Adsorption of Metolachlor and Its Transformation Products, ESA and OXA, on Activated Carbons

Alicia Gomis-Berenguer,Pauline Sidoli,Benoît Cagnon

doi:10.3390/app11167342

Abstract

Three activated carbons from lignocellulosic residues and a commercial carbon have been tested for the removal of the herbicide metolachlor and its two degradation transformation products, named ESA and OXA, in aqueous solutions. The kinetics and equilibrium adsorption were studied for the four materials, showing higher adsorption capacities for the three molecules on the carbon materials chemically activated by potassium carbonate, mainly associated with its greater porous development, especially in the range of microporosity. Additionally, the chemical composition of the adsorbents also highlighted their important influence on the ESA and OXA adsorption process. The efficient adsorption of both compounds—even at low initial concentrations—allows a removal efficiency of up to 80% to be reached, revealing promising perspectives for the use of biomass-derived carbon materials for the elimination of not only the herbicide metolachlor, but also its degradation compounds from contaminated wastewater.

Highlights

Pesticides have become indispensable for intensive agricultural areas around the world, since they increase the production and improve the quality of agricultural production
Its degradation in water is promoted by microbial decomposition, provoking the formation of metolachlor oxanilic acid (OXA) and metolachlor ethane sulfonic acid (ESA) which are commonly quantified in groundwater at concentrations over that of metolachlor, which can reach up to 5 μg/L [11,12,13,14,15]
Four activated carbons have been tested for the adsorption of metolachlor and its metabolites OXA and ESA, one commercially available and three synthesized from lignocellulosic residues

Summary

Introduction

Pesticides have become indispensable for intensive agricultural areas around the world, since they increase the production and improve the quality of agricultural production When they are sprayed on crop plants, a fraction of pesticides is transferred through the soil and can reach aquifers, affecting the groundwater quality, making it unsuitable for human and agricultural uses [1,2,3]. Pesticides’ transformation products (TPs) have emerged as an area of concern due to their high mobility and their less degradation compared to the parent molecule [4]. For this reason, the protection of water resources is an essential issue to be treated at worldwide scale. It seems clear that there is a need for an efficient methodology to remove the excess of pesticides and their TPs from water

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Results

Conclusion