The use of commercially available emulsifiable concentrate (EC) formulations of alachlor and metolachlor may be an environmental hazard because of their volatilization to the atmosphere and photodecomposition, which requires increased applied amounts. The objectives of this study were to develop organo--clay based formulations which would be less volatile and better protected from photodegradation. Bioassays have shown that the use of organo--clay formulations improves photoprotection, reduces volatilization and maintains herbicidal activity in the soil under labora- tory and field conditions. Largest adsorption of herbicides by organo--clays correlates with an optimal reduction of photodecomposition and volatilization. It appears that the role of the organic cation, e.g., benzyltrimethylammonium (BTMA) is to enhance the adsorption of the non-polar herbicides to the organo-clay complex, whereas the actual photoprotection is mainly provided by the clay.
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