Mineralization of monosubstituted aromatic compounds in unsaturated and saturated subsurface soils

Abstract

The mineralization of benzoic acid, phenol, and benzylamine was determined as a function of depth in two 20-m sandy soil profiles, one of which was adjacent to a leach field receiving wastewater from a laundromat. Soil samples were collected aseptically, adjusted to 20–25% water content and amended with a trace level (50 ng/g soil) of the 14C-ring-labeled compounds. Evolution of CO2 was followed with time. First-order rate constants and the extents of mineralization were estimated from the resulting data by nonlinear regression. All three compounds were mineralized in every sample examined without a lag period. In general, phenol was mineralized more rapidly than benzoic acid, which was more rapidly mineralized than benzylamine. Benzylamine had the highest sorption coefficient; phenol had the lowest. Average half-life was 0.56 days for phenol, 0.84 days for benzoic acid, and 1.31 days for benzylamine. Mineralization rates did not correlate with bacterial number, fluorescein diacetate hydrolysis rate, or any soil characteristic. The ultimate percentage of all three compounds mineralized was lowest in the upper 3 m of both soil profiles. The total amounts of phenol and benzoic acid mineralized negatively correlated with cation-exchange capacity and silt content. Statistical analysis (2-level nested ANOVA) revealed that only the rate of phenol mineralization varied significantly as a function of soil profile, but rates for all three compounds varied significantly as a function of depth within a profile.

Effect of chlorpyrifos on microbial biomass and activities in tropical clay loam soil

“…Hydrolysis of fluorescein diacetate is a measure of lipases, proteases and esterases activities (Federle et al 1986;Federle 1988). FDHA is widely accepted as an accurate and simple method for measuring total microbial activity in soils (Adam and Duncan 2001).…”

Microbial Processes in the Vadose Zone

“…However, first‐order rate constants are generally higher when soils are biovented (Moyer et al, 1996). Biodegradation kinetics are also highly dependent on site characteristics (Dobbins et al, 1987) and vadose zone depth (Dobbins et al, 1987), but depth dependency can be highly irregular (Federle, 1988). Biodegradation of a spiked hydrocarbon into already‐contaminated vadose materials may appear particularly slow if preexisting hydrocarbons are used as preferential substrates.…”

Use of Biodegradation Data in Chemical Assessment

“…Even as close as 10 m, greater than 80% of a chemical will be removed if the BHL is less than 40 d. For reference, under aerobic conditions (e.g., in shallow unconfined systems), chemicals like toluene [17], nitrilotriacetic acid [18], linear alkylbenzene sulfonate [19], phenol, benzoic acid, benzylamine [20], aniline and mcresol [21] fall into this range. First, the minimum BHL needed to remove significant quantities of chemicals from ground water can be orders of magnitude higher than that required in rivers.…”