Airborne quartz concentration in an urban site

The International Agency for Research on Cancer, IARC, has recently classified crystalline silica as carcinogenic to man. This new assessment calls for the determination of the concentration levels of crystalline silica to which the general population is exposed to. This paper reports the results of the determinations of airborne quartz – the most common form of crystalline silica – in a site of the metropolitan area of Rome, Italy. We studied the respirable fraction of the airborne particulate (PM10) sampled in spring 1996 with a cascade impactor, by means of a scanning electron microscope equipped with an X-ray microprobe. Ten components were identified of which 3.7% on the average was total silica (crystalline and amorphous). On the basis of these data we started a methodical study of quartz concentrations in the historical series of the PM10 daily sampled with an Airborne Particles Monitor (APM) apparatus at the above-mentioned site. PM10 was collected on cellulose filters which were then incinerated in oxygen plasma at low temperature to eliminate the organic component. The residue was deposited on silver membrane filters that were then read with a conventional X-ray diffractometer to determine quartz amounts. Twenty eight filters were analysed which corresponded to four weeks representative of the four seasons of 1994, the year when samples started to be systematically collected. Results show that the mean weekly concentration of airborne quartz ranged between 0.6 and 1.5 μg/Nm3, which corresponded to 1.7% and 3.4% of total PM10, respectively. These data are substantially in agreement with our previous data obtained with electron microscopy, and show that the quartz levels present in the urban atmosphere under study were approximately 100-fold lower than the threshold limit value (TLV), currently suggested by the American Conference of Governmental Industrial Hygienists (ACGIH) for the workplaces, namely 100 μg/Nm3 – threshold that is currently applied in Italy. ©