Nano and biology
Nanotoxicology: studying what small particles do
The same properties that make nanomaterials interesting, their size and their enormous surface area, also raise questions about how they behave in living systems and in the environment. Nanotoxicology is the research field that asks those questions. This page describes what it studies and how public agencies approach it; it offers no verdict on any material.
What the field studies
The Wikipedia article on nanotoxicology defines it as the study of the toxicity of nanomaterials. It explains that quantum size effects and a large surface-area-to-volume ratio give nanomaterials properties different from those of larger particles of the same substance, and that these differences can affect how they interact with biological systems. The article notes that, because the technology is relatively recent, the health and safety effects of exposure and the levels of exposure that may be acceptable are not yet fully understood. It also points out that nanoparticles come from several sources: combustion, such as diesel soot; deliberate manufacture, such as carbon nanotubes; and natural processes, such as volcanic eruptions.
The article identifies the main exposure routes studied: inhalation, skin contact and ingestion. It reports that inhalation appears to present the most concern among them, based on animal studies of some nanomaterials. Those are research findings about particular materials under particular conditions, and the literature is careful to treat each material and route separately.
Naming a discipline
A 2005 paper by Oberdörster and colleagues in Environmental Health Perspectives helped define the field. Its abstract begins from the observation that people have always been exposed to airborne nanosized particles, that such exposure increased over the last century from human sources, and that engineered nanomaterials could become another source. The authors argued that older studies of how small particles move through the body, together with newer research on airborne ultrafine particles, form the basis of the expanding field of nanotoxicology, which they defined as the safety evaluation of engineered nanostructures and nanodevices.
The abstract then sets out emerging concepts. It describes how inhaled particles of particular sizes are deposited throughout the respiratory tract, how small size facilitates uptake into cells and passage into the circulation, and how a particle's uptake and fate depend largely on its surface chemistry and on changes to that surface inside the body. It notes that the greater surface area per mass of nanosized particles makes them more biologically active, and that this activity can include pro-oxidant but also antioxidant effects, which the authors suggest may explain mixed early results. It ends by calling for basic research on how such particles interact with structures inside cells. The framing matters: the paper presents questions and concepts for a new field, not settled conclusions.
Mechanisms: a later review
Sixteen years later, a review in the Annual Review of Pharmacology and Toxicology by Yang and colleagues surveyed the state of the field. Its abstract starts from the point that nanoparticles from natural and human sources are abundant in the environment, so human exposure is inevitable, and that understanding possible acute and chronic effects is therefore important. The review focuses on mechanisms at the level of organs, tissues, cells and biomolecules, and discusses the generation of reactive oxygen species, the breakdown of nanoparticles, effects on cell signalling, the formation of a protein corona, and immune responses associated with a common polymer coating. The authors conclude that better understanding could lead to strategies for safer use and inform efforts to establish standardised regulatory frameworks.
The protein corona, which appears in that list, is described in more detail on the nanomedicine page. Its presence in both fields is telling: the coating that shapes how a particle behaves in research on carriers is the same coating that shapes how it behaves in research on toxicity.
How agencies study it
Several United States agencies describe research programmes on the health and environmental aspects of nanomaterials, each from its own angle.
The National Institute of Environmental Health Sciences says it is working to understand potential risks associated with exposure to nanomaterials. Its page notes that scientists have not unanimously settled on a precise definition of nanomaterials, and describes team efforts to develop standardised methods for assessing the health effects of commonly used engineered nanomaterials.
The Environmental Protection Agency's research page explains that the rapid and diverse growth of engineered nanomaterials makes it difficult for regulators and risk assessors to know whether methods used for conventional chemicals apply to them. It describes research on where nanomaterials occur, how they move and change in the environment, and how exposure to people can be estimated.
The Occupational Safety and Health Administration approaches the subject from the workplace. Its overview defines engineered nanomaterials as materials purposefully made with at least one dimension of approximately 1 to 100 nanometres and unique size-dependent properties, and organises its resources around standards, applications, potential health effects and workplace controls, and research priorities.
Reading nanotoxicology papers
Results in this field are especially sensitive to details. Which material, with which surface coating, at what dose, by what route, in what system, and over what time? A finding about one form of a material at a high dose in a cell culture may not apply to another form, a realistic dose or a whole organism. Good papers characterise their particles carefully, including their corona and aggregation state in the test medium, and compare them with appropriate controls. For the broader reasons that nanoscale materials differ from bulk ones, see what nanotechnology is; for how governments came to fund both the technology and its safety research, see nanotechnology policy and the NNI.