Endosulfan Transport: II. Modeling Airborne Dispersal and Deposition by Spray and Vapor

Abstract

Endosulfan (C9H6O3Cl6S; 6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro-6,9-methano-2,4,3-benzodioxathiepin 3-oxide) and other agricultural chemicals can be transported from farms to rivers by several airborne pathways including spray drift and vapor transport. This paper describes a modeling framework for quantifying both of these airborne pathways, consisting of components describing the source, dispersion, and deposition phases of each pathway. Throughout, the framework uses economical descriptions consistent with the need to capture the major physical processes. The dispersion of spray and vapor is described by similarity and mass-conservation principles approximated by Gaussian solutions. Deposition of particles to vegetation is described by a single-layer model incorporating contributions from settling, impaction, and Brownian diffusion. Vapor deposition to water surfaces is described by a simple kinetic formulation dependent on an exchange velocity. All model components are tested against available field and laboratory data. The models, and the measurements used for comparisons, both demonstrate that spray drift and vapor transport are significant pathways. The broader context, described in another paper, is an integrative assessment of all transport pathways (both airborne and waterborne) contributing to endosulfan transport from farms to rivers.

Correlating Agricultural Use of Organophosphates with Outdoor Air Concentrations: A Particular Concern for Children

“…This distance is large compared with that studied after single applications on specific agricultural fields: Researchers have generally measured or estimated air concentrations at 10 feet to one-half mile (800 m) from the field (Raupach et al 2001; Watanabe 2000; Woodrow et al 1997). There is, however, considerable potential for the atmospheric persistence and long-range movement of vapor and droplets of semivolatile pesticides through vaporization of larger to smaller droplets, vertical air mixing resulting in increased droplet and vapor height, and deposition of droplets with subsequent re-entry into the atmosphere (Van den Berg et al 1999; van Dijk and Guicherit 1999).…”

“…The oxon degradation compounds are also formed in mammals, are more reactive, and are more potent inhibitors of acetylchlolinesterase than are the parent compounds (Chambers and Russell 1993; Huff et al 1994; Poet et al 2003). Spatially, pesticide air dispersion models estimate postapplication, off-field dispersal of ≤1 km (0.62 miles) after single applications of pesticides to specific agricultural fields (Raupach et al 2001; Watanabe 2000). Yet deposition and some air measurements suggest that organophosphates may have an atmospheric dispersion of ≥100 km (62.1 miles) (Seiber et al 1993; van Dijk and Guicherit 1999; Zabik and Seiber 1993).…”

Numerical simulation of the October 2002 dust event in Australia

“…The treatment of subgrid convective dust transport built upon the Kain and Fritsch [1993] scheme is as described by Jung et al [2005]. The dry deposition velocity is parameterized following Raupach et al [2001], and the (below cloud) wet deposition is as described by Jung and Shao [2006].…”

Northeast Asian dust storms: Real‐time numerical prediction and validation

“…Dust particles are delivered back to the surface by dry and wet deposition. Dry deposition is estimated using the scheme of Raupach et al [2001]. Wet deposition is not considered, but additional work is being carried out on this aspect.…”