Progress 11/01/16 to 09/30/20
Outputs
Target Audience:Producers, natural resources managers, and community leaders in agricultural regions will rely on this knowledge to ensure that crops used to support their economy are not contaminated by these naturally-occurring elements. We have reached out to extension and natural resources personnel within the state, describing the scope of the project. We also informed researchers, faculty, and the general public through newsletters about the project's broad scope. We have discussed our findings and devised plans to mitigate the contaminant uptake issue with our collaborators in the University of Nebraska's extension and outreach centers. We have delivered science-based knowledge gained through the project in the form of Undergraduate course study (NRES320) during the spring semester through formal classroom instruction and experiential learning opportunities. Changes/Problems:Some problems related to COVID research restrictions were experienced andresolved during the last project period. What opportunities for training and professional development has the project provided?This project has provided training opportunities for a post-doctoral researcher, two graduate students, and three undergraduate students. Additionally, the postdoc was also charged to manage the project to the extent possible by coordinating various activities at the two research stations, communicating with research collaborators, and conducting sampling as needed. The postdoc also developed a research proposal, which was submitted to USDA AFRI program. The postdoc assembled a team for the proposal that included a new faculty member and soil chemist in the UNL Agronomy and Horticulture Department, another aspect of professional development. Postdoc also developed a method for simultaneous detection of arsenic and selenium species in IC-ICP-MS and have trained the graduate student to do these analyses periodically. How have the results been disseminated to communities of interest?The postdoc presented ongoing results in weekly research group meetings. The data generated has been discussed with the Panhandle and West Central Research and Extension Centers' collaborators, where field experiments were conducted. The postdoc presented data from the first year study at an annual University of Nebraska Agricultural Research Division meeting. The project Co-PI presented this data at annual W3045 Multi-state Hatch project meetings. Additional results of past four year experiments are currently being summarised for 4-5 journal articles. Two review articles and an article with results of the first greenhouse experiment has already been published in peer-reviewed journals. Results were also presented in the fall meeting of AGU, spring and fall meeting of ACS, and at 41st SETAC North America Meet by the postdoc and Co-PI. What do you plan to do during the next reporting period to accomplish the goals?N/A
Impacts
What was accomplished under these goals?
The two most important resources required for agriculture are soil and water, both of which contain elevated levels of natural "geogenic" contaminants such as arsenic, cadmium, chromium, selenium, uranium in many parts of the United States. Irrigation water with elevated levels of these contaminants can increase these contaminants' concentration in the surface soil. Further, edible plants and crops are known to accumulate trace contaminants. Mobilization and transfer of arsenic, uranium, and selenium in soil pore water or irrigation water to soils, food, and feed crops. The knowledge gained from this work improved our understanding of the fate of these geogenic contaminants in the environment, as well as their potential impacts on the health of humans and animals, supporting one of the key goals of the United States Department of Agriculture (USDA), which is to provide all Americans, access to a safe, nutritious and secure food supply. The study has helped devise remediation mechanisms that mimic natural soil iron minerals and seek alternative approaches to increasing food production without affecting food quality and safety. Producers, natural resources managers, and community leaders in agricultural regions will rely on this knowledge to help ensure that crops and livestock used to support their economy are unlikely to be affected by elevated levels of these trace elements. Field and greenhouse studies suggest that iron transformation in root zone-soil-pore water interface is critical for controlling arsenic, uranium, and selenium mobilization and bioavailability in irrigated soils. Iron transformation has previously been implicated with arsenic uptake in heavily irrigate rice crops under flooded conditions, but is not well understood, especially in intermittently irrigated soils for corn and beans production prevalent in the Midwest. Nanoscale transformation of iron and iron-bearing reactive minerals such as ferrihydrite is a prevailing knowledge gap that was in part addressed by this project. The addition of ferrihydrite nanomineral and occurrence of natural ferrihydrite seems to be effective in limiting uptake of trace contaminants by crops grown in the greenhouse under unsaturated and saturated conditions mimicking natural rhizosphere chemistry. 1) Major activities conducted: Field experiments were carried out at two sites located in central and western Nebraska. At the test plots at North Platte, NE, the effect of various water and fertilizer management practices on a single crop type (corn) was studied. In contrast, the plots at Scotts Bluff, NE evaluated a single water management practice over three crops (corn, soybean, and dry beans). Soil solution access tubes (SSAT) were installed in triplicate to collect root zone pore water under different crop types in both study sites, at three depths (15, 30, and 45 cm). Soil cores (45 cm depth) and plant samples were collected periodically throughout the harvest season to study the temporal variation of contaminants in each location's rhizosphere soil column. Four separate greenhouse experiments were conducted at the University of Nebraska East Campus greenhouse to follow the iron mineral transformation pathway under unsaturated and saturated soil moisture conditions. The experiment utilized a synthetic Fh nanomineral to understand Fh transformation and solubilization at the root zone-soil-pore water interface. 2) Data Collected: In the field experiments, 453 soil core, 137 pore water samples, and 144 plant tissue samples were collected. In the unsaturated system greenhouse experiment, 162 soil samples, 142 pore water leachate, and 100 samples were collected. This year's flooded rice greenhouse experiment had 90 water samples, 72 soil samples, and 78 plant tissues. Porewater was analyzed for reduced iron (II), nitrite, pH, and conductivity immediately after collection, while samples for dissolved organic carbon, iron, arsenic, selenium, uranium, nitrate, ammonia, major cations, and anions were analyzed in the laboratory. Soil conditions during the greenhouse experiment were monitored biweekly for pH, ORP, and conductivity. Periodic soil samples were characterized for nitrate, ammonia, dithionite extractable iron, As, Se, and U. In selected soil samples, x-ray photoelectron spectroscopy (XPS) were carried out to understand the oxidation state of iron. Plant tissue samples were analyzed to determine U, Se, and total As. Arsenic speciation in pore water was done in year 3 and 4 samples. 3) Discussion of results: Field Experiment: The pore water collected at the different study sites and under different crop conditions show higher concentrations of iron together with elevated arsenic, uranium, and selenium levels. Reactive iron mineral concentration of root zone soil followed an opposite trend to soil arsenic, selenium, and uranium concentrations. The reactive iron concentration in soils reached a peak in the early growth stage, suggesting a rise in the iron demand of crops. Uptake of these contaminants was observed in the crops with significant transport of these contaminants to the grains. A strong correlation of pore water iron with trace contaminants and a negative correlation of soil reactive iron mineral and soil trace contaminants confirms the definitive role of iron minerals transformation in semi-arid soil, controlling nutrient and non-essential contaminant's bioavailability. Transformation or dissolution of the iron mineral can effectively release these attenuated trace elements to soil pore water. Greenhouse Experiments: The greenhouse experiment under unsaturated conditions complemented the field observations. A higher concentration of iron in pore water was found along with arsenic, uranium, and selenium. These observations provided the mechanistic understanding that iron mineral reduction and subsequent dissolution can happen in unsaturated soil conditions, releasing trace contaminants for crop uptake. Adding natural iron nanomineral Fh to soil may limit the mobility of released contaminants by effectively binding with the added Fh mineral. The greenhouse experiment indicated significantly higher biomass in Fh amended soils and 2-3 times less trace contaminants in corn grains grown under unsaturated soil. Rice experiment of this year, under flooded conditions, also shows favorable results with half arsenic uptake compared to control, keeping arsenic levels in grains below the safe limit suggested by the FDA. 4) Key outcomes The project led to the understanding of the critical role iron plays in an intermittently irrigated agricultural setup such as pivot or sprinkler irrigation comprising more than half of the US's irrigated system. This mechanistic understanding of the root zone phenomenon led to devising a simple Fh amendment plan, which mimics the natural soil geochemistry to limit trace contaminant uptake and lower nutrient loss. This research supports commercial development of Fh as a soil amendment.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Malakar, A., Kaiser, M., Snow, D. D., Walia, H., Panda, B., & Ray, C. (2020). Ferrihydrite reduction increases arsenic and uranium bioavailability in unsaturated soil. Environmental Science & Technology, 54(21), 13839-13848.
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Malakar, A., Kanel, S. R., Ray, C., Snow, D. D., & Nadagouda, M. N. (2020). Nanomaterials in the environment, human exposure pathway, and health effects: A review. Science of The Total Environment, 143470.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Malakar, A., Ray, C., Snow, D.D., Rudnick, D., Maharjan, B., 2020 Natural iron dynamics in irrigated soils, SETAC SCICON2, SETAC North America 41st Annual Meeting, November 15-19, Virtual.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Malakar, A., Ray, C., Snow, D.D., Saluja, M., Cooper, J., Kaiser, M., Walia, H. and Roberts, T. L., 2020 Ferrihydrite soil amendment limit arsenic uptake in rice by promoting iron plaque formation, ACS Fall 2020 National Meeting & Expo, August 17-20, 2020, USA DOI: 10.1021/scimeetings.0c06723
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Progress 10/01/18 to 09/30/19
Outputs
Target Audience:Producers, natural resources managers, and community leaders in agricultural regions will rely on this knowledge to help insure that crops and livestock used to support their economy are not contaminated by these naturally-occurring elements. We have reached out to extension and natural resources personnel within the state describing the scope of the project. We also informed researchers, faculty, and general public through newsletters about the general scope of the project. We have discussed our findings and devised plans to mitigate the contaminant uptake issue with our collaborators in the extension and outreach centers of the University of Nebraska. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project has provided training opportunities for a post-doctoral researcher, one graduate student and one undergraduate student. Additionally, the postdoctoral researcher manages both the field and laboratory project to the extent possible by coordinating various activities at the two research stations, communicate with research collaborators, and conduct sampling as needed. The postdoctoral researcher developed a research proposal, which has been submitted to USDA AFRI program. The postdoc assembled a team for the proposal that included a new faculty member and soil chemist in the University of Nebraska Agronomy and Horticulture Department, which was another aspect of professional development. Postdoc also developed a method for simultaneous detection of arsenic and selenium species in IC-ICP-MS and have trained the graduate student to do these analysis periodically. Finally, the project also included training a Central City, NE highschool science student who presented her results at the Nebraska Junior Academy of Sciences. How have the results been disseminated to communities of interest?Ongoing results are presented and discussed in weekly research group meetings. The data generated has been discussed with the collaborators at the University of Nebraska Panhandle and West Central Research and Extension Centers, where field experiments are conducted. The postdoc presented data from the first year study at an annual University of Nebraska Agricultural Research Division meeting. The project Co-PI presented this data at an annual W3045 Multi-state Hatch project meeting at the University of Nevada, Reno. Results of last three year experiments are currently being summarized in 3 or 4 journal articles. A review article describing the current state of knowledge on irrigation water quality has already been published. Results will be presented in fall meeting of AGU and spring meeting of ACS. What do you plan to do during the next reporting period to accomplish the goals?Next year our greenhouse experiment will focus on iron induced mobilization of arsenic for a single crop type, rice over a longer growing period to enable harvest of grain but under flooded condition. As the present greenhouse study showed ferrihydrite limits arsenic uptake, we intend to evaluate uptake of arsenic in rice under continuously flooded conditions. Temporal variation of uptake will be closely monitored using repeated collection of soil, water, and plant tissues.
Impacts
What was accomplished under these goals?
There are rising pressures to increase agricultural production using increasingly stressed freshwater resources, with probable impacts to water and food quality. Two critical resources required for agriculture production are soil and water, both of which can contain elevated levels of natural "geogenic" contaminants such as arsenic, cadmium, chromium, selenium, and uranium. Irrigation water in many parts of United States is now reported to have elevated levels of geogenic contaminants and is likely to lead to increasing concentrations of these contaminants in the soils and crops on which they are grown. Edible plants and crops are already known to accumulate traces of these contaminants, though the processes which control bioaccumulation of geogenic contaminants in soils and irrigation waters is not well understood. In the present study, we observe a steady increase in contaminant levels in soil, likely due to existing levels of arsenic and uranium in irrigation water. Contaminant concentrations are directly correlated to concentrations in plant tissue including grains and legumes. This four-year study looks closely at mobilization and transfer of arsenic, uranium and selenium in soil pore water or irrigation water to soils, food and feed crops. The primary objectives of this research are to gain a better understanding of processes controlling uptake of uranium, selenium, and arsenic in different stages of plant development, and ultimately determine concentrations in harvested crops irrigated with surface and groundwater likely to contain elevated concentrations of these elements. The knowledge gained from this work will improve our understanding of bioaccumulation of these potentially toxic trace elements and impacts to human and animal health. This project supports a key goal of United States Department of Agriculture (USDA), which is to provide all Americans, access to a safe, nutritious and secure food supply. This study will help in devising remediation mechanisms and seeks alternative approaches to increasing food production without affecting food quality and safety. Producers, natural resources managers, and community leaders in agricultural regions will rely on this knowledge to help ensure that crops and livestock used to support their economy are not affected by elevated levels of these trace elements in food and water. Correlation with dissolved iron suggests that iron transformation is one of the key factors controlling arsenic, uranium, and selenium mobilization and bioavailability in irrigated soils. It is well known that the release of organic acids, or plant root exudates, likely leads to iron reduction and transformation in soils. While iron reduction and transformation has been shown to lead to arsenic uptake in irrigated rice under flooded soils, few studies have examined iron transformation and accumulation in other crops. The role of iron mineral transformation and bioaccumulation of trace elements is not well understood, especially in ephemerally irrigated soils such as those prevalent in corn and bean production of the Midwest. Knowledge of the nanoscale transformation of iron and iron-bearing reactive minerals such as ferrihydrite is clearly needed to fill a prevailing knowledge gap. In the current project year, our focus was to characterize iron mineral transformation and geogenic contaminant mobilization bioaccumulation. In addition, an iron-based nanomineral soil amendment was synthesized and showed promising results at controlling uptake in greenhouse experiments simulating actual field conditions.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2019
Citation:
Malakar, A., Snow, D.D. and Ray, C., 2019. Irrigation Water QualityA Contemporary Perspective. Water, 11(7), p.1482.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Malakar, A., Snow, D. D., Kaiser, M., Walia, H., Maharjan, B., Rudnick, D., Panda, B., Shields, J., Ray, C. 2019. Role of Ferrihydrite at the Root Zone in Uptake of Arsenic, Selenium and Uranium by Crops in Intermittent Irrigation System, CSIR-CSIO Seminar, 19 September 2019, Chandigarh, India.
- Type:
Other
Status:
Published
Year Published:
2019
Citation:
Keyes, L. 2019. The Effect of Well Water Content on Geogenic Contaminants in Garden Vegetables. Nebraska Junior Academy of Sciences. Central Regional Science Fair. Tuesday, March 12, Hastings, NE.
- Type:
Other
Status:
Published
Year Published:
2019
Citation:
Snow, D.D. 2019. Groundwater and vadose zone nitrate-association with geogenic contaminants. Nebraska Agri-Business Association & University of Nebraska Lincoln. Advanced Topics Soils School 2019, January 30-31, 2019.Grand Island, NE
- Type:
Book Chapters
Status:
Accepted
Year Published:
2020
Citation:
Malakar, A., and D.D. Snow, 2019. Nanoparticles as inorganic pollutant in water, In: Inorganic Pollutants in Water, Editors, 1st Edition: P. Devi, P. Singh, and S.K. Kansal. Elsevier Scientific, 440 p. ISBN: 9780128189658.
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Progress 10/01/17 to 09/30/18
Outputs
Target Audience:The target audience for this project includes individuals and communities in Nebraska. Science based findings will be delivered to them via one-to-one meetings, seminars, and news articles. Other audiences include Natural Resource Districts, commodity groups, and state agencies. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?This project has provided training opportunities for a post-doctoral researcher and two graduate students. Two undergraduate volunteers also worked closely with the postdoc in setting up the greenhouse experiment. Additionally, the post-doc is also charged to manage the project to the extent possible by coordinating various activities at the two research stations, communicate with research collaborators, and be able to conduct sampling as needed. The postdoc also developed a research proposal, which was submitted to USDA AFRI program. The postdoc assembled a team for the proposal that included a new faculty member and soil chemist in the UNL Agronomy and Horticulture Department, which was another aspect of professional development. A visiting doctoral student also helped the postdoc in sample collection from the field and greenhouse experiment. An secondary school student supervised by a local high school science teacher in central Nebraska, also actively took part in this project, and she ran uptake experiments using groundwater-irrigated garden vegetables to study plant uptake of As, Se and U. This data will be used for a Nebraska science fair competition. How have the results been disseminated to communities of interest?Ongoing results are presented by the postdoc in weekly research group meetings. The data generated has been discussed with the collaborators at the Panhandle and West Central Research and Extension Centers, where field experiments are conducted. The postdoc presented data from the first year study at an annual University of Nebraska Agricultural Research Division meeting. The project Co-PI presented this data at an annual W3045 Multi-state Hatch project meeting at the University of California-Riverside. Results of the first and second-year experiments are currently being analyzed for 1 or 2 journal articles. A review article describing the current state of knowledge on irrigation water quality is also underway. What do you plan to do during the next reporting period to accomplish the goals?Next year greenhouse experiments focus on iron and As, Se, U mobilization for a single crop type over a longer growing period to enable harvest of grain. Temporal variation of uptake will be closely monitored using repeated collection of plant tissues. Changes in extractable forms of iron, mainly ferrihydrite and its redox transformation will be studied, together with redox changes of arsenic, selenium and uranium. We propose to apply for beamtime at the Advanced Photon Source (APS) at Argonne National Laboratory, where we plan to study iron K-edge X-ray absorption spectrum, to understand the mineralization or transformation processes of iron in the greenhouse experiment. We also plan to repeat the field test plot experiments if it seems possible to increase our success with pore water samplers.
Impacts
What was accomplished under these goals?
Global increases in population have led to a significant pressure to increase agricultural production using increasingly stressed freshwater resources while at the same time producing food that is safe for human consumption. The two most important resources required for agriculture are soil and water, both of which can contain elevated levels of natural "geogenic" contaminants such as arsenic (As), cadmium (Cd), chromium (Cr), selenium (Se), and uranium (U) in many parts of United States. Edible plants and crops are known to accumulate trace element contaminants, esepcially in areas associated with high level of contaminants in soils and irrigation waters. This four-year study looks at mobilization and transfer of As, U and Se in soil or irrigation water to soils, food and feed crops. The primary objectives of this research are to gain a better understanding of root zone-soil-pore water interface with respect to the uptake of As, Se, and U in different stages of plant development, and ultimately determine concentrations in harvested crops irrigated with surface and ground water likely to contain elevated concentrations of these elements. Knowledge gained from this work will greatly improve our understanding of the fate of these chemicals in the environment as well as their potential impacts to the health of humans and animals, supporting one of the key goals of United States Department of Agriculture (USDA), which is toprovide all Americans access to a safe, nutritious and secure food supply. During the first year of this project, correlations with dissolved iron concentrations suggested that iron transformation in soil pore water is likely one of the key factors controlling As, Se and U mobilization and bioavailability in irrigated soils. While it is well known that release of organic acids, or plant root exudates, likely leads to dissolution of iron in a variety of crops, iron transformation has only recently been implicated with arsenic uptake in heavily irrigated rice crops. The role of soil iron mineral transformation in mobilization and bioaccumulation of trace elements is not well understood, especially in ephemerally irrigated soils for corn and bean production. In the current project year, our focus was to characterize iron-related factors initiating contaminant mobilization at root zone. Field Experiment: Field experiments were carried out at two sites and were kept identical to the last year's experiment. Field sites were located in central and western Nebraska. The test plots near North Platte, NE continued our study the effect of various water and fertilizer management practices on a single crop type (corn), while and the plots at Scotts Bluff, NE evaluated a single water management practice over three crops (corn, soybean and dry beans). Soil solution access tubes (SSAT) were installed in triplicate to collect root zone pore water at two depths. Soil cores and plant tissue samples were collected through out the harvest season to study the temporal variation of contaminants at each location. Greenhouse experiment: At the same time, a controlled experiment was conducted at a University of Nebraska greenhouse to test a hypothesis developed using the previous year field experiments. Our hypothesis is that trasformation and solubilization of naturally-occurring ferrihydrite controls As, Se and U mobilization and uptake by plants in emphemerally-irrigatied soils. Crops irrigated in the greenhouse simulation included soybean, dry beans and corn. Leachate samples from the pots of the plants were collected at 20-day intervals shortly after irrigation water as applied through the 60th day of experiment. Irrigation conditions were maintained as close as possible to field conditions, generally below field capacity. Plants were grown in artificial soil made from a mixture of sand, kaolinite and synthesized ferrihydrite fortified with arsenic, selenium and uranium. Soil composition was characterized before and after the growing period. Plant tissue samples were collected at the end of the 60 days experiment. In total 123 soil core samples, 29 porewater samples and 63 plant tissue samples were collected and analyzed from the two test plots in this year field experiment. In the greenhouse experiment, in total of 54 leachate or porewater samples, 36 soil samples and 35 plant tissue sample were collected. Samples from soil cores were analyzed for nitrate, ammonia and arsenic (As), selenium (Se), and uranium (U). Leachate and porewater were analyzed for reduce iron (II), pH, and conductivity immediately after collection, while samples for dissolved organic carbon, iron, arsenic, selenium, uranium, nitrate, ammonia, major anions and cations were analyzed in the laboratory. Soil conditions during the greenhouse experiment were monitored weekly for pH and conductivity. Initial and final artificial soil were characterized for nitrate, ammonia, iron, As, Se, and U. In selected soil samples, x-ray photoelectron spectroscopy (XPS) was used to quantify the oxidation state of iron. Leachate data of greenhouse were modeled thermodynamically using PHREEQC to characterize dissolved complexes and mineral species. Plant tissue samples were analyzed to determine As, Se and U uptake. Results Concentration trends in SSATs were similar to last year, with dissolved iron correlating with arsenic, selenium and uranium. Fewer pore water samples we obtained from the SSATs. Soil core profiles indicated significant differences in the concentrations of iron, As, Se and U at both the locations during the irrigation season. Chemical analysis of plant tissues from the field experiment also suggest a seasonal variation in uptake. As in the previous year, highest uptake rates were found in soybeans. Seasonal changes in dissolved pore water iron, together with differences in labile soil iron concentrations, likely determined As, Se, and U mobility in ephemerally irrigated soils. The greenhouse experiment was designed to simulate ferrihydrite transformation under ephemerally irrigated conditions, and demonstrate its potential for affecting mobility of As, Se, and U. Carefully prepared synthetic soil mix, using a lab-synthesized ferrihydrite fortified with known concentrations of arsenic, selenium and uranium provided controlled plant soil conditions for monitoring transformation. Reduced iron (II), indicating ferrihydrite dissolution, was consistently measured in the leachate, and correlated with As, Se and U concentrations. Thermodynamic modeling provided additional evidence for speciation and formation of iron (II) in the leachate solution, and matched closely to the experimental values. Characterization of soil samples demonstrated a change in the overall oxidation state of iron. Plant uptake was also measured in greenhouse samples, and shows a similar trend to the field samples with Se uptake highest followed by As and U. Mobility and uptake of these trace elements in soil pore water is likely dependent on the redox-driven iron transformation. Interestingly, the total amount of uptake in greenhouse crops is much higher compared to field samples.
Publications
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Progress 11/01/16 to 09/30/17
Outputs
Target Audience:Producers, natural resources managers, and community leaders in agricultural regions will rely on this knowledge to help insure that crops and livestock used to support their economy are not contaminated by these naturally-occurring elements. We reached out to extension and natural resources personnel within the state describing the scope of the project. We also informed researchers, faculty, and general public through newsletters about the general scope of the project. Particulalrly, we interacted with Nebraska's 23 Natural Resource District (NRD) managers about the scope of the project once it was funded. There was interest from managers where we were planning to do the study (North Platte NRD and Twin Platte NRD). The Bulletin of the Nebraska Water Center reaches to about 2800 subscribers and many of them are producers, land managers, regulatory agency personnel, and acdemic institution faculty and staff. Changes/Problems:There was a delayed start on the project due to staffing issues. However, there has been no change in the objectives and methods. What opportunities for training and professional development has the project provided?This project has provided training opportunities for a post-doctoral researcher and an undergraduate student. Additionally, the post-doc is also charged to manage the project to the extent possible by coordinating various activities at the two research stations, communicate with research collaborators, and be able conduct sampling as needed. A visiting doctoral student also helped the postdoc in sample collection from the field sites. How have the results been disseminated to communities of interest?The results are preliminary as the work only began mid-way into the first summer season. However, the postdoc has presented the results obtained so far in the annual symposium of the Nebraska Water Center in the form of a poster as well as in our weekly research group meetings. What do you plan to do during the next reporting period to accomplish the goals?Next season, we plan to collect samples during the entire growing season to confirm and replicate trends observed, and collect plant samples at different growth stages throughout the year. Analysis of field samples will be coupled with greenhouse experiments where we can control the irrigation and nutrient input parameters, which would give a better understanding on the mobilization and uptake pathways of these contaminants in plants.
Impacts
What was accomplished under these goals?
Project Impact: Irrigation water quality is an often overlooked, but critically important research area in food production systems worldwide. Historically, research on irrigation water quality has focused on reduced production and salinization of soils, however there are more subtle changes that can affect crop quality, value, and even human health. While our growing population has fueled demands to increase agricultural production, the occurrence and effects of chemicals in irrigation water is slowly emerging and with it the need to mitigate impact. For example, the occurrence and effects of arsenic in irrigation water are becoming particularly relevant in food crops grown in regions such as the Bengal Delta of Bangladesh. Mobilization of naturally occurring contaminants in these regions leads to uptake by crops with resulting implications to food safety. Producers growing crops regions susceptible to contamination discover that the crops value is tainted. If not discovered in time, the crops contaminated with these elements can be consumed leading to exposure and potentially toxic effects to animals and humans. This work will better characterize the chemistry and mobility of naturally-occurring contaminants in soils and irrigation water to help prevent this from occurring. Producers, natural resources managers, and community leaders in agricultural regions will rely on this knowledge to help insure that crops and livestock used to support their economy are not contaminated by these naturally-occurring elements. It will accomplish this work using new analytical tools to measure these contaminants in water and soils used to grow a variety of crops under realistic and controlled conditions. Major activities completed, and experiments conducted thus far, include collection of pore water samples, soil cores and plant tissue samples from irrigated crops (corn, soybeans and dry beans) grown in western Nebraska. The majority of these samples have been analyzed for trace elements, water chemistry and other variables that can affect element mobility. Preliminary results suggest that there are significant differences in mobility between crop type. Uranium concentrations, in particular, are significantly different between crops and may be related to differences in root zone chemistry. Uptake will be quantified in all plant tissue samples using a newly acquired instrumentation at the University of Nebraska and provide evidence for the contamination risk between crop types. Methods for measuring different forms of these elements in water and plant tissue will be developed in the coming year and be quite helpful in estimating any risk to human health. Soil cores were collected to a depth of 36 inches in most locations, and also in control locations where no irrigation activity was carried out, for direct comparison to suction lysimeters sampler installed at 2 different depths. Changes in soil and pore water chemistry a compared at each location and between treatment. Pore water was collected after every other irrigation cycle, which was once after two weeks and was coupled with monthly soil core collection but was unavailable during several of the sampling events. At the end of irrigation season (i.e. just prior to harvest) whole plant samples were collected in each of the locations will be processed and analyzed this winter. Root zone water and irrigation water samples were analyzed for the concentration of uranium, arsenic, selenium, iron (a major factor in controlling arsenic chemistry), as well as nitrate, ammonia and total organic carbon. Soil cores were processed and were analyzed for nitrate, ammonia, uranium, arsenic and selenium. Preliminary results suggest that crop type and root zone chemistry effects mobility and very likely uptake of these contaminants. For example, mobilization of uranium concentrations were significantly elevated in soybeans as compared to other crops, and associated with higher pore water iron and nitrate. This may indicate that nitrate and iron transformation affect uranium mobilization in pore water. Further studies and analysis of plant samples is needed to determine if elevated uranium also occurs in plant tissues. Plant samples will be sub-divided into different parts, processed and analyzed for U, As, Se, and Fe. Concentrations from water, soil and plant will be used to estimate uptake as well as generate a mass balance for detailed characterize of these contaminants in the crop root zone.
Publications
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