The Oro Loma Living Levee is a new type of natural treatment system designed to remove trace organic contaminants from municipal wastewater effluent. It mimics wetlands that exist in riparian zones or at the edges of estuaries by using subsurface flow through a layer of sandy sediments overlain by a layer of fine sediments colonized by native plants. These conditions facilitate denitrification and trace organic contaminant removal through microbial processes. During the summer, high evapotranspiration rates result in losses of as much as 75% of the applied water volume. As a result, we have been studying plant uptake of trace organic contaminants both as a mechanism of removal and as an exposure route for terrestrial organisms living in the wetland. Monitoring of 13 pharmaceutical compounds including antibiotics, antivirals, beta-blockers, and an antiepileptic conducted over the past 16 months indicate that microbial transformation in the subsurface and plant uptake remove over 95% of the mass of pharmaceuticals entering the wetland. Measurements of known biotransformation products in water and concentrations of parent compounds and metabolites in plant tissues are being used to discriminate between plant uptake and transformation in the field. Preliminary results indicate the presence of pharmaceuticals including antivirals and antiviral metabolites in plant leaf extracts. Potted plant studies with several species of native hydrophytes are being used to estimate the rates of compound uptake, translocation and in-planta transformation. Although phytoremediation may improve water quality, plant uptake has the potential to introduce new types of ecosystem exposure routes. The most pertinent plant-derived ecosystem exposure routes for trace organic contaminants in the Living Levee include accumulation in hydrophyte seeds and release from decomposing plant material. The benefits and sustainability of plant uptake as a removal mechanism in this system will be evaluated by considering both of these ecosystem exposure routes.

Plant uptake and transformation of pharmaceuticals in a novel treatment wetland configuration

2019 Spring National Meeting

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