Nanotoxicology myth buster

Scientists believe that, with the increased mass production of engineered nanoparticles like carbon nanotubes, there is a realistic chance for these particles to interact with water, soil and air, and subsequently enter the food chain (see for instance: "Nanotoxicology - mammalian and plant cells respond differently to fullerenes"). However, understanding the behavior and impacts of nanomaterials in the environment and in human health is a daunting task.

Today, we don't even know what the impact of most chemicals is, and that includes products we have been using for many years. Nevertheless, a general understanding about nanotoxicity is slowly emerging as the body of research on cytotoxicity, genotoxicity, and ecotoxicity of nanomaterials grows.

What we are currently seeing is that individual research groups are picking certain areas of toxicological concern and forge ahead with – often highly specific – toxicology studies. Unfortunately, for lack of a common standard system (see: "Meaningful nanotechnology EHS research requires independent nanomaterial characterization"), these studies are difficult to compare and sometimes they even appear to contradict each other; a situation that is especially confusing in risk assessments of carbon nanotubes (see: "Comparing apples with oranges – the problem of nanotubes risk assessment").

As a result, many of the published toxicity studies have limited relevance, due, in large part, to study design limitations, including inadequate justification for dose selection or route of exposure criteria.

David B. Warheit from the DuPont Haskell Global Centers for Health and Environmental Sciences has written an article in the October 29, 2010 online edition of Nano Letters ("Debunking Some Misconceptions about Nanotoxicology"), where he addresses issues that he perceives to be myths and misconceptions regarding nanotoxicology:

Myth 1: Nanoparticles are always more toxic than bulk particles of similar or identical composition.

Myth 2: Particle size and surface area are the critical indices that influence nanoparticle toxicity.

Myth 3: All forms of nanotitanium dioxide particles have similar toxicity profiles – or nano TiO2 is nano TiO2 – i.e., we can identify nanoparticle types by their "core identities" without specifying their compositional physicochemical characteristics.

Myth 4: No current methodologies are available for the responsible development of nanoscale materials.

Myth 5: Pulmonary hazard assessments for nanoparticles can be accurately evaluated using in vitro orin silico methodologies.

Most of the documented adverse effects from studies of nanomaterial toxicity have been attributed to the small particle size (see for instance: "Size matters. Comparing the toxicity of micro- to nanoparticles"). However, some studies have demonstrated that factors other than particle size, such as particle surface reactivity, may play important roles in defining nanomaterial toxicity.

Warheit notes that "perhaps the most important point to be made is that nanoparticle toxicological effects are complex and involve a variety of factors including physicochemical characteristics, particle-cellular interactions, routes and degrees of exposure, biokinetics, logistics, and other considerations. Unfortunately, these effects cannot yet be accurately modeled using simple systems."

He points out that risk determination is a product of both exposure and hazard assessments. "However, in many cases the exposure potential cannot be quantified, due to current technological limitations of measuring nanoparticle exposures in the workplace. Despite these limitations, the risk management framework could include a minimum base set of toxicity (hazard) screening studies, thus providing a fundamental hazard characterization for the nanoscale particulates of interest."

The minimum base set of acute toxicity assays – not intended to provide for a comprehensive evaluation of toxicity but is designed to facilitate a practical strategy for the development of new nanoscale materials – could include the following criteria: substantial particle characterization; pulmonary toxicity studies; acute dermal toxicity and sensitization studies; acute oral and ocular toxicity studies; along with screening type genotoxicity; and aquatic toxicity studies.

After reviewing a number of nanotoxicology research papers addressing the above-mentioned five 'myths', Warheit concludes that, because hazard effects cannot yet be accurately modeled and the hazard database for nanomaterials is very limited, it will be important to rigorously characterize the material of interest and generate substantive hazard data that is accurate and can be confirmed independently by other research investigators.

In his view, evaluations of human health and ecological implications of nanoparticle exposures will be required to attain nanotechnology's full commercialization potential.

By Michael Berger. Copyright 2010 Nanowerk