Evaluation of the Adsorption and Desorption Capacity of Two Natural Materials used as Support Media for Constructed Wetlands for the Treatment of Water Contaminated with Pesticides

LIZETH BERMEO GONZÁLEZ; FEDERICO RIMOLDI; CARINA APARTÍN; DARÍO ANDRINOLO

Montevideo

Congreso; SETAC Latin America 15th Biennial Meeting "?Cutting-Edge Knowledge and Technologies for Environmental Health Management and Research?; 2023

SETAC Lationoamerica

Constructed Wetlands (CW) are promising alternatives for the treatment of contaminated water from agricultural activities, due to their ecological benefits and low operation and maintenance costs. The pollutants elimination occurs through physical, chemical and biological processes such as sedimentation, volatilization, adsorption, microbial decomposition and plant uptake. Among the CW components, the support medium or substrate plays an important role in the growth and development of plants and microorganisms; however, very little information is available on its influence on the elimination of contaminants. In order to select the most efficient substrate to removal of pesticides by CW, the adsorption and desorption of two of the most used natural materials in these systems (Gravel and Pometine) were evaluated, using the insecticide Imidacloprid (IMD) as a model. The IMD removal capacity of both substrates was assessment through insecticide concentration and the ecotoxicity of the solution measured before and after treatment. Determination of imidacloprid in water and soil samples was performed by HPLC-DAD system, and the ecotoxicity of the samples were assessment using the crustacean Daphnia magna as a standard test species. Each treatment consisted in 500 mL glass flasks where 150 g of substrate were placed with 200 mL of IMD solution and left on a shaker at 150 rpm and 20°C for 24 h. The evaluated IMD solution concentrations were 36 and 180 mg/L that correspond with the lethal concentration 50 and the maximum recommended doses for use in the field, respectively. The adsorption capacity was determined at different time intervals; aliquots of the aqueous phase were taken at 15, 30 min, 1, 6 and 24 h. Once this assay was completed, desorption was determined for the IMD solutions at 24 h time. None of the evaluated substrates significantly reduced the IMD concentration, so there was no evidence of the insecticide in the desorption samples. However, it was observed that the treatment with pometine reduced the toxicity of IMD by 73% and no differences were found in the attenuation of toxicity with the use of gravel as a substrate. The findings demonstrate that, although the adsorption capacity of pometine against IMD is low, this substrate modifies its bioavailability, making it a good potential material for the treatment of pesticides in CW compared to gravel.