Small particles: big implications for our health and the environment

The governance of small particles has remained firmly in the headlines recently. UK cities continue to exceed EU air pollution limits (including airborne particle standards), due to emissions from vehicles. Reports continue to emerge of substantial health consequences for Europe and globally; air pollution exposure is rated the eighth most common cause of death in the world by the World Health Organisation (WHO). Even before the VW diesel emissions scandal diesel particle emissions were of special concern due to the relatively high concentration of nanoparticles (ultrafines) and sub-micron particles which penetrate deep into the lung, delivering toxic cargo. The VW scandal extends now to other car companies and resulted recently in the first US court class action pay-out of >$15 billion from VW alone. More will follow in the US, and the prospects of pay-outs for European car owners remain distinctly unclear. Despite having far fewer diesel vehicles, the fraud was discovered by US scientists, and first prosecuted in the US raising further serious questions about air quality governance in Europe.

Even though linking environmental pollutant exposures to disease is notoriously difficult, small airborne particles have been linked for decades to premature death, since a seminal air pollution study by Harvard published in 1993. Previously, studies of worker exposures provided evidence to assess the impact of a material exposure on health. With the ubiquity of combustion emissions, high numbers of people were exposed to well-measured pollutant concentrations, for example in cities. This meant that diseases of the lung and heart in exposed populations could be correlated with varying particle levels. Thousands of studies have now shown that small particles, especially the ultrafine diesel emissions, are a significant human health concern, with no identifiable safe level and currently no specific regulation.

Concerns over engineered nanoparticles are also growing since nanomaterials are now included in a wide range of consumer products. Nanoparticles go into our bodies every day in a variety of forms, such as in toothpastes, food additives, drug formulations and increasingly, as medical or aesthetic implants. The field of nanotoxicology emerged from the study of fine and ultrafine combustion particles in the air, but focuses on health impacts from engineered or manufactured nanomaterials.

During a recent Royal Society conference 'Bio-nano Interactions: new tools, insights and impacts' international scientists discussed how the translation of nanotechnology science is starting to be deployed in clinical applications, without special consideration or assessment of their safety and regulation. Ironically, exposure to nanomedicines (for example in diagnostics such as contrast agents or therapeutics like drug delivery agents) and nano-coated surfaces of implants may represent a significant new direct exposure route for people. 

One factor which makes the gathering of data, related to the mapping of disease, more complex is globalisation. At present there is no way to measure human exposures to nanomaterials in the environment. Occupational epidemiology does not work well where material production is geographically dispersed and consumer usage patterns change rapidly. Due to the manufacturing, release and distribution of products to global markets now operating on increasingly compressed timelines, long-term exposures among workers are also diminishing. All this points to the fact that workers may no longer represent the highest exposure group for epidemiological studies on nanomaterials; consumers of medical formulations and cosmetic implants may well be the new highest exposure group. The use of nanomaterials and other advanced materials in clinical practice could be of particular concern because of the unpredictable effects of cumulative nanoparticle exposures from many sources, including those from medical procedures and general consumer exposure to nanomaterial-containing products. This means humans are likely to experience high exposures and potentially harmful doses of certain nanomaterials from implantation and/or the use of nano-enhanced medicinal products.

The rapid rise in implants globally has occurred without understanding the potential long-term effects of the materials, and there remains a strong concern about wear (both abrasion and leakage) and autoimmunity. This suggests a need for surveillance to assess the long-term impact of nanoparticle exposure on health.

Dr Michaela Kendall

School of Metallurgy and Materials