RESUMO
Experimental systems allowing aerosol exposure (AE) of cell cultures at the air-liquid-interface (ALI) are increasingly being used to assess the toxicity of inhaled contaminants as they are more biomimetic than standard methods using submerged cultures, however, they require detailed characterisation before use. An AE-ALI system combining aerosol generation with a CULTEX® exposure chamber was characterised with respect to particle deposition and the cellular effects of filtered air (typical control) exposures. The effect of system parameters (electrostatic precipitator voltage, air flowrate to cells and insert size) on deposition efficiency and spatial distribution were investigated using ICP-MS and laser ablation ICP-MS, for an aerosol of CeO2 nanoparticles. Deposition varied with conditions, but appropriate choice of operating parameters produced broadly uniform deposition at suitable levels. The impact of air exposure duration on alveolar cells (A549) and primary small airway epithelial cells (SAECs) was explored with respect to LDH release and expression of selected genes. Results indicated that air exposures could have a significant impact on cells (e.g., cytotoxicity and expression of genes, including CXCL1, HMOX1, and SPP1) at relatively short durations (from 10 mins) and that SAECs were more sensitive. These findings indicate that detailed system characterisation is essential to ensure meaningful results.
RESUMO
A substance may have one or more nanoforms, defined for regulatory purposes under EU chemicals legislation REACH based on differences in physicochemical properties such as size, shape, specific surface area and surface chemistry including coatings. To reduce the burden of testing each unique nanoform for the environmental risk assessment of nanomaterials, grouping approaches allow simultaneous assessment of multiple nanoforms. Nanoforms with initially different intrinsic properties, could still be considered similar if their environmental fate and effects can be demonstrated to be similar. One hypothesis to group nanoforms with different organic surface modifications is to use parameters linked to biodegradation of the organic surface. The hypothesis contends that nanoforms with a similar core chemistry, but different organic surface treatments may be grouped, if the surface treatment is likely to be lost through biodegradation rapidly upon entering an environmental compartment, such that it no longer modulates fate, exposure and toxicity of the nanoform. To implement grouping according to surface treatment biodegradability, a robust approach to measure the breakdown of particle surface treatments is needed. We present a tiered testing strategy to assess the biodegradation of organic surface treatments used with nanomaterials that can be implemented as part of an Integrated Approach to Testing and Assessment (IATA) for grouping based on surface treatment stability. The tiered approach consists of an initial pre-screening MT2 colorimetric carbon substrate utilisation assay, to provide a rapid assessment of coating degradation, and a second tier of testing using OECD Test Guideline 301F for assessing organic chemical biodegradability. Six common surface treatment substances are assessed using the tiered testing strategy to refine rules for escalating between tiers. Similarity assessment using absolute Euclidean distances and x-fold difference concluded that the Tier 1 assessment can be used as conservative binary screening for biodegradability (no false positive results in Tier 1), whilst for substances showing intermediate biodegradation (10-60% in OECD 301F, Tier 2), similarity assessments can be informative for grouping surface treatments not considered readily biodegradable. Further validation using higher tier tests (e.g., mesocosms) is needed to define acceptable limits of similarity between intermediately biodegradable substances, where differences in biodegradability of the surface coating lead to negligible differences in fate, behaviour and toxicity of the nanoforms, and this is critically discussed.