Silicate compounds are added as extenders to dusts, flow dusts (FDs) and wettable powders, meaning that it can be predicted to contain free silica, which in turn affects the incidence of pneumoconiosis. The percentage of free silica content was measured by X-ray diffraction in 18 pesticides consisting of 3 types of dusts, 4 types of FDs and 11 types of wettable powders. As a results, free silica was identified in 14 of pesticides as follows: 22-34% in dusts, 3-11% in FDs and less than 1% to 20% in wettable powders. The percentages contained in the FDs were lower than in the dusts, probably because crystal structures became amorphous during the processing of FDs into super fine gradules with a mean particule size of 2μm.
The levels of dust exposure during spraying were measured with respect to Sumithion dust, Morestan FD and TPN FD by classifying them into respirable dust of less than 7.07μm in aerodynamic diameter (which is liable to be deposited in the lung) and total dust. When the concentration of a dust to which sprayers were exposed was compared with the TLV established taking into free silica content based on recommendation of the Japan Association of Industrial Health, the dust spray levels were 75-fold in the case of respirable dust and 53-fold for total dust, those for the spraying of FDs were 7-fold for respirable dust and 3-fold for total dust.
These results suggest the necessity of using pesticides with low free silica content. It is also considered necessary for sprayers to wear dust respirators.