Modelling of the long-term fate of pesticide residues in agricultural soils and their surface exchange with the atmosphere: Part II. Projected long-term fate of pesticide residues

• Published in: The Science of the total environment 2007-05, Vol.377 (1), p.61-80
• Main Authors: Scholtz, M.T., Bidleman, T.F.
• Format: Article
• Language: English
• Subjects: Agriculture - standards; Agronomy. Soil science and plant productions; Air Movements; Air Pollutants - analysis; Air–soil surface exchange model; Applied sciences; Atmospheric pollution; Biological and medical sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Monitoring - methods; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Long-term fate; Models, Theoretical; Persistent pesticides; Pesticide Residues - analysis; Pollutants physicochemistry study: properties, effects, reactions, transport and distribution; Pollution; Pollution, environment geology; Seasons; Soil and sediments pollution; Soil and water pollution; Soil concentration profiles; Soil Pollutants - analysis; Soil residues; Soil science; Volatilization
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/j.scitotenv.2007.01.084

In the first part of this paper, a simple coupled dynamic soil–atmosphere model for studying the gaseous exchange of pesticide soil residues with the atmosphere is described and evaluated by comparing model results with published measurements of pesticide concentrations in air and soil. In Part II, the model is used to study the concentration profiles of pesticide residues in both undisturbed and annually tilled agricultural soils. Future trends are estimated for the measured air and soil concentrations of lindane and six highly persistent pesticides (toxaphene, p, p′-DDE, dieldrin, cis- and trans-chlordane and trans-nonachlor) over a twenty-year period due to volatilization and leaching into the deeper soil. Wet deposition and particle associated pesticide deposition (that increase soil residue concentrations) and soil erosion, degradation in the soil (other than for lindane) and run-off in precipitation are not considered in this study. Estimates of the rain deposition fluxes are reported that show that, other than for lindane, net volatilization fluxes greatly exceed rain deposition fluxes. The model shows that the persistent pesticides studied are highly immobile in soil and that loss of these highly persistent residues from the soil is by volatilization rather than leaching into the deeper soil. The soil residue levels of these six pesticides are currently sources of net volatilization to the atmosphere and will remain so for many years. The maximum rate of volatilization from the soil was simulated by setting the atmospheric background concentration to zero; these simulations show that the rates of volatilization will not be significantly increased since soil resistance rather than the atmospheric concentration controls the volatilization rates. Annual tilling of the soils increases the volatilization loss to the atmosphere. Nonetheless, the model predicts that, if only air–soil exchange is considered, more than 76% of current persistent pesticide residues will remain after 20 years in the top 7 cm of annually tilled soils. In contrast, lindane is relatively mobile in soil due to weaker binding to soil carbon and leaching of lindane into soil is the main removal route for current lindane residues near the soil surface. The model predicts that the soil is a sink for lindane in the atmosphere and that soil residue levels of lindane in the surface soil are determined by a balance between dry gaseous deposition to the soil from the atmosphere and leachin