Source: MICHIGAN STATE UNIV submitted to
CONTAMINATION MECHANISMS OF ENGINEERED NANOPARTICLES IN FRESH PRODUCE AND CONTROL STRATEGIES DURING PROCESSING
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
TERMINATED
Funding Source
AFRI COMPETITIVE GRANT
Reporting Frequency
Annual
Accession No.
1011870
Grant No.
2017-67017-26168
Project No.
MICL08531
Proposal No.
2016-10349
Multistate No.
(N/A)
Program Code
A1331
Project Start Date
Jun 1, 2017
Project End Date
May 31, 2021
Grant Year
2017
Project Director
Zhang, W.
Recipient Organization
MICHIGAN STATE UNIV
(N/A)
EAST LANSING,MI 48824
Performing Department
Plant Soil & Microbial Science
Non Technical Summary
Engineered nanoparticles are increasingly being used in many products (including nanopesticides), and released into agricultural soil and water. Food crops (e.g., fresh produce) are prone to elevated exposure to ENPs, thus raising food safety concerns with foodborne ENPs. As fresh produce is often minimally processed prior to consumption, we envision that improving food safety of fresh produce requires fundamental understanding of contamination mechanisms of fresh produce by ENPs, as well as effectiveness of ENP removal in commercial processing. We thus propose to mechanistically examine fundamental interactions between agriculturally relevant ENPs, fresh produce, wash water, and processing equipment surfaces, and to design effective strategies for the removal of foodborne ENPs. Our objectives are to: 1) Investigate the sorption of selected ENPs (nano-Ag and nano-TiO2 ) to fresh produce (lettuce, spinach, tomato ); 2) Evaluate the influence of wash water conditions on ENP sorption to the fresh produce and equipment surfaces; and 3) Quantify ENP removal efficiency by tracking the transfer and distribution of ENPs among the produce, equipment surfaces, and wash water in an existing pilot-scale processing line. New fundamental knowledge gained will help assess the risk of ENP residue in fresh produce and design feasible management strategies. This project is expected to improve assessment of the fate and dissemination of ENPs in fresh produce production and processing, which will contribute to management strategies for decreasing the ENP contamination, consequently ensuringfood safety and protecting human health.
Animal Health Component
0%
Research Effort Categories
Basic
100%
Applied
(N/A)
Developmental
(N/A)
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
7111499200025%
7111499201025%
1331499200020%
1331499201020%
7111499106010%
Knowledge Area
711 - Ensure Food Products Free of Harmful Chemicals, Including Residues from Agricultural and Other Sources; 133 - Pollution Prevention and Mitigation;

Subject Of Investigation
1499 - Vegetables, general/other;

Field Of Science
2010 - Physics; 1060 - Biology (whole systems); 2000 - Chemistry;
Goals / Objectives
Our long-term goal is to improve food safety of fresh produce through elucidating fundamental interactions between agriculturally-relevant ENPs, fresh produce, water and equipment surfaces commonly used in commercial processing facilities, as well as through designing effective strategies for the removal of foodborne ENPs. In order to achieve this long-term goal, we designed the following specific objectives in this project, including:1) Investigate the sorption of selected ENPs (nano-Ag and nano-TiO2) to fresh produce (lettuce, spinach, tomato). The principal goal is to determine fundamental mechanisms contributing to the sorption of ENPs by fresh produce under representative scenarios of nanopesticide application or irrigation with ENP-containing water. Particular emphasis will be given to quantifying the contribution of stomata to the internalization of ENPs into leafy greens.2) Evaluate the influence of wash water conditions on ENP sorption to the fresh produce and equipment surfaces. We will investigate the sorption and desorptionbehaviors of ENPs to fresh produce and equipment surfaces under a range of wash water conditions (e.g., sanitizer type, surfactant, organic matter concentration, and temperature).3) Quantify ENP removal efficiency by tracking the transfer and distribution of ENPs among the produce, equipment surfaces, and wash water in an existing pilot-scale processing line. The goal is to find optimal wash water conditions that can be implemented, thereby improving food safety by decreasing the ENP levels in fresh produce.
Project Methods
We will employ a combination of innovative techniques to study fundamental mechanisms of ENP sorption to fresh produce and equipment surfaces. Sorption and/or desorption of the selected ENPs will be measured for fresh produce and equipment surfaces using our previously tested batch-type technique, under conditions representative of field exposure or washing. The importance of stomata in sorption (or internalization) of ENPs to fresh produce will be evaluated using stomatal aperture-modulating chemicals (abscisic acid [ABA]) and with the use of our existing model plant mutants defective in ABA-regulated stomatal closure. A pore-diffusion sorption model will be used to quantify the contributions from surface attachment and stomata-facilitated internalization, corroborated by measured surface and interior sorption data. A novel quartz crystal microbalance (QCM) will be employed to measure trace amounts of ENPs sorbed to and desorbed from model produce and equipment surfaces under varying wash water conditions. Surface interaction energy calculations for ENP/surface interactions will be compared with the sorption and desorption data. The purpose is to identify optimal conditions for desorbing ENPs from the produce and equipment surfaces. Finally, the existing pilot-scale processing line will be used to evaluate ENP transfer and distribution among equipment surface, produce, and wash water under simulated commercial conditions.More specifically, for Objective 1, we will perform kinetic and equilibrium ENP sorption experiments under a range of exposure conditions, including varying solution chemistry and varying fresh produce type (i.e., intact produce, mechanically-damaged produce, fresh-cut produce, and live plants). In addition to manipulating the stomatal closure of intact lettuce, spinach and tomato leaves with 10 µM ABA, we will also use existing plant mutants defective in ABA-regulated stomatal closure, including the ost1 and scord7 mutants of Arabidopsis thaliana, and tomato mutants flacca and sitiens. If stomata play a critical role in the internalization of ENPs, we expect to observe higher levels of ENPs in the mutant leaves compared with wild type leaves in the presence (and maybe even in the absence) of ABA treatment. In the live plant exposure experiments, we will simulate the nanopesticide application and irrigation scenarios to understand the ENP residual levels in fresh produce under realistic field conditions, using both greenhouse-grown and field-grown plants.For Objective 2, we will study ENP sorption/desorption to various model surfaces that the ENPs may encounter during growth of produce in fields, harvesting, and processing (including stainless steel, and polyurethane surfaces) using a quartz crystal microbalance with dissipation monitoring (QCM-D). We will examine how typical wash water conditions influence the sorption of ENPs to fresh produce and equipment surfaces. Then the ENP-loaded fresh produce and equipment surfaces will be washed with different types of produce wash waters to assess the removal of ENPs from fresh produce and equipment surfaces. We will first evaluate the ENP removal effectiveness of the wash water conditions commonly found in the current practices (including temperature, sanitizer type, and organic matter concentrations). We will then design a better wash water formulation that is safe, cost-effective, and acceptable.For Objective 3, we will determine the fate and dissemination of ENPs in our unique pilot-scale produce processing line, using romaine lettuce, spinach, and cherry tomato. We will test three scenarios: 1) the baseline scenario that only uses tap water as wash water; 2) the best available scenario that uses the current industrial practice shown to sorb the lowest ENPs on fresh produce and equipment surfaces in Objective 2; and 3) the optimized scenario that uses the optimal washing procedure developed in Objective 2.The outcome of this project will mainly be evaluated by the quality and number of conference presentations and peer-reviewed journal publications, as well as the academic progress and achievement of students supported by this project. Specifically, the quality and impact of journal publications can be evaluated by the impact of the journal and the papers themselves. The accumulated citation of the papers up to the date of final report will be reported. The degree completion and career advancement of graduate students will be tracked.

Progress 06/01/17 to 05/31/21

Outputs
Target Audience:The target audience included the scientific community and extension professionals in the field of food safety, vegetable production, agricultural and environmental nanotechnology, soil science, and environmental science, etc. Engagement with the target audience was performed primarily through conference presentations and scientific publications. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project provided the support for the work of four graduate students, one postdoctoral research associate, one undergraduate student, and two high school students. The interactions among the students, postdoc, and faculty benefited the professional development of students, postdoc and faculty. The project also provided travel support for the attendance in multiple scientific conferences. How have the results been disseminated to communities of interest?The project results were published in 7 refereed journal articles, and presented in 13 conference presentations. Additionally, more than 20 invited presentations were delivered in universities and research institutes, and at least 4 more manuscripts will be submitted for journal publications. These activities have increased the impact of our research effort. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? To address Objective 1, the nano-Ag uptake and foliar sorption to vegetables were investigated, using batch sorption experiments and greenhouse pot experiments. Briefly, we investigated the sorption of nano-Ag to plant leaves via stomata by taking advantages of stomata differences between Arabidopsis thaliana ecotypes (Ler and Col-7) and their respective mutants (ost1-2 and scord7) via batch sorption experiments, in combination with microscopic visualization. The Arabidopsis mutants (ost1-2 and scord7) are defective in the abscisic acid (ABA)-regulated stomata closure, whereas the stomata of ler and col-7 plants expect to close in the presence of ABA. Indeed, when comparing to that of the ABA-free control treatment, the stomatal aperture of the ecotypes Ler and Col-7 decreased remarkably, but remained unchanged for the ABA-deficient mutants ost1-2 and scord7 (p < 0.05), after exposure to 10 µM ABA treatment for 1 h. In general, nano-Ag sorption to the leaves of the Ler and Col-7 ecotypes treated with 10 µM ABA was lower than that in the ABA-free control, primarily resulted from the ABA-induced stomatal closure. Conversely, no significant difference in foliar sorption of nano-Ag to the leaves of the ost1-2 and scord7 mutants were found with and without the ABA treatment. Using scanning electron microscopy and transmission electron microscopy, we identified the surface and subcellular localization of nano-Ag. Specifically, nano-Ag were widely attached to the Arabidopsis leaf surface, and located at cell membrane, cytoplasm and plasmodesmata, demonstrating the location and transfer pathway of nano-Ag in plants. These results highlight the important role of stomata in the internationalization of nano-Ag in plants and may have broad implications in foliar application of nanopesticides and minimizing contamination of food crops by nano-Ag. In the greenhouse pot experiments, we investigated the uptake of nano-Ag and Ag+ ions by radish in biochar-free and biochar-amended soils (0%, 0.1% and 1% of biochar by weight). The loamy sand soils were spiked with 1 mg/kg nano-Ag and Ag+ ions and the effects of biochar amendment (0.1% and 1.0%) on soil sorption of nano-Ag and Ag+ ions, their soil-bound fractions, and their uptake and translocation by radish grown were investigated. Ag concentrations in the soils, soil pore water, radish roots, and radish leaves after 35-days growth were measured. Sorption of Ag ions to the soils was much greater than that of nano-Ag, primarily due to attraction of positively charged Ag ions to and repulsion of negatively charged nano-Ag from the negatively charged soil particles. Biochar addition at 1.0% (by weight) significantly decreased the reducible fraction of Ag+ ions in the soils and increased the oxidisable fraction of nano-Ag in the soils only with radish plants. Because of low exchangeable Ag fractions in all experimental treatments, the Ag uptake by radish plants was not significantly affected by biochar addition (p > 0.05). In this 35-days short-term experiment, the exposure to 1 mg/kg Ag NPs or Ag+ ion in soils did not substantially increase the Ag level in radish roots (0.05 ± 0.02-1.06 ± 0.98 mg/kg) and shoots (0.01 ± 0.00-0.03 ± 0.01 mg/kg), compared to those of the blank control treatment (p > 0.05). The uptake of nano-Ag and Ag+ ions at the environmentally-relevant concentration (1 mg/kg) was low with root concentration factors between 0.03 ± 0.03 to 0.29 ± 0.21 and root-to-shoot translocation factors between 0.08 ± 0.10 to 0.89 ± 1.21, probably resulting in the non-significant effect of biochar amendment on the Ag uptake by radish. To address Objective 2, we investigated behaviors of nano-Ag when exposed to commercially applicable chlorine concentrations in simulated lettuce wash water. The aggregation of nano-Ag (5 mg/L) were investigated at three chlorine concentrations (2, 50 and 100 mg/L) in the absence of dissolved lettuce extract (DLE) and in the DLE solution (0.1%, w/v) with or without 50 mg/L chlorine, using 5 mg/L nano-Ag in deionized water as the control (~pH 6.5). Aggregate size of nano-Ag increased overtime in the presence of chlorine (49-431 nm), suggesting greater aggregation of nano-Ag than that in the control treatment (p < 0.05). Greater size measurements with DLE likely resulted from the presence of DLE. Lower dissolved Ag concentrations and increasingly negative zeta potentials were observed in the presence of chlorine (0.01- 0.03 mg/L and -39 to -95 mV) and DLE (0.01-0.14 mg/L and -28 to -32 mV), as compared to those of the control treatment (0.54-0.8 mg/L and -10 to -20 mV) (p < 0.05). Aggregate morphology of nano-Ag were visualized by transmission electron microscopy with energy dispersive spectroscopy, confirming formation of composite of nano-Ag and AgCl precipitates in the presence of chlorine. Additionally, nano-Ag and AgCl precipitates were embedded in the DLE matrix, suggesting their strong binding to the DLE. These observations suggest that chlorine and plant-released organic matter could substantially change environmental behavior and fate of nano-Ag in wash water and subsequently their environmental risks. To address Objective 3, we first evaluated the impact of sanitizers and simulated leafy green processing water on the removal of nano-Ag from contaminated romaine lettuce using a simple batch-type system. Romaine lettuce pieces were first contaminated with nano-Ag and then washed in a batch-type carboy system (4 liters). Peroxyacetic acid solution (PAA, 80 mg/L, Tsunami 100) and chlorine solution (100 mg/L, pH 6.5-7.0; XY-12, Ecolab) were used with/without the presence of organic load (OL, 2.5% w/v) as washing water treatments and deionized water served as the control treatment. Washing the contaminated lettuce with deionized water, PAA solution, and chlorine solution decreased the Ag residue levels by 4.7%, 6.6%, and 3.5%, respectively. The treatments of OL, chlorine+OL, and PAA+ OL decreased the Ag residue levels by only 2.7%, 3.0%, and 0%, respectively. These results indicate that commercial postharvest washing may be inadequate for removing nano-Ag from contaminated romaine lettuce. We further evaluated the effectiveness of chlorine sanitizer on decontamination of nano-Ag from contaminated romaine lettuce using a pilot-scale processing line. Briefly, shredded lettuce (2 × 2 inches) were contaminated with nano-Ag and then separated into mesh bags (50 g/bag), which were mixed with uncontaminated shredded lettuce and washed in the flume tank using tap water with or without 100 mg/L chlorine, followed by centrifugation. The contaminated and uncontaminated lettuce samples as well as water samples were collected every 30 seconds during 90-second flume washing, and after centrifugation. The Ag concentration was increased in the wash water during washing, but the resultant nano-Ag removal from the contaminated lettuce was minor (< 3.3%), corroborating with the results of the batch-type experiment. Interestingly the centrifugation removed the highest nano-Ag from the contaminated lettuce (43-70%), suggesting that centrifugation may be better at removing sorbed nano-Ag from lettuce and repeated washing and centrifugation may be a more effective decontamination strategy. This project also provided beneficial synergisms to other relevant research on vegetable food safety and environmental application of ENPs. Finally, this project allowed us to collaborate with other scientists with expertise in food science and plant science. It resulted in measurable impact to advancement of agricultural sciences. The results were published in 7 refereed journal articles, and presented in 13 conference presentations. Four more manuscripts are expected to be published. Therefore, an increasing impact of this project is expected after all results are published in scientific journals.

Publications

  • Type: Journal Articles Status: Other Year Published: 2021 Citation: Gunathilaka, G., J. He, H. Li, W. Zhang, and E.T. Ryser. 2021. Behavior of silver nanoparticles in simulated leafy green wash water with chlorine (in preparation).
  • Type: Journal Articles Status: Under Review Year Published: 2021 Citation: He, J., L. Zhang, S.Y. He, E.T. Ryser, H. Li, and W. Zhang. 2021. Stomata facilitate foliar sorption of silver nanoparticles by Arabidopsis thaliana.
  • Type: Journal Articles Status: Published Year Published: 2021 Citation: Shen, Y., J.A. Hamm, F. Gao, E.T. Ryser, and W. Zhang. 2021. Assessing consumer buy and pay preferences for labeled food products with statistical and machine learning methods. Journal of Food Protection, 84(9): 15601566.
  • Type: Journal Articles Status: Published Year Published: 2021 Citation: Shen, Y., E.T. Ryser, H. Li, and W. Zhang. 2021. Bacterial community assembly and antibiotic resistance genes in the lettuce-soil system upon antibiotic exposure. Science of the Total Environment, 778, 146255.
  • Type: Journal Articles Status: Published Year Published: 2021 Citation: Shen, Y., H. Li, E.T. Ryser, and W. Zhang. 2021. Comparing root concentration factors of antibiotics for lettuce (Lactuca sativa) measured in rhizosphere and bulk soils. Chemosphere, 262, 127677.
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: He, J., Y. Li, H. Qi, H. Li, and W. Zhang. 2020. Biochar amendment changed soil-bound fractions of silver nanoparticles and ions but not their uptake by radish at an environmentally-relevant concentration. Biochar, 2, 307317.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Zhang, W. 2020. Emerging trends on biocolloid research in agroecosystems. ASA-CSSA-SSSA International Annual Meeting (Virtual), November 9-13 (oral presentation).
  • Type: Conference Papers and Presentations Status: Published Year Published: 2020 Citation: Shen, Y., E.T. Ryser, H. Li, and W. Zhang. 2020. Uptake and accumulation of antibiotics and associated impact on bacterial microbiome and Salmonella survival in growth chamber grown lettuce. ASM microbe online (eposter).


Progress 06/01/19 to 05/31/20

Outputs
Target Audience:We engaged the target audience mainly through conference presentations and scientific publications, including the scientific community and extension professionals in the field of food safety, vegetable production, agricultural and environmental nanotechnology, soil science, and environmental science, etc. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project provided the support for three graduate students. Their research results were presented in the international and national meetings (such as the ACS National Meeting, the International Association for Food Protection Annual Meeting, and ASA-CSSA-SSSA International Annual Meeting). How have the results been disseminated to communities of interest?The results have been presented in three scientific meetings including four conference presentations. Three manuscripts were published, two manuscripts are in review, and two manuscripts are currently in preparation. The reach and impact of our project has been increased by the research output. What do you plan to do during the next reporting period to accomplish the goals?Next year we will complete the microscopy study on the internalization of Ag NPs into fresh produce and continue the batch decontamination experiments. A substantial effort will be directed to analyzing the experimental data and manuscript writing.

Impacts
What was accomplished under these goals? In Year 3 of the project, we continued microscopic investigation on surface and subcellular localization of Ag NPs in Arabidopsis thaliana leaves using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively, in combination with elemental analysis by energy dispersive X-ray spectroscopy (EDS). This work serves as ancillary evidence on the sorption study of Ag NPs by Arabidopsis thaliana leaves of two ecotypes (ler and col-7) and their respective mutants (ost1-2 and scord7). Additionally, to further elucidate the behaviors of Ag NPs in the presence of chlorine and dissolved lettuce extract (DLE), we obtained the TEM images of particles under various experimental treatments and analyzed the elemental composition with EDS. This analysis provides evidence to elucidate mechanisms underlying the behaviors of Ag NPs with chlorine and DLE. Currently two papers summarizing the data are in preparation for journal publications, respectively. We also started batch decontamination experiments by washing lettuce leaves. However, our laboratory research activities were disrupted since March due to the COVID-19 pandemic. We thus directed our effort to data analysis and writing. One paper on the uptake of Ag NPs and Ag ions by radish in soils amended with 0%, 0.1% and 1% of biochar (by weight) was submitted to the journal Biochar and is currently in revision. The other papers are progressing as planned.

Publications

  • Type: Journal Articles Status: Under Review Year Published: 2020 Citation: He, J., Y. Li, H. Qi, H. Li, and W. Zhang. 2020. Biochar amendment changed soil-bound fractions of silver nanoparticles and ions but not their uptake by radish at an environmentally-relevant concentration. Biochar (in revision).
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Gunathilaka, G., J. He, H. Li, W. Zhang, and E. Ryser. 2019. Fate of silver nanoparticles in lettuce wash water as impacted by chlorine and organic matter. ACS National Meeting & Exposition, San Diego, CA, August 25-29.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: He, J., L. Zhang, S.Y. He, E. Ryser, H. Li, and W. Zhang. 2019. Role of stomata in foliar sorption of silver nanoparticles by Arabidopsis thaliana. ACS National Meeting & Exposition, San Diego, CA, August 25-29.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: Gunathilaka, G., J. He, H. Li, W. Zhang, and E. Ryser. 2019. Behavior of silver nanoparticles under various wash water conditions for leafy green processing. International Association for Food Protection Annual Meeting, Louisville, KY, July 21-24.
  • Type: Journal Articles Status: Under Review Year Published: 2020 Citation: Shen, Y., H. Li, E.T. Ryser, and W. Zhang. 2020. Comparing root concentration factors of antibiotics for lettuce (Lactuca sativa) measured in rhizosphere and bulk soils. Chemosphere (in revision).
  • Type: Journal Articles Status: Published Year Published: 2020 Citation: Li, Y., J. He, H. Qi, H. Li, S.A. Boyd, and W. Zhang. 2020. Impact of biochar amendment on the uptake and fate of pharmaceuticals in soil-radish systems. Journal of Hazardous Materials, 398, 122852.
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: He, J., Y. Zhang, Y. Guo, G. Rhodes, J. Yeom, H. Li, and W. Zhang. 2019. Photocatalytic degradation of cephalexin by ZnO nanowires under simulated sunlight: Kinetics, influencing factors, and mechanisms. Environment International, 132, 105105.
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Shen, Y., R.D. Stedtfeld, X. Guo, G.D. Bhalsod, S. Jeon, J.M. Tiedje, H. Li, and W. Zhang. 2019. Pharmaceutical exposure changed antibiotic resistance genes and bacterial communities in soil-surface- and overhead-irrigated greenhouse lettuce. Environment International, 131, 105031.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2019 Citation: He, J., Y. Li, H. Qi, H. Li, and W. Zhang. 2019. Biochar mediated the uptake of silver nanoparticles and ions by radish (Raphanus sativus). ASA-CSSA-SSSA International Annual Meeting, San Antonio, TX, November 10-13.


Progress 06/01/18 to 05/31/19

Outputs
Target Audience:The primary target audience reached by our efforts during this reporting period was the scientific community and extension professionals in the field of food safety, vegetable production, agricultural and environmental nanotechnology, plant biology, environmental science, etc. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project provided the support for three graduate students. Their research results were presented in the international and national meetings (such as the ACS national meeting and EGU General Assembly 2019). How have the results been disseminated to communities of interest?The results have been presented in fourscientific meetings including fourconference presentations. Three manuscripts were published and threemanuscripts are currently in preparation. The research output has increased the impact of our project. What do you plan to do during the next reporting period to accomplish the goals?Next year, we will complete the manuscript writing on the role of stomata to the internalization of ENPs in fresh produce. We will complete the investigation on the interactions between ENPs and fresh produce (primarily fresh cut produce) in wash water, and then optimize wash water chemistry to improve the decontamination of ENPs from fresh produce. We will also initiate the flow-through experiment to examine the decontamination of ENPs from fresh produce in flowing wash water, which serves a critical linkage between the batch experiments and thepilot-scale processing study.

Impacts
What was accomplished under these goals? In Year 2 of the project, we completed the investigation on the contribution of stomata to the internalization of ENPs into plant leaves. We used four Arabidopsis thaliana types (including two ecotypes ler and col-7 and their respective mutants ost1-2 and scord7). The Arabidopsis mutants (ost1-2 and scord7) are defective in the abscisic acid (ABA)-regulated stomata closure. Fully expanded leaves of 5-week-old Arabidopsis plants were used. Our preliminary results in Year 1 showed that stomatal apertures in ecotypes Ler and Col-7 decreased remarkably, but remained unchanged in ABA-deficient mutants ost1-2 and scord7 (P<0.05), after exposure to 10 µM ABA treatment for 1 h. In Year 2 we completed the batch experiments to assess the role of stomata in sorption of silver nanoparticles (AgNPs) to the Arabidopsis thaliana leaves. The sorbed amount of AgNPs by the leaves of the ecotypes (Ler and Col-7) treated with 10 µM ABA were much lower than that in the ABA-free control treatment, mainly due to the ABA-induced stomatal closure. There was no significant difference in the sorption of AgNPs to the leaves of the mutants ost1-2 and scord7 with and without ABA exposure. Ongoing experiments are being performed to determine surface and subcellular localization of AgNPs in Arabidopsis thaliana leaves using scanning electron microscopy (SEM, JEOL 7500F) and transmission electron microscopy (TEM, JEOL 2200FS), respectively. SEM images with energy dispersive X-ray spectroscopy elemental analysis confirmed the presence of AgNPs near the stomatal opening. We also completed the study on the behaviors of AgNPs when exposed to commercially applicable chlorine concentrations in simulated lettuce wash water. We specifically investigated the aggregation and dissolution of AgNPs (5 mg/L) at three chlorine concentrations (2, 50 and 100 mg/L) in the absence of dissolved lettuce extract (DLE, 0.1% W/V), and in the DLE solution with or without 50 mg/L chlorine, using 5 mg/L AgNPs in deionized water as the control (~pH 6.5). We found that particle size increased with time at all chlorine levels tested in the presence (89 to 168 nm) and absence (49 to 431 nm) of DLE as compared to the control treatment (58 to 60 nm) (P < 0.05) indicating greater aggregation of AgNPs in the presence of chlorine and/or DLE. However, increasingly negative zeta potentials were found in the presence of chlorine (−39 to −95 mV) and DLE (−28 to −32 mV) as compared to the control treatment (−10 to −20 mV). This observation would suggest smaller aggregation of AgNPs with the presence of chlorine and DLE, which was contradictory to the particle size measurements. Also, lower dissolved Ag concentrations were found at all chlorine levels tested in the presence of chlorine (0.01 to 0.03 mg/L) and DLE (0.01 to 0.14 mg/L), as compared to the control (0.54 to 0.8 mg/L) (P < 0.05). To reconcile these contradictions, we further obtained the SEM images, showing that the surface of the AgNPs was dissolved and formed AgCl precipitates, which may be responsible for the low dissolved Ag concentrations in solution and the more negative zeta potential than that of the control treatment. The AgCl precipitation may promote coalesces of AgNPs during co-precipitation, and facilitate the formation of larger aggregates. The DLE layer may have more negative zeta potentials than AgNPs and also promote the bridging of AgNPs. These results indicate that the fate of AgNPs could be greatly impacted by both chlorine and organic matter in lettuce wash water. Additionally, we continued several relevant work on environmental nanotechnology, including the photodegradation of pharmaceuticals by ENPs, and the uptake of AgNPs and Ag ions by radish in soils amended with 0%, 0.1% and 1% of biochar (by weight). Building on this project we have also collaborated with other researchers on environmental nanoscience research.

Publications

  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Wang, H., W. Zhang, S. Zeng, C. Shen, C. Jin, and Y. Huang. 2019. Interactions between nanoparticles and fractal surfaces. Water Research, 151, 296-309.
  • Type: Journal Articles Status: Published Year Published: 2019 Citation: Hu, X., B. Yang, W. Zhang, Q. Chao, X. Sheng, P. Oleszczuk, and Y. Gao. 2019. Plasmid binding to metal oxide nanoparticles inhibited lateral transfer of antibiotic resistance genes. Environmental Science: Nano, 6, 1310-1322.
  • Type: Journal Articles Status: Published Year Published: 2018 Citation: Wei, J., W. Zhang, W. Pan, C. Li, and W. Sun. 2018. Experimental and theoretical investigations on Se(IV) and Se(VI) adsorption to UiO-66-based metal-organic frameworks. Environmental Science: Nano, 5, 1441-1453.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2018 Citation: Zhang, W. 2018. Soil pollution, food safety and human health in the one health era. International Workshop on Soil Health, Nanjing, China, November 1.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2018 Citation: Zhang, W. 2018. Soil pollution, food safety and human health in the one health era. The 5th Young Scientist Forum of Earth Science, Nanjing, China, October 26-29.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2019 Citation: Zhang, W., J. He, L. Zhang, S. Y. He, E.T. Ryser, and H. Li. 2019. Stomata facilitated sorption of silver nanoparticles by Arabidopsis thaliana. EGU General Assembly 2019, Vienna, Austria, April 7-12.
  • Type: Conference Papers and Presentations Status: Other Year Published: 2018 Citation: He, J., Y. Zhang, G.R. Rhodes, J. Yeom, H. Li, and W. Zhang. 2018. Effective photodegradation of antibiotic cephalexin by ZnO nanowires under simulated sunlight. ACS National Meeting & Exposition, Boston, MA, August 19-23.


Progress 06/01/17 to 05/31/18

Outputs
Target Audience:The primary target audience reached by our efforts during this reporting period was the scientific community and extension professionals in the field of food safety, vegetable production, agricultural and environmental nanotechnology, plant biology, environmental science, etc. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?The project provided the support for three graduate students, one postdoc and one undergraduate student. Their research results were presented in the international and national meetings (such as the ACS national meeting). The PD's attendance at the annual USDA PD meeting was supported by the project. How have the results been disseminated to communities of interest?The results have been presented in two scientific meetings including three conference presentations. One manuscript was published and two manuscripts are currently in preparation. The research output has increased the impact of our project. What do you plan to do during the next reporting period to accomplish the goals?Next year, we will continue to investigate the role of stomata to the internalization of ENPs in fresh produce. We will also initiate the live plant exposure experiments. We will continue to investigate the interactions between ENPs and fresh produce (primarily fresh cut produce) in wash water, and then optimize wash water chemistry to improve the decontamination of ENPs from fresh produce.

Impacts
What was accomplished under these goals? In Year 1 of the project, we started investigating the contribution of stomata to the internalization of ENPs into plant leaves. To do so, we established the growth of four Arabidopsis thaliana types (including two ecotypes ler and col-7 and their respective mutants ost1-2 and scord7) in growth chambers. The Arabidopsis mutants are defective in the abscisic acid (ABA)-regulated stomata closure. The stomata images in the presence and absence of ABA were captured by confocal laser scanning microscope, from which the stomata aperture was measured. The stomata aperture of Arabidopsis ecotypes and mutants agreed with the expected responses of these plants to the ABA exposure. The kinetic and equilibrium sorption of nano-Ag to the Arabidopsis leaves was investigated with and without ABA. The results will allow us indisputably demonstrate the role of stomata in the internalization of ENPs. This work is an important part of Objective 1 and is ongoing. We also initiated the work on the interactions of ENPs with fresh produce in wash water in batch experiments. We first need to characterize the behaviors of ENPs in wash water, particularly in the presence of sanitizers (chlorine and peroxyacetic acid) and organic loads. We also began to design a flow-through experiment to examine the decontamination of ENPs from fresh produce in flowing wash water, which serves a critical linkage between the batch experiments and the future pilot-scale processing study. Additionally, we completed several relevant work on environmental nanotechnology, including the sorption of pharmaceuticals to ENPs, the photodegradation of pharmaceuticals by ENPs, and the transport of pharmaceuticals as facilitated by black carbon nanoparticles. Finally, we completed a study on the uptake of nano-Ag and Ag ions by radish in soils amended with 0%, 0.1% and 1% of biochar (by weight). Ag concentrations in the soils, soil water, radish root and leaves after 35-days growth were measured. The root concentration factors and translocation factors were determined. The Ag in the exchangeable and carbonate-bound fraction, the Fe and Mn oxide-bound fraction, and the OM and sulfide-bound fraction were measured by the BCR sequential extraction method. Also, the sorption isotherms of nano-Ag and Ag ions to soils was measured. Thus, the uptake of nano-Ag and Ag ions by radish was corroborated with the results of the Ag extraction and sorption.

Publications

  • Type: Journal Articles Status: Published Year Published: 2017 Citation: Sun, W., M. Li, W. Zhang, J. Wei, B. Chen, and C. Wang. 2017. Sediments inhibit adsorption of 17?-estradiol and 17?-ethinylestradiol to carbon nanotubes and graphene oxide. Environmental Science: Nano, 4, 1900-1910.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: He, J., Y. Zhang, H. Li, J. Yeom, and W. Zhang. 2017. ZnO nanowires effectively degrade cefalexin in water under ultraviolet light. EDAR 2017, 4th International Symposium on the Environmental Dimension of Antibiotic Resistance, Lansing, MI, August 13-17.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2017 Citation: Liu, C.-H., Y.-H. Chuang, H. Li, S.A. Boyd, B.J. Teppen, and W. Zhang. 2017. Black carbon nanoparticles facilitated transport of lincomycin, oxytetracycline, and sulfamethoxazole in saturated sand. EDAR 2017, 4th International Symposium on the Environmental Dimension of Antibiotic Resistance, Lansing, MI, August 13-17.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2018 Citation: He, J., Y. Zhang, G.R. Rhodes, J. Yeom, H. Li, and W. Zhang. 2018. Effective photodegradation of antibiotic cephalexin by ZnO nanowires under simulated sunlight. ACS National Meeting & Exposition, Boston, MA, August 19-23.
  • Type: Journal Articles Status: Other Year Published: 2018 Citation: Jeon, S., Y. Tian, H. Li, Y. Zhang, E.T. Ryser, S.Y. He, and W. Zhang. Deposition and internalization of silver nanoparticles in fresh-cut spinach leaves (in preparation).
  • Type: Journal Articles Status: Other Year Published: 2018 Citation: He, J., Y. Li, H. Qi, H. Li, E.T. Ryser, S.Y. He, and W. Zhang. Uptake of silver nanoparticles and ions by radish grown in biochar-amended soils (in preparation).