•Co-transport of o-MWCNTs with organic contaminants in soil columns was investigated.•The eluted PHE was mainly in the o-MWCNTs-associated form.•The eluted OTC was mainly in the dissolved form.•O-MWCNTs acted as vehicles facilitating the PHE transport.•O-MWCNTs competed for adsorption sites on soils and enhanced the OTC mobility.To date mechanisms underlying co-transports of engineered nanomaterials (ENMs) with contaminants have not been adequately explored, which involve complex interactions among ENMs, contaminants, and soils. This study investigated co-transport behaviors of 3 oxidized-multiwalled carbon nanotubes (o-MWCNTs) with phenanthrene (PHE) and oxytetracycline (OTC) in soil and sediment columns. Sorptions and desorptions of PHE and OTC by the o-MWCNTs were examined to facilitate the discussion of co-transport mechanisms. The results showed that mobilities of PHE and OTC in the columns were significantly enhanced by the presences of o-MWCNTs in the influents; the eluted o-MWCNTs were positively correlated to the eluted total PHE but negatively correlated to the eluted total OTC; the eluted PHE was mainly in the o-MWCNTs-associated form, while it was mainly the dissolved OTC breaking through the columns. It was thus concluded that the o-MWCNTs acted as vehicles facilitating the PHE transport, while besides the vehicle effect the o-MWCNTs also competed for the adsorption sites on soil particles with OTC and thereby enhancing the OTC mobility. These findings provide new insight into the mechanisms regulating co-transports of ENMs and contaminants in porous media.Download high-res image (230KB)Download full-size image

Surface oxidation can alter physicochemical properties of multiwalled carbon nanotubes (MWCNTs) and influence their aqueous stabilization. Many techniques have been used to characterize the physicochemical properties and aqueous stabilization of MWCNTs. However, the relationship between the change in physicochemical property and the aqueous stabilization of MWCNTs merits more studies, and the multiple characterization techniques have not been well compared. This study systematically and comparatively investigated the effect of oxidation on the physicochemical properties and aqueous stabilization of MWCNTs using multiple analysis methods. Increased surface area, disclosed tube ends, defects on the sidewalls, disruption of the electronic structure, and removal of metal catalysts and amorphous carbon were observed for the oxidized MWCNTs (o-MWCNTs) using the multipoint Brunauer-Emmett-Teller (BET) method, transmission electron microscope observation, Raman spectroscopy, UV-Vis spectroscopy, and thermogravimetric analysis. An oxidation-time-dependent increase in oxygen content of the MWCNTs was verified by the methods of elemental analysis, mass difference calculation, and X-ray photoelectron spectroscopy (XPS). Fourier transform infrared spectroscopy, XPS, and the Boehm titration were employed to study the functionalities on the MWCNT surfaces. Despite the limitations of these techniques, the results indicated that the dramatic increase in carboxyl groups was mainly responsible for the significant increase in oxygen content after the oxidation. The dissociation of the grafted functional groups increased electronegativity of the o-MWCNTs and facilitated the aqueous stabilization of o-MWCNTs through electrostatic repulsions. The oxidation affected the UV-Vis absorbance of MWCNT suspensions. The absorbances at 800 nm of the stabilized MWCNT suspensions had a good correlation with the MWCNT concentrations and could be used to quantify the MWCNT suspensions. The findings of this work are expected to boost the research on carbon nanotubes and their environmental behaviors.

Ubiquitous dissolved organic matter (DOM) from various sources can interact with discharged multiwalled carbon nanotubes (MWCNTs) and pose distinct effects on the toxicity of MWCNTs to aquatic organisms. This study for the first time compared effects of a natural originated humic acid (HA) and two synthetic surfactants (sodium dodecylbenzenesulfonate – SDBS, octyl phenoxy polyethoxyethanol – TX100) on the toxicity of MWCNTs to a unicellular green alga (Chlorella pyrenoidosa). Algal growth inhibition, cell surface hydrophobicity, oxidative stress, MWCNT-cell agglomeration, and cell morphology change and internalization of MWCNTs were assayed to investigate individual and combined toxicities of MWCNTs and DOMs, and mechanisms underlying different effects of DOMs on the toxicity of MWCNTs were specifically addressed. It is shown that SDBS and TX100 were capable of promoting cell internalization of MWCNTs and triggering higher oxidative stress, and thereby increasing the toxicity of MWCNTs; while HA could alleviate the toxicity of MWCNTs through limiting cell internalization of MWCNTs and reducing oxidative stress. The outcomes of this work shed new light on the assessment of ecological toxicity of discharged nanomaterials.

Discharged oxide nanoparticles (NPs) have been shown toxic to unicellular algae, yet the research on heteroagglomeration between NPs and cells as an important precondition of the toxicity is scarce. This study for the first time investigated heteroagglomerations between various NPs and algal cells (Chlorella pyrenoidosa) and analyzed influencing factors including pH and ionic strength (IS) through cosettling experiment, transmission electron microscopic (TEM) observation, and Derjaguin–Landau–Verwey–Overbeek (DLVO) calculation. The examined NPs included anatase and rutile TiO2, microporous and spherical SiO2, and α-form and β-form Al2O3. The results of cosettling experiments coincided well with the TEM observations, whereas the DLVO theory could only partly explain the NP–cell heteroagglomerations. The NP–cell heteroagglomeration for rutile TiO2 and β-form Al2O3 was weak and insensitive to pH or IS. Preferential heteroagglomeration occurred at low pH or high IS for microporous SiO2, while marked heteroagglomeration only occurred under the neutral and low IS condition for anatase TiO2. The heteroagglomeration for spherical SiO2 was insensitive to pH but increased with increasing IS, while the heteroagglomeration for α-form Al2O3 occurred at low pH and irrelevant to IS. The work will shed new light on the bionano interfacial interaction and help to understand biological effects of NPs.

Natural organic matter (NOM) has a profound effect on the colloidal stability of discharged C60 nanoparticles in the water environment, which influences the environmental behaviors and risks of C60 and therefore merits more specific studies. This study investigates the effects of humic acid (HA), as a model NOM, on the aqueous stabilization of C60 powder and the colloidal stability of a previously suspended C60 suspension (aqu/nC60) with variations of pH values and ionic strengths. Our results reveal that HA could disperse C60 powder in water to some degree, but was unable to stably suspend them. The aqu/nC60 could remain stable at pH>4 but was destabilized at lower pH values. However, the colloidal stability of aqu/nC60 in the presence of HA was insensitive to pH 3–11, owing to the adsorption of HA onto nC60 and the increased electrosteric repulsions among nC60 aggregates. The colloidal stability of aqu/nC60, with and without HA, decreased as we increased the valence and concentration of the added cations. HA was found to mitigate the destabilization effect of Na+ on the colloidal stability of aqu/nC60 by increasing the critical coagulation concentration (CCC) of Na+, while HA lowered the CCCs of Ca2+ and La3+ probably by the bridging effect of nC60 with HA aggregates formed through the intermolecular bridging of the HA macromolecules via cation complexation at high concentrations of cations with high valences.腐殖酸 (HA) 对富勒烯 (C60) 粉末的悬浮作用以及 pH、 离子强度对 HA-C60 悬浮性能的影响。研究水质条件对 C60 悬浮性能的影响。测定 C60 粉末在HA 溶液中的 zeta 电位, 水力学粒径和悬浮浓度; HA 存在下, C60 悬浮体系的 zeta 电位与水力学粒径随 pH 的变化及 C60 悬浮体系团聚动力学随离子强度的变化。HA 对 C60 粉末起到一定的分散作用, 但不能使其长时间稳定悬浮于水中。 当 pH<4 时, C60 水悬液开始沉 而当 HA 存在时, C60 水悬液在 pH 3–11 范围内都保持稳定, 这是由于 HA 吸附于 C60 表面, 通过静电排斥和空间位阻作用, 促进 C60 分散悬浮。 C60 水悬液的稳定性随盐离子价位和浓度升高而降低。 HA 会抑制 Na+ 对 C60 水悬液的脱稳作用; 但高价离子 Ca2+ 和 La3+ 存在时, HA 与 C60 之间会发生桥联从而促进 C60 水悬液脱稳沉淀。

Nano–bio interfacial interactions that can likely regulate the potential toxicity of nanoparticles (NPs) toward aquatic organisms are receiving increasing research interest worldwide and warrant more investigation. This review presents an overview of already-known nano–bio interactions and some speculations on the interfaces between NPs and aquatic organisms, in order to gain a new insight into the biological effects of NPs in the aquatic environment. The fundamental interfaces between NPs and organism cells and the main biophysicochemical interactions that occur at the nano–bio interfaces are described. The interfacial interactions, focused on adsorption and internalization, during the contact of NPs with microorganisms, hydrophytes, invertebrates and fish were reviewed. The effects of NP properties and suspending states as well as environmental conditions including pH, ionic strength, natural organic matter and other factors on the interfacial interactions were elucidated. Furthermore, the analytical methods employed in the interfacial interaction investigations were also briefly introduced. Future research directions of nano–bio interactions were prospected.

Concurrent with the increasing production and application of carbon nanotubes (CNTs) comes an increasing likelihood of CNTs presenting in the aquatic environment, and thereby potentially threatening aquatic organisms via toxic mechanisms that are, at present, poorly understood. This study systematically investigated the toxicity of three multiwalled CNT (MWCNT) samples toward a green alga (Chlorella sp.), focusing on examining and quantifying the contributions of five possible mechanisms to the algal growth inhibition. The results showed that the MWCNTs significantly inhibited the algal growth. The contribution of metal catalyst residues in the MWCNTs to the algal growth inhibition was negligible, as was the contribution from the MWCNTs’ adsorption of nutrient elements. The algal toxicity of MWCNTs could mainly be explained by the combined effects of oxidative stress, agglomeration and physical interactions, and shading effects, with the quantitative contributions from these mechanisms depending on the MWCNT size and concentration. At MWCNT concentrations around 96 h IC50, the oxidative stress accounted for approximately 50% of the algal growth inhibition, whereas the agglomeration and physical interactions, and the shading effects each took approximately 25% of the responsibility.

Numerous studies suggested carbon nanotubes (CNTs) as a type of promising sorbent for heavy metals from water and explained the sorption mechanism mainly by oxygen-containing functional groups on CNT surfaces but neglected the potential role of metal catalyst residues in CNTs. This is a first study showing that metal impurities could dominate the sorption of one type of commercially available CNTs (P-CNTs) for Pb(II) from water, which will help to understand and guide environmental applications of CNTs as a sorbent. Sorption capacity of P-CNTs (27.3 mg g−1) for Pb(II) was much higher than that of the water-washed P-CNTs (W-CNTs, 4.7 mg g−1). SEM-EDS and ICP-MS analyses showed that both P-CNTs and W-CNTs contained metal impurities (mainly Co and Mo) which released into the solutions during the sorption, especially P-CNTs. XAFS examination and precipitation experiments demonstrated that PbMoO4 formation between Pb(II) and CNT-released MoO42− and subsequent precipitation in the sorptive solutions was the dominant mechanism for the apparent sorption of Pb(II) by P-CNTs.

Carbon nanotubes (CNTs) are prone to aggregation and precipitation in water due to their high hydrophobicity and aspect ratio. However, the addition of dissolved organic matter (DOM) has been reported to disperse and stabilize certain CNTs, suggesting the potential transport and bioavailability of CNTs in natural aqueous environments. For a better understanding of the CNT–DOM interaction, five multiwalled CNTs with outer diameters of <10 (MWCNT10), 10–20 (MWCNT20), 20–40 (MWCNT40), 40–60 (MWCNT60), and 60–100 nm (MWCNT100) were used to investigate their sorptive and suspension behavior in tannic acid (TA, as a DOM surrogate) solution; the effects of ionic strength and pH on the TA–CNT interaction were examined. Suspension of MWCNTs sharply improved with increasing TA concentration and leveled off at an initial TA concentration ca. 20 mg/L. Suspension of MWCNTs was in the order of MWCNT40 > MWCNT60 > MWCNT20 > MWCNT100 > MWCNT10. The TA-stabilized CNTs were stable within pH 5–11, while they quickly precipitated at pH < 5. Different ions (Na+, Mg2+, Ca2+, or La3+) aggregated the stabilized CNTs, with a critical coagulation concentration exponentially correlated to ionic valence. Changes of steric repulsion and electrostatic interaction with the added TA could account for the variation of CNT stability.

Nano–bio interfacial interactions that can likely regulate the potential toxicity of nanoparticles (NPs) toward aquatic organisms are receiving increasing research interest worldwide and warrant more investigation. This review presents an overview of already-known nano–bio interactions and some speculations on the interfaces between NPs and aquatic organisms, in order to gain a new insight into the biological effects of NPs in the aquatic environment. The fundamental interfaces between NPs and organism cells and the main biophysicochemical interactions that occur at the nano–bio interfaces are described. The interfacial interactions, focused on adsorption and internalization, during the contact of NPs with microorganisms, hydrophytes, invertebrates and fish were reviewed. The effects of NP properties and suspending states as well as environmental conditions including pH, ionic strength, natural organic matter and other factors on the interfacial interactions were elucidated. Furthermore, the analytical methods employed in the interfacial interaction investigations were also briefly introduced. Future research directions of nano–bio interactions were prospected.