Grantee Research Project Results
Final Report: Reclaimed Water Irrigation: Plant Accumulation and Risks of Contaminants of Emerging Concern (CECs)
EPA Grant Number: R835829Title: Reclaimed Water Irrigation: Plant Accumulation and Risks of Contaminants of Emerging Concern (CECs)
Investigators: Gan, Jay , Trumble, John T. , Dudley, Stacia , Pennington, Marcus , sun, Chengliang
Institution: University of California - Riverside
EPA Project Officer: Packard, Benjamin H
Project Period: September 1, 2015 through August 31, 2018 (Extended to February 28, 2020)
Project Amount: $749,631
RFA: Human and Ecological Health Impacts Associated with Water Reuse and Conservation Practices (2014) RFA Text | Recipients Lists
Research Category: Water , Human Health
Objective:
In arid and semi-arid regions such as the southwestern U.S., municipally treated wastewater (or reclaimed water) is potentially a valuable water resource that may be used for augmenting agricultural irrigation, thus alleviating water scarcity caused by urbanization and droughts. A hurdle to this beneficial reuse, however, is the potential uptake of and risks from contaminants of emerging concern (CECs) from the treated wastewater via food crops. In this project, we aim to identify CECs with the highest potential for plant accumulation, obtain first-hand values of occurrence of CECs in edible products of common vegetables and other food crops, understand processes governing uptake, translocation, metabolism and accumulation, and characterize acute and sublethal effects of selected CECs on a range of important insects. This project will provide the much-needed first-hand information on the occurrence and potential risks of CECs in food plants when treated wastewater is used for irrigation. The study findings will be of great value to the scientific community and the society-at-large for developing knowledge that promotes the safe reuse of treated wastewater.
Summary/Accomplishments (Outputs/Outcomes):
The proposal had 4 specific objectives: 1) controlled experiments to evaluate plant uptake and metabolism of emerging contaminants; 2) field studies to evaluate plant accumulation of emerging contaminants under realistic conditions; 3) controlled experiments to evaluate effects of emerging contaminants on terrestrial insects and risk assessment to predict human exposure and risks; and 4) educational and outreach activities. We have completed the research to address all objectives.
Novel Analytical Methods:
Plants are complex matrices for analysis and identification of trace contaminants and their metabolites in plant tissues is a great challenge. In particular, it is often formidable to identify unknown biotransformation products in the absence of reference standards, and this analytical challenge is particularly true for contaminants of emerging concern (CECs) that are mostly polar molecules without characteristic structures (e.g., Cl, Br) and in complex matrices such as plants. Using the fibrate drug gemfibrozil as a model CEC and Arabidopsis thaliana as a model plant, we developed and demonstrated a novel analytical framework coupling deuterium stable isotope labeling with high-resolution mass spectrometry (SILAMS) in identifying plant biotransformation products. When exposed in A. thaliana cells, gemfibrozil was quickly taken up into the cells and extensively metabolized. The use of non-labeled and deuterated gemfibrozil at 3:1 ratio created unique diagnostic patterns in mass spectra, enabling the identification of 11 novel Phase II amino acid/peptide conjugates. Similarity in mass fragmentation patterns and chromatographic behaviors was then employed to establish the probable structures. Two major metabolites were further confirmed as glutamate and glutamine conjugates using authentic standards. Most of the identified conjugates were also detected in the whole A. thaliana plant. Therefore, SILAMS offers unique advantages by excluding false matrix positives and helping discern unknown metabolites, including polar conjugates with endogenous biomolecules, with a high degree of confidence. This novel framework may be readily applied to other CECs for high-throughput metabolite screening in plants to improve our understanding of their food safety and human health risks and potential deleterious effects on other species living on plants.
Plant Uptake and Metabolism of CECs:
We have carried out experiments to evaluate uptake potentials of different emerging contaminants by vegetable plants, and also explore metabolism pathways of some common CECs using Arabidopsis thaliana cells and commonly consumed vegetables (i.e., radish, cucumber, lettuce, and carrots) as model plants. These studies have provided novel information on what processes and factors regulate plant uptake of trace contaminants such as CECs, and highlighted that plants can extensively metabolize CECs, but their metabolites, such as conjugates, may maintain partial biological activity and should be considered in comprehensive risk assessment.
In one study, we tested the hypothesis that addition of biosolids could increase the sorption of certain CECs in soil, decreasing their bioavailability and found that contamination of food crops by biosolids-borne contaminants does not linearly depend on biosolids use rates. This finding bears significant implications in the overall risk evaluation of biosolids-borne contaminants.
In yet another study, the metabolism of diazepam was investigated in Arabidopsis thaliana cells and cucumber (Cucumis sativus) and radish (Raphanus sativus) seedlings grown in hydroponic solution following acute (7 d)/high concentration (1 mg L-1), and chronic (28 d)/low concentration (1 μg L-1) exposures. Liquid chromatography paired with mass spectrometry, 14C tracing, and enzyme extractions, were used to characterize the metabolic phases. Findings of this study also highlighted the need to consider the formation of bioactive transformation intermediates and different phases of metabolism to achieve a comprehensive understanding of risks of CECs in agroecosystems.
Effect of CECs on Plant Development and Hormone Homeostasis and Enzymatic Response
We have carried out a series of laboratory experiments to understand if and how exposure to low levels of CECs affects plant development, as well as the role of various enzymes in mediating or mitigating the toxicity. These studies provide novel information on the interactions of CECs with plant hormones and enzymes.
Contamination of agricultural soils by pharmaceutical and personal care products resulting from the application of treated wastewater, biosolids and animal wastes may confer phytotoxicity to plants. We investigated the uptake and transport, physiological responses and detoxification of a mixture of 17 CECs in cucumber seedlings. The findings illustrated the complexity of phytotoxicity after exposure to CEC mixtures, and provided insights into the molecular mechanisms likely responsible for the detoxification of CECs in higher plants.
In a follow up study, we used acetaminophen, one of the most-used pharmaceuticals, to explore roles of glutathione (GSH) conjugation in its biotransformation in crop plants. In a related study, we investigated the mechanism by which plant development is affected by triclosan, the most commonly used antimicrobial agent. Findings of this study improve our mechanistic understanding on how antimicrobial agents such as triclosan affect plant root growth. Addtionally, we further explored nitric oxide (NO) production and its roles in regulating triclosan tolerance in plants using wheat as an example.
In a separate study, we evaluated the effect of low-dose, chronic exposure to a mixture of 10 CECs, including 4 antibiotics, 3 anti-inflammatory drugs, 1 antiepileptic, 1 beta-blocker, and 1 antimicrobial, on lettuce (Lactuca sativa) and cucumber (Cucumis sativa L.) plants.The results of this study suggested that chronic exposure to low levels of CEC mixtures may compromise the fitness of plants, and the impairments are underlined by alterations in hormone balances.
Effects of CECs on Terrestrial Invertebrates:
In a parallel line of research, we evaluated potential biological effects of CECs on agriculturally and economically important insects, including Megaselia scalaris, Trichoplusia ni, and Myzus persicae.
In a study published in the prestigious scientific journal PNAS, we assessed the effects of common pharmaceuticals on an agricultural pest, Trichoplusia ni (Lepidoptera: Noctuidae). The results suggest that use of reclaimed wastewater for irrigation of crops can affect the developmental biology and microbial communities of an insect of agricultural importance.
In a separate study, we assessed the effects of common pharmaceuticals on a cosmopolitan saprophagous insect, Megaselia scalaris (Diptera: Phoridae). The results suggest that CECs at environmentally relevant concentrations can affect the biology and microbial communities of an insect of ecological and medical importance.
In another study, we further assessed the effects of common pharmaceuticals on an agricultural pest, the aphid Myzus persicae (Sulzer, Hemiptera: Aphididae). The results suggest that the use of reclaimed wastewater for crop irrigation would not affect aphid populations, but could hinder or delay crop production.
Conclusions:
The use of treated wastewater for irrigation is an important tool to addressing water scarcity due to urbanization and population growth, and/or climate change induced shifts in precipitation patterns. The crisis is especially acute in arid and semi-arid areas such as California and the rest of America Southwest. On the other hand, animal wastes and biosolids are produced in enormous quantities as byproducts; their high contents of macro and micronutrients make them ideal for use in agricultural fields as fertilizers. Although these beneficial reuses have great societal and economic benefits, these resources contain numerous emerging contaminants. With the funding from USEPA and additional funding from USDA, we have carried out systematic research on plant uptake of a range of emerging contaminants under hydroponic, greenhouse or field conditions, metabolism in plant callus tissues and whole plants, and exposure prediction through human dietary intakes. Through this project, we have obtained some of the most substantial first-hand data on levels of PPCPs in a wide range of vegetables grown with treated wastewater irrigation. Our work on recognizing conjugation as an important pathway in plant metabolism, and back conversion of metabolites to the parent compound, is highly novel and has important implications in obtaining more comprehensive and accurate risk assessment of emerging contaminants in the soil-plant continuum. We are likely among the most active and productive research groups in the world addressing this urgent issue. This research has direct societal significance, as it pertains to safeguarding reuse of wastewater and biosolids/animal wastes in agriculture, addressing water scarcity, and protecting environmental and human health.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
Other project views: | All 23 publications | 16 publications in selected types | All 16 journal articles |
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Fu Q, Liao C, Du X, Schlenk D, Gan J. Back Conversion from Product to Parent:Methyl Triclosan to Triclosan in Plants. ENVIRONMENTAL SCIENCE & TECHNOLOGY LETTERS 2018;5(3):181-185. |
R835829 (Final) |
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Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
- 2019 Progress Report
- 2018 Progress Report
- 2017 Progress Report
- 2016 Progress Report
- Original Abstract
16 journal articles for this project