Researchers studying the health effects of tiny particles from vehicular emissions are finding out more on a new threat: nanoparticles

ith growing awareness of the detrimental effects of particulate matter on human health and environment, international research forums are faced with a number of concerns. One of the most important is to determine the size of particulate matter that has the most harmful effects on human health. Only this can determine the size of particles to be monitored on priority.
Recent research has revealed that as the size of the particle decreases, its lethal effect on human health increases. According to M G Constantine of Health Effects Institute in Massachusetts, USA, penetration and deposition of particulate matter in the lungs depends on the size of the particle. That is, the smaller the particle, the greater its ability to penetrate the lungs.
Moreover, the cells of our lungs react first with the components on the surface of the particles. This makes the ultra fine particles (smaller than 0.1 micron in size) more dangerous as they have a larger surface area where they absorb a greater amount of toxic chemicals than the larger particles. One micron is a millionth of a meter. These findings have made researchers shift their attention to minute particles whose size is measured in nanometer (nm), that is, a billionth of a meter. Hence, these particles are called nanoparticles.

Focus on smaller particles:
cientific studies in recent times have thrown up a highly interesting and relevant debate regarding the monitoring of particles in the ambient air. It is being argued that the measurement of particulate matter only in terms of mass does not bring out the risk of exposure to particles. Therefore, it is more important to monitor the number of particles in different size categories. A recent joint report by Lidia Morawska of the Centre for Medical and Health Physics at Queensland University of Technology, and Dietrich Schwela of the World Health Organisation in Geneva has raised some critical issues in this regard. The report says that large particles from bulk of the total mass of the particles present in the ambient air. But, when considered in terms of number, ultrafine particles matter, although their total mass is usually insignificant in comparison with the mass of the larger particles.
The report further argues that the highest level of concentration of toxic compounds is related to these ultra fine particles and therefore, throws up the question of measuring physical, chemical and biological characteristics in addition to numbers.
While scientists are trying to grapple with the impact of the new findings, results of a study by the University of Birmingham in 1999 implicate road transport for the emission of ultra fine particles. The study shows that at a busy roadside, more than 44 percent of the measured particles are below 10 nm, while corresponding figure at an urban background can be 30 percent. Researchers now say that it is more sensible to measure the number of particles in the ambient air in order to evaluate air quality, instead of just the mass of particles. However, at present, air quality standards of all countries monitor the concentration of particles only in terms of mass.

Special Report
Down to Earth
February 15, 2000