Evaporation from soil

More than 99% of natural thorium exists in the form (isotope) thorium-232. Besides this natural thorium isotope, there are more than 10 other different isotopes that can be artificially produced. In the environment, thorium-232 exists in various combinations with other minerals, such as silica. Most thorium compounds commonly found in the environment do not dissolve easily in water and do not evaporate from soil or water into the air. 

To estimate the tendency of a compound to evaporate from soil... 

Taylor, A.W., Glotfelty, D.E. (1988) Evaporation from soils and crops. In Environmental Chemistry of Herbicides. Vol. I, Grover, R., Editor, Chapter 4, pp. 89-130, CRC Press, Boca Raton, Florida. 

Patten and Gallagher (1908) presented data showing that the rate of evaporation from soils is linear until the moisture content approaches 1 percent. Some of their results for fine quartz exposed to atmospheres of different humidities are given in Figure 68. 

During evaporation from soil or field crops, the stirring of liquid layers is not important, but it should not be neglected in laboratory comparisons. Pesticide solutions subject to evaporation in the field occur in three main situations ... 

The volatility potential (slope of the vapor pressme vs. concentration in soil organics) of GA is 2.4 x 10" mm Hg/mg/kg and its air-soil partition coefficient (for a soil density of 1.4 g/cm ) of 1 x 10 mg/m (MacNaughton and Brewer, 1994), indicate that GA will evaporate from soil into the air. Results of a field trial with GA showed 10% evaporation in 0.27 horns and 90% evaporation in 4.66 hours (Morrill et al., 1985). 

Henry s Law constant (tendency to evaporate from soil/water/plant surface into air)... 

Natural sources of mercury include volcanoes, evaporation from soil and water surfaces, degradation of minerals, and forest fires. It is estimated that today less than half of the global mercury emissions is due to natural sources (Fitzgerald et al. 1998, Jackson 1997, Lamborg et al. 2002, Coolbaugh et al. 2002). Although it is not possible to control natural emissions, it is important to mention that evaporation from soils may also include re-emission of Hg from previously contaminated sites. 

PROBABLE FATE photolysis , no direct photolysis, indirect photolysis is too slow to be important, atmospheric and aqueous photolytic half-life 144-200 days oxidation not an important process, photooxidation half-life in water 44-584 days, photooxidation half-life in air 2.9-29 hrs hydrolysis too slow to be important (half-life of several years) volatilization not a likely transport process, should not evaporate from soil or water sorption sorption onto particles and biota and complexation with humic materials are most important transport processes, attaches strongly to soil particles biological processes bioaccumulation and metabolization by many organisms, and biodegradation are all very important fates... 

PROBABLE FATE photolysis photooxidation to DDE occurs slowly, indirect photolysis may be important oxidation photoxidation occurs, photooxidation half-life in water 7-350 days, photoxidation half-life in air 7.4 days hydrolysis may be an important process under certain conditions, first-order hydrolytic half-life 22 yrs volatilization is an important process, some will evaporate from soil and surface water into the air sorption is an important process, will adsorb very strongly to soil if released to the soil, will adsorb very strongly to sediments if released to water biological processes biotransformation and bioaccumulation are important processes, may be subject to biodegradation in flooded soils or under anaerobic conditions, may be significant in sediments... 

Figure 4.8 Schematic diagram of the apparatus used to measure the rate of pesticide evaporation from soil as influenced by relative humidity of gas moving across the surface of the soil column. The soil column was 5.8 cm in diameter and 10 cm deep. [Reproduced from W. F. Spencer and M. M. Cliath, i. Environ Qual. 2, 285 (1973) by permission of the American Society of Agronomy, Crop Science Society of American and Soil Science Society of America.]...

From the standpoint of water conservation, the main aim should be to minimize evaporation losses from the soil surface, thus leaving as much as possible of the soil moisture for the use of the crop. In recent years much research (see Pierre etal., 1965) has been conducted in attempts to reduce evaporation from soils and lakes by means of chemicals. Hexadecanol, for example, suppresses the evaporation of water from either a free-water surface or from soil. Olsen et al. (1964) observed that this chemical decreased water loss from a loam soil 43% during a 10-day period. A portion of the data is shown in Fig. 17.3. A surface placement was most effective, remaining unchanged during a... 

A.W. Taylor and D.E. Glotfelty, in Evaporation From Soils and Crops (R. Grover, ed.). Environmental Chemistry of Herbicides, CRC Press, Boca Raton, FL, 1988. 

Evapotranspiration Combined loss of water from evaporation from soils, streams, and lakes, plus plant transpiration. 

Evaporation. The evaporation from the oceans is about 400 000 km /yr. The evaporation from soil, streams, rivers and lakes is less than a tenth of this value 30000 km /yr. Transpiration from vegetation is higher than the latter value 41000 km /yr. 

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