Estimativa do volume de água cinza de misturas de pesticidas utilizados em zona canavieira do Estado de Pernambuco

Abstract

There is a strong and unavoidable commitment between water protection and its conditions of use to meet human needs, such as obtaining food, feed, fiber, biofuels and biomass. However, the inappropriate use of technologies such as agricultural pesticides can jeopardize the evolution observed in the agricultural sector. In sugarcane, several agricultural pesticides are applied simultaneously, and a set of these can be detected in the same body of water, characterizing a contamination of the water by means of mixtures of pesticides with different concentrations occurring simultaneously in a body of private water. Thus, the objective of this work was to estimate the gray water volume of the pesticide mixture (herbicides) based on the toxicity of each pesticide used in a sugarcane cultivation system in a soil in the Sugarcane Zone of Pernambuco. For this, the model developed by Paraiba et al. (2014), who assumes that pesticides are organic compounds with well-defined functions and known toxic effects, and follow first order kinetics and linear sorption process. The gray water volume is then determined by: physical-chemical characteristics of pesticides, such as soil half-life (t1/2) and organic carbon partition coefficient in the soil of the pesticide (KOC); of pesticide application rates (dose); of soil physical-chemical properties, such as soil density (ρd), soil organic carbon fraction (fOC), and volumetric water content in field capacity (θfc); and the lowest concentration value inducing half the maximum effect of a substance in a population of organisms (EC50). The volume of gray water is calculated for each of the pesticides used in the different situations in which it was applied, the gray water volume of the pesticide mixture being obtained by the sum of the gray water volume of each of the pesticides. The gray water volume of the pesticide mixture was 1.57x106 m3 in the 11.86 ha, or 1.32x105 m3 ha-1 The largest volumes of gray water and higher rankings of the blend were Amicarbazone and Hexazinone, with 1.05x105 m3 ha-1 (r = 5) and 3.71x104 m3 ha-1 (r = 4.6), respectively, influenced by the high dose applied in the case of Amicarbazone, and the low PNEC in the case of Hexazinone, which demonstrates the importance of considering the organism more susceptible to PNEC calculation, making the volume of gray water found safe for the whole ecosystem. The lowest volumes of gray water were from Paraquat and Glyphosate, with gray water volume of 1.64 and 8.43 m3 ha-1, respectively. Finally, the gray water volume for the yield of the sugarcane crop under cultivation at the Argisol dystrophic Yellow at 1731.1 m3 ton-1 was estimated, being a high value for the gray footprint of the sugarcane, which demonstrates the as this crop may require water resources to dilute its load of contaminants. Therefore, a combination of pesticides should be used to reduce the volume of gray water, taking into account the ranking of the pesticides used in this mixture, so that they bring the same results of productivity and quality. With the approximation of gray water volume of pesticides per hectare and pesticide ranking, it was possible to validate the model developed by Paraiba et al. (2014) to estimate the gray water volume of the pesticide mixture, which model is more accurate and conservative of the environment among the existing models to obtain this component of the water footprint.