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PERCHLORATE UPTAKE AND TRANSFORMATION IN AQUATIC PLANTS
Citation:
Susarla, S., S T. Bacchus, AND S C. McCutcheon. PERCHLORATE UPTAKE AND TRANSFORMATION IN AQUATIC PLANTS. Presented at 15th Annual International Conference on Contaminated Sediments, Soils and Water, Amherst, MA, October 12-14, 1999.
Description:
Ammonium Perchlorate (AP) is produced on a large scale by the chemical industry, for a wide range of applications for example, as a strong oxidizing agent in solid rocket fuel. AP must be washed out of the inventory periodically due to its limited shelf-life,and replaced with a fresh supply. Contamination of groundwater has occurred as the result of these practices. The problem was also compounded by disposal practices during the 1950s through the 1970s, prior to expanded knowledge of the impacts of fuels on ground water and soils. Wastewater generated by industrial use can have AP in the concentration range of grams per liter levels. The large solid rocket motor disposal inventory alone has 55 million pounds of propellant ready for treatment. Over the next 8-10 years this amount is expected to increase to 164 million pounds, which will be targeted for safe disposal. Perchlorate currently is not regulated under the Safe Drinking Water Act, although the California Department of Health Services has established an action level for Perchlorate in drinking water of 18 micrograms per liter. The primary human health concern related to Perchlorate is that it can interfere with the thyroid gland's ability to utilize iodine to produce thyroid hormones, required for normal body metabolism, as well as growth and development. ne majority of data available regarding impacts of Perchlorate on humans is from clinical reports of patients treated with potassium Perchlorate for hyperthyroidism resulting from an autoimmune condition known as graves' disease. Iodine deficiencies in pregnant women are detrimental to fetal development. Interference with the normal function of the thyroid gland, suggests that Perchlorate is an endocrine disrupter. Phytoremediation is the use of plants to cleanse soil and water contaminated with organic or inorganic pollutants. Four vascular plant species were selected for evaluation in these initial experiments. The species of plants included waterweed (Elodea canadensis), parrot-feather (Myriophyllum aquaticum), white water-lily (Nymphaea odorata) and duck meat (Spirodela polyrhiza). Perchlorate was depleted from solution in the presence of parrot-feather and water-lily. Depletion was calculated as a first-order kinetics reaction, with k values (day-1) in sand treatments in the range of 0-0.09 for water-lily. Upper values for parrot-feather was 2. 1. Plant tissues (e.g., roots, stems, leaves) were analyzed for all treatments to identify Perchlorate and its metabolic products. The results showed that Perchlorate, or transformation metabolites (chlorate, chlorite, chloride) were observed in all tissue samples. Results suggested that significant influences on depletion of Perchlorate include: 1) plant species present, 2) concentration of Perchlorate, 3) substrate (sand versus aqueous treatments), 4) the presence or absence of nutrients, and 5) the presence of chloride ions. This study demonstrates that certain plant species withstand exposure to Perchlorate and are also capable of chemically altering a major portion of what is taken up by the plant. If these properties are shared by numerous plant species growing at waste sites, then vascular plants may have a much greater influence on the fate of Perchlorate than has ever been realized. Their potential importance in this regard is further emphasized by recognizing that vascular plants account for the majority of the biomass in terrestrial ecosystems. Thus the results of this study strongly suggest that plants play a major role in governing the fate of Perchlorate.