The sorption and irreversible binding of naphthalene and R-naphthol to two sandy soils were evaluated. To determine the extent that biologically-mediated oxidative coupling contributed to the irreversible binding of R-naphthol, the presence/absence of O 2 and the presence/absence of biological activity were varied during the sorption period to operationally define biological coupling conditions. After a 2-d sorption period, sorbed material was removed by successive water and solvent extractions, alkali extractions, and combustion. Nonextracted material was defined as the amount of test compound remaining after solvent extraction (Q NONEX ). Naphthalene that was not extracted after the 2-d sorption period was caused by mass transfer-limited entrapment within micropores and was used to estimate the fraction of entrapped R-naphthol. The principle of superposition was applied to the R-naphthol results to determine the contribution of individual irreversible binding processes. Biologically-mediated oxidative coupling accounted for 49.4 ( 15.0% of Q NONEX of R-naphthol. Oxidative coupling catalyzed by mineral surfaces accounted for 40.5 ( 15.8% of Q NONEX of R-naphthol. Over contact times up to 200 d, nonextracted naphthalene increased from 1.6% to 11.7% of the initially sorbed material, coincident with the biological production of a more polar metabolite.

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Halogenated phenolic compounds such as chlorophenols are capable of binding to organic matter during the humification processes in soil. The incorporation of phenols into organic macromolecules, i.e., covalent bond formation, results from biologically or chemically catalyzed reactions. Standard batch sorption experiments performed in our laboratory showed a significant enhancement in soil associated 4-monochlorophenol (4-MCP) in the presence of oxygen possibly as a result of covalent binding. Sorbed 4-MCP was subjected to desorption by consecutive water and solvent extractions. Nearly 15% of the soil-associated 4-MCP remained unextracted. The unextracted [U-ring-14 C]-4-MCP consisted of a fraction incorporated into humic and fulvic acids and a second fraction associated with humin or soil mineral surface and recovered as 14 CO 2 during soil combustion. Autoclaving the soil before 4-MCP addition resulted in a reduction in the amount of the nonextractable 14 C. The addition of H 2 O 2 caused a 4.4-fold increase in 4-MCP binding. Hydrogen peroxide, which appears to enhance both biological and abiotic coupling processes, can be added to soil as a stimulant of oxidative coupling activity.

A field monitoring study of a riparian forest buffer zone was conducted to determine the impact of the riparian ecosystem on reducing the concentration of agricultural nonpoint source pollutants. Groundwater samples were collected from 20 sampling locations between May 1993 and December 1994, and analyzed for NO3‐N, PO4, and NH4‐N. Statistical analyses such as Friedman's test, cluster analysis, cross correlation analysis and Duncan's test were performed for the nutrient data. The study showed that the ripanan buffer zone was effective in reducing nitrate concentrations originating from upland agricultural fields. Instream nitrate concentrations were 48 percent less than those measured in the agricultural field. Reductions in concentrations in sampling locations at the wetland edge ranged from 16 to 70 percent. The mean nitrate concentrations in forested hill slope were 45 percent less than concentrations in a well located in an upland agricultural field. Meanwhile, the concentrations of phosphate and ammonia did not follow any specific spatial trend and were generally higher during the summer season for most sampling locations.

Degradation of indole by an indole-degrading methanogenic consortium enriched from sewage sludge proceeded through a two-step hydroxylation pathway yielding oxindole and isatin. The ability of this consortium to hydroxylate and subsequently degrade substituted indoles was investigated. Of the substituted indoles tested, the consortium was able to transform or degrade 3-methylindole and 3-indolyl acetate. Oxindole, 3-methyloxindole, and indoxyl were identified as metabolites of indole, 3-methylindole, and 3-indolyl acetate degradation, respectively. Isatin (indole-2,3-dione) was produced as an intermediate when the consortium was amended with oxindole, providing evidence that degradation of indole proceeded through successive hydroxylation of the 2and 3-positions prior to ring cleavage between the C-2 and C-3 atoms on the pyrrole ring of indole. The presence of a methyl group (-CH3) at either the 1or 2-position of indole inhibited the initial hydroxylation reaction. The substituted indole, 3-methylindole, was hydroxylated in the 2-position but not in the 3-position and could not be further metabolized through the oxindole-isatin pathway. Indoxyl (indole-3-one), the deacetylated product of 3-indolyl acetate, was not hydroxylated in the 2-position and thus was not further metabolized by the consortium. When an H atom or electron-donating group (i.e.,-CH3) was present at the 3-position, hydroxylation proceeded at the 2-position, but the presence of electron-withdrawing substituent groups (i.e.,-OH or-COOH) at the 3-position inhibited hydroxylation.

The biodegradability of dicamba was investigated under anaerobic conditions with a consortium enriched from wetland soil. Degradation proceeded through an initial demethylation reaction, forming 3,6-dichlorosalicylic acid, followed by reductive dechlorination, forming 6-chlorosalicylic acid. The consortium, consisting of a sulfate reducer, three methanogens, and a fermenter, was unable to mineralize the aromatic ring.