cells in vitro with insoluble particles may lead to misleading results.

474, 475 or 486

In vivo genotoxicity tests

Positive results in vitro would need to be followed up in vivo if the bone marrow or liver were appropriate target organs, and this would depend on systemic availability.

477, 478, 479, 480, 481, 482, 483, 484, 485

Genotoxicity tests

Unlikely to be used when investigating the mutagenicity of nano materials.

451, 452, 453

Chronic toxicity and carcinogenicity

Unlikely to be used for nanomaterials, except in very exceptional circumstances.

421, 422, 415, 416

Reproductive toxicity

Appropriate for investigating the reproductive toxicity of nanomaterials by way of the oral route.

Needs to be modified if exposure was by inhalation and needs careful consideration.

414

Developmental toxicity

Last update 30 November 2016