A Review of Carbon Nanotube Toxicity and Assessment of Potential Occupational and Environmental Health Risks

Abstract

Nanotechnology has emerged at the forefront of science research and technology development. Carbon nanotubes (CNTs) are major building blocks of this new technology. They possess unique electrical, mechanical, and thermal properties, with potential wide applications in the electronics, computer, aerospace, and other industries. CNTs exist in two forms, single-wall (SWCNTs) and multi-wall (MWCNTs). They are manufactured predominately by electrical arc discharge, laser ablation and chemical vapor deposition processes; these processes involve thermally stripping carbon atoms off from carbon-bearing compounds. SWCNT formation requires catalytic metals. There has been a great concern that if CNTs, which are very light, enter the working environment as suspended particulate matter (PM) of respirable sizes, they could pose an occupational inhalation exposure hazard. Very recently, MWCNTs and other carbonaceous nanoparticles in fine (<2.5 µm) PM aggregates have been found in combustion streams of methane, propane, and natural-gas flames of typical stoves; indoor and outdoor fine PM samples were reported to contain significant fractions of MWCNTs. Here we review several rodent studies in which test dusts were administered intratracheally or intrapharyngeally to assess the pulmonary toxicity of manufactured CNTs, and a few in vitro studies to assess biomarkers of toxicity released in CNT-treated skin cell cultures. The results of the rodent studies collectively showed that regardless of the process by which CNTs were synthesized and the types and amounts of metals they contained, CNTs were capable of producing inflammation, epithelioid granulomas (microscopic nodules), fibrosis, and biochemical/toxicological changes in the lungs. Comparative toxicity studies in which mice were given equal weights of test materials showed that SWCNTs were more toxic than quartz, which is considered a serious occupational health hazard if it is chronically inhaled; ultrafine carbon black was shown to produce minimal lung responses. The differences in opinions of the investigators about the potential hazards of exposures to CNTs are discussed here. Presented here are also the possible mechanisms of CNT pathogenesis in the lung and the impact of residual metals and other impurities on the toxicological manifestations. The toxicological hazard assessment of potential human exposures to airborne CNTs and occupational exposure limits for these novel compounds are discussed Address correspondence to Chiu-wing Lam, JSC Toxicology Group, Space Life Sciences, NASA Johnson Space Center, SF23/Wyle, Houston, TX 77058, USA. E-mail: Chiu-wing. 189This document is a U.S. government work and is not subject to copyright in the United States. 190C.-W. LAM ET AL. in detail. Environmental fine PM is known to form mainly from combustion of fuels, and has been reported to be a major contributor to the induction of cardiopulmonary diseases by pollutants. Given that manufactured SWCNTs and MWCNTs were found to elicit pathological changes in the lungs, and SWCNTs...

In vitro and in vivo toxicity assessment of nanoparticles

“…The effect of soot-containing carbon nanotubes containing Co/Ni was observed on guinea pig [166]. Effect of single-walled carbon nanotubes containing metals was evaluated in mouse and rat by various researchers [167][168][169][170]. In one of the above studies, acute lung toxicity was evaluated for intratracheally instilled SW-CNTs in rats [170].…”

Polysulfone ultrafiltration membranes impregnated with silver nanoparticles show improved biofouling resistance and virus removal

“…Currently, most of the toxicological evaluations conducted on cultured cells or in vivo support the toxicity of CNTs (Ding and Liu, 2005;Lam et al, 2006) although the antimicrobial response depends on the degree of sidewall functionalization (Sayes et al, 2006). Although the toxicity of CNTs towards prokaryotes may be different than CNT toxicity towards eukaryotes, one study showed that multi-walled carbon nanotubes (MWCNTs) caused cell death and apoptosis with corresponding changes in the protein expression of human skin fibroblasts; however, this study did not conclusively define the mechanism of cell death (Ding and Liu, 2005).…”

Update on UHMWPE research From the bench to the bedside

“…Innovations to potentially improve mechanical properties using composite materials have been reported, where multiwalled carbon nanotubes are added as a reinforcing component for different polymers and fibrous materials (Polizu et al 2006, Cao et al 2007). However, the biocompatibility of nanotubes is still in question (Lam et al 2006, Zhu et al 2007). …”