Phytoremediation of Radionuclides: Cleaning Up Chernobyl

Dominic Aebi and Caitlin Henderson-TothMarch 31, 2011CHEE 591 Environmental Bioremediation

Chernobyl Explosion

April 26, 1986

Reactor #4 at Chernobyl

NPPmelts down and explodes

Cause: human error▪ Disabled cooling system during testing

Present Day Reactor 4

Radioactive Pollution Radioactive

material released into air, water, soil.

Exclusion Zone 30 km radius

around Chernobyl Units

1 Bq = 1 decay / s 1 Ci = 3.7 x 1010

Bq

The “Red Forest”

Dangerous Radionuclides

Iodine Cesium Strontium Barium

Degradation product of Cs

Plutonium Small

amounts

Radionuclide Risk Over Time

Why Remediate Radionuclides? Without Intervention

200 yrs to farm within 30 km radius 20,000 yrs to inhabit land within 1.5 km radius

Contaminates Water, Food, Soil Illegal farming in Exclusion Zone Effect on animal life Plant workers monitoring sarcophagus

Health Affects Iodine irradiates thyroid Strontium causes bone cancer Cesium mimics potassium Plutonium can cause lung, liver cancer Birth defects

Phytoremediation

Use of Plants, their associated microbes to accelerate remediation of organic and non-organic contaminants TCE, Hydrocarbons, PCBs

Cost Effective Option to use native/common plants

Sunflower Poplar Reed

Phytoremediation

Mechanisms

Phytodegradation Rhizosphere

Remediation PhytostabilizationPhytoextraction Phytovolotalization

EvapotranspirationFigure 2. The phytoremediation mechanisms. Pollutants may be stabilized or degraded within the rhizosphere, accumulated or degraded within the plant body, or transpired into the air .

Water Case Study

Water Case Study

Chernobyl Cooling Pond 23 km2

1 km from reactor, dilute contaminant Small Pond (75 m2)

9.2x106 Bq 137Cs 1.4x108 Bq 90Sr

Phytotech Inc. Researchers sampled water Over 1000 plants tested 600 L sample treated Conclude sunflowers rapidly/preferentially

remove 137Cs/90Sr

Water Case Study cont’d

Ex Situ 8 wk old plants Placed in 50 L water, for 48 hrs each 12 days - Removal 90% 137Cs, 80% 90Sr

In Situ 1.0 m2 raft 4-8 weeks floating 24 plants Anaylsis: 137Cs in roots, 90Sr in shoots

▪ Found that 55 kg dry weight Sunflower could remove all contaminants

▪ 60 Sunflowers employed for complete remediation

Water Case Study Critiques Bad

Information limited on remediated levels “Black Box” approach

▪ Limited understanding of mechanism▪ No information on uptake of other contaminants

Pilot study short▪ Questions as to seasonal variation in 137Cs, 90Sr uptake

Good Sunflowers grow naturally in the Ukraine, acclimated,

resist pestilence Successful remediation (2nd attempt) Valuable bioaccumulation coefficient obtained

Water Case Study Conclusion Bioaccumulation coefficients

determined Can calculate sunflower biomass

required to remediate other ponds After 4-8 wks

Sunflower accumulate 8x the 137Cs in roots as other plants

Shoots contain enough 90Sr to warrant quarrantine (2.5x106 Bq 90Sr /kg dry biomass)

Soil Case Study

Soil Case Study

Dushenkov et. al., Env. Sci. Tech., 1999.

Goals1. Find an additive to desorb 137Cs from

soil2. Find a plant which bioaccumulates 137Cs3. Test additive for bioaccumulation

stimulation4. Test nascent bioremediation

effectiveness in-situ

Additives for 137Cs Desorption

Phytoremediation Plant Screening

Additives in Phytoremediation

In-Situ

Using Indian Mustard Improvement measured

More than control?

Alternative Technologies

Encasement Prevents further contamination

Natural Attenuation Adsorption/Encasement with minerals Very long time period

Capping/Vitrification (ex situ) Useful for very high concentrations Expensive

Permeable Reactive Multibarriers Efficient for removal of radionuclides in

groundwater

Conclusions

Chernobyl phytoremediation of WATER shows excellent promise

Chernobyl phytoremediation of SOIL hampered by adsorption phenomena Has shown minimal but measureable

effectiveness Phytoremediation

Versatile, Inexpensive, In situ, Natural Apply lessons to present day Fukushima

NPP disaster.

Thanks!

Any questions?