• Current Knowledge on the Use of Computational Toxicology in Hazard Assessment of Metallic Engineered Nanomaterials.

      Chen, Guangchao; Peijnenburg, Willie; Xiao, Yinlong; Vijver, Martina G (2017-07-12)
      As listed by the European Chemicals Agency, the three elements in evaluating the hazards of engineered nanomaterials (ENMs) include the integration and evaluation of toxicity data, categorization and labeling of ENMs, and derivation of hazard threshold levels for human health and the environment. Assessing the hazards of ENMs solely based on laboratory tests is time-consuming, resource intensive, and constrained by ethical considerations. The adoption of computational toxicology into this task has recently become a priority. Alternative approaches such as (quantitative) structure-activity relationships ((Q)SAR) and read-across are of significant help in predicting nanotoxicity and filling data gaps, and in classifying the hazards of ENMs to individual species. Thereupon, the species sensitivity distribution (SSD) approach is able to serve the establishment of ENM hazard thresholds sufficiently protecting the ecosystem. This article critically reviews the current knowledge on the development of in silico models in predicting and classifying the hazard of metallic ENMs, and the development of SSDs for metallic ENMs. Further discussion includes the significance of well-curated experimental datasets and the interpretation of toxicity mechanisms of metallic ENMs based on reported models. An outlook is also given on future directions of research in this frontier.
    • Developing species sensitivity distributions for metallic nanomaterials considering the characteristics of nanomaterials, experimental conditions, and different types of endpoints.

      Chen, Guangchao; Peijnenburg, Willie J G M; Xiao, Yinlong; Vijver, Martina G (2017-04-05)
      A species sensitivity distribution (SSD) for engineered nanomaterials (ENMs) ranks the tested species according to their sensitivity to a certain ENM. An SSD may be used to estimate the maximum acceptable concentrations of ENMs for the purpose of environmental risk assessment. To construct SSDs for metal-based ENMs, more than 1800 laboratory derived toxicity records of metallic ENMs from >300 publications or open access scientific reports were retrieved. SSDs were developed for the metallic ENMs grouped by surface coating, size, shape, exposure duration, light exposure, and different toxicity endpoints. It was found that PVP- and sodium citrate- coatings enhance the toxicity of Ag ENMs as concluded from the relevant SSDs. For the Ag ENMs with different size ranges, differences in behavior and/or effect were only observed at high exposure concentrations. The SSDs of Ag ENMs separated by both shape and exposure duration were all nearly identical. Crustaceans were found to be the most vulnerable group to metallic ENMs. In spite of the uncertainties of the results caused by limited data quality and availability, the present study provided novel information about building SSDs for distinguished ENMs and contributes to the further development of SSDs for metal-based ENMs.
    • Elucidating the effects of TiO nanoparticles on the toxicity and accumulation of Cu in soybean plants (Glycine max L.).

      Xiao, Yinlong; Du, Ying; Xiao, Yue; Zhang, Xiaohong; Wu, Jun; Yang, Gang; He, Yan; Zhou, Yaoyu; Peijnenburg, Willie J G M; Luo, Ling (2021-05-11)
      Copper (Cu) pollution is common in the soil. Due to the widespread application of TiO2 NPs, there is a high propensity for the co-occurrence of TiO2 nanoparticles (NPs) and Cu in agricultural soils. It is therefore imperative to evaluate the joint effects of TiO2 NPs and Cu on crops. In this study, the mutual effects of TiO2 NPs and Cu on their toxicity and accumulation in soybean seedlings and on their fates in a hydroponic system were determined. When Cu was at levels of 1 and 2 mg/L, the co-occurring TiO2 NPs at a non-toxic concentration (10 mg/L) significantly enhanced the toxicity and accumulation of Cu and Ti in soybeans, and inhibited the translocation of Cu from soybean roots to shoots. However, when the Cu concentration for co-exposure was ≥ 5 mg/L, such mutual effects disappeared. The amount of Cu ions adsorbed onto TiO2 NPs after 48 h of co-exposure gradually increased from 31 to 118 mg/g when the Cu concentration was increased from 1 to 20 mg/L. The aggregation and sedimentation of TiO2 NPs were significantly increased after 48 h of co-exposure with the Cu at a concentration higher than 5 mg/L, as compared to the single TiO2 NPs exposure. The increasing aggregation and sedimentation might reduce the bioavailability of TiO2 NPs associated with the adsorbed Cu to soybeans, and consequently alleviate or even neutralize the enhanced toxicity and accumulation of Cu in soybeans exerted by the co-existing TiO2 NPs. Our results thus suggest that consideration of the impact of TiO2 NPs on the phytotoxicity of heavy metals, and specifically Cu, needs to be interpreted with care, and highlight the importance of integrating the interaction and fates of TiO2 NPs and metals into their risk assessment.
    • Impact of water chemistry on the behavior and fate of copper nanoparticles.

      Xiao, Yinlong; Vijver, Martina G; Peijnenburg, Willie J G M (2018-03)
      A full-factorial test design was applied to systematically investigate the contribution and significance of water chemistry parameters (pH, divalent cations and dissolved organic carbon (DOC) concentration) and their interactions on the behavior and fate of copper nanoparticles (CuNPs). The total amount of Cu remaining in the water column after 48 h of incubation was mostly influenced by divalent cation content, DOC concentration and the interaction of divalent cations and DOC. DOC concentration was the predominant factor influencing the dissolution of CuNPs, which was far more important than the effect of pH in the range from 6 to 9 on the dissolution of the CuNPs. The addition of DOC at concentrations ranging from 5 to 50 mg C/L resulted in a 3-5 fold reduction of dissolution of CuNPs after 48 h of incubation, as compared to the case without addition of DOC. Divalent cation content was found to be the most influential factor regarding aggregation behavior of the particles, followed by DOC concentration and the interaction of divalent cations and DOC. In addition, the aggregation behavior of CuNPs rather than particulate dissolution explained most of the variance in the sedimentation profiles of CuNPs. These results are meaningful for improved understanding and prediction of the behavior and fate of metallic NPs in aqueous environments.
    • Impact of water chemistry on the particle-specific toxicity of copper nanoparticles to Daphnia magna.

      Xiao, Yinlong; Peijnenburg, Willie J G M; Chen, Guangchao; Vijver, Martina G (2018-01-01)
      Toxicity of metallic nanoparticle suspensions (NP(total)) is generally assumed to result from the combined effect of the particles present in suspensions (NP(particle)) and their released ions (NP(ion)). Evaluation and consideration of how water chemistry affects the particle-specific toxicity of NP(total) are critical for environmental risk assessment of nanoparticles. In this study, it was found that the toxicity of Cu NP(particle) to Daphnia magna, in line with the trends in toxicity for Cu NP(ion), decreased with increasing pH and with increasing concentrations of divalent cations and dissolved organic carbon (DOC). Without the addition of DOC, the toxicity of Cu NP(total) to D. magna at the LC50 was driven mainly by Cu NP(ion) (accounting for ≥53% of the observed toxicity). However, toxicity of Cu NP(total) in the presence of DOC at a concentration ranging from 5 to 50mg C/L largely resulted from the NP(particle) (57%-85%), which could be attributable to the large reduction of the concentration of Cu NP(ion) and the enhancement of the stability of Cu NP(particle) when DOC was added. Our results indicate that water chemistry needs to be explicitly taken into consideration when evaluating the role of NP(particle) and NP(ion) in the observed toxicity of NP(total).
    • 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.
    • A Review of Recent Advances towards the Development of (Quantitative) Structure-Activity Relationships for Metallic Nanomaterials.

      Chen, Guangchao; Vijver, Martina G; Xiao, Yinlong; Peijnenburg, Willie J G M (2017-08-31)
      Gathering required information in a fast and inexpensive way is essential for assessing the risks of engineered nanomaterials (ENMs). The extension of conventional (quantitative) structure-activity relationships ((Q)SARs) approach to nanotoxicology, i.e., nano-(Q)SARs, is a possible solution. The preliminary attempts of correlating ENMs' characteristics to the biological effects elicited by ENMs highlighted the potential applicability of (Q)SARs in the nanotoxicity field. This review discusses the current knowledge on the development of nano-(Q)SARs for metallic ENMs, on the aspects of data sources, reported nano-(Q)SARs, and mechanistic interpretation. An outlook is given on the further development of this frontier. As concluded, the used experimental data mainly concern the uptake of ENMs by different cell lines and the toxicity of ENMs to cells lines and Escherichia coli. The widely applied techniques of deriving models are linear and non-linear regressions, support vector machine, artificial neural network, k-nearest neighbors, etc. Concluded from the descriptors, surface properties of ENMs are seen as vital for the cellular uptake of ENMs; the capability of releasing ions and surface redox properties of ENMs are of importance for evaluating nanotoxicity. This review aims to present key advances in relevant nano-modeling studies and stimulate future research efforts in this quickly developing field of research.