FATE AND TRANSPORT OF PERCHLORATE IN SOILS OF THE LOWER COLORADO REGION OF ARIZONA

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: COMPLETE
• Funding Source: HATCH
• Reporting Frequency: Annual
• Accession No.: 0203838
• Project Start Date: Jul 1, 2005
• Project End Date: Sep 30, 2009
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UNIVERSITY OF ARIZONA
888 N EUCLID AVE
TUCSON,AZ 85719-4824

Performing Department
SOIL & ENVIRONMENTAL SCI

Non Technical Summary
The Colorado River is contaminated with low levels of perchlorate. This contamination is primarily wastes from missile propulsion systems and aerospace accelerant systems present in the Las Vegas wash. There is concern that food and feed crops irrigated with this water may bioaccumulate perchlorate. Perchlorate is linked to thyroid dysfunction and considered a health threat to humans in excessive amounts. It is not known how long perchlorate laden irrigation water has been applied to agricultural land in the region. Furthermore, we have no understanding of chemical, physical, and biological processes affecting the transformations and distribution of perchlorate. This information is needed for understanding the scope and magnitude of the problem and devising effective remediation efforts.

Animal Health Component

50%

Research Effort Categories

Basic

50%

Applied

50%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
133	0110	1000	10%
133	0110	2000	10%
133	0110	2010	20%
133	0210	1000	10%
133	0210	2000	10%
133	0210	2010	10%
133	0310	1000	10%
133	0310	2000	10%
133	0310	2010	10%

Knowledge Area
133 - Pollution Prevention and Mitigation;

Subject Of Investigation
0310 - River basins; 0110 - Soil; 0210 - Water resources;

Field Of Science
2010 - Physics; 1000 - Biochemistry and biophysics; 2000 - Chemistry;

Keywords

fate

transport

perchlorates

soils

soil contamination

soil movement

river basins

arizona

pollution control

soil pollution

water pollution

soil mineralization

food

forage

food safety

feed safety

feed contamination

food contamination

irrigation water

Goals / Objectives
The objectives of this project are to evaluate biotic and abiotic factors influencing the transport, transformation, and redistribution of perchlorate in the lower Colorado River region.

Project Methods
One objective will be to determine the mineralization rates of perchlorate enriched residues added to soils. The soils will be sieved to pass a 2 mm sieve and then amended with perchlorate enriched plant material and packed into 5 cm PVC tubes at the natural bulk density upon a layer of acid washed sand that rests on a nylon screen. The columns will then be placed in 1-liter jars fitted with gas sampling values to facilitate the measurement of CO2 evolved during flushing of flasks with CO2-free air with an infrared gas analyzer and incubated at 80% field capacity (-34 kPa) and 22 oC for up to 12 weeks. This will allow the columns to be removed from the incubation jar and leached with water at predetermined times. The leached solution will be processed for perchlorate concentrations. Another objective is to evaluate potential for biochemical reduction of perchlorate in soils. The soils will be incubated under a range of redox conditions by manipulating the O2 levels in the atmosphere above the soil. Treatments will also include NO3 (100 ug N g-1 soil) additions to determine the impact of NO3 as an electron acceptor on perchlorate reduction. The columns will then be placed in 1 liter jars fitted with gas sampling values to facilitate the measurement of CO2 evolved and O2 concentrations during flushing of flasks with CO2 and O2 free air with an infrared gas analyzer equipped with an O2 meter to facilitate incubation with the prescribed O2 levels for 24 weeks at 80% field capacity (-34 kPa) and 22 oC. This will allow the columns to be removed from the incubation jar and leached with water at a predetermined time. The solution will be processed for perchlorate concentrations. A third objective is to determine perchlorate transport under field conditions. At each location 24 basins 4 m2 in size will be constructed. During irrigation, water depth profiles (infiltration) will be monitored using pressure transducers installed at the soil surface. For the first evaluations, all basins will be irrigated with 15 cm of Colorado River water with perchlorate spiked to a final concentration 20 ug L-1. After drainage and some drying we will collect soil samples from three basins at random. The remaining 21 basins will again be irrigated with 15 cm of perchlorate spiked Colorado River water and three will be sampled at random. This process will be repeated through two more irrigation cycles, for a total of four irrigations, with the perchlorate spiked river water. For the second evaluation, we will use synthetic Colorado River Water free of perchlorate. We will add 15 cm of this perchlorate free synthetic Colorado River water to the 12 remaining basins at each of the three locations. We will sample three basins after each irrigation event for four events as described previously. Perchlorate in all water samples and soil extracts will be determined. These data will be used to calibrate and validate an appropriate model to predict perchlorate transport under a wide range of conditions.

Progress 07/01/05 to 09/30/09

Outputs
OUTPUTS: Over 300,000 hectares of agricultural land are irrigated with Colorado River water which is contaminated with low levels of perchlorate. Trace level of perchlorate have been found in food and forage crops produced in the lower Colorado River region. The objective of this project was to develop models aimed at gaining an understanding of the fate and transport of perchlorate in agricultural fields and evaluate, by simulation, alternative management strategies for reducing potential perchlorate exposure in food produced in these fields. Batch sorption studies with selected soils of the lower Colorado River region showed distribution coefficients (Kd values) were not significantly different from zero and perchlorate could be modeled as an unreactive chemical. A one dimensional zero-inertia model is the hydrodynamic basis for the surface model. A numerical solution of the area averaged advection-dispersion equation, based on the split operator approach, forms the solute transfer component of the coupled surface model. This combined surface model was further coupled to an existing subsurface model (Hydrus 1D) using a driver program to effect internal iterative coupling. The Hydrus model solves a mixed form of the Richards equation to describe water flow and a 1D advection-dispersion equation to describe solute transport in porous medium. The models were calibrated using field-scale irrigation events with bromide, and subsequently validated using independent data sets. PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Growers, regulators, and general public. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
A comparison of model predicted and field observed data show good agreement. Based on these observations and those of other experiments, we conclude that as the perchlorate loads to the Colorado River are reduced, the agricultural soils in the region will be mitigated concurrently, and human exposure of perchlorate through food produced on these soils will decline.

Publications

• No publications reported this period

Progress 01/01/08 to 12/31/08

Outputs
OUTPUTS: Over 300,000 hectares of agricultural land are irrigated with Colorado River water which is contaminated with low levels of perchlorate. Trace level of perchlorate have been found in food and forage crops produced in the lower Colorado River region. The objective of this project was to develop models aimed at gaining an understanding of the fate and transport of perchlorate in agricultural fields and evaluate, by simulation, alternative management strategies for reducing potential perchlorate exposure in food produced in these fields. Batch sorption studies with selected soils of the lower Colorado River region showed distribution coefficients (Kd values) were not significantly different from zero and perchlorate could be modeled as an unreactive chemical. A one dimensional zero-inertia model is the hydrodynamic basis for the surface model. A numerical solution of the area averaged advection-dispersion equation, based on the split operator approach, forms the solute transfer component of the coupled surface model. This combined surface model was further coupled to an existing subsurface model (Hydrus 1D) using a driver program to effect internal iterative coupling. The models were calibrated using field-scale irrigation events with bromide, and subsequently validated using independent data sets. A comparison of model predicted and field observed data show good agreement for basin irrigation events. More recently we have developed simplified models that simulate transport in furrow irrigation scenarios. PARTICIPANTS: D. Zerihun, Assistant Research Scientist, Dept. of Soil, Water, and Environmental Sciences, University of Arizona, Tucson, AZ TARGET AUDIENCES: Growers, regulators, and water managers. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
Based on model prediction, we conclude that as the perchlorate loads to the Colorado River are reduced, the agricultural soils in the region will be mitigated concurrently, and human exposure of perchlorate through food produced on these soils will decline.

Publications

• No publications reported this period

Progress 01/01/07 to 12/31/07

Outputs
OUTPUTS: Over 300,000 hectares of agricultural land are irrigated with Colorado River water which is contaminated with low levels of perchlorate. Trace level of perchlorate have been found in food and forage crops produced in the lower Colorado River region. The objective of this project was to develop models aimed at gaining an understanding of the fate and transport of perchlorate in agricultural fields and evaluate, by simulation, alternative management strategies for reducing potential perchlorate exposure in food produced in these fields. Batch sorption studies with selected soils of the lower Colorado River region showed distribution coefficients (Kd values) were not significantly different from zero and perchlorate could be modeled as an unreactive chemical. A one dimensional zero-inertia model is the hydrodynamic basis for the surface model. A numerical solution of the area averaged advection-dispersion equation, based on the split operator approach, forms the solute transfer component of the coupled surface model. This combined surface model was further coupled to an existing subsurface model (Hydrus 1D) using a driver program to effect internal iterative coupling. The models were calibrated using field-scale irrigation events with bromide, and subsequently validated using independent data sets. A comparison of model predicted and field observed data show good agreement. The use of these coupled models to predict perchlorate concentrations in the crop rooting zone under differing scenarios are on-going. PARTICIPANTS: D. Zerihun, Assistant Research Scientist, Dept. of Soil, Water, and Environmental Sciences, University of Arizona, Tucson, AZ TARGET AUDIENCES: Growers, regulators, and water managers.

Impacts
A coupled model suitable for perchlorate transport in agricultural fields has been developed and calibrated. Evaluations are on-going.

Publications

• No publications reported this period

Progress 01/01/06 to 12/31/06

Outputs
Over 300,000 hectares of agricultural land are irrigated with Colorado River water which is contaminated with low levels of perchlorate. Trace level of perchlorate have been found in food and forage crops produced in the lower Colorado River region. The objective of this project was to develop models aimed at gaining an understanding of the fate and transport of perchlorate in agricultural fields and evaluate, by simulation, alternative management strategies for reducing potential perchlorate exposure in food produced in these fields. Batch sorption studies with selected soils of the lower Colorado River region showed distribution coefficients (Kd values) were not significantly different from zero and perchlorate could be modeled as an unreactive chemical. A one dimensional zero-inertia model is the hydrodynamic basis for the surface model. A numerical solution of the area averaged advection-dispersion equation, based on the split operator approach, forms the solute transfer component of the coupled surface model. This combined surface model was further coupled to an existing subsurface model (Hydrus 1D) using a driver program to effect internal iterative coupling. The models were calibrated using field-scale irrigation events with bromide, and subsequently validated using independent data sets. A comparison of model predicted and field observed data show good agreement. The use of these coupled models to predict perchlorate concentrations in the crop rooting zone under differing scenarios is underway.

Impacts
Ultimately we hope to gain an understanding of transport and fate of perchlorate applied to agricultural land with irrigation water.

Publications

• No publications reported this period

Progress 01/01/05 to 12/31/05

Outputs
Over 300,000 hectares of agricultural land are irrigated with Colorado River water which is contaminated with low levels of perchlorate. Trace level of perchlorate have been found in food and forage crops produced in the lower Colorado River region. The objective of this project was to develop models aimed at gaining an understanding of the fate and transport of perchlorate in agricultural fields and evaluate, by simulation, alternative management strategies for reducing potential perchlorate exposure in food produced in these fields. Batch sorption studies with selected soils of the lower Colorado River region showed distribution coefficients (Kd values) were not significantly different from zero and perchlorate could be modeled as an unreactive chemical. Work to calibrate coupled transport models is in progress.

Impacts
Ultimately we hope to gain an understanding of transport and fate of perchlorate applied to agricultural land with irrigation water.

Publications

• No publications reported this period