Impact of nanoparticle surface charge and phosphate on the uptake of coexisting cerium oxide nanoparticles and cadmium by soybean (<i>Glycine max. (L.) merr</i>.)

Engineered nanoparticles (ENPs) often interact closely with coexisting environmental pollutants; however, the effect of their surface properties on such interactions in a plant system has not been examined. This study investigated the roles of ENP surface charge and growth media chemistry on the mutual effects of cerium oxide nanoparticles (CeO2NPs) and cadmium (Cd) on their plant uptake and accumulation in a hydroponic system. Soybean seedlings were exposed to five nanoparticle/Cd treatments including: 100 mg L−1 CeO2NPs(+); 100 mg L−1 CeO2NPs(−); 100 mg L−1 CeO2NPs(+) + 1 mg L−1 Cd; 100 mg L−1 CeO2NPs(−) + 1 mg L−1 Cd; and 1 mg L−1 Cd only, in the presence or absence of 15 mg L−1 phosphorous in the form of phosphate. After 4 days of exposure, concentrations of Cd and Ce in plant tissues were quantified by inductively coupled plasma-mass spectrometry. Roots exposed to CeO2NPs(+) contained 87% higher Ce than plants exposed to CeO2NPs(−). Phosphate significantly increased the root concentration of Ce by 61% and 66% exposed to CeO2NPs(+) and CeO2NPs(−), respectively. The mutual effect of CeO2NPs and Cd was also affected by phosphate, and the net effect of phosphate depended upon the surface charge of CeO2NPs.</p

Activation of Peroxymonosulfate by Phosphate and Carbonate for the Abatement of Atrazine: Roles of Radical and Nonradical Species

While the activation mechanisms of peroxymonosulfate (PMS) by various homogeneous and heterogeneous catalysts have been reported, the chemistry of PMS in a catalyst-free system and its interactions with background oxyanions are still poorly understood. This paper demonstrated the activation of PMS by two prevalent oxyanions (phosphate and carbonate) and revealed the mechanisms for the enhanced atrazine (ATZ) degradation by PMS at neutral pH. Both oxyanions activated PMS to produce a sulfate radical (SO4•–), which reacts with ATZ rapidly, but phosphate exhibited a stronger effect than carbonate. The reaction between SO4•– and ATZ produced other possible radicals in the presence of dissolved oxygen (e.g., ATZ–O–O•), which subsequently generated singlet oxygen (1O2) with superoxide radical (O2•–) as a precursor. However, their contributions to ATZ degradation were minimal. The formation of radical species in the PMS–ATZ–phosphate system was supported by selective quenching and electron paramagnetic resonance measurements under different conditions [oxic, anoxic, and different solvents (H2O and D2O)]. Direct oxidation of ATZ by PMS was also observed. Overall, SO4•– and direct oxidation by PMS accounted for 75–78% and 22–25% of ATZ degradation, respectively

Adsorptive Structure and Mobility on Carbon Nanotube Exteriors Using Benzoic Acid as a Molecular Probe of Amphiphilic Water Contaminants

Benzoic acid is the simplest aromatic carboxylic acid that is also a common water contaminant. Its structural and amphiphilic properties are shared by many other contaminants of concern. Based on a molecular dynamics study, this work reports the competitive adsorption of benzoic acid with water on the curved exteriors of carbon nanotubes of varying oxygen content. With the help of cylindrically approximated pair correlation functions, carboxyl–carboxyl associations were found to serve as an additional mechanism providing stability to the adsorbed benzoic acid on tube exteriors. These associations are secondary to the main aromatic–aromatic interactions during the adsorption process and therefore were not sufficient to establish the energy hierarchy at the adsorbed state with increase in surface oxygen content. The same mechanism was previously ascribed to the adsorption of the structurally similar but bulkier tannic acid. Both water and benzoic acid were organized into numerous mobility groups and a correspondence was established between species residence time and the average translation time taken to escape the tube vicinity. Vigorous exchange of water molecules among the first adsorption shell, the second adsorption shell, and the immediate vicinity radially outside was estimated to take place within a short time of about 10 ps

Cerium Oxide Nanoparticles and Bulk Cerium Oxide Leading to Different Physiological and Biochemical Responses in <i>Brassica rapa</i>

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 <i>Brassica rapa</i> 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 <i>Brassica rapa</i> 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 <i>Brassica rapa</i>. Altogether, the results demonstrated that plant responses to CeO₂ exposure varied with the particle sizes and the growth stages of plants

Effects of Aging on the Fate and Bioavailability of Cerium Oxide Nanoparticles to Radish (<i>Raphanus sativus</i> L.) in Soil

The fate and impact of cerium oxide nanoparticles (CeO₂NPs) on soil-grown plants have been intensively studied. However, all previous studies were performed in freshly prepared soils, without considering the temporal changes of the properties of CeO₂NPs in the environment. A growing body of evidence suggests that the properties of CeO₂NPs will change with aging, and therefore, it is essential to understand how the aging process affects the fate and bioavailability of CeO₂NPs in the environment. In this study, the effects of aging on the fractionation of CeO₂NPs in a silty loam soil and their bioavailability to radish were investigated. The results indicated that aging for 7 months did not affect the fractionation of CeO₂NPs in soil. However, the aging process significantly increased the concentration of Ce³⁺ in soil. The soil with aged CeO₂NPs contained a 40.5% higher concentration of Ce³⁺ than soil with fresh CeO₂NPs. The aging process also resulted in a significantly higher Ce concentration in the radish shoots (87.1% higher) grown in aged soil than in freshly contaminated soil, even though the Ce concentrations in radish storage root and fine roots were comparable between plants grown in these soils. The radish growth and nutritional status were unaffected by either the fresh or the aged CeO₂NPs. This study provides the first comprehensive evaluation of the effects of aging of CeO₂NPs on their fate and impact on soil-grown plants

Mutual Effects and Uptake of Organic Contaminants and Nanoplastics by Lettuce in Co-Exposure

Organic contaminants, such as pesticides and pharmaceuticals, are commonly found in agricultural systems. With the growing use of plastic products, micro- and nanoplastics (MNPs) are increasingly detected in these agricultural systems, necessitating research into their interactions and joint effects to truly understand their impact. Unfortunately, while there has been a long history of research into the uptake of organic pollutants by plants, similar research with MNPs is only beginning, and studies on their mutual effects and plant uptake are extremely rare. In this study, we examined the effects of three agriculturally relevant organic pollutants with distinctive hydrophobicity as measured by log KOW (trimethoprim: 0.91, atrazine: 2.61, and ibuprofen: 3.97) and 500 nm polystyrene nanoplastics on their uptake and accumulation by lettuce at two different salinity levels. Our results showed that nanoplastics increased the shoot concentration of ibuprofen by 77.4 and 309% in nonsaline and saline conditions, respectively. Alternatively, organic co-contaminants slightly lowered the PS NPs uptake in lettuce with a more pronounced decrease in saline water. These results underscore the impactful interactions of hydrophobic organic pollutants and increasing MNPs on a dynamic global environment

Microplastics and nanoplastics in the soil-plant nexus: Sources, uptake, and toxicity

The agricultural sector is increasingly dependent upon the use of plastic products to enhance productivity. In addition to many incidental inputs, plastic fragments are progressively accumulating in soil following the degradation of plastic products. Microplastics (MPs, <5 mm) and nanoplastics (NPs, <1 µm) in agricultural soils have caused substantial concerns recently. The insidious interactions between plants, soil, and MPs/NPs in the agricultural environment could affect soil health, crop productivity, and threaten food safety and human health. Importantly, finer NPs can be taken up by plants, induce oxidative stress and negatively affect plant growth. Even though interactions of MPs/NPs with plants in the plant-soil nexus have been reported, a comprehensive review of the state of knowledge is lacking, which hinders continued progress in this emerging field. This review aims to fill the gap by extensively summarizing MPs/NPs sources in agriculture, techniques to investigate, impact on soil properties and accumulation in the plants. The synergistic effect of organic and inorganic co-contaminants and MPs/NPs are highlighted due to the widespread presence of these chemicals in agricultural soils. This review also presented possible mechanisms of MPs/NPs phytotoxicity. Although new information is emerging there is a paucity of data on the fate and impact of MPs/NPs in the plant-soil nexus. More efforts are needed to elucidate the fate and impact of MPs/NPs in agricultural soils to gain a deeper understanding of their health and safety implications.</p

Zinc Oxide Nanoparticles Alleviated the Bioavailability of Cadmium and Lead and Changed the Uptake of Iron in Hydroponically Grown Lettuce (<i>Lactuca sativa L.</i> var. <i>Longifolia</i>)

Leafy vegetables are a rich source of iron and fibers for the human diet, which may become hazardous if exposed to heavy metal contamination. Cadmium (Cd) and lead (Pb) are two highly toxic metals even at trace concentrations. Engineered nanoparticles (ENPs) can alter the uptake of heavy metals and localization of essential minerals such as iron (Fe) through different mechanisms. The goal of this study was to understand the mutual effects of zinc oxide nanoparticles (ZnONPs) and coexisting heavy metals Pb2+ and Cd2+ on their uptake and accumulation as well as their effects on Fe concentrations in romaine lettuce (Lactuca sativa L. var. Longifolia) in a hydroponic system. At termination, shoots were gently separated from the roots, and the concentrations of Pb, Cd, Fe, and Zn in all plant tissues were quantified by inductively coupled plasma-mass spectrometry (ICP-MS). In addition, microbial density analysis in the growth media was performed for each treatment. The results indicated active interactions between ZnONPs and coexisting divalent heavy metals. ZnONPs significantly reduced the accumulation of Cd and Pb in roots by 49% and 81%, respectively. In shoots, Cd was reduced by 30%, and Pb elevated by 44%. Fe concentration in shoots was strongly affected by ZnONPs, and the total Zn in shoots was negatively correspond with the microbial population in the growth media. Exposure to ZnONPs alone increased the total Fe in shoots by 80% compared to controls, and the copresence of ZnONPs and heavy metals increased Fe concentration by about 77%. The results revealed the role of ENPs in governing the uptake and translocation of some essential elements and toxic heavy metals in plants

Zinc Fertilizers Modified the Formation and Properties of Iron Plaque and Arsenic Accumulation in Rice (Oryza sativa L.) in a Life Cycle Study

This study examined the effect of three forms of zinc fertilizers on arsenic (As) accumulation and speciation in rice tissues over the life cycle of this cereal crop in a paddy soil. The formation and properties of iron plaque on rice roots at the maximum tillering stage and the mature stage were also determined. Elevated As at 5 mg/kg markedly lowered the rice yield by 86%; however, 100 mg/kg Zn fertilizers significantly increased the rice yield by 354–686%, regardless of the Zn form. Interestingly, only Zn2+ significantly lowered the total As in rice grains by 17% to 3.5 mg/kg and As­(III) by 64% to around 0.5 mg/kg. Zinc amendments substantially hindered and, in the case of zinc oxide bulk particles (ZnOBPs), fully prevented the crystallization of iron oxides (Fe3O4 and Fe2O3) and silicon oxide (SiO2) and altered the composition of iron plaques on rice roots. SiO2 was first reported to be a significant component of iron plaque. Overall, ZnOBPs, ZnO nanoparticles, and Zn2+ displayed significant yet distinctive effects on the properties of iron plaque and As accumulation in rice grains, providing a fresh perspective on the potentially unintended consequences of different Zn fertilizers on food safety