Volatilization.--All compounds are volatile to some degree. Volatility of some 
herbicides is very low and of little significance. However, measurable loss of others 
occurs from soil surfaces by vaporization. 
The volatilities of formulations of the same basic herbicide structure may be quite 
different. The isopropyl ester of 2,4-D is more volatile than the octadecyl ester, which 
in turn is more volatile than the sodium salt (39). Many other esters and salts of 2,4-D 
exhibit various rates of vaporization. 
Vapors of soil-applied herbicides have caused severe injury to treated crop plants 
in some instances. Vapors of 4,6-dinitro-o-sec-butylphenol [DNBP] after preemergence 
applications caused extensive injury to cottoninthe Mississippi Delta in 1952 (25, 26, 34). 
DNBP injury was associated with high temperatures. Hollingsworth and Ennis (34) found 
that vapor injury to young cotton plants increased as soil moisture increased. 
DNBP injury to cotton was reduced by application of lime and other basic materials 
to the treated soil surface (9, 19). Uponaddition of a base, the phenol-phenate equilibrium 
was probably shifted to the phenate, which is less volatile than the phenol (9). 
Volatilization of the carbamates has been related to their effectiveness as pre- 
emergence herbicides. IPC and CIPC volatilized rapidly from tinfoil and glass surfaces 
at high temperatures (4). IPC volatilized more rapidly than CIPC, particularly at tem- 
peratures of 60° to 85°F. The most volatile carbamates were found to be most phytotoxic 
(38); however, loss by volatility following preemergence application reduced the con- 
centration of the more volatile compounds to nonherbicidal levels more rapidly than the 
less phytotoxic, less volatile compounds. 
Many herbicides are formulated on granular carriers to reduce loss by volatility 
and leaching after application to the soil surface. The vapor and contact activities of 
CIPC-impregnated granular carriers were investigated by Danielson (17). The vapor 
activity of CIPC was related to the physical structure and adsorptive capacity of the 
granular carriers. When the physical structure of attapulgite granules was changed by 
moistening with water, vapor activity increased. Carriers that did not change in physical 
structure on contact with water exhibited unchanged or reduced vapor activity. Danielson 
proposed the use of impervious granular carriers to obtain immediate short-term ac- 
tivity of CIPC and more adsorptive carriers for long-term activity. 
Adsorption.--The activity of most herbicides varies with soil composition. Since 
many herbicides are adsorbed by colloidal particles and since the amounts of mineral 
and organic colloids vary among soils, much of the variation in herbicidal activity is 
attributed to differences in the adsorptive capacity. 
The adsorption of six growth-regulator herbicides by several ion-exchange resins 
was demonstrated by Weaver (59). Weaver (60) and Smith and Ennis (53) used activated 
charcoal as a soil amendment to protect germination seeds from 2,4-D applied to the 
soil surface. 
In a greenhouse experiment the initial toxicity of 2,4-D was greater in sandy soils 
than in most clay soils (16). Abutylester of 2,4-D was fixed in a clay-sand mixture more 
strongly than a triethanolamine salt form (2). Bothamine and polypropylene ester formu- 
lations of 2,4-D were adsorbed by montmorillonite, illite, and kaolinite clays (32). The 
adsorption of 2,4-D increased as the cation-exchange capacity and specific surface 
increased. 
CIPC was adsorbed by activated charcoal andcertain other materials (17). In labora- 
tory and greenhouse experiments EPTC was adsorbed least by those soils in which it was 
most phytotoxic (5). 
Sherburne and Freed (51) demonstrated adsorption of monuronby activated charcoal, 
sawdust, straw, and soil. The amount of monuron adsorbed by soils was correlated with 
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