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Inorganic ligands, ubiquitous in the natural environment, can interact with iron oxide minerals. To date, our knowledge regarding the effects of inorganic ligands on the adsorption properties of antibiotics onto iron oxides is still limited. In this work, the influences of different inorganic ligands (chosen iodate, silicate, and phosphate as the model ligands) on the adsorption of tetracycline (TC) onto hematite were examined. Adsorption isotherms indicated that inorganic ligands inhibited TC adsorption. The observations were attributed to the increase of electrostatic repulsion between anionic species (i.e., TC - ) and negatively charged hematite particles as well as the competition between TC - species and inorganic ligand anions for the adsorption sites on hematite surfaces. Interestingly, the inhibitory effects of the three inorganic ligands were in the order of phosphate > silicate > iodate; the trend was stemmed from their differences in the binding affinities to hematite and the molecular size. When the background solutions contained divalent cations (e.g., Ca 2+ ), surface precipitation of Ca-inorganic ligand compounds on hematite was another important mechanism for the inhibitory effects. Furthermore, adsorption of TC onto hematite with or without inorganic ligands was strongly affected by solution pH, which was due to the combination of the amphoteric behavior of TC and highly pH-dependent surface charges of the hematite mineral. Current results highlight the critical roles of ubiquitous inorganic ligands in revealing the fate of tetracycline antibiotics in natural systems., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

With the broadly application of antibiotics to treat infectious diseases in humans and animals, antibiotic contaminants such as tetracycline (TC) and ciprofloxacin (CIP) have been detected in soil environments, where iron oxide minerals and phosphate are ubiquitous. To date, the influence of phosphate on the adsorption behaviors of TC/CIP onto iron oxides is still poorly understood. In this study, the effects of phosphate on the adsorptions of TC and CIP onto iron oxide minerals were investigated. Adsorption isotherms showed that the adsorption affinities of TC and CIP onto the three iron oxide minerals were in the order of goethite > hematite > magnetite with or without phosphate, the trend was dominated by different surface area and amount of surface hydroxyl groups of iron oxide minerals. Meanwhile, TC contains more functional groups than CIP for bonding, which resulted in greater adsorption affinity of three iron oxides to TC than that to CIP. Interestingly, phosphate weakened TC adsorption, while enhanced CIP adsorption, on the three iron oxides. This observation was ascribed to that phosphate anion enhanced the surface negative charge of iron oxides, which reinforced the electrostatic repulsion between iron oxides and negatively charged TC, also reinforced the electrostatic attraction between iron oxides and positively charged CIP. Furthermore, the inhibitory effect of phosphate on TC adsorption was dramatically enhanced at high pH, while the promoting effect of phosphate on CIP adsorption was slightly changed with various pH. Our results highlight the importance of phosphate in exploring the environmental fate of antibiotics in natural environment., (Copyright © 2020 Elsevier Inc. All rights reserved.)

In this study, batch and column tests were performed to investigate the co-transport of graphene oxide (GO) nanoparticles and tetracycline in saturated porous media under various solution chemistry conditions. Research indicated that GO and tetracycline had mutual promotion effect on their transport in the porous media under all the tested conditions, which was ascribed to the high adsorption capacity of tetracycline onto GO and the increased electrostatic repulsion as well as their competition for deposition sites on sand surfaces. Interestingly, the mutually promoting function of GO and tetracycline under acidic conditions was greater than that under alkaline conditions, the dominant mechanism was that the increased solution pH decreased the sorption of tetracycline onto GO and weakened the deposition site competition. Furthermore, the mutually promoting effect of GO and tetracycline was Na+ or Ca2+ concentration-dependent. Specially, increased Ca2+ concentration weakened the promoting effect of GO on tetracycline transport but magnified the promoting effect of tetracycline on GO transport. This is because higher Ca2+ concentration could cause a decrease in the adsorption of tetracycline on GO and facilitate more tetracycline molecules to occupy the deposition sites on sand surfaces. Additionally, sodium dodecyl sulfate had enhancement effect on co-transport of GO and tetracycline. Findings from this study clearly indicated that antibiotics and carbon based nanomaterials may transport together under various solution chemistry conditions, and consequently affect their fates in aquatic environments. Image 1 • GO and tetracycline have mutual promotion function on co-transport. • Sorption and deposition site competition contribute to mutually promoting effects. • Extent of tetracycline-mobilizing capability of GO depends on solution pH. • Different co-deposition mechanisms are involved in the presence of Ca2+ vs. Na+. • SDS has enhancement effect on co-transport of GO and tetracycline. GO and tetracycline had mutual promotion effect on their transport in the porous media under various solution chemistry conditions. [ABSTRACT FROM AUTHOR]

[Display omitted] • Citric acid and phosphate both enhance TC transport. • Citric acid exhibits a greater transport-enhancement effect than phosphate. • Ferrihydrite colloids inhibit TC transport under neutral condition. • Both ligands weaken the inhibitory effect of ferrihydrite colloids on TC mobility. • Citric acid has a greater effect on colloid-mediated mobility of TC than phosphate. Considering that the ubiquitous organic/inorganic ligands and iron oxide minerals play significant roles in antibiotic fate in the aquifers. In this study, the influences of two ligands (i.e., citric acid and phosphate) on the transport of tetracycline (TC, a broad-spectrum antibiotic) with or without ferrihydrite colloids in quartz sand were explored. In the absence of ferrihydrite colloids, column studies indicated that the two ligands promoted TC transport and citric acid exhibited a greater transport-enhancement effect than phosphate. The observation was mainly ascribed to a stronger competition effect, steric hindrance, and electrostatic repulsion in the addition of citric acid compared to phosphate. Moreover, ferrihydrite colloids inhibited TC transport, which was mainly caused by contaminant retention associated with colloid deposition and the additional active sites for TC provided by the deposited iron oxide colloids with positive charges. Another interesting finding was that both ligands weakened the inhibitory influences of ferrihydrite colloids on the mobility of TC. This observation stemmed from the enhanced transport of free TC molecules (i.e., TC unassociated with colloids), colloids acting as carriers of TC, as well as the competitive deposition of TC− species and ferrihydrite colloids. Meanwhile, the extent of ferrihydrite colloid-mediated mobility of TC affected by citric acid was much greater than phosphate. Because citric acid exhibited a much greater influence on the interaction of colloids, TC molecules, and sand grains during the transport process. These results reveal the importance of accounting for the impacts of natural ligands on colloid-mediated transport of antibiotics in the subsurface systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mobility of TCs through the column follows the order of OTC > TC > CTC. • SDS significantly enhances TC transport at pH 7.0 through multi-mechanisms. • SDS inhibits OTC and CTC mobility due to the strong hydrophobic interaction. • The extent of the effects of SDS on the mobility of TCs is pH-dependent. Tetracyclines (TCs), a class of antibiotics that are most widely used veterinary and human medicine, possessed an ability to produce irreversible damage towards humans and environment. Antibiotics transport and deposition are critical processes in their environmental fate. In this study, the mobility properties of various TCs such as oxytetracycline (OTC), chlortetracycline (CTC) and tetracycline (TC), in quartz sand columns with sodium dodecylsulfate (SDS), a typical anionic surface-active agent over the pH array of 5.0∼9.0 were investigated. The mobility of TCs through the column was in the order: OTC > TC > CTC. The difference in the molecular structures of various TC antibiotics could explain the trend. Interestingly, SDS enhanced TC transport via deposition site competition between surfactant and TC molecules, increased electrostatic interaction, and steric hindrance. SDS, on the other hand, inhibited OTC and CTC mobility primarily owing to the strong aquaphobic collaboration between antibiotics and the absorbed surfactant on the sand surface (i.e., SDS molecules as bridge agents between antibiotics and sand grains). Furthermore, at higher pH conditions (5.0∼9.0), the enhanced or inhibitory effect of surfactant on the mobility of TCs declined. The observed decrease in the steric hindrance effect, competitive deposition, or hydrophobic interaction was attributed to the decreased deposition of SDS. Innovative information obtained from this work provides insight into the important role of an anionic surfactant on the mobility and deposition of various tetracycline antibiotics in aquifers. [ABSTRACT FROM AUTHOR]

[Display omitted] • Biochars are produced in air-limitation (AL), CO 2 , and N 2 to adsorb tetracycline. • Biochars from AL and CO 2 pyrolysis present better sorption performance. • The better sorption performance results from high SSA, pore volume, and ash content. • The sorption behavior of biochar from N 2 pyrolysis depends on its graphitic degree. • The sorption ability of biochars from CO 2 and AL pyrolysis is more pH-dependent. Presently, as the prevalent pyrolysis atmospheres, N 2 is widely used, while air-limitation and CO 2 are rarely considered, to produce biochar to adsorb tetracycline. This study thus used N 2 , CO 2 , and air-limitation to produce various biochars at 300 ∼ 750 °C, and explored their structure-performance relationship for tetracycline sorption. The maximum sorption capacities of biochars produced in CO 2 and air-limitation were 55.36 mg/g and 71.11 mg/g (at 750 °C), respectively, being 2.34 and 3.01 times that of biochars produced in N 2 (23.60 mg/g at 750 °C). Interestingly, except for high pore volume and specific surface area supported pore filling and sites providing effect, ash (containing metal cations, P-O, and S=O) induced complexing effect was the primary mechanism for tetracycline sorption, rather than hydrophobic effect, π-π interaction, and hydrogen bond caused by C composition. This study provides important information about adjusting the pyrolysis atmosphere to improve the sorption performance of biochar toward tetracycline. [ABSTRACT FROM AUTHOR]

Knowledge of the mobility of tetracycline (TC) antibiotics in porous media is critical to understand their potential environmental influences. The transport characteristics of TC in sand columns with three different surfactants, including Tween 80, sodium dodecylbenzene sulfonate (SDBS), and didodecyldimethylammonium bromide (DDAB) under various conditions were investigated in this study. Results demonstrated that all surfactants enhanced TC transport under neutral conditions (10 mM NaCl at pH 7.0). The observation was attributed mostly to deposition site competition, higher electrostatic repulsion between TC molecules and sand grains, steric hindrance, and the increase of TC hydrophilicity. Furthermore, the order of the transport-enhancement effects was generally observed as follows: DDAB > SDBS > Tween 80. The trend was controlled by the variation in the physicochemical properties of surfactants. It was noticed that the presence of Cu2+ (a model divalent cation) in the background solution, the cation-bridging contributed to the promotion effects of DDAB or Tween 80 on TC mobility. Interestingly, SDBS considerably suppressed TC transport due to the precipitation of SDBS–Cu2+ complexes onto sand surfaces. Moreover, the enhancement order of surfactants at pH 5.0 was similar to that pH 7.0. However, DDAB could inhibit TC transport in sand columns at pH 9.0, which were mainly caused by the decrease of electrostatic repulsion and the hydrophobicity induced by the binding cationic surfactant. Findings from this work provide novel insight into involvement of surfactants in antibiotic transport behaviors in the subsurface environment. [Display omitted] • Surfactants significantly enhance TC transport at pH 7.0 through multi-mechanisms. • The transport-enhancement effects followed the order: DDAB > SDBS > Tween 80. • SDBS inhibits the TC mobility in the presence of Cu2+due to surface precipitation. • Hydrophobicity interaction contributes to the inhibitory effects of DDAB at pH 9.0 [ABSTRACT FROM AUTHOR]

Tetracycline (TC) is known to be one of the most widely used antibiotics and is released into the natural environment, where amounts of iron oxides exist. Low-molecular-weight organic acids (LMWOAs), widespread water-soluble organic substances in the eco-environment systems, may affect the interactions between iron oxides and TC molecules. Nevertheless, our knowledge about the impacts of LMWOAs on the adsorption process of TC onto iron oxides still remains incomplete. In this study, we investigated the adsorption characteristics of TC onto hematite (as a model iron oxide) with various LMWOAs (i.e., acetic acid, glycolic acid, oxalic acid, malic acid, and citric acid). The results clearly showed that LMWOAs suppressed TC adsorption onto hematite particles at pH 7.0 (e.g., the maximum adsorption amounts (q max) decreased from 9.05 mg/g (without LMWOAs) to 5.90 mg/g (with 0.5 mM citric acid)), which was mainly ascribed to the competitive adsorption between TC and LMWOAs on the hematite surface, the increased electrostatic repulsion between negatively charged iron oxide particles and TC– species, and the steric hindrance. Additionally, divalent cations (Ca2+ and Cu2+) enhanced the adsorption-inhibition effects by forming cation-bridging with deprotonated LMWOAs. Interestingly, different mechanisms were involved in the adsorption process with increasing pH from 3.0 to 10.0. At pH < 5.0, electrostatic repulsion, adsorption site competition, and steric effect co-controlled the inhibitory effects. Differently, at pH > 5.0, electrostatic repulsion solely dominated the adsorption-inhibition effects. The findings of this study reveal that ubiquitous LMWOAs are critical factors controlling the fate of antibiotics in the natural environment. [Display omitted] • Effects of LMWOAs on TC adsorption onto hematite was studied. • LMWOAs inhibited TC adsorption onto hematite via multi-mechanisms. • The extent of adsorption-inhibition effects depended on organic acid species. • Cation-bridging contributed to inhibitory effects in the presence of Ca2+/Cu2+. • Different mechanisms were involved in the adsorption process with increasing pH. [ABSTRACT FROM AUTHOR]

Given the ubiquitous mineral (e.g., clays and iron oxides) playing critical roles in impacting the fate of antibiotics in the subsurface environment, the effects of two mineral colloids (i.e., ferrihydrite and montmorillonite) on tetracycline (TC, a representative of antibiotic) transport in sand columns were investigated in this study. Interestingly, the results clearly showed that ferrihydrite colloids inhibited TC transport, while montmorillonite colloids enhanced TC mobility under neutral conditions (pH 7.0). This phenomenon resulted from the positively charged ferrihydrite colloids with weak mobility, which assisted TC deposition; besides, providing additional deposition sites for TC by the deposited ferrihydrite colloids was another important mechanism. In contrast, the transport-enhancement effect of montmorillonite on TC was attributed to the strong binding affinity of TC to clay particles as well as the competition between colloids and TC for deposition sites on sand surfaces. Moreover, the transport-inhibition effect of ferrihydrite at pH 7.0 was greater than that at pH 5.0, mainly due to more colloid-associated TC under neutral conditions. Surprisingly, ferrihydrite colloids could act as carriers of antibiotics and enhanced TC transport at pH 9.0. Because the surface charge of colloids was altered to negative and could break through the column. Meanwhile, the transport-enhancement effect of montmorillonite decreased with increasing pH from 5.0 to 9.0, resulting from the decrease of colloid-adsorbed TC. Furthermore, colloid-mediated transport of TC was influenced by ionic strength, which affected the aggregation characteristics of colloids and the binding affinities of TC to minerals. These findings provide critical information for assessing the risks of antibiotics in aquatic ecosystems where abundant natural minerals are present. [Display omitted] • A comparison regarding the effect of iron oxide and clay on TC mobility was studied. • Ferrihydrite inhibited TC transport mainly due to colloid-associated TC deposition. • Providing additional sites by ferrihydrite was another deposition mechanism for TC. • Highly mobile montmorillonite acted as a carrier of TC and enhanced TC transport. • Colloid-mediated transport of TC considerably depended on solution chemistry. [ABSTRACT FROM AUTHOR]

Biochar, a cost-effective carbonaceous material, has shown great promise in many applications such as soil remediation and wastewater treatment. Citric acid in soil and water environments may affect interactions between biochar and organic contaminants (e.g., tetracycline). To evaluate the effect of citric acid on the adsorption of tetracycline onto biochars, this study investigated the adsorption behavior of tetracycline onto biochars of two different pyrolysis temperatures (300 and 450 °C, referred to as BC_300 and BC_450) in the present of citric acid, accompanying with the effects of solution pH and Cu2+. The results indicated that citric acid significantly inhibited the adsorption of tetracycline onto both biochars, that was mainly due to the multi-mechanisms including pore blocking effect, surface adsorption sites competition, and steric hindrance induced by citric acid. Moreover, citric acid more significantly suppressed the adsorption of tetracycline onto the two biochars at pH 9.0 than at pH 5.0 and 7.0. Because increasing pH could promote electrostatic repulsion between the negative tetracycline and the negatively charged surface of biochars. Cu2+ had greater enhancing effect on the sorption of tetracycline onto BC_300 than BC_450 via cation-bridging effect. Meanwhile, citric acid inhibited the adsorption of tetracycline onto BC_300 to a larger extent than the adsorption onto BC_450 in the presence of Cu2+. That is possibly due to BC_300 has more surface oxygen-containing functional groups than BC_450. Thus, the effect of coexisting citric acid needs to be taken into account when biochar is increasingly used as an amendment in soil and water systems. [ABSTRACT FROM AUTHOR]