For years, a rapidly expanding quantity of engineered nano-products have flooded the consumer marketplace and are unregulated as evidence of toxicities accumulate.
Nanotechnologies are technologies at the scale of nanometres (10-9m), where new quantum effects can alter the chemistry and physics of elements and compounds, offering exciting new possibilities in industrial applications, and for exactly the same reasons, posing unprecedented risks to health and the environment.
Writing in Environmental Engineering Science, researchers used a model of the human gut to test how exposure to three different nanoparticles (NP) that are commonly used in consumer products - zinc oxide, cerium dioxide, and titanium dioxide -- affects the make-up of the bacterial communities in our gut (known as the microbiota).
"Understanding the interactions between NPs and bacteria in an engineered model colon can indicate potential impacts of NP exposure on the gut, and therefore overall human health," suggested the research team -- led by senior author Professor Sharon Walker from the University of California, Riverside.
It was difficult to separate hype from reality when it all began, and almost no one worried about safety and nanotoxicology became established as a discipline in 2005 (Nanotoxicity: A New Discipline, SiS 28). By then, many serious health impacts had already been observed in laboratory experiments; and more appeared in subsequent years.
Walker and her colleagues found that exposure to environmentally relevant concentrations of NPs led to distinct changes in the microbial community -- causing a partition into three distinct phases: "initial conditions, a transition period, and a homeostatic phase, with the NP-exposed community displaying significant differences from the unexposed community in multiple phenotypic traits."
Overall, the team found that the nanoparticles caused non-lethal, yet significant changes to the microbial community's phenotype -- which they suggested could be related to an overall impact on health.
In 2009, researchers at University of California Los Angeles Jonsson Cancer Center led by Robert Schiest reported that titanium dioxide nanoparticles (TiO2), found in “everything from cosmetics and sunscreens to paint and vitamins” (see Box), caused DNA damage when fed to mice. They induced breaks in DNA, damaged chromosomes, and caused inflammation of tissues; “all of which increase the risk of cancers.”
The team used a model gut to expose normal gut flora to nanoparticles at levels that are typically found in consumer goods including foods and cosmetics.
Zinc oxide (0.01 microg/L), cerium dioxide (0.01 microg/L), and titanium dioxide (3 mg/L) were introduced into a model colon to identify the subsequent impact on the gut microbial community.
Walker and her colleagues noted that the addition of nanoparticles to the model gut system clearly affected the phenotypic characteristics of the microbial community as well as the gut microenvironment when compared to model gut systems in which NPs had not been added.
"Notably, phenotypes, including short-chain fatty acid (SCFA) production, hydrophobicity, sugar content of the extracellular polymeric substance, and electrophoretic mobility, which indicate changes in the community's stability, were affected by the NPs," wrote the team.
Indeed, they noted that titanium dioxide led to extended phenotypic transformations for hydrophobicity when compared with the other NPs -- something the team suggested was likely due to its lack of dissociation and greater stability.
The team said the technique used in the new study has provided unique insights into alterations to the microbial metabolic processes caused by NPs.
However, the noted that an important consideration when studying the gut microbiota and interpreting results is that one human sample does not represent the high variability and diversity of gut microbiomes present in the human population.
"This work highlights the relevance of studying a complex matrix and microbial community in situ rather than individual microbial species in vitro," said the authors.
"The techniques used and presented here offer a novel combination of indicators for identifying NP-induced perturbances within the gut microbiota," they added.
One Big Experiment
"There has been a great deal of research into the use of manufactured carbon nanomaterials in various products, but there are still a lot of questions about how these materials will interact with biological systems," says Dr. Nancy Monteiro-Riviere, a professor of investigative dermatology and toxicology at the Center for Chemical Toxicology Research and Pharmacokinetics at NC State. See Scientists Continue Using Nanoparticles Without Knowing How They Affect Us.
One of the complications of nanotoxicology is that the toxicity of a specific nanomaterial cannot be predicted from the toxicity of the same material in a different form. For instance, while the toxicity of inert systems such as iron oxides, gold, or silver has been investigated for nearly isotropic particles (i.e., with a low aspect ratio), the toxicity of these materials in nanofilament form cannot be predicted from their known toxicity as nanoparticles. Fully understanding the toxic mechanisms of nanoscale materials is an essential prerequisite in being able to design harmless nanomaterials whose interactions with biological cells is non-lethal.
There is clearly an urgent need not only to stem but also to reverse the unregulated tide of nanoparticles that are released onto the market. In view of the existing evidence, the following actions should be taken.
- Engineered nano-ingredients in food, cosmetics and baby products for which toxicity data already exist (e.g., silver, titanium oxide, fullerenes, etc.) should be withdrawn immediately
- A moratorium should be imposed on the commercialization of nano-products until they are demonstrated safe
- All consumer products containing nanotechnology should be clearly labelled
- The Health and Consumer Protection Directorate General (SANCO) of the European Commission should require manufacturers of nano-products to register their products in a database that is publicly available on the SANCO website.
- The voluntary code of conduct for nanotechnology research that the European Commission adopted in 2008 should become mandatory: Nanotechnology research activities must be made comprehensible to the public, performed in a transparent manner, accountable, safe and sustainable, and not pose a threat to the environment
- A robust regulatory programme on nanotechnology - including characterisation and standardisation of manufacture - should be implemented as soon as possible
- There should be earmarked funding for research into the hazards of nanotechnology.
Marco Torres is a research specialist, writer and consumer advocate for healthy lifestyles. He holds degrees in Public Health and Environmental Science and is a professional speaker on topics such as disease prevention, environmental toxins and health policy.