Effect of copper ions on the degradation of thiram in aqueous solution: identification of degradation products by HPLC-MS/MS

Ag-modified CuO cavity arrays as a SERS-electrochemical dual signal platform for thiram detection

Rapid and sensitive determination of pesticide residues in fruits and vegetables is critical for human health and ecosystems. This paper used an Ag-modified CuO sphere-cavity array (CuO@Ag) electrode as a thiram SERS/electrochemical dual readout detection platform. Numerous Raman "hotspots" generated by uniformly distributed silver nanoparticles, charge transfer at the CuO@Ag interface, and the formation of Ag-thiram complexes contribute to the significant enhancement of this SERS substrate, which results in excellent SERS performance with an enhancement factor up to 1.42 × 106. When using SERS as the readout technique, the linear range of the substrate for thiram detection was 0.05-20 nM with a detection limit (LOD) of up to 0.0067 nM. Meanwhile, a correlation between the value of change in current density and thiram concentration was established due to the formation of stable complexes of thiram with Cu2+ generated at specific potentials. The linear range of electrochemical detection was 0.05-20.0 μM, and the detection limit was 0.0167 μM. The newly devised dual-readout sensor offers notable sensitivity and stability. The two signal readout methods complement each other in terms of linear range and detection limit, making it a convenient tool for assessing thiram residue levels in agro-food. At the same time, the combination of commercially available portable equipment makes on-site monitoring possible.

Reactivating Hippo by drug compounds to suppress gastric cancer and enhance chemotherapy sensitivity

The Hippo signaling pathway plays an essential role in organ size control and tumorigenesis. Loss of Hippo signal and hyper-activation of the downstream oncogenic YAP signaling are commonly observed in various types of cancers. We previously identified STRN3-containing PP2A phosphatase as a negative regulator of MST1/2 kinases (i.e., Hippo) in gastric cancer (GC), opening the possibility of selectively targeting the PP2Aa-STRN3-MST1/2 axis to recover Hippo signaling against cancer. Here, we further discovered 1) disulfiram (DSF), an FDA-approved drug, which can similarly block the binding of STRN3 to PP2A core enzyme and 2) CX-6258 (CX), a chemical inhibitor, that can disrupt the interaction between STRN3 and MST1/2, both allowing reactivation of Hippo activity to inhibit GC. More importantly, we found these two compounds, via an MST1/2 kinase-dependent manner, inhibit DNA repair to sensitize GC towards chemotherapy. In addition, we identified thiram, a structural analog of DSF, can function similarly to inhibit cancer cell proliferation or enhance chemotherapy sensitivity. Interestingly, inclusion of copper ion enhanced such effects of DSF and thiram on GC treatment. Overall, this work demonstrated that pharmacological targeting of the PP2Aa-STRN3-MST1/2 axis by drug compounds can potently recover Hippo signal for tumor treatment.

Portable ratiometric fluorescence detection of Cu2+and thiram

Food contaminants pose a danger to human health, but rapid, sensitive and reliable food safety detection methods can offer a solution to this problem. In this study, an optical fiber ratiometric fluorescence sensing system based on carbon dots (CDs) and o-phenylenediamine (OPD) was constructed. The ratiometric fluorescence response of Cu2+and thiram was carried out by the fluorescence resonance energy transfer (FRET) between CDs and 2,3-diaminophenazine (ox-OPD, oxidized state o-phenylenediamine). The oxidation of OPD by Cu2+resulted in the formation of ox-OPD, which quenched the fluorescence of CDs and exhibited a new emission peak at 573 nm. The formation of a [dithiocarbamate-Cu2+] (DTC-Cu2+) complex by reacting thiram with Cu2+, inhibits the OPD oxidation reaction triggered by Cu2+, thus turning off the fluorescence signal of OPD-Cu2+. The as-established detection system presented excellent sensitivity and selectivity for the detection of Cu2+and thiram in the ranges of 1 ∼ 100μM and 5 ∼ 50μM, respectively. The lowest detection limits were 0.392μM for Cu2+and 0.522μM for thiram. Furthermore, actual sample analysis indicated that the sensor had the potential for Cu2+and thiram assays in real sample analysis.

G-site residue S67 is involved in the fungicide-degrading activity of a tau class glutathione S-transferase from Carica papaya

Thiram is a toxic fungicide extensively used for the management of pathogens in fruits. Although it is known that thiram degrades in plant tissues, the key enzymes involved in this process remain unexplored. In this study, we report that a tau class glutathione S-transferase (GST) from Carica papaya can degrade thiram. This enzyme was easily obtained by heterologous expression in Escherichia coli, showed low promiscuity toward other thiuram disulfides, and catalyzed thiram degradation under physiological reaction conditions. Site-directed mutagenesis indicated that G-site residue S67 shows a key influence for the enzymatic activity toward thiram, while mutation of residue S13, which reduced the GSH oxidase activity, did not significantly affect the thiram-degrading activity. The formation of dimethyl dithiocarbamate, which was subsequently converted into carbon disulfide, and dimethyl dithiocarbamoylsulfenic acid as the thiram degradation products suggested that thiram undergoes an alkaline hydrolysis that involves the rupture of the disulfide bond. Application of the GST selective inhibitor 4-chloro-7-nitro-2,1,3-benzoxadiazole reduced papaya peel thiram-degrading activity by 95%, indicating that this is the main degradation route of thiram in papaya. GST from Carica papaya also catalyzed the degradation of the fungicides chlorothalonil and thiabendazole, with residue S67 showing again a key influence for the enzymatic activity. These results fill an important knowledge gap in understanding the catalytic promiscuity of plant GSTs and reveal new insights into the fate and degradation products of thiram in fruits.

Factors affecting the durability of dimethyl dithiocarbamate-stabilized air pollution control (APC) residues derived from municipal solid waste incineration

Sodium dimethyl dithiocarbamate (SDD) is widely used for stabilizing heavy metals to minimize pollution from air pollution control (APC) residues derived from municipal solid waste incineration. However, the effect of environmental conditions on heavy metal leaching from SDD-stabilized APC residues remains unknown. Therefore, this study aimed to evaluate the durability of SDD-stabilized APC residues and determine the relationship between heavy metal leaching and environmental factors, including pH, temperature, and oxygen. The results revealed that accelerated SDD decomposition and the decline in durability of SDD-stabilized APC residues were caused by acidic and aerated conditions and temperatures above 40 °C. A decrease in pH from 12.25 to 4.69 increased the Cd and Pb concentrations in SDD-stabilized APC residue leachate from below detection (0.002 mg/L) to 1.32 mg/L and 0.04 mg/L to 3.79 mg/L, respectively. Heating at 100 °C for 2 d increased the Cd and Pb concentrations from below detection (0.002 mg/L and 0.01 mg/L) to 2.96 mg/L and 0.47 mg/L, respectively. Aeration for 5 d increased the Cd and Pb concentrations from below detection to 0.09 mg/L and 0.49 mg/L, respectively. The decline in durability was attributed to acid hydrolysis, thermal decomposition, and oxidative damage of SDD, resulting in breakage of the chelated sulfur-metal bond, which was confirmed by the decrease in the oxidizable fraction of heavy metals and the SDD content. This study improves the understanding of the factors contributing to the decline in durability of heavy metals in SDD-stabilized APC residues, which is important for ensuring the long-term stabilization and environmental safety of these residues.

Cu2+-assisted sensing of fungicide Thiram in food, soil, and plant samples and the ratiometric detection of Hg2+ in living cells by a low cytotoxic and red emissive fluorescent sensor

Metal ions and pesticides are extensively used in many industries and agriculture. However, they cause significant environmental pollution and various adverse health effects. Therefore, the development of sensitive and selective techniques to detect them is necessary for human health and the ecosystem. In this paper, we report a novel red-emitting fluorescence probe with a large Stokes shift (∼220 nm) based on rhodamine and isophorone units. The probe shows a ratiometric fluorescence response toward Hg²⁺ ions; however, Cu²⁺ ions quench the red fluorescence signal. The decomposition of the probe-Cu²⁺ complex allows detection of Thiram followed by recovery of the red fluorescence signal of the probe. In addition, the probe shows a good linear response to Hg²⁺, Cu²⁺, and Thiram, with detection limits of 122.0 nM, 29.0 nM, and 72.0 nM, respectively. The practical applicability of the probe has been successfully tested in real samples. Moreover, smartphone detection and light-responsive capsule fabrication have been established, for easy and quick detection. The probe possesses very low cytotoxicity and allows visualization of Hg²⁺ and Cu²⁺ ions in HeLa cells. Therefore, the present probe is expected to be an effective tool assisting in easy, quick, and reliable detection of Thiram, Hg²⁺, and Cu²⁺ ions.

Bimetallic metal-organic frameworks-based ratiometric fluorescence sensor for the quantitative detection of thiram in fruits samples

The identification of residual thiram (Tr) in foods is vital in view of its harmful effects on human health. Herein, a ratiometric fluorescence sensor (I₄₃₅/I₅₉₀) based on rhodamine B/NH₂-MIL-53(Al_0.75Fe_0.25) was constructed for the detection of Tr. Interestingly, the probe RhB/NH₂-MIL-53(Bim) assisted by Cu²⁺ could rapidly and sensitively recognize Tr with a low detection limit of 0.11 μg/mL in 10 min. The fluorescence sensing mechanism was investigated using fluorescence spectra, UV-Vis absorption spectra, the fluorescence lifetime and quantum yield. The results showed that the excellent sensing performance was attributed to fluorescence resonance energy transfer, electrostatic interaction, and photoinduced electron transfer. In addition, the practical application of this platform showed acceptable relative recoveries for Tr (84.03-107.81 %), and precisions were also achieved (relative standard deviation ≤ 8.69 %, n = 3). These results show that the presented herein can be applied to monitor the Tr content in real fruit samples.

Determination of thiram residues in fresh water using flow injection diperiodatonickelate(IV)-quinine chemiluminescence detection

This study developed a simple flow injection (FI) method based on diperiodatonickelate(IV)-sulfuric acid reaction using chemiluminescence (CL) detection for the determination of thiram (THI) fungicide in fresh water using quinine as the sensitizer. The possible mechanism of the CL reaction was described using UV-Vis. absorption and CL spectra. Experimental variables were optimized by applying a univariate approach, and a linear calibration curve was obtained in the range of 1.0 × 10^-3 -2.0 mg L^-1 (R²  = 0.9994, n = 9) with a limit of detection of 5.0 × 10^-4  mg L^-1 (S/N = 3) and an injection throughput of 200 h^-1 . This approach was successfully applied to determine THI in fresh water by using solid-phase extraction and achieved a good recovery rate of 94%-110% with a relative standard deviation of 1.9%-3.7% (n = 4). The results obtained were compared with the reported FI-CL and high-performance liquid chromatography-ultraviolet methods, and the three methods did not differ significantly at the 95% confidence limit.

Ag nanocubes monolayer-modified PDMS as flexible SERS substrates for pesticides sensing

A new approach is presented to fabricate flexible surface-enhanced Raman scattering (SERS) substrate of Ag nanocubes monolayer-modified polydimethylsiloxane (Ag NCs/PDMS) through a powerful three-phase interface self-assemble method. The morphologies and crystal structures were characterized by scanning electron microscopy and X-ray diffraction. The self-assembled Ag NCs/PDMS substrate exhibited high SERS activity and good signal homogeneity, which was successfully used for quantitative detection of thiram; the detection limit reached 10 ng/mL, and the linear range is 10-1000 ng/mL. Furthermore, the flexible SERS substrates were successfully employed to detect thiram residues on factual apple samples, and trace amount (1 ng/cm²) of thiram residues was detected on apple peels. The excellent SERS detection ability of self-assembled Ag NCs/PDMS substrate indicated that it will play an important role in pesticide detection in the future.

Uptake, translocation and metabolism of imidacloprid loaded within fluorescent mesoporous silica nanoparticles in tomato (Solanum lycopersicum)

Fluorescence-labeling technology has been widely used for rapid detection of pesticides in agricultural production. However, there are few studies on the use of this technology to investigate pesticide uptake and transport in plants with fluorescent nanoparticle formulations. Here, we investigated uptake, transport, accumulation and metabolism of imidacloprid loaded in fluorescent mesoporous SiO₂ nanoparticles (Im@FL-MSNs) in tomato plants, and compared the results with the pesticide application in granular formulation. The results revealed that Im@FL-MSNs applied via root uptake and foliar spray both could effectively transport in tomato plants and carry the imidacloprid to plant tissues. Neither Im@FL-MSNs nor imidacloprid was detected inside of tomato fruits from root uptake or foliar spray applications. Compared with the foliar application of granular formulation, imidacloprid in Im@FL-MSNs demonstrated a higher concentration in leaves (1.14 ± 0.07 mg/kg > 1.08 ± 0.04 mg/kg, 1.13 ± 0.09 mg/kg > 1.11 ± 0.02 mg/kg), longer half-life (0.84 d < 1.31 d, 0.90 d < 1.36 d) and small numbers of metabolites formed. These results suggest that mesoporous silica nanoparticles could serve as an effective and efficient pesticide carrier for achieving the high use efficiency in plant protection. The information is also helpful to guide the pesticide applications and assess the risks associated with environmental quality and dietary consumption of vegetables.

Copper ions assisted fluorescent detection of some dithiocarbamates based on nickel nanocluster with aggregation-induced emission enhancement behavior

Pesticide residue contamination has become an urgent issue since it threatens both the natural environment and public health. In this study, a fluorescent method for detecting dithiocarbamate (DTC) compounds was constructed based on novel nickel nanoclusters (Ni NCs) and copper ions (Cu²⁺). The water-soluble fluorescent Ni NCs were synthesized for the first time through a one-pot method using glutathione as stabilizer and ascorbic acid as reducing agent. The as-prepared Ni NCs exhibited a maximum fluorescence emission at 445 nm when excited by 380 nm. And they displayed aggregation-induced emission enhancement when ethylene glycol was introduced into the nanocluster aqueous solution. Based on the Ni NCs, a label-free fluorescence quenching sensor was established for sensitive and selective detection of DTC compounds with the assistance of Cu²⁺. The complex formed by DTC and Cu²⁺ led to fluorescence quenching of Ni NCs through inner filter effect. The sensing method was successfully applied to two typical DTC compounds, thiram and disulfiram, with good linearity over a wide linear range and a low detection limit. Moreover, the proposed approach was capable of thiram detection in real samples, which confirms the potential of this sensing method as a platform for DTC compound detection.

Chlorogenic acid inhibits apoptosis in thiram-induced tibial dyschondroplasia via intrinsic pathway

Tibial dyschondroplasia (TD) is a common skeletal disease occurred in growth plate of fast-growing broilers. Thiram is a sort of chemical used for pesticide and fungicide. The excessive use of thiram increased the threat to animal and human health. In this study, we aimed to investigate the therapeutic mechanism of chlorogenic acid (CGA) on thiram-induced tibial dyschondroplasia. Broiler chickens were divided into three different groups, e.g., control, TD, and CGA. CGA was administrated after the induction of TD from 4^th day to 7^th day. Biochemical analysis was performed to detect the content of calcium (Ca) and phosphorus (P). Histological changes and degradation of extracellular matrix were observed through hematoxylin-eosin (H & E) and Masson staining. To further determine the mechanism, TUNEL staining and western blot were also performed to detect the apoptosis changes in growth plate of all groups. The results showed the disproportionation of Ca and P content and upregulation of apoptosis during the development of TD. But, after the administration of CGA, the ratio of Ca:P was upregulated, and the apoptosis was also downregulated. The current study shows the toxic effect of thiram on chickens and suggests that CGA is associated with a mechanism that plays a significant role in apoptosis induced by thiram in poultry industry.

Chitosan functionalized Halloysite Nanotubes as a receptive surface for laccase and copper to perform degradation of chlorpyrifos in aqueous environment

Chitosan (CTS) functionalized Halloysite Nanotubes (HNT) have been used as receptive nano-supports for the grafting of copper (Cu) and laccase (Lac) for the degradation of chlorpyrifos. The developed nanocomposite Lac@Cu-CTS-HNT showed 83.4% Lac immobilization which was further characterized by TEM, SEM-EDX, FTIR, XRD, DSC and TGA. The chlorpyrifos degradation studies were performed under constant stirring for 24 h with both free enzyme and Lac@Cu-CTS-HNT and were analysed through HPLC. Percentage degradation of chlorpyrifos with the nanocomposite went as high as 97% for 50 μg/mL chlorpyrifos at neutral pH and room temperature. Variable pesticide and nanocomposite concentration, pH, and temperature studies for pesticide degradation were also performed, followed by reusability studies. The nanocomposite maintained its degradation ability at ~97% even at variable temperature and pH conditions. Reusability study was performed 5 times wherein the degradation percentage remained the same after 5 cycles (~<95%). Degradation kinetics were also performed for the nanocomposite in the presence and absence of the immobilized enzyme. Through this study, it is suggested that Lac@Cu-CTS-HNT can be a potential nano-catalyst for the degradation of chlorpyrifos in aqueous environment.

Detect, remove and re-use: Sensing and degradation pesticides via 3D tilted ZMRs/Ag arrays

The objective of this study was to design a versatile and reusable pesticide detection surface-enhanced Raman scattering (SERS) substrate in combination with SERS enhancement and self-cleaning properties. In this paper, we present an inexpensive way to synthesize three-dimensional tilted ZnO micron rods with an Ag hierarchical structure (ZMRs/Ag arrays). Although expensive materials and complex methods were not used, the detection limit of thiram residue was 10^-11 M, with a quantitative relationship (R² = 0.9929) between the thiram concentration and the intensity of the SERS peaks. Additionally, the substrates exhibited fast and efficient photocatalytic activity for the degradation of adsorbed thiram, and the degradation rate in 30 min was close 100 % under visible-light irradiation. The enhancement and photocatalytic mechanism of this substrate were meticulously analyzed in detail. Furthermore, the residues of several mixed pesticides (e.g., thiram and methamidophos compounds) in various juices (such as grape, pear, orange, apple, and cherry juices) were quickly detected using ZMRs/Ag substrates. The main advantages of this substrate are recyclability, stability, selectivity, handiness, and cost-eff ;ectiveness. The substrate can prevent single-use problems associated with conventional SERS substrates and can be applied in pesticide residue and food security.

Photolysis of clethodim herbicide and a formulation in aquatic environments: Fate and ecotoxicity assessment of photoproducts by QSAR models

The photochemical fate of the herbicide clethodim in natural waters was investigated under simulated and natural sunlight radiation. This herbicide exhibited a rapid degradation rate in simulated aquatic environment with half-lives ranged from 27.9min to 4.6h. The commercial formulation of clethodim showed a faster degradation with half-lives from 19.3min to 1.4h. It has also been demonstrated that the photolytic behavior of clethodim was affected by the water composition and the radiation intensity. Nine major photoproducts were identified and their distribution was dependent on the experimental conditions. Photodegraded solutions of clethodim were shown to be more toxic to the bacteria Vibrio fischeri than the herbicide itself, reaching the maximum toxicity when the herbicide is completely degraded. QSAR analysis of the fate, ecotoxicological and physicochemical endpoints of the degradation products provided positive alerts for several identified by-products. Environmental fate and transport estimates showed that all photoproducts, unlike the active substance, are potential leachers. Moreover, predicted vapor pressures suggested that dermal contact and ingestion are the most probable exposure routes for workers and general population to both clethodim and its photoproducts. These results highlight the importance of the degradation products in attaining a complete knowledge of the fate and behavior of an herbicide in the environment. To our knowledge, this is the first study to report a detailed QSAR study on clethodim photoproducts under environmental conditions. These results provide a very valuable information that will guide further experimental studies leading to a better pesticide risk assessment.

Detection of Dithiocarbamate Pesticides with a Spongelike Surface-Enhanced Raman Scattering Substrate Made of Reduced Graphene Oxide-Wrapped Silver Nanocubes

Dithiocarbamate (DTC) pesticides are widely used for fruits, vegetables, and mature crops to control fungal diseases. Their residues in food could pose a threat to human health. Therefore, a surface-enhanced Raman scattering-based (SERS-based) sensor is developed to detect DTC pesticides because SERS can provide the characteristic spectrum of pesticides and avoid the use of a molecular recognition probe in the sensor. For the acquisition of high sensitivity, good anti-interference ability, and robustness of the SERS sensor, a silver nanocube-reduced graphene oxide (AgNC-rGO) sponge is devised. In the AgNC-rGO sponge, the rGO sheets form a porous scaffold that physically holds the AgNCs, which create narrow gaps between the neighboring AgNCs, leading to the formation of "hot spots" for SERS-signal amplification. When DTC pesticides coexist with aromatic pesticides in a sample matrix, the AgNC-rGO sponge can selectively detect DTC pesticides because of the preferential adsorption of DTC pesticides on the Ag surface and aromatic pesticides on the rGO surface, which can effectively eliminate the interference of the SERS signals of aromatic pesticides, and facilitate the qualitative and quantitative analysis of DTC pesticides. The AgNC-rGO sponge shows great potential as a SERS substrate for selective detection of DTC pesticides.