Effects of toluene on microflora and hydrolysis of urea in a black spruce humus.

Abstract

The value of toluene as an antiseptic in determining the activity of urease in soil was studied in the surface organic horizon of a black spruce (Picea mariana Mill.) forest soil. Toluene was added in various amounts to layers of the humus suspended in water or in phosphate buffer, or sterilized by radiation, and incubated for various periods of time, followed by 8-h treatments with urea. Viable bacteria and fungi were detected by the dilution plate technique and the products of urea hydrolysis were determined by extraction and distillation. By increasing the amount of toluene or the time of contact of toluene with the humus, bacteria and fungi were reduced in number but not completely eliminated. The presence of urea resulted in a larger decrease of bacteria and fungi. With an increase in the amount of toluene, but not in the time of contact of toluene, a decrease was observed in urea hydrolysis. Some of the decrease was due to the inhibition of urease by toluene, and possibly some to the absorption of the products of urea hydrolysis and (or) to a lower production of urease by the surviving microorganisms. The last two possibilities render questionable the use of toluene in the determination of urease activity in soils.