Contaminação por glifosato e 2,4-D sob efeito de chuva intensa: reflexos no solo, água de escoamento superficial e planta

Abstract

The use of pesticides, throughout global agricultural development, has generated discussions related to residual effects, mainly on water, soil and non-target plants. Among the pesticides questioned in terms of product residuals are the two most sold and used herbicides in the world: glyphosate and 2,4-D. Seeking to evaluate the residue of these two herbicides in runoff water, plants and soil, under the effect of intense simulated rain immediately after their application, an experiment was set up in a real field situation. It consists of six plots, installed on a slope of approximately 7%, on sandy loam soil, located in the municipality of Santa Maria, RS. Each plot has an area of 77 m² (3.5 m x 22 m), three of which received cover crops: Avena strigosa in winter and Phaseolus vulgaris in summer, and three remained fallow. The equivalent of 200 L of spray hectare-1 was applied to all plots, with 0.5 L ha-1 for 2,4-D and 2 L ha-1 for glyphosate, as per technical recommendation, corresponding to the total area of the experiment. at 15.48 and 44.35 g of active ingredient (a.i.), respectively. Eight field campaigns were carried out: 1, 3, 5 and 7 without herbicide application and 2, 4, 6 and 8 herbicides were applied. 60 minutes after application of these, 80 mm of rain were simulated for a period of 60 minutes. During surface runoff, water samples were collected from all plots at the irrigation system collection point. Of these samples, analysis of the following water quality parameters was carried out: temperature (in situ), pH, conductivity, nitrate, sulfate, phosphate, total suspended, volatile and fixed solids (LEMA). The herbicides glyphosate and 2,4-D (LARP) were also quantified. There was a significant difference in the quality parameters of runoff water in the presence and absence of the herbicides 2,4-D and glyphosate. The correlation between electrical conductivity, nitrate and phosphate parameters was observed; 2,4-D, sulfate and total volatile solids; glyphosate, pH and electrical conductivity and glyphosate nitrate and pH. When Phaseolus vulgaris seeds were subjected to a germination test with runoff water collected with 2,4-D herbicide residue (579.7 μg L-1), there was a significant difference between those that germinated with pure water, showing effects negative effects on the initial development of seedlings, both aerial parts and roots, reducing the physiological quality of the initial development of the crop, consequently affecting productivity. For the herbicide glyphosate and its metabolite AMPA, there are no methods for quantifying it in the soil. For the 2,4-D herbicide, concentrations were quantified very close to the method limit, only up to 20 cm from the surface. The incidence of intense rain shortly after the application of the herbicide in the field removes, through surface runoff water, a large part of its residue. Furthermore, the use of the recommended dosages of the herbicide does not have a residual effect beyond 20 cm depth.