Constructed Wetlands for Reducing Pesticide Inputs into Surface Water and Groundwater

In this review, the current knowledge on the use of constructed wetlands (CWs) to reduce pesticide inputs into surface water and groundwater and their effectiveness when applied in practice are discussed. Field data show that plants accelerate pesticide dissipation from aquatic systems by increasing sedimentation, biofilm contact, and photolysis. One of the main mechanisms of pesticide removal in CWs is sorption onto plants, support media, and sediments; yet, CWs effectiveness still has to be demonstrated for weakly and moderately sorbing compounds. The hydraulic design (hydraulic retention time, HRT) and the use of adsorbing materials can be useful to increase the pesticides residence time and the contact between pesticides and biocatalysts. Pesticide fluxes can be reduced by 50–80% when increasing ten times the retention time. This, in turn, leads to CW lengths that are much longer than those for municipal wastewater treatment. CWs are a viable and economic alternative technology for the treatment of effluents contaminated with pesticides, compared to conventional treatment systems. Yet, there are some limitations of CWs, inter alia, they are not suitable for high concentrations of xenobiotics, and they should be carefully managed in order to avoid an over contamination by pesticides of the wetland site and associated negative effects (i.e., wetlands that require remediation).