The environmental behaviour and the bioavailability of polycyclic aromatic hydrocarbons (PAHs) are strongly affected by dissolved organic matter (DOM) in aquatic environments. In this study, we investigated the dynamics of the bioavailability and character of the intracellular DOM (IDOM) from Microcystis aeruginosa (M. aeruginosa-IDOM) during 10 days oxic and anoxic incubations by spectroscopy. Subsequently, the binding affinity of pyrene with the initial/altered M. aeruginosa-IDOM was estimated by fluorescence quenching method. The incubation results indicated that changes in dissolved organic carbon (DOC) concentration and selected spectral descriptors of the M. aeruginosa-IDOM under oxic condition were different from those of anoxic condition. The microbial transformation of the M. aeruginosa-IDOM resulted in an enhancement of the organic carbon-normalized binding coefficient (KDOC) of pyrene in both oxic and anoxic treatments. Moreover, only for the oxic condition, Pearson correlation analysis demonstrated that aromaticity (specific UV absorbance at 254 nm, SUVA254), humification degree (humification index, HIX) and the percent distribution of humic-like component 2 (%C2) presented significantly positive correlations with the pyrene KDOC, while the percent distribution of protein-like component 1 (%C1) exhibited a negative correlation with the KDOC. However, no significant correlation was observed between any spectral descriptor and the KDOC under anoxic condition. This result suggested that the binding affinity of pyrene may be primarily influenced by the altered M. aeruginosa-IDOM characteristics associated with the biological transformation. Hence, our results provided potential evidence for resolving the inconsistency in the relationships between DOM characteristics and the binding affinities of PAHs.

The room-temperature phosphorescence (RTP) of Mn-doped ZnS quantum dots (Mn–ZnS QDs) was quenched by the addition of selenite in the presence of glutathione. The quenching of the RTP emission of Mn–ZnS QDs was due to HSe− ions which was the reaction product of selenite and glutathione. Based on the above finding, a simple, rapid, sensitive probe for selective detection of selenite was successfully fabricated. Under the optimal experimental conditions, a linear relationship was obtained covering the linear range of 0.1–5.0 μmol L−1 and the detection limit (3σ) was 0.085 μmol L−1. The proposed method was successfully applied for the determination of selenite in sodium selenite tablets and sodium selenite and vitamin E injection with satisfactory results.

The interaction between a typical PAH metabolite, 1-hydroxypyrene (1-OHP), and a transport protein, bovine serum albumin (BSA), has been investigated using fluorescence, UV-visible absorption (UV-vis), circular dichroism (CD) spectra, docking and molecular dynamics (MD) simulation methods under simulated physiological conditions (in Tris–HCl buffer, pH = 7.40). The experimental results suggested that the fluorescence quenching of BSA by 1-OHP occurred through a mixed static and dynamic quenching mechanism with a binding constant of 2.40 × 106 L mol−1 at 291 K. The thermodynamic parameters together with the docking and MD study revealed that van der Waals forces dominate the formation of the 1-OHP–BSA complex. Applying Förster's non-radiation energy transfer theory, the binding distance of 1-OHP to BSA was calculated to be 2.88 nm. In addition, as confirmed by time-resolved fluorescence, UV-vis, three-dimensional (3-D) fluorescence and CD spectra, high concentrations of 1-OHP induced conformational transitions of BSA, increasing the content of the α-helix of BSA and exposing its tryptophan residue to a more hydrophilic microenvironment. An inhibition test showed that 1-OHP strongly inhibits the binding constant of vitamin B2 with BSA. A molecular docking study visualized the binding mode of 1-OHP with BSA. 1-OHP inserted into the binding pocket IB of BSA, leaving its hydroxyl group outside. Based on that, the MD study further unveiled the stability of 1-OHP–BSA complex and their dynamic binding modes, and clarified the contributions of each binding force component and the key residues to the binding process.

•A new RTP sensor for Pb2 + detection based on GSH-Mn-ZnS QDs has been fabricated.•The RTP sensor showed good sensitivity for Pb2 + with detection limit of 0.45 μg·L− 1•The sensor was applied to determine Pb2 + in water samples without interference.The room-temperature phosphorescence (RTP) of glutathione-capped Mn-doped ZnS quantum dots (GSH-Mn-ZnS QDs) was effectively quenched by the addition of Pb2 +. A simple and sensitive RTP sensor for Pb2 + detection based on the quenching effect was developed. Under the optimal conditions, good linear correlations were obtained for Pb2 + over a concentration range from 1.0 to 100 μg·L− 1, and the detection limit was 0.45 μg·L− 1. The established method has been successfully applied for the determination of Pb2 + in real water samples without complicated sample pretreatment with the recoveries in the range of 95.4%–104.0%.

The interaction between inorganic mercury(II) (Hg(II)) and catalase (CAT) was investigated using fluorescence, UV-visible absorption (UV-vis), circular dichroism (CD) spectroscopic techniques and molecular docking methods under simulated physiological conditions (in Tris–HCl buffer, pH = 7.40). The fluorescence quenching analysis showed that the intrinsic fluorescence of CAT was quenched by Hg(II) through a static quenching mechanism. Hg(II) can bind with CAT to form a Hg(II)–CAT complex, with a binding constant of 13.24 L mol−1 at 295 K. Thermodynamic analysis indicated that electrostatic force and van der Waals forces were the dominant intermolecular forces in stabilizing the complex. The results of UV-vis absorption and CD spectral analysis indicated that the formation of the Hg(II)–CAT complex induced some conformational changes in CAT, increasing and decreasing its α-helical content at low and high concentrations of Hg(II), respectively. The CAT activity can be inhibited by Hg(II) significantly, about a 67.2% drop with the presence of 5.0 × 10−4 mol L−1 Hg(II), and the relative activity values of CAT showed a good linear relationship with its fluorescence intensity. Molecular docking was employed to further investigate the interaction of CAT with different species of Hg(II) (HgCl2, [HgCl3]− and [HgCl4]2−), to seek the optimum binding sites of Hg(II) in CAT, and to obtain detailed binding information. This study contributes to the understanding of the interaction mechanism between Hg(II) and CAT at the molecular level in vitro, which is helpful for clarifying the toxicity mechanism of Hg(II) on an antioxidant enzyme system in vivo.

A novel method for the simultaneous in situ determination of phenanthrene (Phen) and fluoranthene (Fla) adsorbed onto mangrove root surfaces was established using laser-induced time-resolved nanosecond-fluorescence spectroscopy combined with a first-order derivative fluorometry (D-LITRF) method. The linear dynamic range, detection limit and recoveries of D-LITRF and laser induced time-resolved nanosecond fluorescence spectroscopy (LITRF) were of the same order. Using the established method, the transport of Phen and Fla from the mangrove root surface to tissues was simultaneously investigated in situ. The transportation coefficients of Phen and Fla adsorbed onto the root surface showed a good linear relationship with the content of root lipids, while the inhibition rates showed no significant correlation with the content of root lipids (p > 0.05). Further studies showed that the interaction between Fla and Phen decreased the transport kinetics, especially the slow and very slow transport kinetics. In addition, the coefficients and inhibition rates of the transport of Phen and Fla to Kandelia obovata (Ko) root tissues were evaluated at different temperatures. The results acquired by these in situ methods provide new information about how two PAHs components are transported from the mangrove root surface to the tissues.

To further achieve the field detection of PAHs in actual leaf samples, it is important to develop novel methods for in situ determination of polycyclic aromatic hydrocarbons (PAHs) in plant leaves. Normally, phenanthrene (Phe) is adsorbed onto the leaf surfaces of three kinds of mangrove species, named Kandelia obovata (Ko), Bruguiera gymnorhiza (Bg) and Aegiceras corniculatum (Ac). A set of laser-induced nanosecond time-resolved fluorescence (LITRF) system was utilized for the in situ quantitative detection of the absorbed phenanthrene (Phe) Experimental results showed that the linear dynamic ranges for the in situ determination of the Phe adsorbed onto the leaf surfaces of Ko, Bg and Ac were 2–1400 ng/spot, 1–1000 ng/spot and 4–2000 ng/spot, with the detection limits of 0.20, 0.14 and 0.42 ng/spot, respectively. The relative standard deviations were less than 6.0% (n = 9). The experimental recoveries for the Ko, Bg, and Ac were 89.6%–108.1%, 78.2%–92.4% and 93.2%–112.9%, respectively. Satisfactory results were obtained for the in situ determination of the Phe adsorbed onto the surfaces of the lab-exposure mangrove leaf samples contaminated by the Phe. The sensitivity of the established method was much higher than that of the previously established fiber optical fluorimetry, and the linear dynamic range got improved. The LITRF method marked a significant step towards to realizing the field detection of PAHs adsorbed onto the mangrove leaves.This figure shows the fluorescence emission spectra of phenanthrene adsorbed onto the leaf surfaces of Bruguiera gymnorhiza. It can be seen that the autofluorescence of the uncontaminated leaves did not interfere with the determination of phenanthrene, and the fluorescence intensity increased with the increasing of the concentration of the adsorbed phenanthrene.

•A highly sensitive, rapid, and in situ method was developed for determination of Fla.•The method provides a very low detection limit than previous methods.•The method was applicable for a real-time in situ survey of the depuration of Fla.•The main mechanisms for the rapid and slow depuration phases were evaluated.A novel approach for the in situ determination of fluoranthene (Fla) that was adsorbed onto the leaf surfaces of Avicennia marina (Am), Kandelia obovata (Ko), Bruguiera gymnorrhiza (Bg), and Aegiceras corniculatum (Ac) was established using laser-induced nanosecond time-resolved fluorescence (LITRF). The detection limits for the in situ determination of the Fla adsorbed onto the Am, Ko, Bg and Ac leaf surfaces were 0.03, 0.14, 0.16 and 0.31 ng spot−1, respectively. Using the LITRF method, the depuration of the adsorbed Fla from the leaf surfaces of the four selected mangrove species was investigated in situ. The results showed that the method was very simple and rapid to perform and it was applicable for a real-time in situ survey of the depuration processes of PAHs that were adsorbed onto the mangrove leaves. The depuration of Fla that was adsorbed onto the Am, Ko, Bg and Ac leaf surfaces followed fast and slow phases, both of which varied significantly between the mangrove species in terms of the elimination rate, the remaining Fla residues, and the effect of temperature on the remaining Fla residues on the leaf surfaces. Variations in leaf wax content and the leaf surface roughness among the four mangrove species were responsible for the differences in the rapid phase, while photolysis and penetration into the inner cuticle were dominant mechanisms for the slow depuration.

Metal-enhanced room temperature phosphorescence of diiodofluorescein was first observed on filter paper surface. The phosphorescence intensity is 2.5-fold brighter from diiodofluorescein on silver nanoparticles-deposited filter paper as compared with an identical control sample without silver nanoparticles. Furthermore, enhanced absorption was also observed for the same system. Our findings suggest that both singlet and triplet states can couple to surface plasmons and enhance phosphorescence quantum yields at room temperature, as well as to increase the excitation rate of lumophores at room temperature.

A fiber-optic fluorimetry for in situ simultaneous determination of fluorine (Flu), phenanthrene (Phe) and fluoranthene (Fla) adsorbed on the leaf surfaces of Kandelia candel (Kc) seedlings was developed. Experimental results showed that the linear ranges for determination of Flu, Phe and Fla adsorbed on Kc leaves were 35–700, 5–900 and 2–450 ng/spot, respectively. The detection limits for Flu, Phe and Fla were 9.11, 1.65 and 0.90 ng/spot and with the relative standard deviations less than 10.32%, 7.56% and 4.29% (n = 9), respectively. The recovery results for Flu, Phe and Fla adsorbed on Kc leaves were 83.0–91.2, 78.5–88.5 and 91.5–107.3%, respectively. Under the laboratory experimental conditions, the photolysis processes of Flu, Phe and Fla individual and in mixtures adsorbed on the leaf surfaces of living Kc seedlings were studied. Results showed that the photolysis of Flu, Phe and Fla individual and in mixtures adsorbed on the leaf surfaces of Kc seedlings followed first-order kinetics with photolysis rates in the order of Flu > Fla > Phe on the Kc leaves. An antagonistic effect was found when the three polycyclic aromatic hydrocarbons (PAHs) were co-adsorbed on living Kc seedlings. The experimental results also indicated that photolysis was the main transformation pathway for Flu, Phe and Fla both individual and in mixtures adsorbed on Kc leaves, whereas disappearance of the adsorbed Flu, Phe and Fla as a result of volatilization and leaf absorption could be negligible during the experimental period.

A fluorimetric method for simultaneous determination of dissolved acenaphthylene (Ace) phenanthrene (Ph) and pyrene (Py), mixed in an aqueous mineral salts medium (MSM), was developed. The linear ranges for determination of Ace, Ph and Py dissolved in the mixture were 4.00 × 10−6 to 3.00 × 10−3g/L, 2.00 × 10−6 to 1.00 × 10−3 g/L and 7.00 × 10−7 to 1.00 × 10−4 g/L. The limits of detection for Ace, Ph and Py were 8.53 × 10−7, 4.98 × 10−7 and 6.01 × 10−8 g/L and the relative standard deviations 1.05%, 1.62% and 1.16% (n = 8), respectively. Satisfactory results were obtained when this method was used to simultaneously study the biodegradation processes of mixtures of dissolved Ace, Ph and Py in an MSM aqueous solution.

A solid surface fluorimetry approach was established for direct determination of anthracene (An) adsorbed onto fresh mangrove leaves. The experimental results showed that the linear dynamic ranges for determination of An adsorbed onto Avicennia marina (Am), Bruguiera gymnorrhiza (Bg), Kandelia candel (Kc) and Rhizophors stylosa (Rs) leaves varied from 0.92 to 8.71, 0.089 to 0.70, 0.063 to 5.61 and 0.11 to 1.82 μg g−1, with detection limits of 5.77, 1.79, 4.29 and 1.42 ng g−1, respectively, and with a relative standard deviation less than 10% (n = 5). The experimental recovery results for adsorbed An on Am, Bg, Kc and Rs leaves were among 79.2–85.9, 75.1–102.3, 70.2–93.8 and 73.1–110.8%, respectively. Using the established method, we investigated the effects of exposure time of An and the different quantity of leaf-wax among the four species of mangrove on the amount of An adsorbed. Under the same experimental conditions, the adsorption of An on the upper and lower sides of the same mangrove leaf, and at different regions on the upper side of the same mangrove leaf were also studied. The results demonstrated that the leaves of different mangrove species contained different quantities of leaf-wax, and with the same exposure conditions to An, the quantity of leaf-wax among the four species showed a significant positive correlation with the amount of An adsorbed onto the leaves.

•DP exposure induced neurobehavioral toxicity was evaluated in zebrafish.•DP exposure altered motor behavior, inhibited axonal growth and induced lesions in muscle fibers.•DP exposure induced oxidative stress and apoptotic cell death in larval zebrafish.•DP exposure altered mRNA transcript levels of apoptosis-related genes.Developmental neurobehavioral toxicity of Dechlorane Plus (DP) was investigated using the embryo-larval stages of zebrafish (Danio rerio). Normal fertilized embryos were waterborne exposed to DP at 15, 30, 60 μg/L beginning from 6 h post-fertilization (hpf). Larval teratology, motor activity, motoneuron axonal growth and muscle morphology were assessed at different developmental stages. Results showed that DP exposure significantly altered embryonic spontaneous movement, reduced touch-induced movement and free-swimming speed and decreased swimming speed of larvae in response to dark stimulation. These changes occurred at DP doses that resulted no significant teratogenesis in zebrafish. Interestingly, in accord with these behavioral anomalies, DP exposure significantly inhibited axonal growth of primary motoneuron and induced apoptotic cell death and lesions in the muscle fibers of zebrafish. Furthermore, DP exposure at 30 μg/L and 60 μg/L significantly increased reactive oxygen species (ROS) and malondialdehyde (MDA) formation, as well as the mRNA transcript levels of apoptosis-related genes bax and caspase-3. Together, our data indicate that DP induced neurobehavioral deficits may result from combined effects of altered neuronal connectivity and muscle injuries.Download high-res image (372KB)Download full-size image

•The retention and distribution of PAHs on epidermal tissues were firstly investigated.•PAHs distributed on epidermal tissues of mangrove and Poaceae plants were different.•Bacterial degraded the N/O/S-containing PAHs on epidermal tissues of mangrove root.The polycyclic aromatic hydrocarbons (PAHs) located on the epidermal tissues showed distinctive toxic effects to root, while the retention and distribution of PAHs on mangrove seedlings poorly understood. Our results confirmed that the partition coefficients (Kf) of the PAHs retained on the epidermal tissue of mangrove roots, such as Kandelia obovata, Avicennia marina and Aegiceras corniculatum, were much higher than the Poaceae plants roots, for example wheat and maize (Wild et al., 2005). Moreover, to the parent and alkyl PAHs, a well negative correlation was observed between the surface polarity of these three species of mangrove root and the Kf values (p < 0.05). To the N/O/S containing PAHs, these relationships were not obviously due to existing of the π-π, n-π interactions and hydrogen bonding between the N/O/S-containing PAHs and epidermal tissues. The PAHs retained on these three species of mangrove root epidermal tissues formed larger clusters than that of on Poaceae plants, such as wheat and maize (Wild et al., 2005) due to the limitation of the suberization of the root exodermis and endodermis. After exposure of 30 d, rhizo- and endophytic bacteria degraded parts of the N/O/S-containing PAHs to medium-lifetime fluorescence substances. To our knowledge, this is the first time to assess the retention of PAHs on the epidermal tissue of mangrove root, which will improve our understanding of the root uptake PAHs process.Download high-res image (174KB)Download full-size image

•Spectroscopic characterization of DOM from M. aeruginosa during its growth period.•The binding properties of pyrene with the M. aeruginosa-DOM were investigated.•The humification degree was highly associated with the pyrene KDOC values.•The environmental behavior of PAHs was effected by periodic blooms.The autochthonous dissolved organic matter (DOM) released by Microcystis aeruginosa (M. aeruginosa-DOM) during its growth period was characterized by spectroscopy. Furthermore, the relationships between the M. aeruginosa-DOM spectroscopic descriptors and the pyrene binding coefficient (KDOC) values were explored. The results showed that the spectroscopic characteristics of the M. aeruginosa-DOM and the binding properties of pyrene were dynamically changed along with the algae growth. Pearson correlation analysis demonstrated that a higher pyrene KDOC value was observed for the M. aeruginosa-DOM that has a higher humification index (HIX) value, a lower biological index (BIX) value and a lower absorption ratio (E2/E3). The presence of protein-like and long-wavelength-excited humic-like components may impose negative and positive effects on binding of pyrene by the M. aeruginosa-DOM, respectively. Principal component analysis (PCA) further supported that the binding affinity of pyrene may be primarily influenced by the humification degree of the M. aeruginosa-DOM.Download full-size image

A novel method for the simultaneous in situ determination of phenanthrene (Phen) and fluoranthene (Fla) adsorbed onto mangrove root surfaces was established using laser-induced time-resolved nanosecond-fluorescence spectroscopy combined with a first-order derivative fluorometry (D-LITRF) method. The linear dynamic range, detection limit and recoveries of D-LITRF and laser induced time-resolved nanosecond fluorescence spectroscopy (LITRF) were of the same order. Using the established method, the transport of Phen and Fla from the mangrove root surface to tissues was simultaneously investigated in situ. The transportation coefficients of Phen and Fla adsorbed onto the root surface showed a good linear relationship with the content of root lipids, while the inhibition rates showed no significant correlation with the content of root lipids (p > 0.05). Further studies showed that the interaction between Fla and Phen decreased the transport kinetics, especially the slow and very slow transport kinetics. In addition, the coefficients and inhibition rates of the transport of Phen and Fla to Kandelia obovata (Ko) root tissues were evaluated at different temperatures. The results acquired by these in situ methods provide new information about how two PAHs components are transported from the mangrove root surface to the tissues.