Ultrafine Particles

Risk assessment

The risk to humans from exposure to ultrafine particles is not clearly understood. Effects in animal models are not consistent. The lung carcinogenicity seen in the rat at doses calculated on surface area are not seen in the mouse or hamster. This difference in species makes a clear association to man difficult. Frampton conducted studies using healthy volunteer subjects where small amounts of carbon ultrafine particles were inhaled in a controlled manner. There were no changes in lung function or biomarkers of macrophage activation that could be seen in from blood analysis. These experiments are continuing and using exercise to possibly prime the respiratory system and make the assay more sensitive. This lack of response makes the determination of a quantitative risk assessment not feasible with the data so far collected as no clear does response curve can be arrived at. This study also does not take into account sensitive individuals both by age, the very young and very old, and those who may have preexisting conditions. These conditions can be heart disease from a genetic or other environmental exposure or lung disease such as asthma. In order to do an accurate risk assessment it will be necessary to understand the complete mechanism of action in the rat and be able to explain the lack of effect in the mouse. Research will need to be undertaken that can categorize the mechanism of toxicity in man, more like rat or mouse.

Epidemiological studies conducted to date have pointed to a causal effect from polluted air and mortality (Ibald-Mulli et al., 2002). While these studies are not free of confounding factors it indicates that more research is needed in the effects of ultrafine particles in order to arrive at a meaningful risk assessment using a quantitative method.