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ARS Home Pacific West Area Riverside, California Agricultural Water Efficiency and Salinity Research Unit Research





- Ibekwe, Abasiofiok - Mark
- Ashworth, Daniel
- Schmidt, Michael - Mike
- 2023
- 2022
- Publications
- Soil and Air (212)

Research Project: **Location:
                            Agricultural Water Efficiency and Salinity Research Unit** Project Number: 2036-12320-011-000-D
                        
                        Project Type: In-House Appropriated Start Date: Oct 21, 2021
                        
                        End Date: Oct 20, 2026 **Objective:**
                        
                        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.


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