Comparison of the leaching behaviour of two maize herbicides: atrazine and sulcotrione

Abstract - In a soil column experiment under outdoor conditions, we monitored the fate of ¹⁴C-ring-labelled sulcotrione and atrazine in water percolates and in the ploughed horizon of a sandy-silty soil. The application rates were 1000 and 450 g·ha^-1, respectively, for atrazine and sulcotrione. Two months after treatment, the cumulative amounts of herbicide residues leached from the soil were 14.5% and 7% of the applied radioactivity for sulcotrione and atrazine, respectively. The maximum percolate concentrations for each herbicide were observed during the first month following application; 120 mg·L^-1 and 95 mg·L^-1 for sulcotrione and atrazine, respectively. After 2 weeks, 78% of the sulcotrione and atrazine was extractable from the soil, whereas after two months only 10% and 4%, respectively, could be extracted. The maximum sulcotrione and atrazine contents in the first ten centimetres of soil were identical. For both molecules, the content of non-extractable residues was low, being around 15%. The sulcotrione seems to be a more mobile product than the atrazine. Even if much smaller leachate concentrations would be expected to impact groundwater than those found in this study, the classification of the molecules would stay the same.