Decomposition of Benzidine, α‐Naphthylamine, and p‐Toluidine in Soils

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Abstract
Decomposition of 14C‐labeled benzidine, α‐naphthylamine, and p‐toluidine in soil was studied in laboratory experiments by monitoring CO2 production during a 308‐ to 365‐d incubation period. The importance of microbial activity in decomposition of all three aromatic amines was shown by decreased 14CO2 evolution in 60Co treated soils. After 365 d of incubation, 8.4 to 12% of added benzidine (54.3 µmol kg−1) was evolved as CO2 while 17 to 31% of added α‐naphthylamine (69.8 µmol kg−1) and 19 to 35% of added p‐toluidine (93.3 µmol kg−1) were evolved as CO2 in 308 d. Decomposition of benzidine, α‐naphthylamine, and p‐toluidine was greatest at a water potential of −0.033 MPa and decreased at both 0 and −0.5 MPa. Decomposition was enhanced by increasing the temperature from 12 to 30°C. The absolute amount of α‐naphthylamine and p‐toluidine decomposed increased while the percentage of added amine degraded decreased as application rate was increased from 1 to 1000 mg kg−1. For benzidine, both the amount and proportion decomposed increased with an increase in application rate. Decomposition of aromatic amines was not enhanced by the addition of decomposable substrates. Differences in decomposition of aromatic amines occurred among soils, but consistent relationships between decomposition of amines and soil properties were not observed. In batch equilibration studies, the Freundlich equation described aromatic amine sorption. Isotherms were nonlinear for benzidine and α‐naphthylamine and linear for p‐toluidine. Desorption of sorbed amines followed the order: benzidine < p‐toluidine < α‐naphthylamine and was inversely related to the extent of decomposition.