Behavior Assessment Model for Trace Organics in Soil: I. Model Description

Abstract

A mathematical model is introduced for describing transport and loss of soil‐applied organic chemicals. The model assumes linear, equilibrium partitioning between vapor, liquid, and adsorbed chemical phases, net first order degradation, and chemical movement to the atmosphere by volatilization loss through a stagnant air boundary layer at the soil surface. From these assumptions and the assumption of steady state upward or downward water flow, an analytic solution is derived for chemical concentration and volatilization flux.This model, which is intended to classify and screen organic chemicals for their relative susceptibility to different loss pathways (volatilization, leaching, degradation) in the soil and air, requires knowledge of the organic carbon partition coefficient (Koc), Henry's constant (KH), and net, first‐order degradation rate coefficient or chemical half‐life to use on a given chemical.Illustration of the outputs available with the model is shown for two pesticides, lindane (γ‐1,2,3,4,5,6‐hexachlorocyclohexane) and 2,4‐D [(2,4‐dichlorophenoxy)acetic acid], which have widely differing chemical properties. Lindane, with a large Koc, large KH, and small degradation rate coefficient, is shown to be relatively immobile, persistent, and susceptible to volatilization. 2,4‐D, with a small Koc, small KH, and large degradation rate coefficient, is mobile and degrades rapidly, but is only slightly susceptible to losses by volatilization.

Fruit Tree model for uptake of organic compounds from soil and air†

“…In porous solids (such as plant tissue), the diffusion is hampered by a "labyrinth factor", named tortuosity T. This tortuosity is estimated by the method of Millington and Quirk [37], for diffusion in root water and gas pores:…”

Groundwater Contamination Potential from Infiltration of Urban Stormwater Runoff

“…Many researchers have documented groundwater contamination due to toxic organic compounds in runoff (German, 1989;Wilson, et al, 1990;Ku and Simmons, 1985;Wilde, 1994). Many of these were associated with source areas where toxic organic pollutant concentrations exceeded typical stormwater concentrations.…”

“…Factors such as temperature, pH, metal concentration, nutrient availability and other factors affect the ability of a bacterial colony to survive in the water or soil (Ku and Simmons, 1985). Bacteria survive longer in acid soils and when large amounts of organic matter are present.…”

“…In general, studies of recharge basins receiving large stormwater metal loads show that most heavy metals are removed either in the basin sediment or in the uppermost layers of the soil beneath the recharge basin (Ku and Simmons, 1985;Hampson, 1986). Metals' removal by soil may be through one of several processes, including: soil surface association, precipitation, occlusion with other precipitates, solid-state diffusion into soil minerals, and biologic system or residue incorporation (Crites, 1985).…”

The Volatilization of Pollutants from Soil and Groundwater: Its Importance in Assessing Risk for Human Health for a Real Contaminated Site

“…In detail the volatilization models selected are: -Jury's model [9,10], assuming a contamination source with semi-infinite dimensions and time-varying concentrations (estimation of VF ss,J1 and VF ss,J2 for surface soil and VF ds,J for deep soil), -Farmer's model [11], with steady-state assumption (estimation of VF ss,F for surface soil, VF ds,F1 , VF ds,F2 for deep soil and VF gw for groundwater).…”