Residue dissipation

Environmental conditions—residue dissipation. It is well established that environmental conditions modify the behavior of pesticides (38). Long-term worker reentry (5 to 120 days) illnesses have been limited primarily to the hot and dusty central California valley. Since these incidents have been linked to the oxon metabolites and these metabolites reach higher levels in dry areas, rainfall and dew would appear to be additional major components for regionalizing the United States for worker reentry regulations. Davies et (7) proposed such a scheme in 1973. 

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. 

USEPA (1996a). Occupational and Residential Exposure Test Guidelines, OPPTS 875.2100, Eoliar Dislodgeable Residue Dissipation, EPA Report No. 712-C-96-267, Office of Prevention, Pesticides and Toxic Substances, Washington, DC, USA. 

Outdoor dislodgeable (or transferable) foliar residue dissipation study... 

Using the latter two relations we may also approximate the residual dissipation rate, e.g., in terms of the residual viscosity determined by other LES closures, in case this parameter is needed for reactor modeling purposes like in population balance kernels and in species mixing model parameterizations provided that the overall closure models remain consistent [21]. 

Table IV. Residue Dissipation in Ponded Water Following Application of Herbicides...

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... 

A second step is necessary. Even crosslinked polymers have residual dissipative features due to internal motions of molecular segments, a type of internal viscosity. It is therefore necessary to carry out the measurements of strength at very low rates of deformation and at high temperatures, far above the glass transition temperature, to minimize energy absorption from these processes. 

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