Foliar residue calculation

Dislodgeable foliar residues should be reported in units of ig cm and can be calculated using the following equation ... 

The quantitative estimation of available residue data from the published literature may be investigated in a further step, and these data may then be used to calculate the initial residue on the day of application (after drying of the spray mixture). An assessment of literature data by Schrader (1994) has revealed an initial dislodgeable foliar residue (DFR) below or around 1 ug/cm2/kg active substance (a.s.)/ha, if the residue values are corrected for a standard rate of 1 kg a.s./ha. 

Moreover, the LAI in nearly all crops is in reality above 2, primarily in the range of 3 to 5, especially in high growing crops. Correspondingly, the foliar residue will be lower by a factor of 3 to 5 (i.e., 5 pg/cm2 divided by 3 to 5 = 1.66 to 1 pg/cm2). If the crop does not cover the sprayed area completely (e.g., in row crops), then the theoretical calculation of the foliar residue still holds true, at least for conventional spraying equipment, as a proportional part of the spray mixture will not reach the foliage but will fall down to the soil. 

Thus, worker exposures are calculated based on the dislodgeable foliar residue (DFR) and the TC. If the DFR value is not known for the actual day of reentry, it may either be interpolated from the dissipation curve or calculated as the Day 0 DFR multiplied by a dissipation function D(t), or DFRq x D(t). If both exposures and DFRs are measured in a given study, then the following equation may be solved for TC, normalized per hour of task duration ... 

Dislodgeable Foliar Residues and Dermal Exposure. Dislodgeable foliar residues were determined on days 1,3,7,14,15,16, and 17 after carbaryl had been applied to the strawberry fields at the rate of 2 Ib/A. Results of these analyses are found in Figure 2 and Table VIII. The decline of foliar residues appears to follow first-order kinetics, and carbaryl has a half-life of approximately 4.1 days. The three last sampling dates are identical with the study dates. From these data and exposure rates of corresponding days (Table V), a ratio can be calculated by the following equation ... 

There are, however, several apparent discrepancies. The first is the ratio calculated from literature values dealing with carbaryl exposure to pesticide applicators and fruit thinners in an apple orchard (4) This ratio (about 0.6x10 cm h ) was considerably lower than the range seen in Table IX. The difference may be due to the fact that Maitlen et al. (4) measured total and not dislodgeable foliar residues, thus leading to lower values than those obtained by us and others. 

There have In the past been three ways of calculating foliar residue results. One calculates ppm by weight and there are two ways to calculate yg/cm by area. 

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