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Effects of Pesticides on Denitrifying Activity in Salt Marsh Sediments¹

ABSTRACT

Pesticides may alter nutrient cycling in a salt march by affecting various nontarget microorganisms, including denitrifiers. The effects of the herbicides paraquat (1,1'-dimethyl 4,4'-bipyridinium dichloride), 2,4-dichlorophenoxyacetic acid, atrazine ((2-chloro-4)(ethylamino)-6-(isopropylamine)-1-3-5-triazine), and dalapon (2,3-dichloropropionic acid), and the insecticides malathion (O,O-dimethyl dithiophosphate of dimethyl mercaptosuccinate), carbaryl (1,napthyl N-methyl-carbamate), and temephos (O,O,O'O'-tetramethyl O,O'-thiodi-p-phenylene phosphorothioate on the activity of denitrifying bacteria in salt marsh sediments were determined. Sediment samples were amended with glucose, NO₃^–, and pesticides, incubated anaerobically, and gas production was measured by gas chromatography. At a concentration of 10 µg/mL only dalapon clearly inhibited denitrification. When pure cultures of Pseudomonas perfectomarinus were amended with 100 and 250 µg/mL commercial dalapon and 2,2-dichloropropionic acid, NO₂^– reduction activity was inhibited to a greater extent than NO₃^– reduction activity. Aerobically, P. perfectomarinus was not inhibited by dalapon or 2,2-dichloropropionic acid. Dalapon therefore appears to have some capacity to slow the progress of but not suppress denitrification.

Key Words: denitrification • nitrogen transformation

¹ Research supported by National Science Foundation Grant OCE 79-19550.

² Research Associate and Professor, respectively, Department of Microbiology, University of Georgia, Athens, GA 30602.

Received for publication September 21, 1981.