Volatilization process, pesticides

Spencer, W. F., M. M. Cliath, and S. R. Yates. Soil-pesticide interactions and their impact on the volatilization process, in Environmental Impact of Soil Component Interactions—Natural and Anthropogenic Organics, Vol. 1, CRC Press, Boca Raton, FL, 1995, pp. 371-381. 

Many processes are operative in the environment that contribute to the regional elimination of a contaminant by altering its distribution. Contaminants with sufficiently high vapor pressure can evaporate from contaminated terrestrial or aquatic compartments and be transferred through the atmosphere to new locations. Such processes of global distillation are considered largely responsible for the worldwide distribution of relatively volatile organochlorine pesticides such as lindane and hexachlorobenzene. Entrainment by wind and upper atmospheric currents of contaminant particles or dust onto which the contaminants are sorbed also contribute to contaminant redistribution. Sorption of contaminant to suspended solids in an aquatic environment with commensurate sedimentation can result with the removal of contaminants from the water... 

A key parameter used to estimate or model volatilization processes is the pesticide vapour pressure a fundamental property of the chemical agent which is uniquely defined by the temperature. This parameter is readily and reproducibly measured in the laboratory. Two... 

Volatilization of pesticides and other toxic organics from the water column to the atmosphere is a process that can remove some organics from aquatic ecosystems. Volatilization can be quantified using a resistance model, for example, two-fihn model, which describes the limiting factor in the... 

Transport processes describe movement of the pesticide from one location to another or from one phase to another. Transport processes include both downward leaching, surface mnoff, volatilization from the soil to the atmosphere, as weU as upward movement by capillary water to the soil surface. Transport processes do not affect the total amount of pesticide in the environment however, they can move the pesticide to sites that have different potentials for degradation. Transport processes also redistribute the pesticide in the environment, possibly contaminating sites away from the site of apphcation such as surface and groundwater and the atmosphere. Transport of pesticides is a function of both retention and transport processes. 

Desorption is the reverse of the sorption process. If the pesticide is removed from solution that is in equdibrium with the sorbed pesticide, pesticide desorbs from the sod surface to reestabUsh the initial equdibrium. Desorption replenishes pesticide in the sod solution as it dissipates by degradation or transport processes. Sorption/desorption therefore is the process that controls the overall fate of a pesticide in the environment. It accomplishes this by controlling the amount of pesticide in solution at any one time that is avadable for plant uptake, degradation or decomposition, volatilization, and leaching. A number of reviews are avadable that describe in detad the sorption process (31—33) desorption, however, has been much less studied. 

Volatilization and leaching interact with each other and other fate processes. Two of the pesticides, DBCP and lindane, are discussed in some detail to illustrate some of the interactions. The other four are discussed only briefly. 

Experiment 1. Effects of volatile allelochemicals on development of pollen tubes. In this experiment, volatile and liquid excretions from plants with pesticidic properties were tested (Table 3). The development of pollen tubes depend on the concentration and the distance from the object glass with microspores moistened with nutrient medium vapors of lavender oil (active matter) depress the process as well as red pepper, but garlic not. Water extracts of garlic were more effective. 

The plant produced pesticides. An intermediate compound in this process is methyl isocyanate (MIC). MIC is an extremely dangerous compound. It is reactive, toxic, volatile, and flammable. The maximum exposure concentration of MIC for workers over an 8-hour period is 0.02 ppm (parts per million). Individuals exposed to concentrations of MIC vapors above 21 ppm experience severe irritation of the nose and throat. Death at large concentrations of vapor is due to respiratory distress. 

The transport processes that may move disulfoton from soil to other media are volatilization, leaching, runoff, and absorption by plants. Volatilization of disulfoton from wet soil may be greater than from relatively dry soil (Gohre and Miller 1986). Like other pesticides, disulfoton in soil partitions between soil-sorbed and soil-water phases (Racke 1992). This latter phase may be responsible for the volatilization of disulfoton from soil however, due to the low Henry s law constant value, the rate of disulfoton volatilization from the soil-water phase to the atmosphere would be low. 

Sparks DL (ed) (1986) Soil physical chemistry. CRC Press, Boca Raton, Florida Sparks DL (1989) Kinetics of soil processes. Academic Press, San Diego Sparks DL, Huang PM (1985) Physical chemistry of soil potassium. In Munson RE (ed) Potassium in agriculture, ASA, Madison, Wisconsin, pp 201-276 Sparks DL, Jardine PM (1984) Comparison of kinetic equations to describe K-Ca exchange in pure and mixed systems. Soil Sci 138 115-122 Spencer WF, Cliath MM (1969) Vapor densities of dieldrin. Environ Sd Technol 3 670-674 Spencer WF, Chath MM (1973) Pesticide volatilization as related to water loss from soil. J Environ Qual 2 284-289... 

Tadros T (2004) Application of rheology for assessment and prediction of the long-term physical stabdity of emulsions. Adv CoU Interface Sci 108 227-258 Talibuden O (1981) Cation exchange in soils. In Greenland DJ, Hayes MHB (eds) The chemistry of soil processes. WUey, Chichester, pp 115-178 Taylor AW, Spencer WF (1990) Volatilization and vapor transport processes. In Cheng HH (ed) Pesticides in the soil environment. Soil Sci Soc Amer Book Ser 2, Madison, Wisconsin, pp 213-369... 

Despite the advantages, there is concern over the use of such containment methods because the fate of pesticides put into such sites is not well known ( 1 ). One such fate process is volatilization from the disposal site. Organophosphorus pesticide volatilization from water and soil is relatively unlnvestlgated, and if this route of loss occurs to an appreciable extent from disposal sites, a local respiratory hazard may exist. 

The relative importance of the two processes in a model evaporation pond, along with the time lor 97% loss of the applied pesticide (system purification time), were calculated (Table V). This calculation confirmed that mevinphos and malathion dissipated primarily by hydrolysis, with malathion the more rapid of these two chemicals. For methyl and ethyl parathion, both processes were significant, although volatilization was the dominant dissipation route. However, since both processes were relatively slow for these pesticides, the purification time was fairly long. Diazinon was predicted to be lost primarily via volatilization, and the purification time was relatively short. 

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