Formation of tetrachloroazobenzene in some Canadian soils treated with propanil and 3,4-dichloroaniline

The formation of 3,3′,4,4′-tetrachloroazobenzene from the herbicide propanil (N-(3,4-dichlorophenyl)propionamide), and from 3,4-dichloroaniline was studied in nine soils which varied in pH, percentage of organic matter, clay, and sand. Marked differences were observed in these soils in the amounts of azobenzene formed. In five soils whose pH values fell within a range of pH 4.5 to 5.5, azobenzene was produced from both substrates, while in two soils (Guelph loam and Wendigo loamy sand), azobenzene was only detected from 3,4-dichloroaniline. No azobenzene was detected from either substrate in two additional soils (Belleisle marsh soil (site 22, pH 3.4) and Biz silt loam (pH 6.4)). Air-drying soils, as well as extended periods of storage of freshly collected soils at 4 °C, reduced the formation of azobenzene.