• Bioavailability and phytotoxicity of rare earth metals to Triticum aestivum under various exposure scenarios.

      Gong, Bing; He, Erkai; Xia, Bing; Ying, Rongrong; Peijnenburg, Willie J G M; Liu, Yang; Qiu, Hao (2020-09-22)
      It is a daunting challenge to predict toxicity and accumulation of rare earth metals (REMs) in different exposure scenarios (e.g., varying water chemistry and metal combinations). Herein, we investigated the toxicity and uptake of La and Ce in the presence of various levels of Ca, Mg, Na, K, and at different pH values, as well as the combined effects of La and Ce in wheat Triticum aestivum. Major cations (Ca2+ and Mg2+) significantly mitigated the toxicity and accumulation of La3+/Ce3+. Toxicity and uptake of La, Ce, and La-Ce mixtures could be well quantified by the multi-metal biotic ligand model (BLM) and by the Langmuir-type uptake model with the consideration of the competitive effects of Ca2+ and Mg2+, with more than 85.1% of variations explained. The derived binding constants of Ca, Mg, La, and Ce to wheat root were respectively 3.87, 3.59, 6.97, and 6.48 on the basis of toxicity data, and 3.23, 2.84, 6.07, and 5.27 on the basis of uptake data. The use of the alternative WHAM-Ftox approach, requiring fewer model parameters than the BLM but with similar Akaike information criterion (AIC) values, successfully predicted the toxicity and accumulation of La/Ce as well as toxicity of La-Ce mixtures, with at least 76.4% of variations explained. However, caution should be taken when using this approach to explain the uptake of La-Ce mixtures. Our results provided promising tools for delineating REMs toxicity/uptake in the presence of other toxicity-modifying factors or in mixture scenarios.
    • The cation competition and electrostatic theory are equally valid in quantifying the toxicity of trivalent rare earth ions (Y and Ce) to Triticum aestivum.

      Gong, Bing; He, Erkai; Qiu, Hao; Li, Jianqiu; Ji, Jie; Peijnenburg, Willie J G M; Liu, Yang; Zhao, Ling; Cao, Xinde (2019-07-01)
      There is a lack of appropriate models to delineate the toxicity of rare earth elements (REEs) while taking into account the factors that affect bioavailability. Here, standardized wheat (Triticum aestivum L.) root elongation tests were conducted to examine the impact of exposure conditions (i.e., varying Ca, Mg, Na, K and pH levels) on Y and Ce toxicity. Cation competition and electrostatic theory were examined for their applicability in explaining the observed variations in toxicity. Only Ca2+ and Mg2+ significantly alleviated the toxicity of Y3+ and Ce3+, while Na+, K+ and H+ showed no significant effects. Based on the cation competition, the derived binding constants for the hypothetical biotic ligands of wheat logKCaBL, logKMgBL, logKYBL, and logKCeBL were 3.87, 3.59, 6.70, and 6.48, respectively. The biotic ligand model (BLM) succeeded in predicting toxicities of Y and Ce, with more than 93% of the variance in toxicity explained. Given the BLM requires large data sets for deriving model parameters, attempts were further made to explore a simpler electrostatic based model to quantify REEs toxicity. The results demonstrated that the predictive capacity of the electrostatic approach, which considers ion activities at the plasma membrane surface, was comparable to that of BLM with at least 87% of the variations in toxicity explained. This suggested that the electrostatic theory can serve as a surrogate to BLM in modeling Y and Ce toxicities. Therefore, we recommend the BLM and electrostatic-based model as effective approaches to incorporate bioavailability in quantifying REEs toxicity in the presence of various levels of other major cations.
    • Contribution of pristine and reduced microbial extracellular polymeric substances of different sources to Cu(II) reduction.

      Xu, Hang; He, Erkai; Peijnenburg, Willie J G M; Song, Lan; Zhao, Ling; Xu, Xiaoyun; Cao, Xinde; Qiu, Hao (2021-03-12)
    • Coupling mixture reference models with DGT-perceived metal flux for deciphering the nonadditive effects of rare earth mixtures to wheat in soils.

      Gong, Bing; He, Erkai; Peijnenburg, Willie J G M; Iwasaki, Yuichi; Van Gestel, Cornelis A M; Cao, Xinde; Zhao, Ling; Xu, Xiaoyun; Qiu, Hao (2020-06-02)
      The risk assessment of mixtures of rare earth elements (REEs) is hampered by a lack of fundamental understanding of their interactions in different soil types. Here, we assessed mixture interactions and toxicity to Triticum aestivum of Y and Ce in four different soils in relation to their bioavailability. Mixture toxicity was modelled by concentration addition (CA) and independent action (IA), in combination with different expressions of exposure: three equilibrium-based doses (total soil concentrations [M]tot, free ion activity in soil solution {M3+}, and the fraction (f) of metal ions bound to the biotic ligands (BLs)) and one kinetically controlled dose ([M]flux) metrics. Upon single exposure, REE toxicity was increasingly better described when using exposure expressions based on deepened understanding of their bioavailability: [M]flux > f > {M3+} > [M]tot. The mixture analyses based on [M]tot and {M3+} displayed deviations from additivity depending on the soil type. With the parameters derived from single exposures, the BLM approach gave better predictions of mixture toxicity (R2 ~ 0.70) than when using CA and IA based on either [M]tot or {M3+} (R2 < 0.64). About 30% of the variance in toxicity remained unexplained, challenging the view that the free metal ion is the main bioavailable form under the BLM framework based on thermodynamic equilibrium. Toxicity was best described when accounting for changes in the size of the labile metal pool by using a kinetically controlled dose metric (R2 ~ 0.80). This suggests that dynamic bioavailability analysis could provide a robust basis for modeling and reconciling the interplays and toxicity of metal mixtures in different soils.
    • The crucial role of a protein corona in determining the aggregation kinetics and colloidal stability of polystyrene nanoplastics.

      Li, Xing; He, Erkai; Jiang, Ke; Peijnenburg, Willie J G M; Qiu, Hao (2020-12-11)
      Nanosized plastics are considered as being a class of contaminants of emerging concern. The interaction between nanoplastics and proteins may significantly influence the environmental behavior and fate of nanoplastics. Here, we employed time-resolved dynamic light scattering to explore the aggregation kinetics and stability of polystyrene nanoparticles (PSNPs) exposed to a model globular protein (bovine serum albumin, BSA) in the presence of a number of typical electrolytes (NaCl, CaCl2, and Na2SO4). With the increase of the BSA concentration, the amount of BSA adsorbed on the surface of negatively charged PS-Bare (non-modified) and PS-COOH (carboxyl-modified) increased, resulting in higher dispersibility in comparison to the treatment without BSA. This stabilization effect derived from the protein corona structure was revealed by combining characterization techniques and visualized by transmission electron microscopy. Upon addition of NaCl and CaCl2, the aggregation of positively charged PS-NH2 (amino-modified) was inhibited by the BSA addition possibly due to the screening of the attractive patch-charge force and the competition for adsorption of cations between PS-NH2 and the protein. When Na2SO4 was present in the suspension, BSA addition significantly increased PS-NH2 aggregation rate due to patch-charge attraction and the high performance of SO42- in attaching to particles and charge neutralization. These findings shed light on the interactions between PSNPs and proteins, which were shown to vary with the composition of the surface coatings of PSNPs. The newly gained knowledge will help us to forecast the transport and fate of PSNPs in natural aqueous systems.
    • Effective Modeling Framework for Quantifying the Potential Impacts of Coexisting Anions on the Toxicity of Arsenate, Selenite, and Vanadate.

      Ji, Jie; He, Erkai; Qiu, Hao; Peijnenburg, Willie J G M; Van Gestel, Cornelis A M; Cao, Xinde (2020-02-18)
      Hardly any study has focused on the quantitative modeling of the toxicity of anionic metal(loid)s and their mixtures in the presence of potentially competing anions. Here, we designed a univariate experiment (420 treatments) to investigate the influence of various anions (phosphate, sulfate, carbonate, and OH-) on the toxicity of single anionic metal(loid)s (arsenate, selenite, and vanadate) and a full factorial mixture experiment (196 treatments) to examine the interactions and toxicity of As-Se mixtures at 4 phosphate levels. Standard root elongation tests with wheat (Triticum aestivum) were performed. A modeling framework, resembling the biotic ligand model (BLM) for cationic metals, was developed, extended, and applied to explain anion competitions and mixture effects. Carbonate significantly alleviated the toxicity of all three metal(loid)s. The toxicity of As was significantly mitigated by phosphate, while V toxicity was significantly relieved by OH-. The BLM-like model successfully explained more than 93% of the observed variance in toxicity. With the parameters derived from single-metal(loid) exposures, the developed BLM-toxic unit model reached an overall prediction performance of 78% in modeling the toxicity of As-Se mixtures at varying phosphate levels, validating the effectiveness of the model framework. It is concluded that by taking possible anion competitions and interactions into account, the BLM-type approaches can serve as promising tools for the risk assessment of single and mixed metal(loid)s contamination.
    • Elucidating Toxicodynamic Differences at the Molecular Scale between ZnO Nanoparticles and ZnCl in via Nontargeted Metabolomics.

      He, Erkai; Qiu, Rongliang; Cao, Xinde; Song, Lan; Peijnenburg, Willie J G M; Qiu, Hao (2020-03-17)
      Much effort has been devoted to clarifying the comparative toxicity of ZnO nanoparticles (NPs) and Zn ions; however, little is known about their toxicodynamic processes at the metabolic level. Here, we investigated the acute (2d) and chronic (7d) effects to a soil species, Enchytraeus crypticus, of two sublethal doses of ZnO-NPs and ZnCl2 (10 and 30 mg/L Zn) using ultrahigh performance liquid chromatography-quadrupole-time-of-flight/mass spectrometry-based metabolomics. The metabolomics analysis identified 99, 128, 121, and 183 significantly changed metabolites (SCMs) in E. crypticus exposed to ZnO-NPs for 2d, ZnCl2 for 2d, ZnO-NPs for 7d, and ZnCl2 for 7d, respectively, suggesting that ZnCl2 induced stronger metabolic reprogramming than ZnO-NPs, and a longer exposure time caused greater metabolite changes. Among the SCMs, 67 were shared by ZnO-NPs and ZnCl2 after 2d and 84 after 7d. These metabolites were mainly related to oxidative stress and antioxidant defense, membrane disturbance, and energy expenditure. The targeted analysis on physiological and biochemical responses further proved the metabolic observations. Nevertheless, 32 (33%) and 37 (31%) SCMs were found only in ZnO-NP treatments after 2 and 7d, respectively, suggesting that the toxicity of ZnO-NPs cannot be solely attributed to the released Zn ions. Metabolic pathway analysis revealed significant perturbations of galactose metabolism, amino sugar and nucleotide sugar metabolism, and glycerophospholipid metabolism in all test groups. Based on involvement frequency, glucose-1-phosphate, glycerol 3-phosphate, and phosphorylcholine could serve as universal biomarkers for exposure to different Zn forms. Four pathways perturbed by ZnO-NPs were nanospecific upon acute exposure and three upon chronic exposure. Our findings demonstrated that metabolomics is an effective tool for understanding the molecular toxicity mechanism and highlighted that time-series measurements are essential for discovering and comparing modes of action of metal ions and NPs.
    • Impact of CeO nanoparticles on the aggregation kinetics and stability of polystyrene nanoplastics: Importance of surface functionalization and solution chemistry.

      Li, Xing; He, Erkai; Xia, Bing; Van Gestel, Cornelis A M; Peijnenburg, Willie J G M; Cao, Xinde; Qiu, Hao (2020-08-20)
      The increasing application of plastics is accompanied by increasing concern over the stability and potential risk of nanoplastics. Heteroaggregation with metal-based nanoparticles (e.g., CeO2-NPs) is critical to the environmental mobility of nanoplastics, as they are likely to be jointly emitted to the aquatic environment. Here, time-resolved dynamic light scattering was employed to evaluate the influence of CeO2-NPs on the aggregation kinetics of differentially surface functionalized polystyrene nanoplastics (PS-NPs) in various water types. Natural organic matters and ionic strength were dominating factors influencing the heteroaggregation of PS-NPs and CeO2-NPs in surface waters. The critical coagulation concentrations of PS-NPs were dependent on their surface coatings, which decreased in the presence of CeO2-NPs due to electrostatic attraction and/or specific adsorption. Incubation of PS-NPs and CeO2-NPs under different pH confirmed the importance of electrostatic force in the aggregation of PS NPs. A relatively low humic acid (HA) concentration promoted the heteroaggregation of NH2-coated PS-NPs and CeO2-NPs because the introduction of a HA surface coating decreased the electrostatic hindrance. At high HA concentrations, the aggregation was inhibited by steric repulsion. The combined effects of high efficiency of double layer compression, bridging and complexation contributed to the high capacity of Ca2+ in destabilizing the particles. These findings demonstrate that the environmental behavior of nanoplastics is influenced by the presence of other non-plastic particles and improve our understanding of the interactions between PS-NPs and CeO2-NPs in complex and realistic aqueous environments.
    • Interactions of CeO nanoparticles with natural colloids and electrolytes impact their aggregation kinetics and colloidal stability.

      Li, Xing; He, Erkai; Zhang, Miaoyue; Peijnenburg, Willie J G M; Liu, Yang; Song, Lan; Cao, Xinde; Zhao, Ling; Qiu, Hao (2020-03-15)
      The aggregation kinetics and colloidal stability of CeO2-NPs in the presence of monovalent or divalent electrolytes, as well as inorganic (kaolin and goethite) and organic (humic acid, HA) colloids were evaluated using time-resolved dynamic light scattering, advanced spectroscopic tools, and theoretical calculations. Critical coagulation concentrations for CeO2-NPs were generally lower in CaCl2 than that in NaCl electrolyte. The negatively charged kaolin accelerated CeO2-NPs aggregation due to electrostatic attraction, whilst opposite phenomenon was observed for the positively charged goethite in NaCl solution. In CaCl2 solution, goethite destabilized CeO2-NPs because of its well-crystal structure and specific adsorption of Ca2+. The presence of 0.1 mg C/L HA decreased the surface charge of CeO2-NPs, resulting in lower critical coagulation concentrations. Increasing the HA concentration from 0.1 to 1 mg C/L improved CeO2-NPs stability, mainly via electrostatic and steric repulsion. The Ca2+-bridging and complexation contributed significantly to CeO2-NPs aggregation. Additional aggregation experiments in seven natural waters revealed that CeO2-NPs remained stable in water types with high contents of organic colloids and low levels of salts, thus having higher transport potential. These findings provided new insights into the interactive influence of naturally occurring colloids and ions on the heteroaggregation behavior and fate of CeO2-NPs.
    • The promoted dissolution of copper oxide nanoparticles by dissolved humic acid: Copper complexation over particle dispersion.

      Liu, Siqian; Liu, Yang; Pan, Bo; He, Ying; Li, Bowen; Zhou, Dandan; Xiao, Yinlong; Qiu, Hao; Vijver, Martina G; Peijnenburg, Willie J G M (2020-04-01)
      Humic substances are the dominant dissolved organic matter fraction in the aqueous phase of environmental media. They would inevitably react with chemicals released into the environment. The influence of dissolved humic acid (DHA) on the dissolution and dispersion of copper oxide nanoparticles (CuO NPs, 50 nm, 49.57 mg L-1) was therefore investigated in the present study. In addition to dispersing CuO NPs and reducing the size of the aggregates, the amount of released Cu from CuO NPs was found to increase over time with increasing concentrations of DHA, 96% of which was present as organic complexes after 72 h. At DHA concentrations exceeding 16.09 mg C L-1, the complexation coefficients of DHA with Cu and the adsorptivity of CuO NPs to DHA were both reduced due to increased homo-conjugation of DHA as promoted by negative charge-assisted H-bond. Although the adsorption capacity of DHA kept increasing up to 57.07 mg C L-1, the hydrodynamic diameter and ζ-potential were similar and the percentages of total released Cu continued to increase linearly to 4.92% at higher levels of DHA (30.13-57.07 mg C L-1). Thereupon, DHA promoted the dissolution of CuO NPs in a concentration-dependent fashion. The driving force was complexation of Cu by DHA, rather than the balancing between the exposed and the covered surface area of the CuO NPs due to DHA adsorption. Our findings facilitate understanding the underlying mechanisms on how DHA impacts the CuO NPs environmental behavior (or fate) as well as on their kinetics.
    • The shuttling effects and associated mechanisms of different types of iron oxide nanoparticles for Cu(II) reduction by Geobacter sulfurreducens.

      Qiu, Hao; Xu, Hang; Xu, Zibo; Xia, Bing; Peijnenburg, Willie J G M; Cao, Xinde; Du, Huihui; Zhao, Ling; Qiu, Rongliang; He, Erkai (2020-07-05)
    • Two years of aging influences the distribution and lability of metal(loid)s in a contaminated soil amended with different biochars.

      He, Erkai; Yang, Yuxi; Xu, Zibo; Qiu, Hao; Yang, Fan; Peijnenburg, Willie J G M; Zhang, Weihua; Qiu, Rongliang; Wang, Shizhong (2019-04-09)
      A two-year soil incubation experiment was performed to investigate the long-term impacts of biochars (kenaf core and sewage sludge biochar (KBC and SBC) pyrolyzed at 350 °C and 550 °C) on metal(loid)s immobilization. Both KBC and SBC can immobilize Pb and Cu in contaminated soil, whereas they showed little effects on the immobilization of Zn, Cd and As. Interactions between the biochar and soil during two-year aging changed the metal species on both soil and biochar particles. KB350 formed more biochar-mineral complexes and O-containing functional groups than KB550 and thus transferred more residual metal(loid)s to their reducible species. More metal(loid)s sorbed on the KB350 than KB550 after two-year aging. However, SBC changed the acid-soluble species of metal(loid)s into the residual species during the aging process, probably due to the release of phosphate. Upon aging, SB550 exhibited a more significant increase in the residual metal amount and more sorption of metal(loid)s on the biochar particles than SB350 due to sorption of organic carbon and formation of meta-kaolinite. A key finding of our study was that different biochars have contrasting impacts on metal speciation and lability upon 2-year aging. This should be considered in assessing the actual risk of biochar-amended soils.