Decontamination of Pesticide-polluted Water by Constructed Wetlands

Abstract

The increase in crop productions is usually associated with an intensive use of agrochemicals, such as pesticides. However the serious situation of pesticide contamination of waters, including drinking water supplies, has to be addressed and the conventional drinking water treatment methods are not aimed at pesticide removal. Pesticide pollution mitigation systems are therefore needed at the sources of contamination. A variety of physically, chemically and biologically-based processes have been tested to achieve pesticide removal from waters. Studies have been published where removal is accomplished by different adsorption media, chemical reactions with different oxidants, and biodegradation by microorganisms. The physico-chemical and biological depuration processes are somehow combined in the constructed wetland systems (CWS). These systems are planted biofilters where the concerted action between its main components (plants, microorganisms and support matrix) has been proved to remove several xenobiotics including some pesticides from polluted waters. The efficiency of these systems is highly dependent on the matrix materials and the macrophyte species chosen. In the initial applications of CWS for treatment of wastewater contaminated with common pollutants such as organic matter, phosphorous and nitrogen, typical assemblies of support matrix and plants were commonly used and little attention was paid to the careful selection and optimization of the CWS components. However, in the most recent studies for the application of CWS to xenobiotic removal, a greater attention is given to the optimization of each component due to the recalcitrant characteristics of this type of compounds. In this work, a review is made of several studies about the use of CWS for pesticide removal from water. Most of these studies focus on the selection and optimization of some CWS components. The most studied components are the support matrix, the plants and the microorganisms. Research about the support matrix has involved the test of several types of materials as well as the characterization of the main phenomena associated with the retention of pesticide molecules on the support matrix. Research on the plants component has been focused on the toxicological effects of pesticides on several species and their uptake capacity for these compounds. In addition, microorganisms capable of degrading some of these substances have been identified. It is the aim of this work to give a general overview of all these findings that have been attained in the last years.