Rastreability of glyphosate based herbicides using stable isotopes

Glyphosate is an important organophosphate in the agriculture sector, being the best-selling herbicide in the world. Although his market price is reasonable, this pesticide is a target for contraband and counterfeiting. When used irregularly, glyphosate can bring damage to the environment and to the health of those who handle the product. Due to this, a resource that could assist in the identification of the origin of these materials may help differentiate between the counterfeiting and the original product, or determine its brand in the case of seized cargo. Therefore this work has the intention to verify the potential to discern glyphosate based herbicides using the values of δ¹³C and δ¹⁵N. Samples from 5 different brands – a total of 3 manufactures – of the most popular glyphosate based herbicides on the market were analyzed. They will be named in this paper as samples A and B (manufacture 1), C and D (manufacture 2) and E (manufacture 3), 3 of which are granulated (A, B and C) and the other 2 are liquid (D and E). The sample preparation was only necessary for the solid materials, which was pulverized with an agate pestle and mortar manually. Then all the samples were put in tin capsules and analyzed. The equipment used were the FlashSmart™ Elemental Analyzer coupled to the spectrometer IRMS DELTA™ V, both from Thermo Fisher Scientific. The data was processed by the software Isodat 3.0. One of the quartz reactors on the NC configuration recommended in the manual was adapted, being used chromium(III) oxide instead of copper oxide. The results indicate that it is possible to distinguish between the samples, even amid the samples from the same manufacturer, by comparing the δ¹³C, since the differences among the obtained values are greater than the error generated by the equipment. The data obtained for the δ¹⁵N show that the technique has potential, but the low concentration of nitrogen in the glyphosate doesn't allow to reach an assertive conclusion based only on the nitrogen, keeping the δ¹³C as the ideal comparison parameter. Furthermore, for the liquid samples both the ¹⁵N and the δ¹³C present variations, which leads to the doubt of the precise composition of the products, since the labels are not specific regarding the solvent of the liquid products, as well as the excipient of the solid product. In conclusion, this investigation highlights that stable isotopes can be used as reliable differentiation criterion and that they can contribute to the construction of a dangerous and regulated products database, even those that are likely to be used as chemical weapons.