Dislodgeable foliar residues estimation

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. 

Dislodgeable foliar residue as a function of time and estimating... 

Half-life estimates of approximately 28 days for thiophanate-methyl indicate a very slow decay compared to methiocarb with an estimate of half-life of about 11 days. The application of a model based on a first-order decay process resulted in fairly high R2 and significant fit. The results suggest that both pesticides are relatively stable compared to other compounds under similar environmental conditions (Brouwer et al., 1994). With respect to the objectives of the study and the proposed model, it can be stated that the results confirm the assumption of a linear relationship between application rate (for both application techniques) and the increase of dislodgeable foliar residue. This relationship holds for modeling purposes. The contribution of the crop density or total crop surface area to the process of interception cannot be quantified with the results of the present study. Because the interception factor ranges from about 0.35 to 0.9 (Willis and McDowell, 1987), the... 

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. 

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. 

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. 

Washing, wiping and vacuum techniques have also been employed to estimate foliar residue dislodgeability from turf grass (Popendorf et al 1975 Goh et al, 1986 Sears et al., 1987 Cowell et al., 1993 Black and Fenske, 1996). In one of these techniques, boots wrapped with cotton cheesecloth are used to determine the transfer of turf residues to the shoe soles (Sears et al., 1987). Another was somewhat similar to the PUF roller, employing the use of a PUF-covered paint roller (Cowell et al., 1993). 

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. 

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