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Influence of Pesticides on Denitrification in Soil and with an Isolated Bacterium¹

ABSTRACT

Various pesticides were tested for their influence on the denitrification process in soil and on an isolated denitrifying bacterium. In soil the denitrifying activity was essentially inhibited by the fungicides captan (N-trichloromethylmercapto-4-cyclohexene-1,2-dicarboximide), maneb (manganous ethylenebisdithiocarbamate), and nabam (disodium ethylene-1,2-bisdithiocarbamate), and to a lesser extent by the herbicide 2,4-D (2,4-dichlorophenoxy-acetic acid). In pure culture studies with a bacterium whose end product in denitrification was nitrous oxide, the fungicides also caused strong inhibition of the respiratory nitrate reduction process; the insecticide carbaryl (1-naphthyl N-methylcarbamate), the phenylurea herbicides, 2,4-D and propham (isopropyl carbanilate) also functioned as inhibitors, but to a lesser extent. It was of special interest to observe that the inhibition by certain pesticides influenced the formation rate of nitrite and sometimes prevented the reduction of accumulated nitrite during incubation under anaerobic conditions.

Key Words: pesticide toxicity • nitrite formation • microbial ecology • N₂O

¹ Authorized for publication on 19 Feb. 1975 as Paper No. 4818 in the Journal Series of the Penn. Agric. Exp. Sta.

² Associate Professor of Soil Microbiology and Research Aide, respectively, Dep. of Agron., Pennsylvania State Univ., University Park, PA 16802.

Received for publication March 4, 1975.