Exposure dislodgeable foliar residue

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 ... 

Re-entry exposure can be considered to be the result of a chain of processes ending with the transfer of pesticide residues to the worker. Popendorf (1985) assumed a linear relationship between dermal exposure (DE) and the amount of residue available to transfer from the foliage to the worker. This is called the dislodgeable foliar residue (DFR) ... 

Lrom the regression analyses it is clear that significant relationships were observed between respiratory exposure to thiophanate-methyl and methiocarb (adjusted to the number of flowers harvested) and dislodgeable foliar residues during re-entry. 

Brouwer, D.H., de Haan, M., Peelen, S., van de Vijver, L., and van Hemmen, J.J. (1994) Dislodgeable foliar residue as an estimate of source strength for worker exposure to pesticides, in Book of Abstracts from the 8th International Congress of Pesticide Chemistry, American Chemical Society/IUPAC, July 4r-9. 

Haan de, M., Brouwer, D.H., and van Hemmen, J.J. (1996) Re-entry Exposure Estimates Application Technique, Foliar Surface and Re-entry Time as Critical Predictors for Dislodgeable Foliar Residue, Report V96.384, TNO Nutrition and Food Research Institute, Zeist, The Netherlands. 

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 ... 

Whitmyre, G.K., J.H. Ross, C. Lunchick, B. Volger and S. Singer (2004). Biphasic dissipation kinetics for dislodgeable foliar residues in estimating post-application occupational exposures to endosulfan. Arch. Environ. Contam. Toxicol, 46, 17-23. 

Zweig, G., J.T. Leffingwell and W.J. Popendorf (1985). The relationship between dermal pesticide exposure by fruit harvesters and dislodgeable foliar residues, J. Environ. Scl Health, B20, 27-59. 

W. J. Popendorf The Relationship Between Dermal Pesticide Exposure by Fruit Harvesters and Dislodgeable Foliar Residues,/. Environ. Sci. Tilth., 1985, B30, 27-59. 

Y. Li, J. J. Keenan, H. Vega, R. I. Krieger, Human Exposure to Surface Pesticide Residues Dislodgeable Foliar Residues and Pilot Studies to Predict Bioavailability, Abstract, American Chemical Society Meeting, San Francisco, CA., 2006. 

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. 

In conclusion it can be stated that the basic assumptions of the re-entry model — a linear relationship between application rate and initial dislodge-able foliar residue and a first-order decay of the DFR — have been confirmed. The relationship between the transfer factor and re-entry time at various DFR levels should be explored further. Including information on foliage surface area or crop density may lead to a refinement of the model however, crop volume estimating methods should be improved before their influence on the exposure processes can be fully evaluated. 

Canada has generated time-weighted average exposures for occupational and residential post-application exposnre scenarios where dislodgeable (transferable) foliar residue data have yielded dissipation curves which allow generation of daily exposure estimates on snccessive days following apphcation. These estimates have potential utility in risk assessments not based on acute toxicological endpoints. 

Reentry intervals are now established on the basis of (1) data on dermal absorption or dermal dose response (2) inhalation, dermal, and oral acute toxicity studies in animal models (3) foliar and soil residue dissipation data and, (4) available human exposure data. CDFA recommends several sources as useful guides for determining residues of pesticides on soil and leaf surfaces (dislodgeable residue) and conducting field reentry studies involving human volunteers (1-5). Human exposure studies may not be required if adequate animal data from (1) through (3) above are... 

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