REACTIONS OF BENZIDINE, ALPHA-NAPHTHYLAMINE AND PARA-TOLUIDINE IN SOILS
Abstract
Decomposition of ('14)C-labelled benzidine (4,4'-diaminobiphenyl), (alpha)-naphthylamine (1-amino-naphthalene), and p-toluidine (4-amino-toluene) was studied by incubating amine-treated soils for approximately one year and monitoring ('14)CO(,2) evolved. At the end of incubation, 8.4 to 11.9%, 16.6 to 30.7%, and 18.9 to 35.1% of added benzidine, (alpha)-naphthylamine, and p-toluidine, respectively were evolved as CO(,2). Degradation rate was described by two first order reactions. Half-lives calculated using the slow phase rate constant were 11.5, 5.3, and 5.0 years for benzidine, (alpha)-naphthylamine, and p-toluidine, respectively. Comparison of data from sterile and nonsterile soils suggested that microbes were responsible for degrading amines. Optimum conditions for decomposition were: -0.033MPa water potential, 30(DEGREES)C and pH 5.4. Activation energies calculated from the Arrhenius equation were 40.0, 21.5, and 30.2 kL mol('-1) for benzidine, (alpha)-naphthylamine, the p-toluidine, respectively, suggesting that amine decomposition was biologically mediated. Addition of metabolizable organic substrates did not enhance decomposition. A batch equilibrium technique was used to study sorption to aromatic amines by soils. Effect of pH on sorption was investigated by comparing amine retention at natural pH to soils having pH values adjusted to 7. Amine sorption increased with a decrease in pH. Sorption isotherms for all compound:substrate combinations were described by the Freundlich equation. Nonlinear sorption isotherms were obtained with benzidine and (alpha)-naphthylamine. Equilibrium isotherms for p-toluidine were linear. Freundlich constants (K) for benzidine were correlated with organic carbon content of adjusted pH soils. There were no significant relationships between soil properties and K values for (alpha)-naphthylamine. Freundlich constants for p-toluidine were correlated with % clay in soils for unadjusted and adjusted pH systems. Desorption of sorbed amines followed the order: benzidine << p-toluidine < (alpha)-naphthylamine. The binding of aromatic amines was studied by a sequential extraction of amine-treated soils with ethylacetate:methanol, NH(,4)OAc, and NaOH. Results show amines bind in two phases: initially a reversible equilibrium was established between the amine and soil components. Subsequently, amines become strongly associated with the humic fraction of soil presumably through nucleophilic addition to quinones.
Degree
Ph.D.
Subject Area
Agronomy
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