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  • Author or Editor: Erin P. MacNeal x
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Recirculating irrigation systems (RISs) conserve water and decrease fertilizer application, providing cost-effective alternatives to other watering methods in greenhouses. However, RISs can potentially become contaminated from spray or drench pesticide applications. In this study, we determined the amount of metalaxyl residues (the active ingredient in Subdue) in RISs over 3 and 6 weeks using HPLC analysis. Also examined was the potential use of constructed wetlands for the remediation of RIS water contaminated with metalaxyl. Metalaxyl was found to persist in a RIS over 6 weeks with no decrease in concentration. After repeated metalaxyl treatments over an 11 month period, a possible breakdown product or chemical modification of metalaxyl was present in the RISs. Drench applications, 150 ml of an 18.8 ppm metalaxyl solution, (recommended dosage) resulted in 0.5 to 3.0 ppm contamination levels in the RISs. Small scale (≈70 L void volume), indoor, constructed wetlands (two planted with Scirpus and Iris, two unvegetated) were treated with 420 mg metalaxyl. Limited breakdown of metalaxyl occurred in the constructed wetlands during the first 30 days after treatment. After 3 months, metalaxyl concentrations in all wetlands had decreased or were below detection levels. This indicates a possible selection of microbial populations capable of metabolizing or degrading metalaxyl.

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