Abstract
Increasing application of engineered nanomaterials within occupational, environmental, and consumer settings has raised the levels of public concern regarding possible adverse effects on human health. We applied a tiered testing strategy including (i) a first in vitro stage to investigate general toxicity endpoints, followed by (ii) a focused in vivo experiment. Cytotoxicity of laboratory-made functionalized multiwalled carbon nanotubes (CNTs) (i.e., MW-COOH and MW-NH2), compared to pristine MWCNTs, carbon black, and silica, has been assessed in human A549 pneumocytes by MTT assay and calcein/propidium iodide (PI) staining. Purity and physicochemical properties of the test nanomaterials were also determined. Subsequently, pulmonary toxic effects were assessed in rats, 16 days after MWCNTs i.t. administration (1 mg/kg b.w.), investigating lung histopathology and monitoring several markers of lung toxicity, inflammation, and fibrosis. In vitro data: calcein/PI test indicated no cell viability loss after all CNTs treatment; MTT assay showed false positive cytotoxic response, occurring not dose dependently at exceedingly low CNT concentrations (1 μg/mL). In vivo results demonstrated a general pulmonary toxicity coupled with inflammatory response, without overt signs of fibrosis and granuloma formation, irrespective of nanotube functionalization. This multitiered approach contributed to clarifying the CNT toxicity mechanisms improving the overall understanding of the possible adverse outcomes resulting from CNT exposure.
Highlights
Nanotechnology is one of the fastest emerging fields involving development and manipulation of materials ≤100 nm in size
The remarkable diversity of engineered nanomaterials (ENMs), together with their unique properties and behaviour, complicates their risk assessment; there are currently about 50,000 different types of carbon nanotubes obtained by different raw materials and production processes
REACH should be applied to ENMs, the Technical Guidance Documents [3] for preparing a risk assessment currently include very little reference to substances in particulate form, lacking in addressing specific characteristics of ENMs
Summary
Nanotechnology is one of the fastest emerging fields involving development and manipulation of materials ≤100 nm in size. In view of some similar aspects to fibers, such as structural characteristics, extreme aspect ratio, low specific density, and low solubility, CNTs might exhibit toxicity similar to those observed with other fibrous particles such as asbestos [1] Their small size accompanied by high surface area defines the chemical reactivity of CNTs inducing changes in permeability and conductivity of biological membranes; a typical behaviour has been reported regarding translocation and distribution of certain ENMs in the body and their capability to cross internal barriers [2]. Dissimilar results from in vivo studies have been ascribed to differences in CNT size and surface area, rodent species used, route of exposure, and differences in observation period [42,43,44,45,46,47]
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