Fate and effects of amphoteric surfactants in the aquatic environment (2023)

The spread of antibiotic resistance in the aquatic environment severely threatens the public health and ecological security. This study investigated simultaneously capturing and inactivating/oxidizing the antibiotic resistant bacteria (ARB) and cell-free antibiotic resistance genes (ARGs) in waters by flexibly-functionalized microbubbles. The microbubbles were obtained by surface-modifying the bubbles with coagulant (named as coagulative colloidal gas aphrons, CCGAs) and further encapsulating ozone in the gas core (named as coagulative colloidal ozone aphrons, CCOAs). CCGAs removed 92.4–97.5% of the sulfamethoxazole-resistant bacteria in the presence of dissolved organic matter (DOM), and the log reduction of cell-free ARGs (particularly, those encoded in plasmid) reached 1.86–3.30. The ozone release from CCOAs led to efficient in-situ oxidation: 91.2% of ARB were membrane-damaged and inactivated. In the municipal wastewater matrix, the removal of ARB increased whilst that of cell-free ARGs decreased by CCGAs with the DOM content increasing. The ozone encapsulation into CCGAs reinforced the bubble performance. The predominant capture mechanism should be electrostatic attraction between bubbles and ARB (or cell-free ARGs), and DOM enhanced the sweeping and bridging effect. The functionalized microbubble technology can be a promising and effective barrier for ARB and cell-free ARGs with shortened retention time, lessened chemical doses and simplified treatment unit.

The persistence of contaminants such as pharmaceutical products including antibiotics, anti-inflammatory agents, hormones, and many other substances in aquatic environments has significantly increased demand for new remediation alternatives. One such alternative is adsorption using ecologically safe, abundant, and low-cost adsorbent materials such as clay minerals. Montmorillonite is one of the most researched clay minerals for this purpose as its unique physicochemical properties (i.e., cation exchange capacity, intercalation, and adsorption) facilitate the efficient removal of different contaminants, including pharmaceutical compounds. In addition, the incorporation of organic and/or inorganic compounds in modification reactions may alter the hydrophobicity and hydrophilicity of the montmorillonite surface. The production of new active sites on clay minerals improves its affinity to specific chemical species and may even provide a degree of selectivity for adsorptive processes. This review discusses the structural and experimental factors that control the mechanisms and performance of drug adsorption by natural or modified montmorillonite under simulated or real conditions. Adsorptions conducted in batch and column experiments using the clay mineral are presented, and their challenges are discussed. Research to date has demonstrated that montmorillonite-based adsorbents are versatile materials showing promise for drug adsorption.

Weed management remains an important aspect in crop production to improve quality and production. Of the various weed management techniques (including physical, mechanical, cultural, biological and chemical), chemical control measures are prioritized and the first choice of crop growers, and are increasing because of rapid effects and ease of application. Although utilization of herbicides has become a dominant tool, available commercial formulations have the disadvantage that active ingredients that do not reach the target immediately after application (more than 90%) are lost by various mechanisms. These unused herbicides cause contamination of the surrounding environment through water movement and have diverse toxicological effects on plants, animals, and the environment. However, preparation of nanocomposite-supported controlled release formulations (CRFs) of herbicide is a major innovation that can prolong the duration of herbicide efficiency through stabilizing structure, inhibiting immediate release and reducing toxicity. Of the various nanomaterials, layered aluminosilicate is a suitable carrier for CRFs because of its eco-friendly nature. In this context, pristine clays could be modified through various processes. For example, cation exchange using organo-surfactants is a prerequisite for CRFs and converts clay particles from hydrophilic to hydrophobic, thereby facilitating entry of the herbicide into the gallery. In addition, it is important to use less toxic or non-toxic surfactants for clay modification to reduce the toxicological effects on the environment. This review addresses future research areas such as investigation/synthesis of bio-surfactants and their compatibility in clay modifications for CRFs of herbicides.

The hydrophile-lipophile balance (HLB) value provides an important reference for evaluating the performance behaviors of surfactants. In this work, a quantitative structure-property relationship (QSPR) model was established to predict HLB values of non-ionic surfactants based on the norm descriptor concept. The results showed that the calculated HLB values of 237 non-ionic surfactants agreed well with the experimental values with the squared correlation coefficient (R²) for the whole dataset of 0.9901 and the average absolute relative deviation (AARD) of 2.93 %. The R² and AARD of the training set and the testing set are 0.9901 (R_training²) and 0.9900 (R_testing²), 2.92 % and 3.47 %, respectively. The cross-validation results, Y-randomized test, mean absolute error (MAE) test and application domain (AD) analysis suggested that this QSPR model performs well in accuracy, robustness and reliability. These results demonstrated that this model is accurate and stable, and further validated that the norm descriptor concept is suitable for describing the HLB values of non-ionic surfactants.

Cocamidopropyl betaine (CAPB) and poly(acrylamide) (PAM) were used for the formation of an ultra-dry CO₂-in-water (C/W) foam in which the water volume fraction could be as low as 5 %. At water contents between 10 % and 5 % v/v, the C/W foam formed with CAPB and nonionic PAM (NPAM) showed four times longer stabilization times than that formed with only CAPB. The synergistic effect of surfactants and polymers on the viscosity, interfacial density and thickness was also analysed using dissipative particle dynamics (DPD) simulations. NPAM could assemble at the C/W interface, act as a surfactant and stretch between surfactants, which enhanced the density of the surfactant at the interface, prevented the aggregation between the surfactants and improved the foam stability. For the CO₂/water/CAPB system, the addition of NPAM with a shorter chain length was more conducive to improve the stability of the C/W foam.

Colloids and Surfaces A: Physicochemical and Engineering Aspects, Volume 461, 2014, pp. 85-91

The interfacial properties of binary surfactant mixtures, prepared by mixing a poly(isobutenyl) succinic anhydride derivative with a series of non-ionic oil soluble (Spans) and water soluble (Tweens) compounds with varying structure (length, presence of double bonds, number of arms) hydrophobic tails, were investigated. The Rosen method was used to characterize the synergism between the two surfactants. The various surfactant compositions were used in the preparation of super-concentrated (92.4wt%) water-in-oil emulsions. The properties of the interface layers were determined by the Wilhelmy method and correlated with the time to the start of crystallization of the oversaturated aqueous phase, stability with aging and resistance to shearing during emulsification and pumping. It was shown that synergism between the surfactant and co-surfactant is the main factor determining stability of the emulsions, and that it depends on the structure of the co-surfactant. Stability was found to be much more sensitive to the Span structure than to the Tween structure. Some of the Tweens family enables surfactant compositions that provide quite acceptable stability for different technological applications such as droplet refinement during production, an adequate long-term storage time and good pumping characteristics.

Materials Letters, Volume 107, 2013, pp. 299-302

This work reports for the first time on the elaboration, by both chemical (sol–gel) and physical (pulsed laser deposition) routes, of lead-free ferroelectric Na_0.5Bi_0.5TiO₃ nanodots deposited on bare c-sapphire single crystal substrates presenting a 5° miscut angle along the [110] direction. Prior to any deposition, the sapphire substrates were treated at 1350°C, during 24h in air, in order to increase the height of the surface steps, reaching by this way ~8nm. The experimental parameters adjusted for the growth of Na_0.5Bi_0.5TiO₃ dots were the concentration of sols and the number of laser pulses (50 and 100) for the sol–gel and pulsed laser deposition routes, respectively. Whereas the sol–gel route leads to randomly organized Na_0.5Bi_0.5TiO₃ nanodots in respect to the surface steps, the pulsed laser deposition route provokes the self-assembly for some important proportion of these dots along the same surface steps. Despite the lack of organization for the sol–gel dots, the latter present a much more regular distribution in size (~100 and ~10–20nm as an average lateral dimensions and height, respectively) compared to dots deposited by laser ablation, where three different populations of grains can be observed. In each case, the dots do not seem to be epitaxially grown.

Ecological Indicators, Volume 130, 2021, Article 108059

Assessment of ecological quality in streaming surface water is often based on different Biological Quality Elements (BQE) such as plants, fish or invertebrates. Conventional stream-water quality assessment based on invertebrates as BQE relies on taxonomic expertise, which is costly and time consuming. Next-generation sequencing approaches for high-throughput analyses of diverse ecosystems are increasingly used for environmental monitoring and holds a great potential for application in stream-water quality assessments. This approach is to some extent hampered by the currently available reference databases representing freshwater invertebrates. In the present study we apply metabarcoding simultaneously targeting the 16S (prokaryotes) and 18S (eukaryotes) rRNA genes to capture a snapshot of the ecosystem composition across the three domains of life. Results based on the analysis of 50 selected Danish streams showed that the combined, as well as the domain-specific profiles can separate the samples into their respective ecological quality categories as reflected by the parallel conventional assessment based on macroinvertebrates as BQE. Furthermore, it was possible to suggest potential indicator organisms, from all three domains, which correlated specifically to the conventional data e.g. organisms with a strong correlation to ecological status across all categories. The results clearly showed that community structure in all three domains of life reflect the ecological status of the sample location. Hence, when applying a molecular approach for water-quality assessment we are not limited to the composition of visible BQE, such as macroinvertebrates. The microbial community composition in the streams may often capture an even better and more comprehensive and sensitive snapshot of the ecological quality of stream waters.

Water Research, Volume 199, 2021, Article 117203

Plastics can release numerous chemicals and thereby, contribute to the chemical pollution in aquatic systems. To which extent environmental degradation processes influence the release of plastic chemicals, is currently unknown and subject of research. We therefore evaluated aqueous leachates of 12 differently formulated plastics (e.g., pre-production, post-industrial and recycled pellets as well as final products) using in vitro bioassays and chemical analysis via LC-HRMS nontarget approach. We weathered these plastics by UV irradiation (UV-C and UV-A/B) under laboratory conditions in dryness and a subsequent leaching period in ultrapure water (‘atmospheric’ weathering) or directly in water (‘aquatic’ weathering, UV-A/B_aq). A dark control (DC) without UV light served as a reference treatment. Some plastics triggered several toxicological endpoints (low-density polyethylene recyclate (LDPE-R), starch blend (SB), bio-based polybutylene succinate (Bio-PBS) and polyvinyl chloride (PVC)), whereas others caused little to no effects (polyethylene terephthalate (PET), polystyrene (PS), polypropylene (PP) and LDPE). UV irradiation enhanced the plastics’ toxicity, even for samples initially evaluated as toxicologically inconspicuous. The plastic samples caused oxidative stress (85%), baseline toxicity (42%), antiestrogenicity (40%) and antiandrogenicity (27%). Positive findings were measured after UV-C (63%) and UV-A/B_aq (50%) treatments, followed by UV-A/B (48%) and DC (33%). Overall, we detected between 42 (DC) and 2896 (UV-A/B_aq) chemical compounds. Our study demonstrates that differently formulated plastics leach toxic chemicals. UV exacerbates the plastics’ toxicity by either generating active compounds and/or by facilitating their release. UV light even leads to the release of bioactive compounds from plastics of low chemical complexity. To prevent the exposure to plastic-associated chemicals, the application of chemicals could be reduced to a minimum, while on a regulatory level the evaluation of plastic eluates could be another focal point next to singular compounds.

Chemosphere, Volume 144, 2016, pp. 1026-1032

The study mainly investigated the simultaneous adsorption of bisphenol A (BPA) and Cd²⁺ from aqueous solution on octadecane-betaine modified montmorillonite (BS-Mt). The characteristics of the obtained materials were analyzed by X-ray diffraction (XRD), Fourier-transform infrared (FTIR), Specific surface area (BET) and Scanning electron microscopy/Energy disperse spectroscopy (SEM/EDS), confirming that BS-18 was successfully introduced into Mt. Also, factors including initial solution pH, initial Cd²⁺/BPA concentration, contact time and adsorbent dosage on the adsorption processes were shown to be crucial for Cd²⁺ adsorption, whereas had negligible effects on BPA adsorption. In this study, we found that pseudo-second-order model fitted well with the adsorption kinetic studies for both Cd²⁺ and BPA with an equilibrium time of 24h. The Cd²⁺ and BPA adsorption isotherm could be well described by Freundlich model and Langmuir model, respectively. On the basis of kinetic models, the maximum adsorption capacity of Cd²⁺ in aqueous solution was slightly enhanced after modification, indicating that Cd²⁺ adsorption on BS-Mt was mainly attributed to direct electrostatic attraction and the chelate reaction, while the dramatic enhancement of maximum adsorption capacity for BPA was due to the hydrophobic interaction.

Science of The Total Environment, Volume 612, 2018, pp. 415-421

Organosilicon surfactants are the most potent adjuvants available for formulating and applying agricultural pesticides and fertilizers, household cleaning and personal care products, dental impressions and medicines. Risk assessment of pesticides, drugs or personal care products that takes into account only active ingredients without the other formulation ingredients and adjuvants commonly used in their application will miss important toxicity outcomes detrimental to non-target species including pollinators and humans. Over a billion pounds of organosilicon surfactants from all uses are produced globally per year, making this a major component of the chemical landscape to which bees and humans are exposed. These silicones, like most “inerts”, are generally recognized as safe, have no mandated tolerances, and their residues are largely unmonitored. Lack of their public disclosure and adequate analytical methods constrains evaluation of their risk. Organosilicon surfactants, the most super-spreading and -penetrating adjuvants available, at relevant exposure levels impair honey bee learning, are acutely toxic, and in combination with bee viruses cause synergistic mortality. Organosilicon surfactants need to be regulated as a separate class of “inerts” from the more common silicones. In turn, impacts of organosilicon surfactant exposures on humans need to be evaluated. Silicones in their great diversity probably represent the single most ubiquitous environmental class of global synthetic pollutants. Do honey bees, a model environmental indicator organism, forewarn of hidden risks to humans of ubiquitous silicone exposures?