Foliage residues

The heptachlor, dieldrin, and toxaphene examples show that foliage and soil residue dissipation data can be used to estimate the amounts of residues volatilized when no significant degradation or runoff losses are incurred. For toxaphene, residue analyses indicated that 80% of the foliage residue and 51% of the top soil residue was lost by volatilization within ca 50 days. This is considerably more than the 24% vaporization loss reported for toxaphene within 90 days in a model chamber (8), but is comparable to foliage-applied heptachlor and dieldrin (75) both of which overlap in volatility with components of the toxaphene mixture. 

Although injuries to exposed individuals have been few, dermal sensitization has occurred in agricultural workers exposed to foliage residues. 

Mice that were exposed dermally to residues of methyl parathion in emulsifiable concentrate on foliage, and were muzzled to prevent oral intake, developed inhibition of plasma cholinesterase and erythrocyte cholinesterase after two 10-hour exposures (Skinner and Kilgore 1982b). For the organophosphate pesticides tested in this study, cholinergic signs generally were seen in mice with cholinesterase inhibition >50% results for this end point were not broken down by pesticide. 

Diphenyl ethers in the soil are absorbed by roots with limited translocation generally to the foliage. Low levels of herbicide residues can be expected when the compound is used in accordance with good agricultural practice. The parent diphenyl ether compound is defined as the residue of analytical and regulatory concern. 

When applied to wheat. Compound A was readily detected in soil samples collected beneath the treated canopy. Compound B was detected only sporadically in soil. Due in part to a greater application volume (1000 vs 300 Lha water) and a higher application rate for Compound B, both compounds were more consistently detected in soil following application to apple foliage. It is often difficult to establish dissipation kinetics under these conditions because as residues in the soil dissipate, additional compound may continue to be deposited on the soil, resulting in a complex, variable dissipation pattern. As a result, it is not always practical or advisable to study soil dissipation in the presence of a crop. 

DFR studies are designed and conducted to describe the decline profile of the active ingredient on foliage and/or soil surfaces when applications are made at the proposed label rate. These surfaces are limited to those which can be touched or disturbed by workers and from which residues can be dislodged, deposited on human skin and clothing, or inhaled during the performance of field work and harvesting operations. 

Extent of residues remaining on foliage from previous applications, especially in ornamentals... 

If the outlined procedure is followed, the data on the transfer of residues from foliage to the clothes or skin of workers will be limited to data sets for four different pruning and six different harvesting scenarios. In this framework, the available data in literature should be evaluated and the transfer... 

TF = transfer factor, for the transfer of residues from foliage to skin... 

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. 

For some time in the past, a single transfer factor of 5000 for the transfer of residues from foliage to the clothes or skin of the worker was used (Popendorf and Leffingwell, 1982). After generation of further data, it seems to be necessary to consider various transfer factors for the various work tasks, as outlined above. But, in a first attempt to calculate the dermal... 

Iwata, Y, Knaak, J.B., Spear, R.C., and Foster, R. J. (1977) Worker re-entry into pesticide-treated crops. I. Procedure for the determination of dislodgeable pesticide residues on foliage, Bull. Environ. Contam. Toxicol., 18 649-655. 

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) ... 

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. 

Foliage of cotton that initially contained 100 mg/kg DW contained about 60 mg/kg after 7 weeks leaf residues consisted entirely of the parent diflubenzuron (Gartrell 1981). Diflubenzuron applied topically to lima bean (Phaseolus lunatus) foliage was not absorbed by the plant, as expected. Injected diflubenzuron, however, was metabolized, and certain metabolites were similar to those isolated from mites (Franklin and Knowles 1981). 

Adsorption and persistence in plants can be modified by other chemicals or by selected carriers, although mechanisms to account for these phenomena are unclear. The application mixture influences adsorption and persistence of fenvalerate. For example, interception and persistence in sugarcane were increased when fenvalerate was applied in a 25% water/75% soybean oil mixture vs. water or soybean oil alone (Smith et al. 1989). Also, biocidal properties of fenvalerate residues on cotton foliage were increased up to 100% due to enhanced persistence of fenvalerate in the presence of toxaphene (Brown et al. 1982). 

Alfalfa, Medicago sativa Cotton (Gossypium hirsutum) treated with 0.224 kg/ha, residues on foliage 12 days later Half-time persistence (Tb 1/2) of 9-11 days 1... 

Buck, N.A., B.J. Estesen, and G.W. Ware. 1980. Dislodgable insecticide residues on cotton foliage fenvalerate, permethrin, sulprofos, chlorpyrifos, methyl parathion, EPN, oxamyl, and profenofos. Bull. Environ. Contam. Toxicol. 24 283-288. 

Pentachlorophenol in terrestrial ecosystems clears rapidly (Haque et al. 1988). In one case, a terrestrial ecosystem was given a single surface application of radiolabeled PCP equivalent to 5 kg sodium pentachlorophenate/ha. PCP residues on foliage decreased rapidly, with 50% metabolized within 15 days. After 131 days (autumn), most of the remaining PCP was in the topsoil and plant litter. After 222 days (winter), 39% of the radiocarbon remained. There was little bioconcentration in the resident fauna, due to rapid metabolism and excretion (Haque et al. 1988). 

In the first year, the maximum concentrations of sulfoxide and sulfone in soil, seed potatoes, and foliage were approximately 2, 2, and 6 times, respectively, the concentrations of those metabolites measured in the second and third year treatments. These results demonstrated that enhanced microbial degradation of relatively minor insecticidal compounds in the soil can significantly affect insecticide levels in the plant (when these degradation products are the major insecticidal component accumulated). As the sulfoxide and the sulfone metabolites are the major toxicants in the foliage of potato plants grown in disulfoton-treated soil, this reduction in toxicant residues overtime can be expected to reduce insecticide efficacy. 

Andrawes, N.R., Bagley, W.P., and Herrett, R.A. Fate and carryover properties of Temik aldicarb pesticide [2-methyl-2-(methylthio)propionaldehyde 0-(methylcarbamoyl)oxime] in soil, J. Agric. Food Chem., 19(4) 727-730, 1971. Andrawes, N.R., Romine, R.R., and Bagley, W.P. Metabolism and residues of Temik aldicarb pesticide in cotton foliage and under field conditions, J. Agric. Food Chem., 21(3) 379-386, 1973. 

Pieper, G.R. and Richmond, C.E. Residues of trichlorfon and lauroyl trichlorfon in douglas fir, willow, grass, aspen foliage, and... 

Results from these laboratory studies demonstrated that avermectin Bj had high toxicity for the twospotted spider mite (Tetranychus urticae) on bean plants. When applied in solution directly onto adult and nymphal spider mite populations on foliage, avermectin Bj was shown to be 50-200 times as potent as commercially available acaricides, with an LC q of 0.02-0.03 ppm. Additional tests on foliage with insects in the order Lepidoptera, Coleoptera, Homoptera, Orthoptera, Diptera, Isoptera and Hymenoptera confirmed the broad spectrum activity and potency of the avermectin family of compounds and avermectin Bj in particular. Table II provides LC q values for avermectin Bj for the control of larval forms of several of these insects in foliar residue assays (18). 

In the field, parathion is converted to varying degrees to paraoxon, which may persist on foliage and in soil. Exposure to paraoxon from weathered parathion residues by the dermal route on reentry by field-workers has resulted in anticholinesterase poisonings. ... 

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