Jose R. Peralta-Videa

Interaction of Nanoparticles with Edible Plants and Their Possible Implications in the Food Chain

The uptake, bioaccumulation, biotransformation, and risks of nanomaterials (NMs) for food crops are still not well understood. Very few NMs and plant species have been studied, mainly at the very early growth stages of the plants. Most of the studies, except one with multiwalled carbon nanotubes performed on the model plant Arabidopsis thaliana and another with ZnO nanoparticles (NPs) on ryegrass, reported the effect of NMs on seed germination or 15-day-old seedlings. Very few references describe the biotransformation of NMs in food crops, and the possible transmission of the NMs to the next generation of plants exposed to NMs is unknown. The possible biomagnification of NPs in the food chain is also unknown.

The biochemistry of environmental heavy metal uptake by plants: Implications for the food chain

Plants absorb a number of elements from soil, some of which have no known biological function and some are known to be toxic at low concentrations. As plants constitute the foundation of the food chain, some concerns have been raised about the possibility of toxic concentrations of certain elements being transported from plants to higher strata of the food chain. Special attention has been given to the uptake and biotransformation mechanisms occurring in plants and its role in bioaccumulation and impact on consumers, especially human beings. While this review draws particular attention to metal accumulation in edible plants, researched studies of certain wild plants and their consumers are included. Furthermore, this review focuses on plant uptake of the toxic elements arsenic, cadmium, chromium, mercury, and lead and their possible transfer to the food chain. These elements were selected because they are well-established as being toxic for living systems and their effects in humans have been widely documented. Arsenic is known to promote cancer of the bladder, lung, and skin and can be acquired, for example, through the consumption of As-contaminated rice. Cadmium can attack kidney, liver, bone, and it also affects the female reproduction system. Cadmium also can be found in rice. Chromium can produce cancer, and humans can be exposed through smoking and eating Cr-laden vegetables. Lead and mercury are well known neurotoxins that can be consumed via seafood, vegetables and rice.

Nanomaterials and the environment: A review for the biennium 2008–2010

Applications of nanotechnology are touching almost every aspect of modern life. The increased use of engineered nanomaterials (ENMs) in consumer products, chemical and medical equipment, information technology, and energy, among others, has increased the number of publications (informative and scientific) on ENMs. By the 1950s, very few papers were committed to nanomaterials (NMs), but in 2009, more than 80,000 journal articles included the concept nanotechnology. The objective of this review is to compile and analyze publications on NMs in the biennium 2008-2010. This review includes the most recent publications in risk assessment/toxicity, characterization and stability, toxicity, fate and transport of NMs in terrestrial ecosystems, and new ENMs. Carbon nanotubes, metallic, metal oxides and hydroxides nanoparticles, quantum dots, and polystyrene NPs are included.

In Situ Synchrotron X-ray Fluorescence Mapping and Speciation of CeO2 and ZnO Nanoparticles in Soil Cultivated Soybean (Glycine max)

With the increased use of engineered nanomaterials such as ZnO and CeO₂ nanoparticles (NPs), these materials will inevitably be released into the environment, with unknown consequences. In addition, the potential storage of these NPs or their biotransformed products in edible/reproductive organs of crop plants can cause them to enter into the food chain and the next plant generation. Few reports thus far have addressed the entire life cycle of plants grown in NP-contaminated soil. Soybean ( Glycine max ) seeds were germinated and grown to full maturity in organic farm soil amended with either ZnO NPs at 500 mg/kg or CeO₂ NPs at 1000 mg/kg. At harvest, synchrotron μ-XRF and μ-XANES analyses were performed on soybean tissues, including pods, to determine the forms of Ce and Zn in NP-treated plants. The X-ray absorption spectroscopy studies showed no presence of ZnO NPs within tissues. However, μ-XANES data showed O-bound Zn, in a form resembling Zn-citrate, which could be an important Zn complex in the soybean grains. On the other hand, the synchrotron μ-XANES results showed that Ce remained mostly as CeO₂ NPs within the plant. The data also showed that a small percentage of Ce(IV), the oxidation state of Ce in CeO₂ NPs, was biotransformed to Ce(III). To our knowledge, this is the first report on the presence of CeO₂ and Zn compounds in the reproductive/edible portion of the soybean plant grown in farm soil with CeO₂ and ZnO NPs.

Effect of mixed cadmium, copper, nickel and zinc at different pHs upon alfalfa growth and heavy metal uptake

Alfalfa plants were grown in soil-pots contaminated with a mixture of Cd(II), Cu(II), Ni(II), and Zn(II), (at 50 mg/kg each) at pHs of 4.5, 5.8, and 7.1. The plants were fertilized using a nutrient solution, which was adjusted appropriately to the same pH. Plants in the control treatment were grown in the absence of the heavy metals mixture. The growth of the control plants was the same at the three pHs studied and the heavy metal stressed plants also showed similar behavior at each pHs. There were statistically significant differences (P<0.05) between the shoot length of the control treatment plants and the length of plants grown in the presence of the heavy metal mixture. Under the effects of the heavy metal mixture, nickel was the most accumulated element in the shoot tissue, with 437, 333, and 308 ppm at pH 7.1, 5.8, and 4.5, respectively. Cadmium was found to be second in accumulated concentrations with 202 ppm, 124 ppm, and 132 ppm at pH 7.1, 5.8, and 4.5, respectively, while zinc was third, followed by copper. The maximum relative uptakes (element in plant/element in soil-water-solution) were found to be 26 times for nickel, 23 times for cadmium, 12 times for zinc. and 6 times for copper. We considered these relations as indicative of the ability of alfalfa plants to take up elements from a soil matrix contaminated with a mixture of cadmium, copper, nickel, and zinc.

Nanomaterials in the Environment: From Materials to High-Throughput Screening to Organisms

One of the challenges in the field of nanotechnology is environmental health and safety (EHS), including consideration of the properties of engineered nanomaterials (ENMs) that could pose dangers to the environment. Progress in the field of nanomaterial development and nanotoxicology was presented at the International Conference on the Environmental Implications of Nanotechnology at the California NanoSystems Institute (CNSI) on the UCLA campus on May 11-14, 2010. This event was cohosted by the University of California Center for the Environmental Implications of Nanotechnology (UC CEIN) and the Center for the Environmental Implications of NanoTechnology (CEINT) based at Duke University. Participants included scientists and scholars from various backgrounds, including chemistry, biology, engineering, nanomaterial science, toxicology, ecology, mathematics, sociology, and policy makers. The topics of discussion included safety evaluation of ENMs from an environmental perspective, nanotoxicology, ecotoxicology, safe design of ENMs, environmental risk assessment, public perception of nanotechnology, application of ENMs in consumer products, and many more. The UC CEIN presented data on their predictive toxicological approach to the assessment of ENM libraries, which were designed and synthesized to develop an understanding of the material properties that could lead to hazard generation at the cellular and organismal levels in the environment. This article will focus on the first metal oxide ENM library that was introduced to harmonize research activities in the UC CEIN, with particular emphasis on the safety assessment of ZnO on cells and organisms. Methods of decreasing the observed toxic effects will also be discussed as an integral component of the UC CEINs activity in developing safer nanomaterials to lessen their environmental impacts.

Effect of cerium oxide nanoparticles on rice: a study involving the antioxidant defense system and in vivo fluorescence imaging.

Previous studies have reported the uptake of cerium oxide nanoparticles (nCeO2) by plants, but their physiological impacts are not yet well understood. This research was aimed to study the impact of nCeO2 on the oxidative stress and antioxidant defense system in germinating rice seeds. The seeds were germinated for 10 days in nCeO2 suspension at 62.5, 125, 250, and 500 mg L(-1) concentrations. The Ce uptake, growth performance, stress levels, membrane damage, and antioxidant responses in seedlings were analyzed. Ce in tissues increased with increased nCeO2 concentrations, but the seedlings showed no visible signs of toxicity. Biochemical assays and in vivo imaging of H2O2 revealed that, relative to the control, the 62.5 and 125 mg nCeO2 L(-1) treatments significantly reduced the H2O2 generation in both shoots and roots. Enhanced electrolyte leakage and lipid peroxidation were found in the shoots of seedlings grown at 500 mg nCeO2 L(-1). Altered enzyme activities and levels of ascorbate and free thiols resulting in enhanced membrane damage and photosynthetic stress in the shoots were observed at 500 mg nCeO2 L(-1). These findings demonstrate a nCeO2 concentration-dependent modification of oxidative stress and antioxidant defense system in rice seedlings.

Effect of surface coating and organic matter on the uptake of CeO2 NPs by corn plants grown in soil: Insight into the uptake mechanism

Little is known about the fate, transport, and bioavailability of CeO(2) nanoparticles (NPs) in soil. Moreover, there are no reports on the effect of surface coating upon NPs uptake by plants. In this study, Zea mays plants were grown for one month in unenriched and organic soils treated with coated and uncoated CeO(2) NPs. In addition, plants were exposed to fluorescein isothiocyanate (FITC)-stained CeO(2) NPs and analyzed in a confocal microscope. In organic soil, roots from uncoated and coated NPs at 100, 200, 400, and 800mg kg(-1) had 40, 80, 130, and 260% and 10, 70, 90, and 40% more Ce, respectively, compared to roots from unenriched soil. Conversely, shoots of plants from unenriched soil had significantly more Ce compared with shoots from organic soil. Confocal fluorescence images showed FITC-stained CeO(2) NP aggregates in cell walls of epidermis and cortex, suggesting apoplastic pathway. The μXRF results revealed the presence of CeO(2) NP aggregates within vascular tissues. To the authors knowledge this is the first report on the effects of surface coating and organic matter on Ce uptake from CeO(2) NPs and upon the mechanisms of CeO(2) NPs uptake by higher plants.

Synchrotron micro-XRF and micro-XANES confirmation of the uptake and translocation of TiO2 nanoparticles in cucumber (Cucumis sativus) plants

Advances in nanotechnology have raised concerns about possible effects of engineered nanomaterials (ENMs) in the environment, especially in terrestrial plants. In this research, the impacts of TiO(2) nanoparticles (NPs) were evaluated in hydroponically grown cucumber (Cucumis sativus) plants. Seven day old seedlings were treated with TiO(2) NPs at concentrations varying from 0 to 4000 mg L(-1). At harvest, the size of roots and shoots were measured. In addition, micro X- ray fluorescence (micro-XRF) and micro X-ray absorption spectroscopy (micro-XAS), respectively, were used to track the presence and chemical speciation of Ti within plant tissues. Results showed that at all concentrations, TiO(2) significantly increased root length (average >300%). By using micro-XRF it was found that Ti was transported from the roots to the leaf trichomes, suggesting that trichomes are possible sink or excretory system for the Ti. The micro-XANES spectra showed that the absorbed Ti was present as TiO(2) within the cucumber tissues, demonstrating that the TiO(2) NPs were not biotransformed.

Stress response and tolerance of Zea mays to CeO2 nanoparticles: Cross talk among H2O2, heat shock protein, and lipid peroxidation

The rapid development of nanotechnology will inevitably release nanoparticles (NPs) into the environment with unidentified consequences. In addition, the potential toxicity of CeO(2) NPs to plants and the possible transfer into the food chain are still unknown. Corn plants (Zea mays) were germinated and grown in soil treated with CeO(2) NPs at 400 or 800 mg/kg. Stress-related parameters, such as H(2)O(2), catalase (CAT), and ascorbate peroxidase (APX) activity, heat shock protein 70 (HSP70), lipid peroxidation, cell death, and leaf gas exchange were analyzed at 10, 15, and 20 days post-germination. Confocal laser scanning microscopy was used to image H(2)O(2) distribution in corn leaves. Results showed that the CeO(2) NP treatments increased accumulation of H(2)O(2), up to day 15, in phloem, xylem, bundle sheath cells and epidermal cells of shoots. The CAT and APX activities were also increased in the corn shoot, concomitant with the H(2)O(2) levels. Both 400 and 800 mg/kg CeO(2) NPs triggered the up-regulation of the HSP70 in roots, indicating a systemic stress response. None of the CeO(2) NPs increased the level of thiobarbituric acid reacting substances, indicating that no lipid peroxidation occurred. CeO(2) NPs, at both concentrations, did not induce ion leakage in either roots or shoots, suggesting that membrane integrity was not compromised. Leaf net photosynthetic rate, transpiration, and stomatal conductance were not affected by CeO(2) NPs. Our results suggest that the CAT, APX, and HSP70 might help the plants defend against CeO(2) NP-induced oxidative injury and survive NP exposure.