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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
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
Dangerous Radionuclides
Iodine Cesium Strontium Barium
Degradation product of Cs
Plutonium Small
amounts
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
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
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
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.