Interconnected environmental challenges: heavy metal-drug interactions and their impacts on ecosystems

Industrial expansion and inadequate environmental safety measures are major contributors to environmental contamination, with heavy metals (HMs) and pharmaceutical waste playing crucial roles. Their negative effects are most noticeable in aquatic species and vegetation, where they accumulate in tissues and cause harmful results. Interactions between HMs and pharmaceutical molecules result in the production of metal-drug complexes (MDCs), which have the potential to disturb diverse ecosystems and their interdependence. However, present studies frequently focus on individual pollutants and their effects on specific environmental parameters, leaving out the cumulative effects of pollutants and their processes across several environmental domains. To address this gap, this review emphasizes the environmental sources of HMs, elucidates their emission pathways during anthropogenic activities, investigates the interactions between HMs and pharmaceutical substances, and defines the mechanisms underlying the formation of MDCs across various ecosystems. Furthermore, this review underscores the simultaneous occurrence of HMs and pharmaceutical waste across diverse ecosystems, including the atmosphere, soil, and water resources, and their incorporation into biotic organisms across trophic levels. It is important to note that these complex compounds represent a higher risk than individual contaminants.

The role of magnesium ion in the interactions between humic acid and tetracycline in solution

Coexisting tetracycline (TC), dissolved organic matter (DOM), and metal cations in aqueous environments might form complexes and consequently affect the environmental fate of TC. In this study, the interactions among coexisting humic acid (HA), TC, and Mg(II) in solutions were investigated by equilibrium dialysis batch experiments and nuclear magnetic resonance hydrogen spectroscopy (1H NMR) characterization. In the binary systems, the dimethylamine (4Me2NH+) functional group on the A-ring of TC bound to the oxygen-containing functional groups of HA via hydrogen bond. The solution pH affected the agglomeration morphology and dissociation of the oxygen-containing functional groups of HA as well as protonation and spatial conformation of TC, which in turn affected the HA-TC interactions. The complexation sites and ratio of Mg(II) on TC affect the binding mode in the ternary system. When the TC-Mg(II) complexation ratio is 1:1, the B, C, and D rings of TC preferentially complex with Mg(II), resulting in the change of TC from an extended to a twisted conformation. At this time, Mg(II) had a weaker inhibitory effect on binding affinity between HA and TC. When the complexation ratio was 1:2, the second Mg(II) complexation deactivated the 4Me2NH + on the A ring and further stabilized TC twisted conformation, resulting in a stronger inhibitory effect on the binding of TC to HA. Under acidic conditions, the solution pH mainly caused the difficulty in forming TC-Mg(II) complexes. The inhibitory effect of Mg(II) on the binding between HA and TC is weaker than that under alkaline conditions.

Towards direct detection of tetracycline residues in milk with a gold nanostructured electrode

Tetracycline antibiotics are used extensively in veterinary medicine, but the majority of the administrated dose is eliminated unmodified from the animal through various excretion routes including urine, faeces and milk. In dairy animals, limits on residues secreted in milk are strictly controlled by legislation. Tetracyclines (TCs) have metal chelation properties and form strong complexes with iron ions under acidic conditions. In this study, we exploit this property as a strategy for low cost, rapid electrochemical detection of TC residues. TC-Fe(III) complexes in a ratio of 2:1 were created in acidic conditions (pH 2.0) and electrochemically measured on plasma-treated gold electrodes modified with electrodeposited gold nanostructures. DPV measurements showed a reduction peak for the TC-Fe(III) complex that was observed at 50 mV (vs. Ag/AgCl QRE). The limit of detection in buffer media was calculated to be 345 nM and was responsive to increasing TC concentrations up to 2 mM, added to 1 mM FeCl3. Whole milk samples were processed to remove proteins and then spiked with tetracycline and Fe(III) to explore the specificity and sensitivity in a complex matrix with minimal sample preparation, under these conditions the LoD was 931 nM. These results demonstrate a route towards an easy-to-use sensor system for identification of TC in milk samples taking advantage of the metal chelating properties of this antibiotic class.

Enhanced adsorption and colorimetric detection of tetracycline antibiotics by using functional phosphate/carbonate composite with nanoporous network coverage

This work presents efficient tetracycline (TC) antibiotics adsorption using a functional porous phosphate/carbonate composite (PCC). The PCC was fabricated by anion-exchange of phosphate on the surface of vaterite-phase calcium carbonate particle scaffolds. The PCC, having dense nanoporous network coverage with large surface area and pore volume, exhibited excellent TC adsorption in solution. Its adsorption isotherm fitted well to the Freundlich model, with a maximum adsorption capacity of 118.72 mg/g. The adsorption process was spontaneous, endothermic, and followed pseudo-second-order kinetics. From the XPS analysis, the hydrogen bonding and surface complexation were the key interactions in the process. In addition, a colorimetric TC detection method was developed considering its complexation with phosphate ions, originating from PCC dissolution, during adsorption. The method was used to detect TC in mg/L concentrations in water samples. Thus, the multifunctional PCC exhibited potential for use in TC removal and environmental remediation.

Morphological crystal adsorbing tetracyclines and its interaction with magnesium ion in the process of struvite crystallization by using synthetic wastewater

Struvite (MgNH₄PO₄·6H₂O) crystallization is a promising method of phosphorus recovery from wastewater. As for digestive livestock wastewater, the extensive residues of antibiotics could induce struvite recovery to spread antibiotic resistance and thereafter pose ecological risks to the environment. In this study, struvite crystals with different morphologies were produced from synthetic swine wastewater, and tetracyclines (TCs) adsorbing capacities were investigated. The important factors, including the existence of Mg²⁺ ions and initial TCs concentration, were examined. The predominant adsorption between TCs and struvite crystals was electrostatic interaction, with the maximum capacity at doxycycline (DXC) 876.5 μg/Kg, oxytetracycline (OTC) 1946.7 μg/Kg and tetracycline (TC) 2376.2 μg/Kg, respectively. Well-faceted struvite crystallites possessed high adsorption capacities than those of dendritic crystallite, due to higher Mg intensities on the crystallite surface. The increment of phosphorus concentration could trigger the transformation of struvite morphology from needle to dendritic shapes with X-shape as an intermediate stage, which would reduce Mg density in specific crystallite facets and therefore limit TCs adsorption onto struvite crystals. The existence of Mg²⁺ ion would inhibit TCs deprotonation and thereafter improve TCs adsorption onto struvite crystals. Further investigation revealed that continuously elevating initial TCs concentration would promote the formation of 1:2 transferring to 1:1 TCs-Mg chelates, which would result in a fluctuation following a drastic augment of TCs adsorption capacity.

CdTe QDs@ZIF-8 composite-based recyclable ratiometric fluorescent sensor for rapid and sensitive detection of chlortetracycline

The residue problem in animal food products caused by the abuse of chlortetracycline (CTC) is one of the food safety issues that have attracted much attention. Herein, a composite was generated by embedding CdTe quantum dots (QDs) into ZIF-8 for ratiometric fluorescent analysis of CTC. With adding CTC, the green luminescence of CTC appeared under the sensitization effect of Zn²⁺ in ZIF-8, but the red luminescence of CdTe QDs was reduced by the inner filtration effect of CTC. On this basis, CTC was detected by the composite with a short response time of 1 min, and the limit of detection was calculated to be 37 nM that was 17 times lower than the maximum residue limit of CTC in animal food products (626 nM). Excellent recyclability of the composite was also observed, and CTC was consecutively measured at least six times. The composite was used to determine CTC in basa fish and pure milk with satisfactory recoveries (91.0-110.0%). Portable test strips were further manufactured and the visual determination of CTC was obtained. These results convictively demonstrate that CdTe QDs@ZIF-8 composite as a recyclable ratiometric fluorescent sensor achieves the rapid and sensitive measurement of CTC residue in animal food products.

A ratiometric fluorescence-scattering sensor for rapid, sensitive and selective detection of doxycycline in animal foodstuffs

The residue problem of tetracycline antibiotics, especially doxycycline (DC), in animal foodstuffs has attracted much attention. This paper reported ZIF-8 and bovine serum albumin (BSA) as a ratiometric fluorescence-scattering sensor for DC. The mechanism relied on the disassembly of ZIF-8 caused by DC, bringing weakened second-order scattering, and the double fluorescence amplification of DC under ZIF-8 with BSA, inducing enhanced fluorescence. The response of the sensor was completed within 1 min, and the detection limit for DC (3.4 nM) was 1-2 orders of magnitude lower than the reported ones. The distinguishment of DC from other tetracycline antibiotics was also achieved by the sensor. The sensor was applied to detecting DC in animal foodstuffs with satisfactory recoveries (80.0-104.0%). Hence, this work develops a rapid, sensitive and selective ratiometric sensor to monitor the DC residue in animal foodstuffs, also opens the window to construct ratiometric DC sensors with the fluorescence-scattering strategy.

Antibiotic-metal complexes in wastewaters: fate and treatment trajectory

Unregulated usage, improper disposal, and leakage from pharmaceutical use and manufacturing sites have led to high detection levels of antibiotic residues in wastewater and surface water. The existing water treatment technologies are insufficient for removing trace antibiotics and these residual antibiotics tend to interact with co-existing metal ions and form antibiotic-metal complexes (AMCs) with altered bioactivity profile and physicochemical properties. Typically, antibiotics, including tetracyclines, fluoroquinolones, and sulphonamides, interact with heavy metals such as Fe²⁺, Co²⁺, Cu²⁺, Ni²⁺, to form AMCs which are more persistent and toxic than parent compounds. Although many studies have reported antibiotics detection, determination, distribution and risks associated with their environmental persistence, very few investigations are published on understanding the chemistry of these complexes in the wastewater and sludge matrix. This review, therefore, summarizes the structural features of both antibiotics and metals that facilitate complexation in wastewater. Further, this work critically appraises the treatment methods employed for antibiotic removal, individually and combined with metals, highlights the knowledge gaps, and delineates future perspectives for their treatment.

177Lu-doxycycline as potential radiopharmaceutical: electrochemical characterization, radiolabeling, and biodistribution in tumor-bearing mice

PURPOSE

Recent studies with doxycycline as adjuvant therapy to conventional chemotherapy have shown promising results in cancer therapy. The current study aimed to examine the capability of ¹⁷⁷Lu-labeled tetracycline ligand, doxycycline hyclate, to use as an anticancer agent.

MATERIALS AND METHODS

Doxycycline was radiolabeled with beta-emitting radioisotope ¹⁷⁷Lu. Complex formation and its interaction with DNA were investigated electrochemically. Binding of ¹⁷⁷Lu-doxycycline to CT 26 cell line was done. Biodistribution of ¹⁷⁷Lu-doxycycline was examined in healthy Wistar rats and CT26 colon carcinoma tumor-bearing mice by i.v. and i.p. administration, respectively.

RESULTS

Doxycycline hyclate was successfully radiolabeled with ¹⁷⁷Lu in high radiolabeling yield (>99%). The radiolabeled complex was stable in vitro in saline and human serum over 72 h. Non-radioactive Lu-doxycycline complex formation was demonstrated electrochemically as well. Intercalative interactions of the doxycycline and Lu-doxycycline with DNA were proved using simultaneously spectrophotometric and electrochemical methods. The binding of the radiolabeled complex with plasma proteins was 4.0 ± 0.4%. The partition coefficient showed the lipophilic nature of the complex similar to the free ligand. The binding curve demonstrates binding from 0.1 nM concentrations of ¹⁷⁷Lu-doxycycline, with half-binding estimated ∼100 nM. Biodistribution studies of ¹⁷⁷Lu-doxycycline in CT26 colon tumor-bearing mice showed a satisfactory accumulation rate in the tumor (2.88 ± 0.85% ID/g) 3 h after intraperitoneal injection. Both the hepatobiliary system and the urinary system were prominent as excretory routes of the radiolabeled complex.

CONCLUSION

Considering obtained results, ¹⁷⁷Lu-doxycycline complex, due to its excellent electrochemical and biological characteristics, with emphasis on the binding ability to DNA via intercalative interaction as well as significant accumulation in the tumor, is suitable for further in vivo studies to investigate its potential use in cancer treatment.

Emerging Electrochemical Sensors for Real-Time Detection of Tetracyclines in Milk

Antimicrobial drug residues in food are strictly controlled and monitored by national laws in most territories. Tetracyclines are a major broad-spectrum antibiotic class, active against a wide range of Gram-positive and Gram-negative bacteria, and they are the leading choice for the treatment of many conditions in veterinary medicine in recent years. In dairy farms, milk from cows being treated with antibiotic drugs, such as tetracyclines, is considered unfit for human consumption. Contamination of the farm bulk tank with milk containing these residues presents a threat to confidence of supply and results in financial losses to farmers and dairy. Real-time monitoring of milk production for antimicrobial residues could reduce this risk and help to minimise the release of residues into the environment where they can cause reservoirs of antimicrobial resistance. In this article, we review the existing literature for the detection of tetracyclines in cow's milk. Firstly, the complex nature of the milk matrix is described, and the test strategies in commercial use are outlined. Following this, emerging biosensors in the low-cost biosensors field are contrasted against each other, focusing upon electrochemical biosensors. Existing commercial tests that identify antimicrobial residues within milk are largely limited to beta-lactam detection, or non-specific detection of microbial inhibition, with tests specific to tetracycline residues less prevalent. Herein, we review a number of emerging electrochemical biosensor detection strategies for tetracyclines, which have the potential to close this gap and address the industry challenges associated with existing tests.

Occurrence, Distribution, and Ecological Risk Assessment of Antibiotics in Selected Urban Lakes of Hanoi, Vietnam

Residue concentrations of fifteen antibiotics including sulfonamides, quinolones, macrolides, β-lactams, and trimethoprim in lakes from Hanoi metropolitan area, Vietnam, were analyzed using ultra-performance liquid chromatography coupled with tandem mass spectrometry (UPLC/MS-MS) to elucidate their occurrence and behavior in urban environment. For surface water, the average concentrations of five antibiotic classes decreased in the order: sulfonamides (117.9 ng/L) > β-lactams (31.28 ng/L) > quinolones (20.19 ng/L) > macrolides (17.74 ng/L) > trimethoprim (8.93 ng/L). While the highest concentration of SMX was detected at 806.5 ng/L in surface water, those obtained in sediment were only at 1.35 ng/g because of their high solubility in water. Quinolones were found at a maximal concentration of 158.7 ng/L for OFL in water phase whereas those in sediment phase were 4,017 ng/g due to their great affinity in sediment. These findings revealed the different fate and release mechanisms of each antibiotic group in the environment. The ecological risk assessment implied some targeted compounds, and in particular, OFL and AZM could pose high risks to algae in the aquatic ecosystem.

A novel fluorescence probe for rapid and sensitive detection of tetracyclines residues based on silicon quantum dots

A novel rapid and sensitive fluorescence probe based on silicon quantum dots (Si QDs) fluorescence was fabricated for selective detection of tetracyclines (TCs) residues. Si QDs were innovatively prepared via facile One-Pot Solvent-Free Method and characterized by TEM, FT-IR, UV absorption, fluorescence, XPS and XRD. In aqueous solution, Cu²⁺ and Si QDs complexed together and the fluorescence of Si QDs quenched (static quenching) to a certain extent. TCs can be early in binding to Cu²⁺ and prevent Si QDs fluorescence quenching. As a consequence, quantitative screening of TCs can be achieved. The assay is highly selective for TCs. Represented by chlortetracycline (CTC), a member of TCs, under optimized conditions, good linear relationship in the range of 11.32-1086.72 nM was obtained, and the detection limit (LOD; S/N ratio = 3) of this assay for CTC is 0.92 nM. It was successfully applied to the determination of CTC in spiked bee honey and total TCs in actual honey samples. And the evaluation of selectivity, reproducibility and stability of the probe were favorable. These results demonstrated that the presented fluorescent probe can be a promising sensing platform for TCs analysis.

Analysis of Complexation Interactions between Metal Ions and Drugs under Pseudo-physiological pH Conditions by a High-throughput Screening Method Using a Solid-phase Extraction Cartridge

A high-throughput screening method for the complexation between metal ions and drugs was established by combining solid-phase extraction (SPE) using a nitrilotriacetic acid (NTA) modified silica spin cartridge with subsequent HPLC analysis. First, a test metal ion solution was passed through the NTA cartridge, then a test drug solution diluted in phosphate buffered saline (pH 7.4) was passed through the metal-chelated NTA cartridge. The complexation behavior between the metal and the drug on the NTA cartridge was evaluated by HPLC quantification of the drug in the SPE eluate. Comprehensive analysis of the complexation behavior between 11 different metal ions and 55 drugs showed that Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Cr³⁺ and Fe³⁺ formed complexes with 12, 5, 4, 2, 1 and 1 kinds of drugs, respectively. Bromazepam selectively formed complexes with Cu²⁺, Ni²⁺ and Co²⁺.

Occurrence and risk assessment of multiple classes of antibiotics in urban canals and lakes in Hanoi, Vietnam

Very little information on the occurrence and risk assessment of antibiotics in the aquatic environment is reported for Vietnam, where antibiotics are assumed to be omnipresent in urban canals and lakes at high concentrations due to the easy accessibility of antibiotics without doctor prescription. This study provides comprehensive analysis of the occurrence of 23 antibiotics in urban canals (To Lich and Kim Nguu) and lakes (West Lake, Hoan Kiem, and Yen So) in Hanoi, Vietnam. Of these 23 antibiotics, 18 were detected in urban canals at above 67.9% detection frequency (DF). The concentrations of detected antibiotics were in the range from below quantification limit (MQL) to almost 50,000 ng/L, depending on the compound and sampling site. In urban canals, median concentration of amoxicillin, erythromycin, and sulfamethoxazole was >1000 ng/L while other antibiotics such as ampicillin, chloramphenicol, clindamycin, sulfamethazine, tetracycline, tylosin and vancomycin were detected at median concentrations of <100 ng/L. Similarly, 16 target antibiotics were also detected in urban lakes. Macrolides (azithromycin, clarithromycin, and erythromycin-H₂O), fluoroquinolones (enrofloxacin and ofloxacin), lincosamides (clindamycin and lincomycin), and trimethoprim were ubiquitously detected in urban lakes (DF = 100%). In this study, potential risks of antibiotics in the investigated urban canals and lakes were assessed based on the predicted no-effect concentration (PNEC) from the existing literature for antibiotic resistance selection (PNEC_ARM) and ecological toxicity to aquatic organisms (PNEC_Ecotox). Ampicillin, amoxicillin, azithromycin, ciprofloxacin, clarithromycin, enrofloxacin, erythromycin, ofloxacin, tetracycline, and trimethoprim were found in the investigated urban canals at concentrations exceeding their PNEC_ARM and PNEC_Ecotox. Similarly, most of the target antibiotics (i.e. amoxicillin, ciprofloxacin, clarithromycin, clindamycin, enrofloxacin, erythromycin, lincomycin, ofloxacin, sulfamethoxazole, tetracycline, trimethoprim and tylosin) were detected in the investigated urban lakes at concentrations close to or exceeding PNEC_Ecotox for aquatic organisms. Further investigations on the occurrence and fate of antibiotic residues and antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in surface waters are recommended.

Stability of antibiotics in drinking water: An advanced approach towards the impacts of water quality parameters on doxycycline bioavailability

Objective:

This study was considered to explore the possible impacts of drinking water quality from different sources on the bioavailability of doxycycline.

Materials and Methods:

Sixty-four tap and ground drinking water samples collected from poultry farms were scrutinized for their water quality limits (TH, pH, total dissolved solids, electrical conductivity, Cl⁻, Ca⁺², Na⁺, and Mg⁺²) and heavy metals concentrations (Zn, Fe, Cu, and Ni). An in vitro study was conducted by adding the therapeutic concentrations of doxycycline to all tested water samples, and allowed to interact for 1 h, 3 h, 5 h, and 8 h followed by re-estimation of doxycycline concentrations after each contact time using thin layer chromatography.

Results:

The therapeutic concentration of doxycycline was decreased in tap water samples by 1.92%, 9.63%, 22.42%, and 30.83% for the aforementioned contact times, respectively, while the corresponding reduction percentages in ground water samples were 2.14%, 17.14%, 28.57%, and 40.09%. However, the control samples had never showed any recorded decrease in their doxycycline concentrations overall contact times. All measured concentrations of doxycycline were significantly lower in tap and ground water than those of control at all times of contact. Both pH, Mg⁺² showed significant positive correlations with decreasing values of doxycycline in water.

Conclusion:

Different drinking water sources reduce the concentrations of doxycycline in vitro in a time dependent manner, which can be attributed to their different physico-chemical parameters, i.e., pH and Mg⁺² ions. This emphasizes the role of water quality on the stability of antibiotics concentrations administrated via drinking water.

Transient absorption spectroscopic studies on 4-nitroquinoline N-oxide: From femtoseconds to microseconds timescale

The singlet excited state of 4-nitroquinoline N-oxide (¹NQNO*) has been characterized by different spectroscopic techniques, combining transient absorption with steady state and time-resolved emission spectroscopy. The energy of ¹NQNO* has been established as 255 kJ/mol from the fluorescence spectrum, whereas its lifetime has been found to be 10 ps in the femto-laser flash photolysis (LFP) experiments, where a characteristic S₁S_n absorption band with maximum centered at 425 nm is observed. In a first stage, the triplet excited state of NQNO (³NQNO*) has also been characterized by emission spectroscopy in solid matrix, at low temperature. Thus, from the steady-state phosphorescence spectrum the triplet energy has been estimated as 183 kJ/mol, whereas the setup with time resolution has allowed us to determine the phosphorescence lifetime as 3 ms. Formation of ³NQNO* by intersystem crossing in solution at room temperature, has been monitored by femto-LFP, which shows the appearance of a band with maximum at 560 nm (T₁-T_n). It increases with the decreasing intensity of its precursor 425 nm (S₁S_n) band, giving rise to an isosbestic point at 500 nm. The characterization of ³NQNO* has been completed by nano-LFP, using xanthone as photosensitizer and oxygen as well as β-carotene as quenchers. In addition, quenching of ³NQNO* by electron donors (DABCO) is also observed in aprotic solvents, leading to the radical anion of NQNO (^-NQNO). If there is a proton source in the medium (Et₃N as electron donor or MeCN:H₂O/4:1 as solvent system) protonation of the radical anion results in formation of the neutral radical of NQNO (NQNOH). In general, all processes are slower in protic solvents because of the solvation sphere. Overall, this information provides a deeper insight into the formation and behavior of excited states and radical ionic species derived from the title molecule NQNO.

Influence of light and Fe(III) ions on tetracycline degradation

Tetracycline (TC) is an antibiotic produced on the largest scale in the world and used for the treatment of both humans and animals. Its removal from the circulation chain between the natural environment and animals is still a serious problem. Fe(III) ions can be used to break this chain. Fe(III) ions appear in water in spite of irradiation of Fe(III)-Cit complex and oxidation by oxygen present in water. Fe(III)-Cit was a reservoir of Fe(III) ions from which they were continuously released. Therefore, in this paper we studied an interaction between tetracycline (TC) and Fe(III) ions under fluorescent light at 20 °C and 30 °C in the water environment. This interaction leads to TC + Fe(III) coordinating complex formation. Changes caused by this process were monitored within 1860 min by measuring absorption and fluorescence spectra. The absorption spectra showed a charge-transfer stacking band(s) of oxidized and non-oxidized form of TC above 400 nm; in turn the fluorescence spectra revealed decay of initial bands and formation of the new ones. The initial, main fluorescence band at 16,660 cm^-1 associated with the intramolecular proton transfer has gradually disappeared after Fe(III) ions binding to oxygen atoms in the BCD system rings of a TC molecule. Gaussian decomposition of all fluorescence spectra allowed extracting new bands, their evolution in time and calculating the rate of the first reaction step. Temperature rise of 10 °C caused more than a ten-fold increase in the first-order reaction rate.

Abiotic transformation products of tetracycline and chlortetracycline in salt solutions and manure

Tetracyclines belong to the group of the most applied antibiotics in veterinary medicine worldwide. Due to their incomplete absorption and/or metabolism in the animal gut, tetracyclines are frequently detected in manure samples. Within the matrix, an elimination of these compounds has been reported in several studies. However, only little information about potential transformation products of tetracyclines in manure and the environment is available. Therefore, the fate of tetracycline (TC) and chlortetracycline (CTC) was investigated in aqueous solutions and manure. Abiotic incubation of TC in phosphate buffer led to a remarkable red-brown coloring of the solution. Subsequent compound isolation and structure elucidation by MS/MS and NMR techniques revealed the formation of seco-cycline A, a compound formerly described as a fungal biotransformation product of TC. For CTC, two comparable products were identified which were derived from its isomeric form isoCTC. All transformation products showed no antimicrobial activity for concentrations up to 500 mg L^-1. When TC and CTC were incubated in cow manure for 7 d, the above mentioned three transformation products were also formed in this complex matrix (up to 5.1 mg kg^-1). Manure, soil and leachate samples from Lower Saxony revealed the presence of seco-cycline A in manure and soil, but not in water. To obtain a better insight in the fate of tetracyclines in environmental matrices, future analytical and ecotoxicological studies dealing with this subject should include the analysis especially of seco-cycline A.

Sorption-desorption behavior of sulfamethoxazole, carbamazepine, bisphenol A and 17α-ethinylestradiol in sewage sludge

The occurrence of trace organic contaminants (TOrCs) at detectable levels in wastewater and surface waters led to a growing concern over the persistence of toxicological effects in the environment. Sorption is significant process in municipal wastewater treatment plants to remove TOrCs due to low water solubility and high hydrophobic of most TOrCs. The work herein explored the sorption behavior of four typical TOrCs onto sludge solids. The sorption process was spontaneous and exothermic. Greater sorption amount was observed for EE2 that 60.9% of EE2 in liquid phase was removed, followed by BPA (49.4%) and SMX (35.8%), while only 19.5% of CBZ was adsorbed. Sorption of CBZ, BPA and EE2 was primarily a physical process dominated by partition function, while SMX was mainly sorbed through multiple interactions, and this strong affinity between SMX and activated sludge resulted in least desorption rate. Deep insight into the pathway of SMX in SBR revealed that total removal rate in a period was about 50.22%. Sorption process was observed in anaerobic stage, and biological degradation was mainly occurred in aerobic stage with biodegradation rate of 29.18%.

Occurrence and fate of emerging contaminants in municipal wastewater treatment plants from different geographical regions-a review

Emerging contaminants, such as antibiotics, pharmaceuticals, personal care products, hormones, and artificial sweeteners, are recognized as new classes of water contaminants due to their proven or potential adverse effects on aquatic ecosystems and human health. This review provides comprehensive data on the occurrence of 60 emerging contaminants (ECs) in influent, treated effluent, sludge, and biosolids in wastewater treatment plants (WWTPs). In particular, data on the occurrence of ECs in the influents and effluents of WWTPs are systematically summarized and categorized according to geographical regions (Asia, Europe, and North America). The occurrence patterns of ECs in raw influent and treated effluents of WWTPs between geographical regions were compared and evaluated. Concentrations of most ECs in raw influent in Asian region tend to be higher than those in European and North American countries. Many antibiotics were detected in the influents and effluents of WWTPs at concentrations close to or exceeding the predicted no-effect concentrations (PNECs) for resistance selection. The efficacy of EC removal by sorption and biodegradation during wastewater treatment processes are discussed in light of kinetics and parameters, such as sorption coefficients (K_d) and biodegradation constants (k_biol), and physicochemical properties (i.e. log K_ow and pK_a). Commonly used sampling and monitoring strategies are critically reviewed. Analytical research needs are identified, and novel investigative approaches for future monitoring studies are proposed.

Tetracyclines metal complexation: Significance and fate of mutual existence in the environment

Concern over tetracyclines (TCs) complexation with metals in the environment is growing as a new class of emerging contaminants. TCs exist as a different net charged species depending on their dissociation constants, pH and the surrounding environment. One of the key concerns about TCs is its strong tendency to interact with various metal ions and form metal complexes. Moreover, co-existence of TCs and metals in the environment and their interactions has shown increased antibiotic resistance. Despite extensive research on TCs complexation, investigations on their antibiotic efficiency and pharmacological profile in bacteria have been limited. In addition, the current knowledge on TCs metal complexation, their fate and risk assessment in the environment are inadequate to obtain a clear understanding of their consequences on living systems. This indicates that vital and comprehensive studies on TCs-metal complexation, especially towards growing antibiotic resistance trends are required. This review summarizes the role of TCs metal complexation on the development of antibiotic resistance. Furthermore, impact of metal complexation on degradation, toxicity and the fate of TCs in the environment are discussed and future recommendations have been made.

Factors influencing the potency of marbofloxacin for pig pneumonia pathogens Actinobacillus pleuropneumoniae and Pasteurella multocida

For the pig respiratory tract pathogens, Actinobacillus pleuropneumoniae and Pasteurella multocida, Minimum Inhibitory Concentration (MIC) of marbofloxacin was determined in recommended broths and pig serum at three inoculum strengths. MICs in both growth matrices increased progressively from low, through medium to high starting inoculum counts, 10⁴, 10⁶ and 10⁸CFU/mL, respectively. P. multocida MIC ratios for high:low inocula were 14:4:1 for broth and 28.2:1 for serum. Corresponding MIC ratios for A. pleuropneumoniae were lower, 4.1:1 (broth) and 9.2:1 (serum). MIC high:low ratios were therefore both growth matrix and bacterial species dependent. The effect of alterations to the chemical composition of broths and serum on MIC were also investigated. Neither adjusting broth or serum pH in six increments over the range 7.0 to 8.0 nor increasing calcium and magnesium concentrations of broth in seven incremental steps significantly affected MICs for either organism. In time-kill studies, the killing action of marbofloxacin had the characteristics of concentration dependency against both organisms in both growth matrices. It is concluded that MIC and time-kill data for marbofloxacin, generated in serum, might be preferable to broth data, for predicting dosages of marbofloxacin for clinical use.

Degradation of chlortetracycline in wastewater sludge by ultrasonication, Fenton oxidation, and ferro-sonication

Residual emerging contaminants in wastewater sludge remain an obstacle for its wide and safe applications such as landfilling and bio-fertilizer. In this study, the feasibility of individual ultrasonication (UlS) and Fenton oxidation (FO) and combined, Ferro-sonication processes (FO) on the degradation of chlortetracycline (CTC) in wastewater sludge was investigated. UlS parameters such as amplitude and sonication time were optimized by response surface methodology (RSM) for further optimization of FS process. Generation of highly reactive hydroxyl radicals in FO and FS processes were compared to evaluate the degradation efficiency of CTC. Increasing in the ratio of hydrogen peroxide and iron concentration showed increased CTC degradation in FO process; whereas in FS, an increase in iron concentration did not show any significant effect (p>0.05) on CTC degradation in sludge. The estimated iron concentration in sludge (115mg/kg) was enough to degrade CTC without the addition of external iron. The only adjustment of sludge pH to 3 was enough to generate in-situ hydroxyl radicals by utilizing iron which is already present in the sludge. This observation was further supported by hydroxyl radical estimation with adjustment of water pH to 3 and with and without the addition of iron. The optimum operating UlS conditions were found to be 60% amplitude for 106min by using RSM. Compared to standalone UlS and FO at 1:1 ratio, FS showed 15% and 8% increased CTC degradation respectively. In addition, UlS of sludge increased estrogenic activity 1.5 times higher compared to FO. FS treated samples did not show any estrogenic activity.

A cationic naphthyl derivative defies the non-equilibrated excited rotamers principle

Four quasi-isoenergetic ground state (S₀) conformers undergo ultrafast rotamer interconversions in the excited state (S₁) against the non-equilibrated excited rotamers principle.

Occurrence and removal of multiple classes of antibiotics and antimicrobial agents in biological wastewater treatment processes

Very little information on the occurrence and fate of multiple classes of antimicrobials in the aquatic environment is reported for the Southeast Asian region. This study provides the first and comprehensive data on the occurrence of ten different classes of antimicrobials in wastewater samples for Singapore. Among the investigated antimicrobials, 19 out of 21 target compounds were detected in 100% of the collected raw influent samples. Concentrations of the detected antimicrobials in raw influent varied from 23.8 to 43,740 ng/L. Removal of antimicrobials by conventional activated sludge (CAS) and membrane bioreactor (MBR) systems at a local wastewater treatment plant was evaluated. MBR exhibited better performance over CAS for most target antimicrobials. Beta-lactam, glycopeptide, and fluoroquinolone classes were largely eliminated by biological wastewater treatment processes, whereas trimethoprim and lincosamides appeared to be persistent. Effects of physicochemical properties and chemical structures of target antimicrobials on their removal efficiencies/mechanisms during wastewater treatment process were also discussed.

The effect of Cu(2+) chelation on the direct photolysis of oxytetracycline: A study assisted by spectroscopy analysis and DFT calculation

The extensive usage of OTC and Cu(2+) in livestock and poultry industry caused high residues in natural environment. Co-contamination of OTC and Cu(2+) was a considerable environmental problem in surface waters. In this study, Cu(2+) mediated direct photolysis of OTC was studied. Cu(2+) chelating with OTC was found to greatly inhibit OTC photodegradation. To reveal the chelation mechanism of OTC-Cu complexes, multiple methods including UV-Vis absorption spectra, Infrared (IR) spectra, mass spectroscopy, and density functional theoretical (DFT) modeling were performed. Four OTC-Cu complexes were proposed. Cu(2+) preferably bond to O11O12 site with the binding constants logK = 8.19 and 7.86 for CuHL+ and CuL±, respectively. The second chelating site was suggested to be O2O3 with the binding constants of logK = 4.41 and 4.62 for Cu2HL3+ and Cu2L2+, respectively. The suppressed quantum yield of OTC by Cu2+ chelation was accused for their intra-/inter-molecular electron transfer, by which the energy in activated states was distributed. The occurrence of electron transfer between BCD ring and A ring also from BCD ring to Cu was evidenced by the TD-DFT result only for the OTC-Cu complexes. Besides, the cyclic voltammetry measurement also suggested one OTC-Cu(II)/OTC-Cu(I) redox couple. These results suggested that the persistence of OTC in environmental surface waters will probably be underestimated for neglecting the chelating effect of Cu2+. The photolysis quantum yield of OTC-Cu complexes, as well as the specific molar absorption constants, the equilibrium binding constants of Cu2+ with OTC could contribute to more accurate kinetic models of OTC.

Simultaneous analysis of multiple classes of antimicrobials in environmental water samples using SPE coupled with UHPLC-ESI-MS/MS and isotope dilution

A robust and sensitive analytical method was developed for the simultaneous analysis of 21 target antimicrobials in different environmental water samples. Both single SPE and tandem SPE cartridge systems were investigated to simultaneously extract multiple classes of antimicrobials. Experimental results showed that good extraction efficiencies (84.5-105.6%) were observed for the vast majority of the target analytes when extraction was performed using the tandem SPE cartridge (SB+HR-X) system under an extraction pH of 3.0. HPLC-MS/MS parameters were optimized for simultaneous analysis of all the target analytes in a single injection. Quantification of target antimicrobials in water samples was accomplished using 15 isotopically labeled internal standards (ILISs), which allowed the efficient compensation of the losses of target analytes during sample preparation and correction of matrix effects during UHPLC-MS/MS as well as instrument fluctuations in MS/MS signal intensity. Method quantification limit (MQL) for most target analytes based on SPE was below 5ng/L for surface waters, 10ng/L for treated wastewater effluents, and 15ng/L for raw wastewater. The method was successfully applied to detect and quantify the occurrence of the target analytes in raw influent, treated effluent and surface water samples.

Twisting in the excited state of an N-methylpyridinium fluorescent dye modulated by nano-heterogeneous micellar systems

The fluorescence of an N-methylpyridinium dye was modulated by nano-heterogeneous micellar systems, where its excited state twisting is gradually impaired by the increasing viscosity of the surrounding environment.

Doxycycline and oxytetracycline loading of a zwitterionic amphoteric surfactant-gel and their controlled release

Oxytetracycline (OX) and doxycycline (DX) are antibiotics belonging to the family of tetracyclines. We present a UV-Visible steady state and time-resolved experimental study of OX and DX and their biologically active Mg(2+) complexes loaded within a hydrogel matrix. Hydrogels are a three dimensional network of worm-like micelles, mutually intertwined, forming a pattern of hydrophobic domains and water pools. We resorted to a hydrogel, made of a zwitterionic N-oxide surfactant (p-dodecyloxybenzyldimethylamine N-oxide, pDoAO), which showed promising features as a drug vehicle. The spectral and photophysical properties of the drugs are significantly altered by the inclusion in the hydrophobic domains of the gel and these variations are indicators of the permeation ratio of the drug in between the micelles forming the gel network. We thus get a clear picture of the distribution of the drug molecules and metal chelates into the two different kinds of environment, where the hydrophobic domains are also able to cause a gel-induced deprotonation of these two drugs. Furthermore, the amphoteric nature of the surfactant is responsible for its peculiar acid-base behaviour: under acidic pH conditions, the surfactant gets protonated and the stability of the gel network is damaged. This feature can be thus exploited for the pH controlled release of the tetracycline drugs.

Inclusion of push–pull N-methylpyridinium salts within surfactant hydrogels: is their excited state intramolecular charge transfer mediated by twisting?

By confining two push–pull N-methylpyridinium derivatives within the rigid domains of surfactant hydrogels, the twisted nature of their intramolecular charge transfer state (formed in water upon excitation) was unravelled.

Photoinduced symmetry-breaking intramolecular charge transfer in a quadrupolar pyridinium derivative

We report here a joint experimental and theoretical study of a quadrupolar, two-branched pyridinium derivative of interest as a potential non-linear optical material. The spectral and photophysical behaviour of this symmetric system is greatly affected by the polarity of the medium. A very efficient photoinduced intramolecular charge transfer, surprisingly more efficient than in the dipolar asymmetric analogue, is found to occur by femtosecond resolved transient absorption spectroscopy. TD-DFT calculations are in excellent agreement with these experimental findings and predict large charge displacements in the molecular orbitals describing the ground state and the lowest excited singlet state. The theoretical study also revealed that in highly polar media the symmetry of the excited state is broken giving a possible explanation to the fluorescence and transient absorption spectra resembling those of the one-branched analogous compound in the same solvents. The present study may give an important insight into the excited state deactivation mechanism of cationic (donor-π-acceptor-π-donor)(+) quadrupolar compounds characterised by negative solvatochromism, which are expected to show significant two-photon absorption (TPA). Moreover, the water solubility of the investigated quadrupolar system may represent an added value in view of the most promising applications of TPA materials in biology and medicine.

Role of tetracycline speciation in the bioavailability to Escherichia coli for uptake and expression of antibiotic resistance

Tetracycline contains ionizable functional groups that manifest several species with charges at different locales and differing net charge; the fractional distribution of each species depends on pH-pKa relationship in the aqueous phase. In nature, these species interact with naturally abundant cations (e.g., Ca(2+) and Mg(2+)) to form metal-tetracycline complexes in water. In this study, we used Escherichia coli MC4100/pTGM whole-cell bioreporter to investigate tetracycline uptake from solution under varying conditions of pH, salt composition and concentration by quantifying the corresponding expression of antibiotic resistance gene. The expression of antibiotic resistance gene in the E. coli bioreporter responded linearly to intracellular tetracycline concentration. Less tetracycline entered E. coli cells at solution pH of 8.0 than at pH 6.0 or 7.0 indicating reduced bioavailability of the antibiotic at higher pH. Both Mg(2+) and Ca(2+) in solution formed metal-tetracycline complexes which reduced uptake of tetracycline by E. coli hence diminishing the bioresponse. Among the various tetracycline species present in solution, including both metal-complexed and free (noncomplexed) species, zwitterionic tetracycline was identified as the predominant species that most readily passed through the cell membrane eliciting activation of the antibiotic resistance gene in E. coli. The results indicate that the same total concentration of tetracycline in ambient solution can evoke very different expression of antibiotic resistance gene in the exposed bacteria due to differential antibiotic uptake. Accordingly, geochemical factors such as pH and metal cations can modulate the selective pressure exerted by tetracycline for development and enrichment of antibiotic resistant bacteria. We suggest that tetracycline speciation analysis should be incorporated into the risk assessment framework for evaluating environmental exposure and the corresponding development of antibiotic resistance.