N-Nitrosamine Formation in Soil from the Herbicide Glyphosate and its Uptake by Plants

Abstract

The herbicide glyphosate was nitrosated in aqueous solution by third order kinetics to N-nitrosoglyphosate. The nitrosation at 25°C was maximum at the reaction pH of 2.5 and had a pH-dependent rate constant of 2.4M -2 sec -1 . An activation energy of 9.5 Kcal mole -1 indicated that glyphosate in water is nitrosated very readily. Formation of N-nitrosoglyphosate was also observed when different soils were treated with sodium nitrite and the herbicide glyphosate at elevated levels. However, at low levels of glyphosate (5 ppm) and nitrite nitrogen (2 ppm) the formation of N-nitrosoglyphosate was not observed. The residues of N-nitrosoglyphosate can be assimilated by the roots of oat plants and translocated to the shoots. Formation of N-nitrosoglyphosate in soil and its uptake by plants under normal field conditions is not expected.In recent years greater attention has been given to nitrogen containing pesticides and the possibility of their nitrosation in soil. The W-nitrosamines that form may arise from the parent pesticide or from a pesticide metabolite. The reaction calls for favourable pH conditions (pH 3-4) and excess nitrite. Under field conditions, the nitrosable residues are usually present in traces and only small quantities of these will actually be nitrosated in soils. However, the possibility exists that the small amounts of W-nitrosamines could be assimilated by plants.Formation of W-nitroso compounds in soil from nitrite and nitrosable pesticides, such as s-triazine (1), dithiocarbamate and carbamate (2) and dinitroaniline (3) has been demonstrated under in vitro conditions. The herbicide glyphosate [W-(phosphonomethyl) glycine] (]) contains a secondary amine nitrogen, which can undergo W-nitrosation to form W-nitrosoglyphosate (2). Glyphosate has been widely used to provide effective control of most herbaceous perennial weeds through postemergence application (4). For this purpose the herbicide is applied to weed foliage at rates up to 4.2 kg/ha, often as a spot treatment.

Trends of Biosensing: Plasmonics through Miniaturization and Quantum Sensing

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