Concentration of Pesticides Slowly Released by Diffusion

Abstract

The active concentration of a pesticide declines with time due to volatilization, absorption and translocation, microbial degradation, adsorption on soil particles and plant parts, chemical reactions, photodecomposition, and other reactions with the environment. However, slow-release formulations can provide a continuing input of pesticide. This leads to a rise and subsequent fall in the active concentration. Because diffusion is a factor in most controlled release methodologies, the concentration to be expected for release by diffusion of a substance, which then decays with time by a first order rate law, is examined theoretically. This provides guidance to the experimenter for separating the effects due to diffusion from these attributable to other and newer concepts such as water-degradable polymers. An approximate result of this exact solution is that the persistence of the substance can be increased. More precisely, the long-term behavior is like that of a more persistent pesticide with smaller first-order rate constant.

Controlled Release of Three Herbicides by the Kraft Lignin PC940C

“…The advantages of a controlled-release mechanism would be the reduction in herbicide injury to deeper rooted crop species as well as the possibility of increasing the weed control spectrum of the herbicide over time. The use of controlled release also has the potential to reduce or eliminate multiple applications of herbicides (2). In addition, a con trolled-release strategy would have the potential environ mental benefit of having less herbicide leached through the soil and into the groundwater.…”

Organophosphate insecticide disappearance from leaf surfaces: an alternative to first-order kinetics

“…Once insecticide has reached the leaf in irregularly positioned small volumes, diffusion of insecticide molecules from each volume ndw commences. Some work on the diffusion of insecticides has been carried out already, mainly in an effort to model insecticide movement in soils (7,8,19,20).…”

Modeling Approach To Assess Clustering Impact on Release Rates of Pesticides from Microencapsulated Products

“…Analytical solutions to the one-dimensional diffusion equation in spherical coordinates for diffusion transport across this polymer layer for a variety of different boundary conditions are summarized elsewhere (14)(15)(16)(17), and when C ¥ = 0, the time (t)-dependent solution becomes…”

“…Analytical solutions to the one-dimensional diffusion equation in spherical coordinates for diffusion transport across this polymer layer for a variety of different boundary conditions are summarized elsewhere − , and when C ∞ = 0, the time ( t )-dependent solution becomes C C 0 = M M 0 = normale − 0.693 t / normalτ where τ is the characteristic half-life for release normalτ = 0.693 a h false( 1 + normalα false) 3 D normalm Mass ( M ) and concentration ( C ) are often used interchangeably when the volume ( V ) of a capsule remains constant over time (e.g., mass equals the product of concentration and volume).…”