Five pesticides decreased oxidation of atmospheric methane in a forest soil

We found that five tested pesticides (the insecticide Dimethoat 40 EC, the herbicide Tolkan, and the fungicides Tilt 250 EC, Tilt Top, and Corbel) decreased the oxidation of atmospheric methane in slurries from a Danish forest soil. Dimethoat 40 EC was the most toxic with an EC50 value (i.e. the concentration which caused a 50% inhibition of the methane oxidation) of 10 mg active ingredient (AI) l−1, followed by Tilt 250 EC (EC50=56 mg AI l−1). EC50 of Tilt Top was 350 AI mg l−1, the value of Tolkan was 410 mg AI l−1, while Corbel had a value of 1600 mg AI l−1. Dimethoat 40 EC and Tolkan inhibited the oxidation of atmospheric methane at concentrations expected in natural soil after application of the pesticides. Pesticides, therefore, may be partly responsible for the lowered methane oxidation rates in arable soils compared to forest soils.