Foliar Dust Research Articles

Procedures for the determination of dislodgeable dust on foliage as related to worker reentry hazards.

Foliar dust was first implicated as the primary vehicle of worker exposure in the early observations of QUINBY and LEMMON (1958) and recently verified by the measurements of SPEAR et al. (1977). The levels of foliar dust were found by POPENDORF et al. (1975) to correlate with the aerosol levels create--~ ~y workers disturbing the foliage. For tree and other high crops, this aerosol of contaminated dust appears to be the primary means of worker exposures to pesticide residues. Further, the extrapolation and utilization of foliar pesticide residue data from the few conditions actually under observation in any one study into other worker exposure situations, will require knowledge not only of pesticide concentrations on foliar dust (ppm) but also its partitioning between foliar dust, leaf surfaces, and water both at the time of application and during the aqueous extraction phase (POPENDORF and LEFFINGWELL, 1978). Finally, foliar dust plays a vital role in the pesticide decay process itself. Not only does the type of dust affect pesticide decay rates (IWATA, et al., 1973 and ADAMS, et al., 1977), but recent data indicates that the quantity o--~liar dust (mg/cm 2) is also an important decay parameter (POPENDORF and LEFFINGWELL, 1978).

Worker environment research. IV. The effect of dust derived from several soil types on the dissipation of parathion and paraoxon dislodgable residues on citrus foliage.

Parathion sorbed to dust can persist as dislodgable residues on citrus leaves. Semi-logarithmic plots of parathion dislodgable residue data were initially linear for the 6 soils studied and then a distinct change to lower rates occurred with 5 of the soils. As initial rates and the residue level at the rate change are dependent on the soil, foliar dust is implicated as a causative factor in the non-uniformity of residue dissipation rates. Soils can influence the conversion of parathion to paraoxon. Paraoxon levels differed greatly with the type of soil and were highest with Pike's Peak clay. Thus, its use in a parathion formulation could produce relatively high levels of paraoxon dislodgable residues. It is significant that, second to Pike's Peak clay, the highest total dislodgable residue level was found with Visalia silt loam which was collected from a grove where a worker poisoning episode had occurred in 1974.