Xingmao Ma

Accumulation of zinc, copper, or cerium in carrot ( Daucus carota ) exposed to metal oxide nanoparticles and metal ions

The release of engineered nanoparticles (ENPs) into the environment has raised concerns about the potential risks to food safety and human health. There is a particular need to determine the extent of ENP uptake into plant foods. Belowground vegetables growing in direct contact with the growth substrate are likely to accumulate the highest concentration of ENPs. Carrot (Daucus carota) was grown in sand amended with ZnO, CuO, or CeO2 NPs or the same concentrations of Zn2+, Cu2+, or Ce4+. Treatment with ZnO or Zn2+ produced a concentration-dependent decrease in root and total biomass. Ionic Cu2+ and Ce4+ caused a greater reduction in shoot biomass as compared to the corresponding ENP treatments. Accumulation of Zn, Cu, or Ce in the taproot was restricted to the taproot periderm. Metal concentrations in the taproot periderm were higher for the ionic treatments than for the ENP treatments. Radial penetration of the metals into the taproot and subsequent translocation to shoots were also generally greater for plants receiving the ionic treatment than those receiving the ENP treatment. The distribution of the metals from the ENP treatments across the periderm, taproot, and shoots differed from that observed for the ionic treatments. Overall, the ENPs were no more toxic than the ionic treatments and showed reduced accumulation in the edible tissues of carrot. The results demonstrate that the understanding of ionic metal transport in plants may not accurately predict ENP transport and that an additional comparative study is needed for this and other crop plants.

Cerium Oxide Nanoparticles and Bulk Cerium Oxide Leading to Different Physiological and Biochemical Responses in Brassica rapa.

Cerium oxide nanoparticles (CeO2NPs) have been incorporated into many commercial products, and their potential release into the environment through the use and disposal of these products has caused serious concerns. Despite the previous efforts and rapid progress on elucidating the environmental impact of CeO2NPs, the long-term impact of CeO2NPs to plants, a key component of the ecosystem, is still not well understood. The potentially different impact of CeO2NPs and their bulk counterparts to plants is also unclear. The main objectives of this study were (1) to investigate whether continued irrigation with solutions containing different concentrations of CeO2NPs (0, 10, and 100 mg/L) would induce physiological and biochemical adjustments in Brassica rapa in soil growing conditions and (2) to determine whether CeO2NPs and bulk CeO2 particles exert different impacts on plants. The results indicated that bulk CeO2 at 10 and 100 mg/L enhanced plant biomass by 28% and 35%, respectively, while CeO2NPs at equivalent concentrations did not. While the bulk CeO2 treatment resulted in significantly higher concentrations of hydrogen peroxide (H2O2) in plant tissues at the vegetative stage, CeO2NPs led to significantly higher H2O2 levels in plant tissues at the floral stage. The activity of superoxide dismutase (SOD) in Brassica rapa also displayed a growth-stage dependent response to different sizes of CeO2 while catalase (CAT) activity was not affected by either size of CeO2 throughout the life cycle of Brassica rapa. Altogether, the results demonstrated that plant responses to CeO2 exposure varied with the particle sizes and the growth stages of plants.

Projected Dietary Intake of Zinc, Copper, and Cerium from Consumption of Carrot (Daucus carota) Exposed to Metal Oxide Nanoparticles or Metal Ions

The expanding production and use of engineered nanomaterials (ENMs) have raised concerns about the potential risk of those materials to food safety and human health. In a prior study, the accumulation of Zn, Cu, and Ce from ZnO, CuO, or CeO2, respectively, was examined in carrot (Daucus carota L.) grown in sand culture in comparison to accumulation from exposure to equivalent concentrations of ionic Zn2+, Cu2+, or Ce4+. The fresh weight concentration data for peeled and unpeeled carrots were used to project dietary intake of each metal by seven age-mass classes from child to adult based on consumption of a single serving of carrot. Dietary intake was compared to the oral reference dose (oral RfD) for chronic toxicity for Zn or Cu and estimated mean and median oral RfD values for Ce based on nine other rare earth elements. Reverse dietary intake calculations were also conducted to estimate the number of servings of carrot, the mass of carrot consumed, or the tissue concentration of Zn, Cu, or Ce that would cause the oral RfD to be exceeded upon consumption. The projections indicated for Zn and Cu, the oral RfD would be exceeded in only a few highly unrealistic scenarios of exceedingly high Zn or Cu concentrations in the substrate from ZnO or CuO or consumption of excessive amounts of unpeeled carrot. The implications associated with the presence of Ce in the carrot tissues depended upon whether the mean or median oral RfD value from the rare earth elements was used as a basis for comparison. The calculations further indicated that peeling carrots reduced the projected dietary intake by one to two orders of magnitude for both ENM- and ionic-treated carrots. Overall in terms of total metal concentration, the results suggested no specific impact of the ENM form on dietary intake. The effort here provided a conservative view of the potential dietary intake of these three metals that might result from consumption of carrots exposed to nanomaterials (NMs) and how peeling mitigated that dietary intake. The results also demonstrate the potential utility of dietary intake projections for examining potential risks of NM exposure from agricultural foods.

Physiological effects of cerium oxide nanoparticles on the photosynthesis and water use efficiency of soybean (Glycine max (L.) Merr.)

Widespread industrial uses of cerium oxide nanoparticles (CeO2 NPs) and their unregulated disposal have raised concerns about their environmental consequences. While studies are abundant on the phyto-effects of CeO2 NPs, detailed understanding of the impact of CeO2 NPs on plant photosynthesis is still lacking. In addition, no studies have evaluated the effects of CeO2 NPs on plant water use efficiency (WUE), a key parameter for crop yield. The goal of this study was to determine the impact of CeO2 NPs with two different surface properties (uncoated and polyvinylpyrrolidone (PVP)-coated) on the photosynthesis and WUE of soybean at four different concentrations (0, 10, 100 and 500 mg kg−1 dry soil). At the concentration of 100 mg kg−1, both types of CeO2 NPs stimulated plant growth and enhanced the photosynthesis rate by 54% for bare CeO2 NPs and 36% for PVP-CeO2 NPs. The maximum rate of Rubisco carboxylase activity represented by Vcmax also increased by 32% and 27%, respectively, for bare and PVP-coated CeO2 NPs at this concentration during the 3 week treatment. Conversely, the net photosynthesis rate was reduced by about 36% for both nanoparticles at 500 mg kg−1 CeO2 NPs. In addition, CeO2 NPs at concentrations >500 mg kg−1 also inhibited Rubisco activity and interfered with CO2 diffusion pathways. The results also confirmed that the physiological effects of CeO2 NPs on soybean depend on both the concentration and surface coating properties of the nanoparticles.

Mutual effects and in planta accumulation of co-existing cerium oxide nanoparticles and cadmium in hydroponically grown soybean (Glycine max (L.) Merr.)

Cadmium (Cd) is a metal toxic to humans even at very low concentrations. Elevated levels of Cd in soil due to various anthropogenic activities have led to higher Cd concentrations in various crop tissues, making it a food safety concern. With the progressive production and continued accumulation of engineered nanoparticles (ENPs) in agricultural soils, understanding the effect of ENPs on the uptake and accumulation of metals by plants is imperative. The goal of this study was to determine the mutual effects of cerium oxide nanoparticles (CeO2NPs) and Cd2+ on their uptake and accumulation by soybean seedlings (Glycine max (L.) Merr.) in a hydroponic system. Soybean seedlings were exposed to four treatments (1.0 mg L−1 Cd2+, 1.0 mg L−1 Cd2+ + 100 mg L−1 CeO2NPs, 100 mg L−1 CeO2NPs and 0 mg L−1 Cd and CeO2NPs as the control) for 10 days. At termination, plant roots and shoots were separated and the concentrations of Cd and Ce in these tissues were determined. In addition, the amounts of ionic Ce and particulate Ce within soybean roots were determined. Significant interactions between co-existing CeO2NPs and Cd were found with regard to their accumulation in plant tissues. While CeO2NPs did not affect the total Cd associated with soybean roots, they significantly reduced the translocation of Cd from roots to shoots by 70%. In contrast, the co-presence of Cd lowered the concentration of Ce in soybean roots by 45% but significantly increased the concentration of Ce in soybean shoots by 60%. The altered plant accumulation of co-existing Cd and Ce was attributed to various physical, chemical and biological processes that occurred in the plant rhizosphere. Specifically, the co-presence of Cd and CeO2NPs led to higher excretion of plant root exudates, which might have altered the chemical environment in the plant rhizosphere and enhanced CeO2NP dissolution, leading to different plant accumulation of both chemicals.

The impact of cerium oxide nanoparticles on the physiology of soybean (Glycine max (L.) Merr.) under different soil moisture conditions

AbstractThe ongoing global climate change raises concerns over the decreasing moisture content in agricultural soils. Our research investigated the physiological impact of two types of cerium oxide nanoparticles (CeO2NPs) on soybean at different moisture content levels. One CeO2NP was positively charged on the surface and the other negatively charged due to the polyvinylpyrrolidone (PVP) coating. The results suggest that the effect of CeO2NPs on plant photosynthesis and water use efficiency (WUE) was dependent upon the soil moisture content. Both types of CeO2NPs exhibited consistently positive impacts on plant photosynthesis at the moisture content above 70% of field capacity (θfc). Similar positive impact of CeO2NPs was not observed at 55% θfc, suggesting that the physiological impact of CeO2NPs was dependent upon the soil moisture content. The results also revealed that VCmax (maximum carboxylation rate) was affected by CeO2NPs, indicating that CeO2NPs affected the Rubisco activity which governs carbon assimilation in photosynthesis. In conclusion, CeO2NPs demonstrated significant impacts on the photosynthesis and WUE of soybeans and such impacts were affected by the soil moisture content. Graphical abstractSoil moisture content affects plant cerium oxide nanoparticle interactions

Uptake, Accumulation, and in Planta Distribution of Coexisting Cerium Oxide Nanoparticles and Cadmium in Glycine max (L.) Merr.

Agricultural soils are likely to be polluted by both conventional and emerging contaminants at the same time. Understanding the interactions of coexisting engineered nanoparticles (ENPs) and trace elements (a common source of abiotic stress) is critical to gaining insights into the accumulation of these two groups of chemicals by plants. The objectives of this study were to determine the uptake and accumulation of coexisting ENPs and trace elements by soybeans and to gain insights into the physiological mechanisms resulting in different plant accumulation of these materials. The combinations of three cadmium levels (0 [control] and 0.25 and 1 milligrams per kilogram of dry soil) and two CeO2 NPs concentrations (0 [control] and 500 milligrams per kilogram of dry soil) were investigated. Measurements of the plant biomass and physiological parameters indicated that CeO2 NPs led to higher variable fluorescence to maximum fluorescence ratio, suggesting that CeO2 NPs enhanced the plant light energy use efficiency by photosystem II. In addition, the presence of CeO2 NPs did not affect Cd accumulation in soybean, but Cd significantly increased the accumulation of Ce in plant tissues, especially in roots and older leaves. The altered Ce in planta distribution was partially associated with the formation of root apoplastic barriers in the co-presence of Cd and CeO2 NPs.

Potential Photochemical Interactions of UV Filter Molecules with Multichlorinated Structure of Prymnesins in Harmful Algal Bloom Events

Harmful algae blooms (HABs) involving Prymnesium parvum (Golden algae) is a worldwide fish killing event, seriously threatening the aquaculture industry and aquatic ecosystems. HABs frequently occur in natural reservoirs such as natural lakes which receive large numbers of visitors throughout the year. As a result, large amounts of Ultra-Violet (UV) chemical filters (the active ingredient of sunscreen products) are released to the lake due to swimming or sun-bathing, which add synergic environmental stresses on the Lake ecosystem. Prymnesium parvum is associated with the production of potent toxins (prymnesins) known for fish kills around the world. The molecular structure of prymnesins possesses both chlorine and nitrogen groups which can actively participate in photochemical reactions with organic and inorganic UV filter molecules. Consequently, reactive oxygen species (ROS) and chlorinated toxins can be potentially formed, leading to fish kill and dangerous biomagnification of reactive molecules in humans through dietary consumption of seafood. In this brief review, we discussed some possible mechanisms for the formation of toxic compounds due to the presence of UV filters and chlorine-containing compounds, using a lake in central Texas as an example. While the properties of various biotoxins released by P. parvum in a HAB event have been investigated, this is the first time that the environmental concern of the toxic behavior of reactive UV filters in a HAB event has been highlighted. Significant new insights are needed for the connections between harmful algae blooms and the accumulation of UV filters in water bodies so that appropriate policies can be established to protect the marine environment. A R T I C L E H I S T O R Y Received: December 20, 2016 Revised: March 10, 2017 Accepted: April 25, 2017

Impact of Nanoparticle Surface Properties on the Attachment of Cerium Oxide Nanoparticles to Sand and Kaolin

Soil texture has been found to be a critical factor in regulating the fate and transport of cerium oxide nanoparticles (CeONPs) in the terrestrial environment. However, the underlying mechanisms for the interactions between CeONPs and different components of soil are still poorly understood. The attachment of CeONPs onto two typical components of soil (sand and kaolin) in batch experiments were investigated to provide insights into the retention and bioavailability of CeONPs in soil. Surface properties of CeONPs, including surface charge and surface coating condition, had strong impacts on the interactions between CeONPs and soil particles. Positively charged CeONPs [CeONPs(+)] displayed the greatest attachment onto kaolin, whereas the negatively charged CeONPs [CeONPs(-)] showed poorest attachment onto sand. The attachment of CeONPs onto kaolin was significantly greater than onto sand, irrespective of surface charge. Homoaggregation of CeONPs increased the size of CeONPs on the surface of sand and kaolin. Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) calculations agreed with the experimental observations that surface charge and coating condition of CeONPs played a vital role in the homoaggregation and adsorption of CeONPs. For CeONPs(-) coated with polyvinylpyrrolidone (PVP), the steric repulsion between soil particles and CeONPs increases rapidly with the increase of maximum surface concentration of PVP. Adsorption isothermal fittings indicated that the adsorption of CeONPs onto sand and kaolin can be properly described by the Dubinin-Radushkevich isotherm. The results obtained in this study are crucial for the understanding of the fate and transport of engineered nanomaterials in the environment.

Elucidating the Effects of Cerium Oxide Nanoparticles and Zinc Oxide Nanoparticles on Arsenic Uptake and Speciation in Rice (Oryza sativa) in a Hydroponic System

The accumulation of arsenic (As) in rice grains depends greatly on the redox chemistry in rice rhizosphere. Intentional or accidental introduction of strong oxidizing or reducing agents, such as metallic engineered nanoparticles (ENPs) into the plant-soil ecosystem, can change As speciation and plant uptake. However, investigation on the effects of ENPs on plant uptake of co-occurring redox sensitive heavy metals and their speciation in plant tissues is scarce. We investigated the mutual effects of two commonly encountered ENPs, cerium oxide nanoparticles (CeO2 NPs) and zinc oxide nanoparticles (ZnO NPs), and two inorganic species of As on their uptake and accumulation in rice seedlings in a hydroponic system. Rice seedlings were exposed to different combinations of 1 mg/L of As(III) or As(V) and 100 mg/L of CeO2 NPs and ZnO NPs for 6 days about 40 days after germination. ZnO NPs significantly reduced the accumulation of As(III) in rice roots by 88.1 and 96.7% and in rice shoots by 71.4 and 77.4% when the initial As was supplied as As(III) and As(V), respectively. ZnO NPs also reduced As(V) in rice roots by 68.3 and 52.3% when the As was provided as As(III) and As(V), respectively. However, the As(V) in rice shoots was unaffected by ZnO NPs regardless of the initial oxidation state of As. Neither the total As nor the individual species of As in rice tissues was significantly changed by CeO2 NPs. The co-presence of As(III) and As(V) increased Ce in rice shoots by 6.5 and 2.3 times but did not affect plant uptake of Zn. The results confirmed the active interactions between ENPs and coexisting inorganic As species, and the extent of their interactions depends on the properties of ENPs as well as the initial oxidation state of As.