Photodecomposition of DDA.

The photodecomposition of aqueous solutions of 2,2-bis (p-chlorophenyl) acetic acid (DDA) was slow in sunlight and rapid in the laboratory, producing p,p'-dichlorobenzophenone (DCB), p-chlorobenzaldehyde, p-chlorophenol, and several unidentified polar products. p,p'-Dichlorobenzilic acid, and p,p'-dichlorobenzhydrol gave rise to the same photoproducts, while bis-(p-chlorophenyl) methane (DDM) and chlorogenzilate were converted only to DCB. DCB and p-chlorogenzaldehyde proved to be resistant to photodegradation but gradually produced p-chlorobenzoic acid which, in turn, formed p-hydroxybenzoic and benzoic acids, probably the last environmentally detectable links in the long chain of DDT degradation to CO2 and water. High pressure liquid chromatography (HPLC) proved to be ideal for separating and quantitating the parent compounds and their photoproducts directly from the aqueous photolysates or from methanol solutions of the isolates and standards.

DDT moratorium in Arizona--agricultural residues after seven years.

The moratorium on agricultural use of DDT in Arizona that began in January 1969 proved very effective during the first 7 years of enforcement. Residues on green alfalfa declined significantly to a probable inherent level of 0.02 ppm wet weight. Soil residues of sigmaDDT-related degradation products declined significantly, averaging 23 percent; residues in desert soils declined 60 percent. The sigmaDDT half-life in irrigated soils was about 7 years; it decreased to 2.5 years in nonirrigated soils.