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.