Professor Robert Hurt from the Laboratory for Innovation in Nanostructured Carbon and co-author Professor Agnes Kane from the Department of Pathology and Laboratory Medicine, both at Brown University, together with Marc Monthioux from the Center for Material Elaboration & Structural Studies (CEMES) in France edited a special issue of the journal Carbon on the subject of Toxicology of Carbon Nanomaterials.
As the authors explain to Nanowerk, the goal was to compile the most recent work by leading experts in the emerging field of nanotoxicology with a special focus on carbon. Carbon nanomaterials are arguably the most celebrated products of nanotechnology to date, encompassing fullerenes, nanotubes, nanofibers, and a wide variety of related forms. These nanomaterials can enter the human body through inhalation, skin contact, ingestion, or intentional injection, and may affect microorganisms, plants, or animals if released into the environment in significant quantities.
This combination of new materials, multiple exposure routes, and environmental fate and transport issues creates a complex set of research questions that scientists have just begun to tackle and early studies of nanomaterial toxicity have produced apparently conflicting results and raised more questions than were answered.
"Both biological systems and real nanomaterial formulations are complex, so fundamental progress in this new field will require teaming of toxicologists and materials scientists" says Hurt.
While there is universal consensus among scientists that significantly more work is needed on all of the new carbon nanomaterials to adequately assess their toxicity and health risks, it is promising that research into the toxicity of nanomaterials has begun in earnest.
"These issues are being discussed openly. This is one of the few areas in toxicology that I've been involved in, where there has been discussion at the very beginning" says Kane.
In their lead article, titled "Toxicology of carbon nanomaterials: Status, trends, and perspectives on the special issue" the authors highlight some of the critical issues and research needs that are relevant in the developing field of nanotoxicology, especially as it relates to carbon nanomaterials:
# Need for detailed materials characterization: toxicity of carbon materials may depend on byproducts or residues of complex carbon structures as much or more than on the primary carbon structures.
# Need for realistic exposure scenarios: risk is the product of hazard and exposure, and little is currently known about realistic exposure levels, especially for lung exposure.
# Need for methods to track nanomaterials in biological experiments: sensitive methods of detection are required to quantitate the extent of systemic transport and persistence at distant organs following dermal exposure, inhalation, ingestion, injection, or implantation.
# Issue of adsorptive interferences with fluorescent assays: the question needs to be addressed whether nanomaterials such as carbon black may interfere with fluorescent probes through adsorption or other means.
# Dose metrics: Sensitive detection methods are required to determine the dose metrics required in toxicology studies. However, it is possible that lipophilic nanomaterials (e.g. fullerenes) may interact with plasma membrane lipids and exert toxicity directly in the absence of cellular uptake.
# What are the most important indicators of toxicity? Carbon nanomaterials may elicit additional types of pathologic reactions and not be limited to the usually used short-term indicators of toxicity, altered cellular function or inflammation.
The authors specifically propose "that future submissions in this area include the following minimal materials characterization: complete bulk chemical composition (specifically including metals and heteroatom content >0.1%), specific surface area, and detailed descriptions of morphology (aspect ratios, secondary carbon forms, metals location) by electron microscopy examination of multiple fields. Further desirable characterization would include surface chemical composition (by energy dispersive or X-ray photoelectron spectroscopies), texture (spatial arrangement of graphene layers) and the degree of crystallinity, or perfection of the graphene layers."
"A realistic long-term goal for toxicologists as well as materials scientists is the development of "green" nanomaterial formulations – those co-optimized and surface engineered for both function and minimal health impact" concludes Hurt.
By Michael Berger, Copyright 2006 Nanowerk LLC. All rights reserved.