Tacoma Smelter Plume - Chinese Brake Ferns
Phytoremediation Study
December 2005 Update - Further Details

Spring 2005, Ecology planted One hundred Chinese Brake Ferns (Pteris vittata) in each test plot in April and May (Vashon-Maury Island plots) and June (Point Defiance plots) in fenced, covered enclosures with warning signs. The following is further detail of the first year’s results.

Arsenic uptake by the Chinese Brake Fern

The young ferns planted in April through June this year contained less than 1 part per million (ppm) arsenic in their fronds at the time of planting. At season’s end, the arsenic concentration in the fronds ranged from 828 to 16,000 ppm (dry weight). Arsenic concentrations in the fronds for each plot are shown in the pale green column in the summary table below.

Some factors affecting the rate of arsenic uptake are understood; certainly others are not. For example, we do not know why the fronds at the Point Defiance maintenance facility plot (PD 1) had almost ten times as much arsenic as any other plot (even though the plot was planted in June). We do know that the ferns are taking up arsenic from the soil.

Arsenic reduction in the soil

Soil samples were collected prior to planting the ferns to determine baseline concentrations for arsenic, lead, and cadmium. Soil samples were collected again in October during frond harvest. The soil concentrations are displayed in the tan columns in the summary table.

In some plots, arsenic concentrations appear to have increased. However, this is likely due to the high variability of arsenic in soil as shown in our past Tacoma Smelter Plume studies. This variability makes determining soil removal rates difficult, especially over only one year and two sample sets (baseline and harvest in 2005). Mass balance calculations indicate a slight reduction, though less than predicted. We cannot point to a definable reduction in soil arsenic concentration in the test plots this year.

Waste disposal of harvested ferns

When the arsenic-containing fronds are harvested, they must be disposed of properly to avoid simply moving the contamination to another place where they could expose people, animals, or other plants to harmful levels of arsenic. Ecology tested the harvested fronds using a laboratory protocol called the Toxicity Characteristic Leaching Procedure (TCLP). This test method is required under the state’s Dangerous Waste rules to determine if a waste is dangerous. Dangerous waste must be disposed of in special landfills for dangerous waste, rather than solid waste landfills that take our household garbage.

The results for all fronds tested show that they are dangerous waste. A waste is a dangerous waste if TCLP arsenic results are more than 5 mg/l (milligrams per liter) in the leachate. The TCLP results ranged from 5.5 to 132 mg/L, and are shown in the summary table. The harvested fronds from this year’s pilot test were shipped to a hazardous waste landfill. Because of the arsenic content, it’s very important that the fronds not be composted (contaminating a much larger volume of compost that will end up on someone’s yard) or burned (putting extremely poisonous arsine gas into the air).

Growing conditions

Dockton Park 2 (VIDP2) received the least water of any plot, because water had to be hauled to it. The fronds in this plot showed a significantly lower arsenic concentration than other plots (828 mg/kg), and the lowest frond growth (1.2 lb or 0.544 kg). This plot was also well shaded. The other forested plots (Dockton Park 1 and Vashon Island School District 3) showed similar low plant mass.

In contrast, the plot near Chautauqua Elementary School (Kindergarten Play Area, VISD1) produced 18.6 lbs (8.44 kg) of fronds that had an average arsenic concentration of 1732 mg/kg, or more than twice the concentration of Dockton Park 2. This plot received 2/3 of a day of full sun, was watered moderately heavily twice per week, and was initially planted with more mature plants.

These observations suggest that in the western Washington climate, significant supplemental watering, in combination with ½ to 2/3 day of full sun, provide optimal growing conditions for the ferns.

What’s next?

Survival:

The next critical part of the study is to see if the ferns will survive the winter here. Chinese Brake Ferns are reportedly not able to survive soil temperatures below 20 degrees Fahrenheit. All plots were straw-mulched to a depth of about four inches to provide some additional frost protection.

Invasiveness:

Only ferns in VISD1 formed mature spores. Two fronds with mature spores were left standing in the plot, and we will look very carefully to see if any young fern plants form in that plot or nearby.

This next year we will see how well the ferns do when started from established rhizomes compared to new plants. We will determine how many survive the winter. If the plants survived the winter, we will continue care for the plants (watering and weeding), and sample the soil every 6 months, and sample the fronds every 3 months.

Phytoremediation Pilot Study Summary Data Table

	Tissue			Soil
		Total Conc.	TCLP Conc.	Metal	Baseline		October 2005
Plot	Metal	Total Conc.	TCLP Conc.	Metal	Conc. S	Conc. D	Conc. S	Conc. D
VISD 1	As	1732.5	13.15	As	25.2	N/A	36	31.3
	Cd	0.34	0.001	Cd	NS	NS	0.4	0.6
	Pb	2.15	0.001	Pb	NS	NS	89.3	72.8
VISD 2	As	983.2	8.44	As	37.3	31	40.3	27.4
	Cd	0.34	0.001	Cd	1.235	0.874	0.2	0.2
	Pb	2.63	0.004	Pb	129.3	81.3	104.5	72.2
VISD 3	As	1846.5	12.5	As	40.5	9.6	37.9	10.9
	Cd	0.4	0.001	Cd	0.38	0.1	0.3	0.3
	Pb	8.02	0.001	Pb	57.5	12.5	61.4	16.5
VIDP 1	As	1710	12.3	As	46.5	29.5	113.4	91.4
	Cd	0.339	0.001	Cd	NS	NS	2.4	1.2
	Pb	10.05	0.013	Pb	109.2	67.9	281.5	146
VIDP 2	As	828.5	5.5	As	80.1	38	80.1	38
	Cd	0.142	0.0001	Cd	NS	NS	0.3	ND
	Pb	9.17	0.004	Pb	173.3	74.3	117.6	53.9
PD 1	As	16000	132.5	As	158.25	153.25	147.5	117.5
	Cd	.03ND	.003ND	Cd	3.13	2.78	1.78	1.48
	Pb	.2ND	0.02ND	Pb	213	196	182.5	162.5
PD 2	As	6975	43.8	As	80.13	38.03	89	20.3
	Cd	.01ND	.001ND	Cd	2.15	0.4	1.24	0.49
	Pb	.2ND	0.02ND	Pb	151.6	34	135	21.8

All concentrations are in parts per million (ppm).

Numbers in RED indicate values that are above regulatory cleanup or waste designation values.

Metals: As = arsenic Cd = cadmium Pb = lead

S = shallow soil samples (0-6 inches) D = Deep soil samples (6-12 inches)
NS = not sampled ND = not detected
N/A = not applicable

Test Plots:
VISD1: Vashon Island School District 1, located just north of the Kindergarten Play Area adjacent to Chautauqua Elementary School.

VISD2: Vashon Island School District 2, located in the southeast corner of the School District/High School Horticultural Garden, near the old district administration building.

VISD3: Vashon Island School District 3, located about 300 yards east of the Chautauqua Elementary School building near the walking path in the woods.

VIDP1: Vashon Island Dockton Park 1, located about 75 yards east and slightly north of the shower/restroom building at Dockton Park, Maury Island, this plot is visible from the path up the hill from the picnic area just before reaching Dockton Road.

VIDP2: Vashon Island Dockton Park 2, located just off the horse/walking trail about 75 yards south of the parking area south of Dockton Road, and visible from the path.

PD 1: Point Defiance 1, located near the north edge of the Metro Parks maintenance facilities on the east side of Point Defiance Park, also just east of the go-cart track.

PD 2: Point Defiance 2 is located near the west end of Never Never Land, just off the east edge of the parking lot.

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Tacoma Smelter Plume - Chinese Brake Ferns Phytoremediation Study December 2005 Update - Further Details