Chapter 20 - An Overview on the Safety of Tubular Clay Minerals

Abstract

Abstract This chapter reviews the studies that have been carried out to investigate the biological effects of halloysite and imogolite nanotubes. It summarises the evolution of the health issues related to fibre exposure, based on our knowledge on the mechanism of action of asbestos fibres, as well as of the determinants of fibre toxicity. Further investigations on the biological effects of carbon nanotubes have been conducted that link the adverse effects of fibres to their high-aspect ratio, justifying the concern about the potential health effects of nanotubular clay minerals. Both halloysite and imogolite are used in medical applications, but from the literature data, most studies performed with halloysite nanotubes were cytotoxicity studies developed in a context of medical research, while more classical toxicological studies (including one animal study) were developed with imogolite nanotubes. In this context, halloysite nanotubes do not appear to exert a cytotoxic effect, and some imogolite nanotubes may show both cytotoxic and genotoxic effects. However, the limited number of studies and end points assessed (mostly cytotoxicity and the diversity of the nanotubes used in the experiments) do not allow one to draw general conclusions on their potential impact on human health. The discussion covers a number of issues specific to the toxicology of nanotubular clay minerals and some perspectives on making proposals to acquire pertinent information on the human health risk from exposure to nanotubular clay minerals.