Location: Agricultural Water Efficiency and Salinity Research Unit
2024 Annual Report
Objectives
This project uses an integrated systems approach to identify dissemination of antibiotic resistant determinants (ARDs) in wastewater to soil, agricultural produce, and earthworms - linking production to consumption and environmental release, as well as conducting research on amendments and our novel mitigation technology that have the promise to reduce the environmental distribution of those determinants.
Objective 1: Identify the potential transmission routes of antibiotics and ARGs from manure and wastewater to soil-plant-earthworm systems for elucidation of key components for developing mitigation strategies.
Sub-objective 1A: Identify the role of agricultural produce, earthworms, and endophytic microbes in the dissemination of AMR in the agricultural environment/food chains.
Sub-objective 1B: Transfer of antibiotics and ARDs through food chains using a whole-system approach under outdoor conditions.
Sub-objective 1C: Determine concentrations of antibiotics and ARDs in the above and below ground edible portions of the plants being grown under nearly natural conditions.
Objective 2: Evaluate the risk associated with the potential dissemination of antibiotics, pathogens, and antimicrobial resistance through the natural ecological food chain-soil-plant-earthworm continuum and in association with relevant food production systems.
Objective 3: Assess the use of biochar application to soil as a mitigation strategy to limit the dissemination of antimicrobial resistance from soil to plants.
Sub-objective 3A: Explore the effects of biochar amendment on ARDs availability in soil and uptake in plants and earthworms.
Sub-objective 3B: Measure the effects of biochar on mitigation of ARDs under field conditions.
Objective 4: Develop a system for removal of antibiotics and other chemicals of emerging concern (CECs) from wastewater by passage through various layers of environmental media. Mitigation of the dissemination of antibiotic resistance through agricultural systems is best served by preventing the release of antibiotics and ARDs into such systems. Therefore, simple, cost-effective treatment systems to remove these CECs from treated wastewater are required, prior to the use of such wastewater for agricultural irrigation. We have recently developed a layered system of environmental media (Figure 3), which has shown the potential for removing antibiotic compounds from wastewater (Ashworth and Ibekwe, 2020). This system would be further developed under the current proposal.
Sub-objective 4A: Assess various environmental media in terms of their removal of CECs from wastewater.
Sub-objective 4B: Quantify the potential for the materials identified under Sub-objective 4A to remove CECs from a layered system based on modeling studies.
Sub-objective 4C: Assess layered systems (at various experimental scales) comprised of these environmental media to determine their effectiveness in CEC removal.
Approach
The research will be conducted to:
Objective 1: Identify the potential transmission routes of antibiotics and ARGs from manure and wastewater to soil-plant-earthworm systems for elucidation of key components for developing mitigation strategies. The work will be conducted using greenhouse (objective1a), outdoor (large- scale) pot (objective1b), and lysimeter experiments (objective1c), which are of a sufficiently large scale to allow for natural biological processes to take place, while still being highly controllable. In the pot studies, we will assess changes in soil microbial composition as well as concentrations of antibiotic compounds, and identify ARDs in the soil, soil solution, rhizosphere, phyllosphere, and earthworm gut in response to wastewater irrigation. The experiment will inform more realistic and integrated studies conducted using intermediate (40-liter pots) and large scale (lysimeter) experiments to assess time-course trends in the transfer of antibiotics and ARDs through food chains using a whole-system approach. The results of these studies will be used to assess the potential risk of antibiotic resistance dissemination by evaluating bioaccumulation/biomagnification factors of AT/ARGs dissemination in the food chain (Objective 2).
Objective 3: Assess the use of biochar application to soil as a mitigation strategy to limit the dissemination of antimicrobial resistance from soil to plants. Since biochar has been shown to effectively mitigate CEC transport, it will be assessed as a mitigation strategy to reduce the dissemination of antibiotic resistance. A greenhouse pot and field experiments will be conducted using the most promising of the biochar materials to quantify any potential mitigation effect in terms of antibiotic and ARD dissemination in the environment. This pot experiment will use soils applied with agriculturally relevant rates of biochar (e.g., 0.1, 0.5 and 1% by mass; equivalent to 2.6, 13, and 26 t/ha, respectively), while the field experiment will measure the impact of biochar application on the dissemination of antibiotics and ARDs from wastewater and manure to soil-plant-earthworm continuum. One limitation in the field work may be low gene targets for qPCR for monitoring of ARGs. Here, we will adopt droplet digital PCR (dd- PCR) if we identify low concentrations using qPCR that reduces reproducibility and efficiencies of qPCR.
Objective 4: Develop a system for removal of antibiotics and other chemicals of emerging concern (CECs) from wastewater by passage through various layers of environmental media. The final phase of this work will focus on developing a system for the removal of CECs, ARB, and ARGs from wastewater using bioreactors that enhance different bioprocesses to reduce the different classes of CEC and biological determinants. Layered system of environmental media consisting of gravel, sand, soil, and soil+biochar will be used to remove antibiotic compounds from wastewater. This system will be developed, tested, scale-up, and modeled (Hydrus 1-D) for removal of antibiotics and other chemicals of emerging concern from wastewater by passing through the various media.
Progress Report
This is the final report for 2036-12320-011-000D, titled, "Protection of Food and Water Supplies from Pathogens and Human Induced Chemicals of Emerging Concern", due to the project being terminated and the resourses being redirected in FY 2024. This research will no longer be conducted by ARS researchers in Riverside, California. The following provides a summary of the research that was accomplished in FY 2024, prior to the project being terminated.
In support of Objective 3, a field study was set up and conducted at the United States Salinity Laboratory to probe the mitigation of antimicrobial resistance determinant (ARD) dissemination in drip irrigated spinach and radish systems with biochar amendments. The study was conducted to probe mitigation under both manure and wastewater-borne ARD inputs and with two distinct biochar amendments. While the study has not been fully analyzed yet, the results will serve to elucidate the impact of biochar in reducing plant uptake and microbial transformation by ARDs in the soil environment. Moreover, this study will help understand how biochar serves as a nutrient source and soil amendment in drip irrigated systems in comparison with other soil amendments (e.g., manure).
Objective 4 was further addressed through production of a range of 24 biochars (4 different types of feedstocks and 6 pyrolysis temperatures) and assessment for removal of antibiotics, antibiotic resistance genes and bacteria from solution. Results from these studies indicate excellent removal of all antibiotics studied, although with different biochars showing variable removal based on pyrolysis temperature and feedstock. Relationship between removal behavior and production condition-dependent biochar characteristics will be better established through these studies and are being used to inform the developments of larger-scale column filtration systems. Bench-scale filtration systems have been designed, constructed, and tested for their removal of antibiotics from treated wastewaters. These studies have shown that appropriate selection of biochar adsorbents can lead to highly effective removal of antibiotic compounds when treated wastewaters are pumped through the biochar materials. Larger (greenhouse) scale systems are currently being constructed and tested for their removal efficacy towards per- and poly-fluoroalkyl substances (PFAS). These systems will also be applied to antibiotics. Ultimately, such systems will lead to low-cost, environmentally-friendly treatment options for producing treated wastewaters with low contaminant loadings for use in agricultural irrigation, thereby helping prevent risks to the human food chain.
Accomplishments
1. Improved understanding of dissemination of antimicrobial resistance in agricultural ecosystem. The increasing demand for food production and the expansion of irrigated agriculture have put significant pressure on water resources, particularly in arid and semi-arid regions. Identifying and developing effective methods for tracking the dissemination of antimicrobial resistance in the agricultural production environment is a recent goal of many International and National Organizations. ARS researchers in Riverside, California, working in collaboration with University of California at Riverside researchers, used high throughput quantitative polymerase chain reaction (PCR) to quantify the number of genes, mobile genetic elements, and antibiotic-resistant bacteria present in spinach and radish. Researchers found that the number of antibiotic resistance genes were significantly higher in spinach compared to radish, and there was a strong correlation between genes and microbial diversities in the spinach and radish production environment. Thus, changes in the abundance of antibiotic resistance genes may exert selective pressure on the microbial community, influencing its composition and diversity. This study provides new knowledge to assist farmers, researchers, and wastewater management professionals in reducing the dissemination of antimicrobial resistance in agricultural systems, ultimately protecting the public from the threat of antimicrobials.
2. Published a comprehensive review paper on the use of biochar to mitigate the impacts of per- and poly-fluoroalkyl substances (PFAS) in agriculture. Growing concern over the presence of per- and polyfluoroalkyl substances (PFAS) in agricultural compartments (e.g., soil, water, plants, soil fauna) has led to an increased interest in scalable and economically feasible remediation technologies. In this comprehensive review paper, ARS researchers in Riverside, California, framed biochar as a strategy for mitigating the detrimental impacts of PFAS in agricultural systems and discuss the benefits of this strategy within the framework of the needs and challenges of contaminant remediation in agriculture. To gauge the optimal physicochemical characteristics of biochar in terms of PFAS adsorption, principal component analysis using more than 100 data points from the available literature was performed. The main biochar-based PFAS treatment strategies (water filtration, soil application, mixing with biosolids) were also reviewed to highlight the benefits and complications of each. Life cycle analyses on the use of biochar for contaminant removal were summarized, and data from selected studies were used to calculate (for the first time) the global warming potential and net energy demand of various agriculturally important biochar classes (crop wastes, wood wastes, manures) in relation to their PFAS adsorption performance. The concepts introduced in this review may assist in developing large-scale biochar-based PFAS remediation strategies to help protect the agricultural food production environment.
Review Publications
Schmidt, M.P., Ashworth, D.J., Ibekwe, A.M. 2024. Cephalexin interaction with biosolids-derived dissolved organic matter: Binding mechanism and implications for adsorption by biochar and clay. Environmental Science: Water Research & Technology. 10:949-959. https://doi.org/10.1039/D3EW00590A.
Bhattacharjee, A.S., Phan, D., Zheng, C., Ashworth, D.J., Schmidt, M.P., Men, Y., Ferreira, J.F., Muir, G., Hasan, N., Ibekwe, A.M. 2024. Dissemination of antibiotic resistance genes through soil-plant-earthworm continuum in the food production environment. Environmental International. 183. Article 108374. https://doi.org/10.1016/j.envint.2023.108374.
Ashworth, D.J., Schmidt, M.P., Ibekwe, A.M. 2023. Performance of acid- and base-modified biochars for the removal of antibiotics from water under dynamic conditions. Journal of Environmental Chemical Engineering. 11(6). Article 111616. https://doi.org/10.1016/j.jece.2023.111616.