Using ¹⁴C-glyphosate to investigate the distribution of two formulations in transgenic glyphosate-resistant soybean

Glyphosate residues in grain can be explained by the concentrations and formulations of glyphosate products. This study aimed to evaluate the residues from glyphosate formulations labeled with ¹⁴C-glyphosate applied to leaves of glyphosate-resistant soybean (GRS) in two life cycles by liquid scintillation spectrometry. Different plant tissues were analyzed after the end of the plants' life cycles. The experimental design was four repetitions of three treatments: Roundup® Original, Roundup Ready^®, and unformulated glyphosate (control). The application of the dosing solution was 120 µL on the first four trifoliate leaves (10 µL per leaflet) of each plant, deposited manually with a 1-µL dispenser. All treatment solutions were calculated at a 1.2 kg a.e ha^-1 of glyphosate. Glyphosate formulations of Roundup^® Original and Roundup Ready^® increased ¹⁴C-glyphosate distribution in GRS compared to the unformulated herbicide, regardless of the experiment (first or second cycle). Overall, the percentages of total radioactivity applied (18.33 kBq) found in grains were less than 5%. Grains, stems, and leaves showed the highest levels of herbicide residues compared to other parts of the plant. Despite the Roundup Ready^® formulation having increased residues, the highest value found in grains, 1.95 mg kg^-1, was less than 10 mg kg^-1, the maximum residue limit (MRL) in Brazil.