The toxicity of derris roots, studied in 1934, was shown to be due in part to other extractives than rotenone. Alcohol and acetone proved to be more efficient than water-insoluble solvents in extracting all toxic ingredients of derris root. Since 1934, much time has been devoted to studies of methods of analysis for the newer insecticides and assaying residues in and on vegetable, forage, and fruit crops. It has become evident that such factors as dosage and formulation of toxicant applied, rate of toxicant decomposition, mechanical weathering, timing and method of toxicant applications, and plant growth all influence amount of toxicant residues on the plant at harvest. Sprays of organic phosphates have been shown to decompose readily upon application whereas chlorinated hydrocarbon insecticides remain toxic for longer periods.
Sunlight is a factor in decomposition.
Practically all DDT was found to be in the upper levels of the soil.