Citric Acid Enhanced Metal UptakeThree Plant Species Studied at Bioretention Field Site
Utah State University, Department of Civil and Environmental EngineeringM. Rycewicz-Borecki, Dr. R.R. Dupont, Prof. J.E. McLean
Outline• Quick Introduction
• Design Methodology
• Results and Discussion
• Conclusions
INTRODUCTION
Pollutants in Stormwater• Untreated Stormwater Runoff Detrimentally Affects
Downstream Water Bodies and Groundwater Recharge
• Planted Bioretention Systems Remove Significantly More Pollutants From Runoff than Unplanted Systems
Plant Uptake• Aboveground Plant Tissue Takes Up some Portion of Pollutants
and can be Harvested and Disposed of Off-Site (Uptake)
• Uptake can be Enhanced with the Use of Synthetic Chelators or Low Molecular Weight Organic Acids (i.e., Citric Acid)
Critical Needs• Design and Develop Inexpensive and Environmentally
Responsible Systems for Maximum Stormwater Pollutant Removal
• Maximize Metal Uptake to Decrease Soil Metal Accumulation and Prevent Hazardous Soil Levels
Research Objective• Evaluate potential for citric acid-enhanced metal uptake as a
stormwater management technique in bioretention
-Does Citric Acid: Increase Soluble Metals in Soil Pore Water?
Increase Leaching of Metals into Groundwater?
Enhance Plant Uptake?
-Identify Plant Species Influence on Uptake Potential
METHODS
Field-Site Design• Green Meadows Subdivision• Built with Logan City• Initially Planted Oct 2010
600
Sou
th
North
Cattail
Sunflower
Sedge
• Small-wing Sedge• Maximilian Sunflower • Broadleaf Cattail
Field Site
Field-Site Design
Vertical separators
Aug 2014 – Oct 2014
Control = 0Low =10 mmol/kgHigh = 50 mmol/kg
Field-Site Design
Citric Acid Applied (August Only) Irrigated
3” depth 6” depth
Suction Cup Samplers Installed
Field-Site Design+ 24 hours
Suction Cup Pore Water Samples
Soil and Pore Water
1.5”
4.5”
7.5”
3” Pore Water
6” Pore Water
Surface Soil
Field-Site Design5 days later
Suction Cup Pore Water Samplers
Above Ground and Root Tissue (3)
Soil and Pore Water
Above Ground Harvest (3 x 1sf)
Root Samples (auger, 3 x 1sf)
Field-Site Design• No Citric Acid Applied for October Sampling
• All Other Experimental Procedure Repeated
Soil and Pore Water
Above Ground and Root Tissue (3)
Same Suction Cup Location
RESULTS
Results – Laboratory Soil Investigation
• Soils analyzed for metal solubility with citric acid and HCl
pH + chelation:
AlAsCaCrCuZn
pH effect
*
*
chelation effect
*
*
Results – Field Study Citrate Recovery
• Linear Relationship in unplanted• At high dose, planted has lower citrate at 6 inch depth
Unplanted Treatment, Aug (24 hours after CA application)
Aug Citrate
3 inch6 inch3 inch6 inch
3 inch depth 6 inch depth
3 inch depth
6 inch depth
Speculation: • Microbes in plant root
environment enhance citric acid degradation
Results – pH
• No pH effect with citric acid addition• calcareous soil with high buffer capacity
• Only pH differences @ 6” depth Planted Treatment
• pH differences (at 3” and 6”) continue in October
pH influenced by root environment microbial activity, not Citric Acid
3 inch6 inch3 inch6 inch
* All CA levels
Results – Pore Water Metal Solubility (3 inch depth, Aug)
Planted:• Increasing trend (Seven metals)
Unplanted: • Increasing trend
(Four metals)• Lower concentrations
than planted
Citric acid increases microbial activity in root environment, and metal solubility
Planted Unplanted Planted Unplanted
Results – Groundwater Leaching Potential
• Aug Citrate Decreased with Depth; Completely Degraded in Oct
3 inch
6 inch3 inch6 inch
3 inch6 inch3 inch
6 inch
plan
ted
unpl
ante
d
• No Risk of Leaching Soluble Metals Under these Conditions
Also:
AlCaCuMgZn .
Results – Above Ground Biomass and Uptake
• Citric Acid Influence NOT Significant
Speculation:• Reducing Conditions in Calcareous Soil Solubilize
Carbonate Minerals (Meng, 2015)• Abundance of Ca cations out compete other metals
Results – Above Ground Biomass and Uptake
Iron Uptake (mg/m2)
August October
SedgeSunflowerCattail
Also Al, Cr, Cu, Pb
•Consistent Species Differences Found
August October
AG b
iom
ass (
g m
-2)
Biomass (g/m2)
Results – Sunflower Speculated Arsenic Toxicity
10 mmol/kg
50 mmol/kg
SedgeSunflowerCattail
Arsenic
August October
Above Ground
16th
SedgeSunflowerCattailUnplanted
SedgeSunflowerCattailUnplanted
3”
dept
h6”
de
pth
Pore Water (Aug 12th)
Conclusions• Soluble Metals in Soil Pore Water Increase with Citric Acid
Dose (Fe, Al, As, Ca, Cr, Cu, Mg).
• Citric Acid Application Does Not Pose a Threat to Groundwater Leaching.
• Citric Acid Does NOT Enhance Plant Uptake Potential Under these Conditions. Species Selection Does.
• Citric Acid is Speculated to Induce Arsenic Toxicity in Sunflower.
Engineering Significance• Citric Acid Application is Not Suggested as a Enhanced Uptake
Technique (Calcareous Soils with Low-Level Metal Concentrations)
• Plant and Harvest Small Wing Sedge (over Cattail and Sunflower) to Slow Soil Metal Accumulation, Optimize Metal Recovery, and Lengthen Bioretention Operating Life
Future Work• Expand Site Conditions
• Experiment earlier in the Growing Season• Increase Replications• Investigate Sunflower Arsenic Toxicity Further
• Calcareous and Acidic Soils• Soil Metal Concentrations (Low, Med, High)
THANK YOU!
Funded by: • Utah Mineral Lease Fund• EPA 2010 Source Reduction Assistant Grant Program
THANK YOU!Questions?