Eficiência de um sistema de tratamento por filtração lenta na redução da toxicidade de água contaminada com imidacloprido

Abstract

This study evaluates the efficiency of a slow sand filtration system in reducing the toxicity of water contaminated with the insecticide imidacloprid. The research was motivated by concerns over the widespread occurrence and persistence of this neonicotinoid in aquatic environments and by the need for low-cost technologies capable of mitigating its effects. The study was conducted at laboratory scale using a pilot slow sand filtration unit composed of a sand bed, gravel, and a subsequent granular activated carbon stage, combined with chronic toxicity bioassays employing the collembolan Folsomia candida. The investigation was structured into three stages: determination of the effect concentration of imidacloprid in sandy soil; evaluation of the toxicity of contaminated water before and after treatment; and integrated synthesis of statistical evidence regarding post-treatment efficiency. Standard assays based on ISO 11267 (2023) were applied, exposing organisms to different water types: distilled water, river water, contaminated water, sand-filtered water, and sand-filtered water followed by granular activated carbon. The results showed that contaminated water maintained significant chronic toxicity, reducing both survival and, especially, reproduction of the organisms. Slow sand filtration, with the formation of the biological surface layer (schmutzdecke), partially attenuated these effects, restoring survival to control levels in most experimental batches. The additional granular activated carbon stage demonstrated superior and more consistent performance, reestablishing both survival and reproduction to values comparable to the controls and achieving maximum efficiency in the integrated assessments. It is concluded that the slow sand filtration system combined with granular activated carbon is a technically viable alternative for reducing the toxicity of imidacloprid-contaminated water, particularly for direct application in rural areas that require low-cost and operationally robust solutions.