NIOSH research has shown that some nanoparticles, including certain types of carbon nanotubes and metal oxides, can be toxic to the heart and lung in mice and rats in laboratory experiments, according to a recent post on NIOSH’s Science blog.

Other research has demonstrated various other adverse effects of nanoparticles. Through its “Approaches to Safe Nanotechnology,” NIOSH recommends that specific precautions be taken to protect workers who might be exposed to any level of nanoparticles or nanoparticle-containing materials.

The question left unanswered is, can nanoparticles cause the same types of disease in humans?

In the September issue of the European Respiratory Journal, the first medical case series of workers with serious disease that the study authors associate with exposure to nano-sized particles has been published.

Investigators Y. Song, X. Li, and X Du of the Chaoyang Hospital of the Capital University of Medical Sciences in Beijing, China, report on a series of seven previously healthy young women who developed serious heart and lung disease after working at a print plant exposed to a chemical "paste" mixture containing undefined "nanoparticles" of approximately 30 nanometers in diameter.

There is no doubt about the severity of the heart and lung disease in these workers. One worker died in the hospital 16 days post-surgery and another died of respiratory failure 21 months after symptom onset.

The question is, did their exposure to nanoparticles cause or contribute to their disease? Unfortunately, the study cannot scientifically answer that question because of a lack of exposure data.

Workers manually scooped coating material and placed it in a machine that automatically air-sprayed the material onto polystyrene boards. The boards were then heated to 100 degrees centigrade to cure the air-sprayed material on the polystyrene boards. The room in which the women worked was small and unventilated for a significant amount of the 5 to 13 months of their exposure. On occasion, they wore "cotton gauze masks."

Workers developed face and arm itching due to "flocculi produced during air spraying." The paste was analyzed by gas chromatography/mass spectroscopy (GC/MS) and found to contain butanoic acid, butyl ester, N-butyl ether, acetic acid, toluene, di-tert-butyl peroxide, 1-butanol, acetic acid ethenyl ester, isopropyl alcohol, and ethylene dioxide.

Electron microscopic examination of both the paste and dust residue found at the intake of the exhaust used to remove smoke from heating the boards revealed the presence of nanoparticles of approximately 30 nanometers in diameter. No information was provided on the chemical composition of the nanoparticles or their relative abundance in the samples.

Sufficient exposure information necessary to draw a causal association between exposure to nano-sized particles in the paste/dust and lung and heart disease in the workers is missing and there may be alternative explanations for what the study authors have described medically.

What was the concentration of nanoparticles in the paste/dust? What was the chemical composition of the nanoparticles found? Were the particles found in the paste/dust identical to the particles found in lung tissue and fluid? Since the exposure was to a complex chemical mixture, could other exposures in the workplace have caused the heart and lung disease?

For instance, formation of thermodegradation fume products are known to cause significant occupational disease (Johnston, et al., 2000). Paint spraying operations have been shown to be harmful many years before nano-sizing of chemicals developed as a technology (Camus & Nemery, 1998). Excluding all other potential exposure mechanisms as causes of occupational disease seen in these workers is just as necessary as it was for the study authors to exclude all other known medical causes to explain the workers' heart and lung disease.

The study authors do acknowledge the limitations of their case series in terms of a lack of exposure information, yet they state "more studies on the [...] prevention of the nano material-related disease are needed." Despite the certainty inherent in their use of the term "nano material-related disease," the study authors have not provided us with scientific evidence nanoparticles were or were not the cause of the tragic medical consequences in these seven workers.

In the meantime, NIOSH continues to recommend that in the face of continuing uncertainty about the risks to worker health associated with exposure to nanoparticles and chemical intermediates containing various concentrations of nanosized particles, a proactive, prudent approach to working with nanomaterials is necessary.