Sites of benzidine, α‐naphthylamine and p‐toluidine retention in soils

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Abstract
The binding of benzidine (4,4′‐diaminobiphenyl), α‐naphthylamine (1‐aminonaphthalene) and p‐toluidine (4‐methylaniline) by three soils was studied by incubating soils amended with the aromatic amines and then sequentially extracting them with 60:40 (v/v) ethylacetate: methanol (EtAc: MeOH), ammonium acetate (NH4OAc) and sodium hydroxide (NaOH) as a function of time. Essentially all of the added α‐naphthylamine and p‐toluidine was extracted initially with EtAc: MeOH and NH4OAc, whereas only 21% of added benzidine was extracted by these reagents. After 24 h, a significant decrease was found for amines extractable with EtAc: MeOH and NH4OAc. During 63 to 84 d after incubation, a gradual increase in the proportion of amine recovered by NaOH extraction was found. Fractionation of the NaOH extract into humic and fulvic acids indicated that benzidine and α‐naphthylamine were primarily associated with the humic acid fraction, whereas p‐toluidine was in the fulvic acid fraction. Simultaneous measurement of 14CO2 evolved showed that the average decomposition rate was 2, 12 and 15% for benzidine, α‐naphthylamine and p‐toluidine, respectively. Results indicate that binding of benzidine, α‐naphthylamine and p‐toluidine to soils involves both rapid, reversible equilibrium with inorganic and organic components of soil and nucleophilic addition to the phenolic components of humus. These retention mechanisms may explain why benzidine, α‐naphthylamine and p‐toluidine resist decomposition in soils.