A simple paper-based nickel nanocluster-europium mixed ratio fluorescent probe for rapid visual sensing of tetracyclines

In this work, a ratiometric fluorometric sensor based on nickel nanoclusters (NiNCs)-europium complex (NiNCs-Eu³⁺) was constructed for the highly selectivity detection of tetracyclines (TCs) in water samples. In the presence of TCs, the blue fluorescence of the sensor NiNCs-Eu³⁺ was quenched at 430 nm and the characteristic red fluorescence of Eu³⁺-TCs appeared at 620 nm because of the combined help of inner filter effect (IFE) and antenna effect. Under the optimized conditions (100 mM Eu³⁺ (100 µL); temperature (25℃); reaction time (10 min), HEPES buffer solution (pH = 7.0)), the sensor offered a wide detection range of tetracycline (TC) and oxytetracycline (OTC) from 0.1 to 50 μM with the detection limit (LOD) of 25 nM and 21 nM, respectively. Moreover, the sensor was able to detect of TC and OTC in tap and lake water with high recovery rate (89.10%-97.60%). In addition, the portable paper-based sensor was constructed using filter paper embedded with NiNCs-Eu³⁺. The distinct fluorescent color of the paper-based sensor varied from bright blue to red against different concentrations of TC and OTC. These above findings demonstrated the potential for wide application of as-prepared ratio metric fluorescence sensor for visual detection of TCs in water samples.

Influence of habitats and physicochemical factors on trophic transfer processes of antibiotics in a freshwater ecosystem: Application of stable isotopes and human health risks

Habitats of species and physicochemical factors are of great importance in determining the trophic transfer of contaminants in freshwater ecosystems. There is little information on how multiple physicochemical factors and habitats influence the trophic transfer of antibiotics in freshwater food webs. This study investigated the concentrations of 7 sulfonamides (SAs), 4 fluoroquinolones (FQs), 4 tetracyclines (TCs) and 2 macrolides (MLs) in the Lake Dianshan food web. Stable isotope analysis (SIA), and mathematical models were used to assign trophic levels and distinguish between the benthic food web (BFW) and pelagic food web (PFW). Values of stable nitrogen isotope (δ¹⁵N‰) and stable carbon isotope (δ¹³C‰) ranged from 10.2 ± 0.11 to 19.72 ± 0.05 and -33.67 ± 0.18 to -20.79 ± 0.50, respectively. Total concentrations of antibiotics ranged from 36.63 ± 12.73 ng/g dry weight (dw) to 105.85 ± 12.95 ng/g dw for all species. The relative abundance of antibiotics was in the following order: ∑FQs (36.49 %) > ∑SAs (26.70 %), >∑MLs (12.63 %) for all biotas. Trophic magnification factor (TMFs) values for individual antibiotics ranged from 0.10 to 1.20 and 0.31 to 1.82 for PFW and BFW, respectively. Three classes of antibiotics ∑FQs (p < 0.05), ∑TCs (p < 0.05), and ∑MLs (p < 0.05) showed significant trophic dilution in PFW, opposite to non-significant trophic dilution in BFW. The influence of various physicochemical factors was not strong over trophic transfer (e.g., octanol-water partition coefficient-LogK_ow (r = -0.05 in PFW, r = -0.14 in BFW) and distribution coefficient-LogD (r = 0.06 in PWF, r = -0.28 in BFW)) except for aqueous solubility (LogS). Results indicated a significantly higher trophic dilution of antibiotics in the PFW than in the BFW. Among the studied six physicochemical factors, only LogS significantly influences (p < 0.05) the trophic transfer of antibiotics in the freshwater food web. Health risk assessments indicated that currently, there were no serious risks present for urban and rural populations.

Effect of iron plaque on antibiotic uptake and metabolism in water spinach (Ipomoea aquatic Forsk.) grown in hydroponic culture

Ferrous ion was added to the culture solution, followed by the introduction of tetracyclines (TCs), to explore the effect of iron plaque (IP) on the uptake and translocation of TCs by water spinach (Ipomoea aquatic Forsk.). The adsorption amount of TCs on the root surface positively correlated with the amount of IP, except for doxycycline and minocycline. The bioconcentration factor of TCs in roots increased and fitted well with the amount of IP. The concentration of TCs in acrial tissues was three to four orders of magnitude lower than that in roots, and the translocation factor of TCs also fitted well with the amount of IP in a negative linear relationship. Furthermore, IP significantly influenced the metabolism of TCs in water spinach. The accumulation of TC metabolites increased with the increment of IP in roots rather than in acrial tissues, which showed the significance of IP in the metabolism and accumulation of TCs in aquatic plants. Therefore, the metabolism of TCs should not be ignored if IP is induced on the root surface, and the distribution of metabolites should be taken into consideration for the risk assessment and antibiotic pollution control for aquatic plants.

Adsorption of tetracyclines onto polyethylene microplastics: A combined study of experiment and molecular dynamics simulation

Microplastics are a kind of new organic pollutant in the environment. In this study, the adsorption of tetracyclines (TCs), including tetracycline hydrochloride (TC), chlortetracycline hydrochloride (CTC) and oxytetracycline hydrochloride (OTC) onto polyethylene (PE) microplastics in aqueous solutions were investigated. The mechanism of the adsorption behavior was preliminarily explored by adsorption kinetics, isotherms, and thermodynamics, in combination with scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). In addition, molecular dynamics (MD) simulation was applied to investigate the adsorption processes of TCs on PE at a molecular level. It was found that the adsorption behaviors of TCs reached an equilibrium state within 30 h. The experimental data showed that adsorption capacities of TCs onto PE were as follows: OTC (64.40 ± 2.38 μg/g)>CTC (63.36 ± 4.92 μg/g)>TC (53.52 ± 3.43 μg/g). TC sorption onto PE increased with pH, peaking at around pH 6 and then decreased. The increase of ionic strength in the solution led to the reduced adsorption capacity of TC onto PE. The results indicated that the experimental data were well fitted by the pseudo-second-order model and the Freundlich isotherm model, indicating both monolayer and multilayer coverage of TCs onto the surface of PE. The results of MD simulation showed that PE can effectively adsorb the TCs molecule mainly through non-bond interactions, and PE exhibited the highest affinity for CTC and OTC, followed by TC.

Desorption kinetics of tetracyclines in soils assessed by diffusive gradients in thin films

Tetracyclines (TCs) are frequently detected in agricultural soils worldwide, causing a potential threat to crops and human health. In this study, diffusive gradients in thin films technique (DGT) was used to measure the distribution and exchange rates of three TCs (tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC)) between the solid phase and solution in five farmland soils. The relationship between the accumulated masses with time suggested that TCs consumption in soil solution by DGT would induce the supply from the soil solid phase. The distribution coefficient for the labile antibiotics (K_dl), response time (T_c) and desorption/adsorption rates (k_b and k_f) between dissolved and sorbed TCs were derived from the dynamic model of DIFS (DGT induced fluxes in soils). The K_dl showed similar sizes of labile solid phase pools for TC and OTC while larger pool sizes were observed for CTC in the soils. Although the concentrations of CTC were lowest in soil solution, the potential hazard caused by continuous release from soil particles could not be ignored. The long response time (>30 min in most cases) suggested that the resupply of TCs from soil solids was limited by their desorption rates (1.26-121 × 10^-6 s^-1). The soils in finer texture, with higher clay and silt contents (<50 μm) showed a greater potential for TCs release.