Method detects residues of different herbicides in a single analysis

Scientists from Embrapa Meio Ambiente, São Paulo, improved a method capable of detecting multiple chemical residues through a single analysis. The procedure is aimed at identifying the presence and quantity of herbicides used to control weeds in elephant grass cultivation. Known for producing a large amount of biomass, the grass is used to generate energy and is widely used to feed dairy cattle. Therefore, it is very important to know whether animals are consuming safe food. With an eye on this application, the method should be used in a project in partnership with Embrapa Gado de Leite, Minas Gerais.

Published in a special issue on herbicides of the international journal Austin Environmenal Science, the multiresidue method is capable of detecting residues of the seven herbicides studied (metsulfuron-methyl, atrazine, chlorimuron-ethyl, halosulfuron-methyl, metsulfuron-methyl, nicosulfuron and S-metolachlor ). “As far as we know, this is the first article on the determination of residues of these herbicides in this type of plant. The method can be used by researchers working in this line of research,” says Embrapa analyst Marcia Assalin.

Elephant grass (Pennisetum purpureum Schum) is a forage traditionally used in animal feed and raw material in the production of alcohol, coal and electricity generation, due to its biomass having high energy power.

According to Embrapa Dairy Cattle researcher Alexandre Brighenti, the productivity and quality of elephant grass forage are directly affected by the interference of weeds. This loss can reach values ​​of 42% of dry matter, if adequate weed control practices are not used. Although chemical control, using herbicides, is one of the efficient strategies for controlling weeds, there are no registered products specific to elephant grass in Brazil. Therefore, research into the chemical control of weedy species in this grass crops is extremely important in order to avoid losses in productivity and forage quality. Furthermore, these studies could support the work to obtain herbicide registrations for elephant grass at the Ministry of Agriculture, Livestock and Supply (Mapa).

However, when herbicides are applied in the field, there is a need to monitor their residues in pastures to avoid possible contamination of foods derived from livestock, such as milk and meat, says Embrapa researcher Sonia Queiroz. Furthermore, the inappropriate use of agrochemicals is a potential threat to the environment and non-target organisms, reinforcing the need for research to understand the fate of these products and establish safe application doses.

Most of the herbicides evaluated in this study are applied to the soil (pre-emergent) and not directly to elephant grass. This, according to the researcher, implies a lower risk of leaving residues compared to post-emergent herbicides, which are applied directly to crops. The application of herbicides to the soil allows the molecules to be degraded mainly by microorganisms.

Furthermore, there is an interval of approximately 120 days between the application of herbicides and the harvest of elephant grass. Queiroz explains that, during this period, other herbicide degradation processes, in addition to microbial degradation, would also be operating. This way, the chances of no longer having waste are great. On the other hand, if any residue of a certain herbicide still persists in the plants at the time of harvest, the method developed will reveal the amount of the chemical present, which can be used to assess whether it is safe for animal consumption.

According to Assalin, the objective was to optimize and validate a reliable multi-residue method for the determination and quantification of herbicide residues (atrazine, chlorimuron-ethyl, halosulfuron-methyl, metsulfuron-methyl, nicosulfuron and S-metolachlor) in elephant grass using high-performance liquid chromatography coupled to high-resolution mass spectrometry (LC-QTof-MS). The implementation of an analytical method involves an evaluation process that estimates its efficiency in the laboratory routine and thus ensures that the analyzes reproduce consistent values ​​when compared to a reference value.

According to the validation parameters evaluated in the study, the method proved to be suitable for determining the residues of the herbicides studied. For metsulfurom-methyl, the method proved to be capable of determining quantities smaller than the maximum residue limit (MRL) established by the National Health Surveillance Agency (Anvisa) of 0,1 mg/Kg, which is the only one that has been registered for application on pasture in Brazil.

Thus, it was possible to analyze samples of elephant grass collected in the experimental field after applying the products and, therefore, select the most efficient herbicides that leave less residue on the plant. Allowing the control of weeds, with safety in relation to the consumption of foods of bovine origin.

 

The development

The quantification of pesticide residues in elephant grass was based on the QuEChERS method (Quick, Easy, Cheap, Effective, Ruged and Safe), which consists of a modern sample preparation methodology well known in the area of ​​pesticide residue analysis, followed by determination by liquid chromatography coupled to mass spectrometry.

Some modifications were made to QuEChERS in order to optimize the extraction procedure depending on the complexity of the matrix studied. The method allows the extraction of numerous compounds in a single analysis, consisting of the extraction step, using an organic solvent; separation, by a jumping out (by adding some salts) followed by the cleaning phase, to eliminate compounds that are co-extracted from elephant grass that could interfere with the quantification of the pesticides of interest.

Mass spectrometry is a highly reliable method that generates results quickly, easily, at an affordable cost and with high quality. The scientist points out that in Brazil there are very few laboratories for analyzing agrochemical residues due to the complex processes involved. “To get an idea, it is necessary to detect quantities at the level of micrograms per kilogram (µg/Kg), which require sophisticated equipment and highly specialized staff,” highlights the researcher when declaring that Embrapa Meio Ambiente houses one of the few laboratories in the Country like that.