Physicochemical Properties and Their Role in Determining Herbicide Transport

Physicochemical Properties and Their Role in Determining Herbicide Transport 

Movement of herbicides in the vapor phase can be important for transport from soil to plant (Section 9.3.2), and also some compounds transported to leaves from roots via the xylem may be then lost from leaves by volatilization. Worthing and Ashton and Crafts give the vapor pressures for most herbicides. 

Transport of pesticides in plants is dictated primarily by the rate at which the compounds are able to cross the membranes that encompass the transport vessels. This process appears to be determined mainly by the lipophilicity of the chemicals rather than by any specific property of the molecule such as its shape or the presence of particular functional groups. Usually, lipophilicity is assessed using the octan-l-ol/water partition coefficient which for most compounds is best measured directly by 

Partitioning of more lipophilic chemicals onto plant solids is an additional factor that limits their long-distance transport, and this is also a simple function of lipophilicity. 

Water solubility is generally rather a poor guide to systemic behavior. Lipophilicity, however, can be estimated from water solubility using relationships such as those given by Briggs  

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