Accumulation of perchlorate in aquatic and terrestrial plants at a field scale

Previous laboratory-scale studies have documented perchlorate (ClO ₄^- uptake by different plant species, but less information is available at field scale, where ClO₄^- uptake may be affected by environmental conditions, such as distance to streams or shallow water tables, exposure duration, and species. This study examined uptake of ClO₄ in smartweed (Polygonum spp.) and watercress (Nasturtium spp.) as well as more than forty trees, including ash (Fraxinus greggii A. Gray), chinaberry (Melia azedarach L.), elm (Ulmus parvifolia Jacq.), willow (Salix nigra Marshall), mulberry [Broussonetia papyrifera (L.) Vent.], and hackberry (Celtis laevigata Willd.) from multiple streams surrounding a perchlorate-contaminated site. Results indicate a large potential for ClO ₄^- accumulation in aquatic and terrestrial plants, with ClO₄^- concentration in plant tissues approximately 100 times higher than that in bulk water. Perchlorate accumulation in leaves of terrestrial plants was also dependent on species, with hackberry, willow, and elm having a strong potential to accumulate ClO₄^-. Generally, trees located closer to the stream had a higher ClO₄ ^- accumulation than trees located farther away from the stream. Seasonal leaf sampling of terrestrial plants indicated that ClO₄ ^- accumulation also was affected by exposure duration, with highest accumulation observed in the late growing cycle, although leaf concentrations for a given tree were highly variable. Perchlorate may be re-released into the environment via leaching and rainfall as indicated by lower perchlorate concentrations in collected leaf litter. Information obtained from this study will be helpful to understand the fate of ClO₄^- in macrophytes and natural systems.