[The concentration levels of airborne quartz at an urban site]

The IARC has recently included crystalline silica among substances considered carcinogenic for man. This new evaluation immediately posed the need to measure the exposure levels of the general population. The paper reports the results of measurements of the concentrations of quartz (i.e., the most common form of crystalline silica) in a location in the urban area of Rome. First we studied the respirable fractions of the airborne particles (PM10) sampled in the Spring of 1996 with a cascade impactor, which were characterized using a scanning electron microscope equipped with an X-ray microprobe. Ten components were identified including total silica (crystalline and amorphous), which was present in a percentage of 3.7% on average. On the basis of these data a methodological study was undertaken of the concentration of quartz in the historic series of PM10 sampled daily at the same site by means of an AMP instrument (Airborne Particles Monitor). The filters of mixed cellulose esters on which the PM10 was collected were incinerated at low temperature in oxygen plasma to eliminate the organic component. The residue was deposited on silver filters which were read with a conventional X-ray diffractometer in order to determine the quantity of quartz. We analyzed 28 filters from four representative weeks of the four seasons of 1994, the year in which systematic sampling was initiated. The results showed a mean weekly concentration of airborne quartz of between 0.6 and 1.5 micrograms/Nmc, which gives a percentage over PM10 of 1.7 and 3.4 respectively. These data substantially agree with previous results obtained with electron microscopy and show that the levels of quartz in the urban atmosphere under study were about one hundred times lower than the TLV currently recommended by the ACGIH for working environments (100 micrograms/Nmc) and which are also in force in Italy.