Volatilization from soils

Sharmila et al. 1988). Little methyl parathion appears to volatilize from soil (EPA 1984a) or leach into groundwater (Albanis et al. 1988a, 1988b Jury et al. 1983, 1987a, 1987b McLean et al. 1988). 

The vapor pressures of most oxygenates, with the exception of ethanol, TBA, and TAME, can result in them being more readily volatilized from soil using certain technologies, such as SVE or MPE.25-26... 

Bacei E, Cerejeira MJ, Gaggi C, et al. 1992. Chlorinated dioxins Volatilization from soils and bioconcentration in plant leaves. Bull Environ Contam Toxicol 48 401-408. 

Di-ft-octylphthalate also strongly adsorbs to soils and does not undergo leaching to groundwater, as indicated by its estimated soil organic carbon/water partition coefficient (Koc) of about 19,000. Volatilization from soils is not expected to be significant (HSDB 1994 Vista Chemical 1992). 

Phenylcarbamates, or carbanilates, generally exhibit low water solubilities, and thus they are almost immobile in soil systems. Chlorpropham and Propham are readily volatilized from soil systems, but Terbutol and Carbaryl (Fig. 10, Table 3) are not. Ester- and amide-hydrolysis, N-dealkylation and hydroxylation are among the chemical reactions that carbamates undergo. The N-methylcar-bamate insecticides (Fig. 10, Table 3) commonly used in soils are Carbaryl, Methiocarb,Aldicarb,and Carbofuran [74,173]. 

Environmental Fate. The fate of bromomethane in the environment is dominated by rapid evaporation into air, where it is quite stable (EPA 1986b). The rates of volatilization from soil and water have been studied and are known with reasonable precision (although such rates are typically site-specific) (Jury et al. 1984 Lyman et al. 1982). The rates of breakdown by hydrolysis, reaction with hydroxyl radical, and direct photolysis in the stratosphere have also been estimated (Castro and Belser 1981 Davis et al. 1976 Robbins 1976). Further studies to improve the accuracy of available rate constants for these processes would be helpful, but do not appear to be essential in understanding the basic behavior of bromomethane in the environment. 

In the past (prior to 1974), exposure of humans to heptachlor and heptachlor epoxide was directly related to the application of heptachlor as an insecticide. However, because of the persistence and bioaccumulation of heptachlor and heptachlor epoxide, exposure of the general population can occur through ingestion of contaminated food (especially cow s or maternal human milk), inhalation of vapors from contaminated soil and water, or direct contact with residual heptachlor from pesticide application. People whose homes have been treated may continue to be exposed to these chemicals in the air over long periods. Occupational exposure can occur in the manufacture of the chemical or from use of heptachlor to control fire ants. The most likely routes of exposure at hazardous waste sites are unknown. Heptachlor has been found infrequently in soil and groundwater at hazardous waste sites. Children who eat contaminated soil or people who obtain tap water from wells located near hazardous waste sites might be exposed to heptachlor. Also, since both compounds can volatilize from soil, people living near hazardous waste sites may be exposed to the compounds in the air. 

Infants and toddlers are exposed to higher levels (based on their greater dose to surface area [or body weight] ratio) of heptachlor epoxide in the diet (particularly from milk) than are adults. Higher exposure rates in indoor air may occur for at least 1 year in homes that have been treated for termites with heptachlor in the past. Although the most likely routes of exposure at hazardous waste sites are unknown, exposure may result from ingestion of contaminated soil near these sites particularly by children. Since both heptachlor and heptachlor epoxide volatilize from soil, inhalation exposure may also be important for persons living near hazardous waste sites. Exposure via... 

Vapor pressure The vapor pressure of a substance is defined as the pressure exerted by the vapor (gas) of a substance when it is under equihbrium conditions. It provides a semi-quantitative rate at which it will volatilize from soil and/or water. The vapor pressure of a substance is a required input parameter for calculating the air-water partition coefficient (see Henry s law constant), which in turn is used to estimate the volatilization rate of compounds from groundwater to the unsaturated zone and from surface waterbodies to the atmosphere. 

The disappearance half-lives of atrazine in soil ranged from 12 d when applied as an emulsion to 28 d when applied as granules (Schulz et al., 1970). The half-lives of atrazine in a sandy loam, clay loam and an organic amended soil under nonsterile conditions were 315-1,947, 162-5,824 and 54-934 d, respectively, while under sterile conditions the half-lives were 324-1,042, 116-3,000, and 53-517 d, respectively (Schoen and Winterlin, 1987). Atrazine has a low volatility. In the laboratory, 0.5, 0.8, and 0.8% of C-ring labeled atrazine was lost to volatilization from soils planted with maize at a concentration of 1 ppm and barley at soil concentrations of 1 and 6 ppm, respectively (Scheunert et al., 1986). 

Fig. 8.4 Rates of selenium volatilization from soil vs. time (Lin et al. 2000)...

It readily volatilizes from soil, but Is stable In sandy loam soil when Incubated In a closed container for 12 weeks (88). In a medium loam soil, some (5%) radioactivity was unex-tractable after 20 weeks of Incubation of [2-l C]1,2-dlchloro-propane (88). 

Figure 3. Capillary Gas Chromatogram of Volatiles from Soil, Chromatographic data adsorption 4 h on Tenax TA desorption 8 min at 200 C column fused silica 0.3 mm, 20 m, SE33 temperature programming 40 to 230 C at 5 C/min carrier gas helium (50 cm/s),...

Ranges and relative values. (From Thomas, R.G., Volatilization from soil, in Handbook of Chemical Property Estimation Methods, Lyman, W.)., Reed, W.F., and Rosenblatt, D.H., Eds., McGraw-Hill, New York, 1982, chap. 16. With permission.)... 

In comparing the factors governing volatilization from soil and plant surfaces, the dominant effect of adsorption that reduces the vapor pressure of pesticides adsorbed on dry soil becomes apparent ( ). Vapor pressures of pesticides are greatly decreased by their interaction with soil, mainly due to adsorption. 

Volatilization very little loss occurred by volatilization from soil surface (Herbicide Handbook 1989). Photolysis under condition of high sunlight intensity in the summer, t,/2 4 d on the soil surface (Herbicide Handbook 1989) ... 

A major reason for the contradictions in this early literature is that in all experiments both root uptake/translocation as well as volatilization from soil followed by deposition to the leaf surface were possible. The authors used... 

Having shown that root uptake/translocation is an insignificant pathway, the implication of many of the laboratory studies cited above is that volatilization from soil and subsequent adsorption on aerial plant parts is an important uptake mechanism. However, using a mathematical model of this process it was shown that in the field only the lowest few centimetres of plant material would be contaminated if volatilization occurred.24... 

Adsorption onto soil particles and transport by runoff or wind erosion Volatilization from soil or vegetation Leaching into ground water Resuspension of contaminated soil particles by wind Uptake by microorganisms, plants, and animals Transformations Biodegradation... 

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