Translocation of Organic Chemicals

Transport of organic compounds from the solid or aquatic phases to the gas phase (and back again) is now known to be a highly important process for the dispersion of chemical compounds around the globe. Dissolution into and volatilization from the aqueous phase is an elaborate process that depends on solubility, vapor pressure, turbulence within the two phases, and other physical and chemical factors. Volatilization of materials from the earth s surface into the troposphere can result in their long-range transport and redeposition, with the outcome being that measurable quantities of such substances can be detected far from their point of release. 

Many chemicals escape quite rapidly from the aqueous phase, with half-lives on the order of minutes to hours, whereas others may remain for such long periods that other chemical and physical mechanisms govern their ultimate fates. The factors that affect the rate of volatilization of a chemical from aqueous solution (or its uptake from the gas phase by water) are complex, including the concentration of the compound and its profile with depth, Henry s law constant and diffusion coefficient for the compound, mass transport coefficients for the chemical both in air and water, wind speed, turbulence of the water body, the presence of modifying substrates such as adsorbents in the solution, and the temperature of the water. Many of these data can be estimated by laboratory measurements (Thomas, 1990), but extrapolation to a natural situation is often less than fully successful. Equations for computing rate constants for volatilization have been developed by Liss and Slater (1974) and Mackay and Leinonen (1975), whereas the effects of natural and forced aeration on the volatilization of chemicals from ponds, lakes, and streams have been discussed by Thibodeaux (1979). 

Once a chemical becomes airborne, atmospheric mixing processes on regional, elevational, and global scales come into play. East-west mixing of air masses is much more efficient than north-south mixing. Because of the intra-hemispheric con- 

We know from studies of gases in solution that the solubility of a gas which does not react with its solvent depends to a considerable degree on its vapor pressure at a given temperature. We can extend these studies to other solutes if we can measure their vapor pressures at higher temperatures and extrapolate them to lower, environmentally realistic temperatures. For the case of air-water partitioning, a simple equation describes the behavior of many substances  

Henry s law constants for chemicals of environmental interest have been tabulated by many authors, including Mackay and Shiu (1981), Burkhard et al. (1985), Gossett 

---

Briggs et al. [92] evaluated plant uptake and translocation of 18 pesticides and found that Eq. (6) correlated the translocation of organic chemicals into plants to the Kqw value of the compovmd ... 

---