In order to determine the mechanisms of the retention of 60Co, 85Sr and 134Cs in natural silica sand columns, desorption experiments were performed by changes of pH and ionic strength and by injection of natural organic matter (NOM). Injection of KCl (0.1 M) resulted in a high release of 60Co (60-100%) and 85Sr (72-100%) but a smaller release of 134Cs (31-66%). Only limited release of 60Co (66%) and 85Sr (71%) and no release of 134Cs were observed by injection of NOM. The different percentages of desorption were related to the chemical characteristics of the organic colloids previously retained in columns before the desorption step. The results evidenced different sorption processes on energetically heterogeneous surface sites. According to the initial conditions, the binding of the radionuclides to the solid phase resulted from weak and easily reversible sorption processes to strong association probably by inner sphere complexes. The rather weak release of 134Cs by KCl was attributed to the strong retention of 134Cs by clay coatings on the natural silica sand surfaces. © 2005 Elsevier Ltd. All rights reserved.

Cropland contamination by toxic trace metal (loid)s (TTMs) has attracted increasing attention due to the serious consequential threat to crop quality and human health. Mitigation of plant TTM stress by silica amendment has been proposed recently. However, the relationship between the siliceous structure of phytoliths and TTMs in plants, and the environmental implications of phytolith-occluded trace metal (loid)s (PhytTMs) remain unclear. This study assessed the accumulation of five metal (loid)s, including lead (Pb), zinc (Zn), cadmium (Cd), copper (Cu) and arsenic (As), in the organic tissues and phytoliths of wheat grown in a mixed-TTM contaminated soil under both lightly and heavily contaminated conditions. The results show that the concentrations of plant TTMs and PhytTMs were significantly (p < 0.05) positively correlated, and higher in heavily contaminated wheats than those in lightly contaminated ones. The bio-enrichment factors between phytoliths and organic tissues were higher for As (1.83), Pb (0.27) and Zn (0.30) than for Cd (0.03) and Cu (0.14), implying that As, Pb and Zn were more readily co-precipitated with silicon (Si) in phytolith structures than Cd and Cu. Network analysis of the relationship between soil and plant elements with PhytTMs showed that severe contamination could impact the homeostasis of elements in plants by altering the translocation of TTMs between soils, plants, and phytoliths. The accumulation of TTMs in phytoliths was affected by the capacity of Si deposition in tissues and chelation of TTMs with silica, which could impact the role of PhytTMs in global biogeochemical TTM cycles.

Due to worldwide production, sales and application, neonicotinoids dominate the global use of insecticides. While, neonicotinoids are considered as pinpoint neurotoxicants that impair cholinergic neurotransmission in pest insects, the sublethal effects on nontarget organisms and other neurotransmitters remain poorly understood. Thus, we investigated long-term neurological outcomes in the decomposer nematode Caenorhabditis elegans. In the adult roundworm the neonicotinoid thiacloprid impaired serotonergic and dopaminergic neuromuscular behaviors, while respective exposures to thiamethoxam showed no effects. Thiacloprid caused a concentration-dependent delay of the transition between swimming and crawling locomotion that is controlled by dopaminergic and serotonergic neurotransmission. Age-resolved analyses revealed that impairment of locomotion occurred in young as well as middle-aged worms. Treatment with exogenous serotonin rescued thiacloprid-induced swimming deficits in young worms, whereas additional exposure with silica nanoparticles enhanced the reduction of swimming behavior. Delay of forward locomotion was partly caused by a new paralysis pattern that identified thiacloprid as an agent promoting a specific rigidity of posterior body wall muscle cells and peripheral neuropathy in the nematode (lowest-observed-effect-level 10 ng/ml). On the molecular level exposure with thiacloprid accelerated protein aggregation in body wall muscle cells of polyglutamine disease reporter worms indicating proteotoxic stress. The results from the soil nematode Caenorhabditis elegans show that assessment of neurotoxicity by neonicotinoids requires acknowledgment and deeper research into dopaminergic and serotonergic neurochemistry of nontarget organisms. Likewise, it has to be considered more that different neonicotinoids may promote diverse neural end points.

Modification of biochar by low-cost iron sources has gained increasing attention to improve pollutants removal performance and reduce production costs compared to conventional chemical modifications. While such iron sources generally have complex compositions, their effects on properties of the iron-biochar composite are not well investigated. This study produced an iron-biochar (RBC) composite from co-pyrolysis of incinerated sewage sludge ash (ISSA) and peanut shell, and examined the role of silica with widespread existence in ISSA and other low-cost iron sources on properties of the iron-biochar composite relevant to As(III)/As(V) removal. Silica was found to react with iron during the pyrolysis process at 850 °C and formed iron silicon at the expense of producing zero valent iron and Fe₃O₄ which resulted in a poorer removal efficacy for As(III) and As(V) compared to the iron-biochar (FBC) made from pure Fe₂O₃ and peanut shell. Moreover, a high leaching of reactive silica from RBC was observed which affected the formation of corrosion products of ZVI and competed with arsenic for active adsorption sites. Despite this, RBC still exhibited a maximum adsorption capacity of 17.44 and 57.56 mg/g towards As(III) and As(V) respectively at pH 3.0. Overall, this study provides an interesting insight into upcycling ISSA into useful media for sorptive removal of arsenic from aqueous solutions.

Direct utilization of waste polyethylene terephthalate (PET) from the environment to form highly porous aerogel technology for oil absorption is an attractive approach from the view point of green chemistry. However, the oil absorption reaction is limited by low oil absorption capacity and less stability. For now, silica aerogel are used to solve these problem. Our goal is to substitute to these silica aerogel with PET aerogel technology. Herein, we have prepared an environmental waste PET based aerogel with 1.0:0.5 wt% PET, polyvinyl alcohol (PVA), and glutaraldehyde (GA) 0.2% v/v were dispersed in 10 mL DI water, followed by homogenization (30 min), sonication (10 min), and ageing (2 h) at 70 °C. To escape macroscopic cracking, cooling (8 h) at 4 °C was followed by freezing (6 h), freeze drying at −80 °C, and 5 mTorr for 18 h. The hybrid PET aerogel displays excellent performance towards oil absorption. Notably it showed high absorption capacity towards the different oils about 21–40 times its own weight, depending on the viscosity and density of the oil and solvents within 15–35 s, 25 °C, and 2 × 2 cm aerogel size. In addition, the aerogel shows there is no change in structure after several recycles due to high mechanical strength. Furthermore, because of the PET aerogel's high porosity (99.74%) and low density (0.0311 g/cm³), close bonding between PET-PVA occurs. Therefore, aerogel shows hydrophobic nature, good mechanical strength, high thermal stability, arrangement of the interconnected fibrillar pore network offers a high surface to volume ratio, low surface energy, high surface roughness, and more reusability. All these parameters are responsible for high oil absorption.

The dissemination of antibiotic resistance (AR) has attracted global attention because of the increasing antibiotic treatment failure it has caused. Through natural transformation, a live bacterium takes up extracellular DNA (exDNA), which facilitates AR dissemination. However, recovery of exDNA from water samples is challenging. In this study, we validated a consecutive ultrafiltration-based protocol to simultaneously recover intracellular DNA (inDNA), dissolved exDNA (Dis_exDNA, dissolved in the bulk water), and adsorbed exDNA (Ads_exDNA, adsorbed to the surfaces of suspended particles). Using hollow fiber ultrafiltration (HFUF), all DNA fractions were concentrated from environmental water samples, after which Dis_exDNA (supernatant) was separated from inDNA and Ads_exDNA (pellets) using centrifugation. Ads_exDNA was washed off from the pellets with proteinase K and sodium phosphate buffer. Dis_exDNA and Ads_exDNA were further concentrated using centrifugal ultrafiltration, from which silica binding was performed. inDNA was extracted from washed pellets with a commercial kit. For inDNA, HFUF showed recovery efficiencies of 96.5 ± 18.5% and 88.0 ± 2.0% for total cells and cultured Escherichia coli, respectively (n = 3). To represent all possible DNA fragments in water environment, exDNA with different lengths (10.0, 4.0, 1.0, and 0.5 kbp) were spiked to test the recovery efficiencies for Dis_exDNA. The whole process achieved 62.2%–62.9% recovery for 10 and 4 kbp exDNA, and 38.8%–44.5% recovery for 1.0 and 0.5 kbp exDNA. Proteinase K treatment enhanced the recovery of Ads_exDNA by 4.0–10.7 times. The protocol was applied to water samples from an urban river in Tokyo, Japan. The abundance of AR genes (ARGs) in inDNA, Dis_exDNA, and Ads_exDNA increased downstream of wastewater treatment plants. ARGs in Ads_exDNA and Dis_exDNA accounted for 1.8%–26.7% and 0.03%–20.9%, respectively, of the total DNA, implying that Ads_exDNA and Dis_exDNA are nonnegligible potential pools for the horizontal transfer of ARGs.

Supported carbon quantum dots (CQDs), used as fluorescent sensors for the detection of metal ions, have rarely been used to remove heavy metals from water. Nitrogen-doped CQDs immobilized in hydrophilic silica hydrogels exhibited a more superior sensitivity and selectivity for the detection of Re(VII) and Cr(VI) than other metal ions, including Fe(III), Fe(II), Zn(II), Cu(II) and Mn(II). For the first time, low limits of detection (LOD) of 2.3 μM for Re(VII) detection and 65 nM for Cr(VI) detection were reported by a facile method. Based on the high selectivity of fluorescent silica hydrogels for Re(VII) and Cr(VI) detection, the removal of Re(VII) and Cr(VI) by graphene oxide (GO) in water was monitored with the hydrogels used as a turn-off fluorescent sensing platform. The consistent results of the sorption isotherms of each metal on GO, which were obtained from the fluorescence spectra and by UV absorption, further verified the possibility of monitoring metal removal by fluorescence detection. Remarkably, GO removed 1186 mg/g of Re(VII) but only 178 mg/g of Cr(VI). The density functional theory (DFT) calculations indicated that both Re(VII) and Cr(VI) formed stable bonds with silica hydrogels, confirming that the interactions between the metal ions and the substrate would promote the fluorescence quenching of the supported CQDs. On the other hand, Re(VII) interacted more strongly with the carboxyl groups of GO than Cr(VI). In addition, a real-time detection system was designed to alarm the service life of a GO filter used for Re(VII) removal.

Agricultural soil is one of the main sink for both heavy metals and nanomaterials (NMs). Whether NMs can impact heavy metals uptake or bioaccumulation in plants is unknown. Here, cucumber plants were cultivated in a multi-heavy metals contaminated soil amended with four types of NMs (SiO2, TiO2, ZnS and MoS2) separately for four weeks. Physiological and biochemical parameters were determined to investigate the impact of NMs on plant growth. Inductively coupled plasma mass spectrometry was employed to determine the metal content in plants. Results showed that none of the tested NMs impacted plants biomass, but all the NMs showed different degrees of reduction in heavy metals bioaccumulation in plant roots, stems and leaves. However, four NMs showed different degrees of reduction in macro and micro nutrients uptake. MoS2 decreased the bioaccumulation of heavy metals (As, Cd, Cr, Cu, Ni, Al, Ti and Pb) for 36.4–60.6% and nutrients (Mg, Fe, K, Si and Mn) for 40.1%–50.1% in roots. Exposure to MoS2 NMs also significantly increased 23.4% of Si in leaves, 205.6% and 83.9% of Mo in roots and stems, respectively. In general, the results of this study showed promising potential for NMs to reduce uptake of heavy metals in crop plants, especially MoS2 NMs. However, the negative impacts of perturbing nutrients uptake should be paid attention as well.

This study aimed at evaluating the interactive effects of acetaminophen (AC; 400 mg kg−1) and silicon dioxide nanomaterial (nano-SiO2;3 mg kg−1) on soil-grown barley. After 14 days of growth, plant growth, evaluated in terms of fresh and dry weight, was greatly inhibited by AC, independently of being or not co-treated with nano-SiO2. Plants growing under high levels of AC did not show any increase in malondialdehyde (MDA) nor thiols contents, though levels of superoxide anion (O2.-) and hydrogen peroxide (H2O2) were increased in leaves and roots, respectively. When plants were co-treated with nano-SiO2, reactive oxygen species (ROS) content remained unchanged, but lipid peroxidation (LP) was diminished and the thiol redox network was up-regulated in roots. The evaluation of the response of the antioxidant system showed that AC affected both non-enzymatic and enzymatic components in an organ-specific manner: proline levels and superoxide dismutase (SOD) activity were enhanced, whilst catalase (CAT) activity decreased in leaves; ascorbate content and CAT activity were diminished in roots. In response to the nano-SiO2 co-treatment, this pattern was not vastly altered, despite for ascorbate peroxidase (APX), whose activity was greatly enhanced in both organs. Overall, combining biometric, biochemical and molecular approaches, this study revealed that, although AC impaired plant growth and development, it did not trigger a harsh oxidative stress condition. Maybe by this reason, the ameliorating potential of nano-SiO2 was not so evident; yet, nano-SiO2 was able to reduce LP and to stimulate thiol content and APX activity, possibly as a defense mechanism against AC-induced stress.

With the growing production and applications of silica nanoparticles (SiNPs), human exposure to these nanoparticles continues to increase. However, the possible hazards that SiNP exposure may pose to human cardiovascular system and the underlying mechanisms remain unclear. In the present study, the flow cytometry was employed to investigate the potential of four sizes (10, 25, 50, 100 nm) of SiNPs to induce the apoptosis of human umbilical vein endothelial cells (HUVECs) in culture. The apoptotic pathway was also explored through the determination of the protein expression and/or activation of p53, Bcl-2, Bax, caspases-9, -7, -3, and PARP by western blot. The results showed that all the four sizes of SiNPs could significantly elicit apoptosis in HUVECs at the tested concentrations (1, 5, 25 μg/mL), compared with the negative control (p < 0.05, p < 0.01). Moreover, the apoptotic rates were increased with the elevating levels and decreasing sizes of administrative SiNPs, showing both dose- and size-dependent effect relationships. Interestingly, the enhancing phosphorylation of p53 protein (Ser15), decreasing ratio of Bcl-2/Bax protein, and elevating activation of the downstream proteins, caspase-9, -7, -3 and PARP, were also observed with the decreasing sizes of tested SiNPs, indicating that the p53-caspase pathway is the main way of the SiNP-mediated apoptosis in HUVECs and that the size is an important parameter that determines the SiNPs' potential to induce cellular response.