Rhizotron Study of Cucurbitaceae: Transport of Soil-Bound Chlordane and Heavy Metal Contaminants Differs with Genera

Abstract

Environmental Context. Many pesticides are difficult to remove from the soil, and remain as persistent pollutants. Some plant species can extract these pollutants from the soil and thereby degrade them, leading to a potential plant-based soil remediation technology. This study examines how plants extract an enduring organic pollutant (chlordane) and heavy metals (zinc, cadmium) from the soil, where they are processed in the plant, and what end-products are generated. Abstract. Two Cucurbitaceae, Cucurbita pepo L. and Cucumis sativus L., were grown in rhizotrons containing soil contaminated with heavy metals and highly weathered chlordane residues. This experimental scheme allowed in situ access to several portions of the soil/plant system. In the root exudates, concentrations of low molecular weight organic acids (LMWOAs) collected from both genera were detected consistently in the order malic > citric > succinic. Xylem sap was collected from severed plant stems over recorded time segments. Chlordane components and elemental analytes in the sap showed distinct, consistent differences between C. pepo L. and C. sativus L. with regard to chlordane flux, enantiomeric fractions of chlordane components, and heavy metal content. This is the first detailed report of patterns of heavy metals and persistent organic pollutants (POPs) in the contiguous compartments of soil, whole root tissue, xylem sap, and aerial tissue.