University of Washington School of Environmental and Forest Sciences Phytoremediation of Arsenic Contamination on Vashon-Maury Island Chelsie D. Johnson INTRODUCTION Arsenic (As) is a semi-metal element that exists in both organic and inorganic form. As is considered highly toxic to humans and wildlife and can cause acute and chronic illness . Common sources of As include contaminated drinking water, contaminated food, air particulates and contaminated soil. As is found in both organic and inorganic form and can naturally accumulate in the environment or be released by anthropogenic pollution from metal smelting, agricultural applications and combustion of fossil fuels (Blaurock-Busch E. 2013). For almost 100 years Vashon-Maury Island was exposed to inorganic As, cadmium and lead contamination released by the ASARCO copper smelter as a byproduct of production (Living With a Toxic Legacy). Prevailing winds carried the As-laced plumes north and northeast, impacting over 1,000 square miles of Puget Sound basin. Located downwind of the smelter, contamination concentrated on the southern tip of Vashon Island and the majority of Maury Island (Tacoma Smelter Plume Mainland King County Preliminary Study). Current methods for As remediation are limited and costly. Washington State requires As-contaminated soils to be cleaned up when contamination on residential property exceeds 20 ppm (Arsenic Facts). The Department of Ecology’s Yard Program on Vashon-Maury island currently offers free removal and replacement of soil for private homes with soil tests showing greater than 100 ppm of As, leaving a gap between State required clean up levels and the qualifying level for free yard clean up (Yards Sampling and Cleanup Program). This gap generates a need for a cost-effective, environmentally conscious solution for As contamination of residential, commercial and public lands. 0000 METHODS Salix Screening for Arsenic Tolerance Objective: to quickly screen Salix species for As tolerance in hydroponic solution to identify candidates for further study. • Screenings were conducted in hydroponic solution spiked with arsenate (AsV) o AsV was a single concentration of 500 uM (~37.5 ppm) o Solution was changed weekly. • Each experiment had six replicates. • Each experiment lasted four weeks. o Two weeks untreated (establishment of roots) o Two weeks treated • Tolerance was assessed using: o Change in [AsV] concentration in the solution, analyzed through ICP-OES. • Controls • Plants with no AsV (x3) • Solution with AsV, not plant (x1) • Species/ Clones screened: S365 99207-018 01X268-105 SX61 S. hookerania S. sessifolia Soil Sampling for Arsenic Contamination Objective: To collect and screen soil samples for elevated As contamination. The purpose of the experiment was to understand the level of contaminants, screen for associative metal pollution and identify sites for field trials. Samples were gathered from second growth, undeveloped land with relatively flat topography. Samples were collected in containers (zip-loc bags) labeled with date and plot number. Onsite • O-horizon was scraped away to expose mineral soil. • An approximately 6” deep hole was dug into the ground. • Soil temperature inside hole was measured using a temperature gun. • Plot number, GPS coordinates and soil temperature was recorded. • Approximately 500 grams of soil was collected from 0-6” depth. • Rocks and roots were removed. • A fresh plastic spoon was used to homogenize soil. • Samples were placed in cooler for transpiration. • Samples stored in refrigerator. Soil Analysis Soil analysis indicated the majority of the area sampled was below the state mandated clean-up threshold for As at 20 ppm. However, analysis performed separately by a private lab had higher results (see table 2: Soil Analysis Results, comparisons highlighted in red). Some possible explanations for the difference in results include the weather conditions at time of collection (soil samples were collected in March during rain, AMTest lab samples were collected in May in dry conditions), soil drying techniques (air dry vs. oven dry) as well as overall special equipment availability and experience conducting an acid digest to prep samples for ICP-OES analysis. Table 2: Soil Analysis Results In Lab Salix Screening Photos Map of Vashon Maury Island • Soil pH (method 9045D using pH meter with temperature compensation) was recorded. • Wet weight for approximately 10g of soil was recorded. • Samples were air dried. • Dried weight was recorded. • Acid digest to prepare for ICP-OES was conducted. RESULTS Salix Screening Salix screening results were inconclusive (see table 1: Salix hydroponic ICP-OES analysis results). Analysis of the treatment samples reflected higher than anticipated results. Further consideration brought to light an issue with the experiment design. Due to transpiration, As concentrated in the hydroponic solution resulting in the abnormally high readings. The starting solution contained approximately 37.5 ppm AsV. It was expected that AsV levels would decrease as plants accumulated AsV from solution. While the blank and control readings were in-line with expectations, the final solution results indicated ppm concentrations of 85 – 164 ppm AsV. Vashon Island Maury Island CONCLUSIONS Endophyte supported phytoremediation holds great potential for safely and effectively removing arsenic and associative metals. Utilizing native Salix species further ensures viability in the Puget Sound region. While the Salix screening experiment results were inconclusive, the assay provided data that can be utilized to develop improved protocols. To properly assess Salix accumulation of As in future screenings, the plant tissues itself should be analyzed to indicate accumulation in the plant tissue. Likewise, the results of the soil sample analysis reveals possible ways to improve sample preparation and execution of the acid digest, including oven drying and finer grinding of the soil sample. Analysis of the soil samples do indicate As contamination as expected, as well as associative metals including cadmium and lead. Further research is warranted to better understand the capabilities of endophyte supported phytoremediation of As contaminated soils on Vashon-Maury Island using Salix species. Table 1: Salix hydroponic ICP-OES analysis results Tacoma/ Ruston BIBLIOGRAPHY 1. Arsenic Facts. King County Public Health – Seattle & King County. http://www.kingcounty.gov/healthservices/health/ehs/toxic/ArsenicFacts.aspx. Accessed May 15, 2014. 2. Blaurock-Busch E. Aresenic (As) Exposure: Diagnosis and Treatment. Orginal Internist [serial online]. December 2013:20(4):174-178. Available from: Academic Search Complete, Ipswich, MA. Accessed May 16, 2014 3. Tacoma Smelter Plume Mainland King County Preliminary Study. Washington State Department of Ecology. Publication No. 02-09-031. https://fortress.wa.gov/ecy/publications/publications/0209031.pdf. Accessed May 18, 2014 4. Toxics Cleanup Program Living With a Toxic Legacy. Washington State Department of Ecology. (December 2006). http://www.ecy.wa.gov/programs/tcp/sites_brochure/tacoma_smelter/2011/tshp.htm. Accessed May 20, 2014. 5. Yards Sampling and Cleanup Program. Washington State Department of Ecology. Accessed http://www.ecy.wa.gov/programs/tcp/sites_brochure/tacoma_smelter/2011/yard. html. Accessed May 20, 2014. Images of S. sessifolia at experiment start, after 1 week and final week. ACKNOWLEDGEMENTS Special thanks to Rob Tournay and Dr. Sharon Doty for their mentorship and guidance.