Sensitive fluorescent chemosensor for Hg(II) in aqueous solution using 4'-dimethylaminochalcone.

Mercury (Hg) is an element with high toxicity, especially to the nervous system, and fluorescent pigments are used to visualize dynamic processes in living cells. A little explored fluorescent core is chalcone. Herein, we synthesized chalcone (2E)-3-(4-(dimethylamino)phenyl)-1-phenylprop-2-en-1-one (8) and assessed its photophysical properties. Moreover, the application of this chemosensor in aqueous media shows a selective fluorescence quenching effect with Hg(II). The figures of merit for the chemosensor were calculated to be LOD = 136 nM and LOQ = 454 nM, as well as a stoichiometry of 1:1. Furthermore, the association constant (Ka) and fluorescence quenching constant (KSV) were calculated using the Benesi-Hildebrand and Stern-Volmer equations to be Ka= 9.08 × 104 and KSV= 1.60 × 105, respectively. Finally, by using a computational approach, we explain the interaction between chalcone (8) and Hg(II) and propose a potential quenching mechanism based on the blocking of photoinduced electron transfer.

Environmental conditions and plant physiology modulate Cu phytotoxicity in field-contaminated soils.

Foliar Cu concentration has been widely used as a biomarker of plant growth in phytotoxicity bioassays. This relation has helped find plant processes altered by Cu in dose-response experiments (a bivariate approach). However, when plants are grown in field conditions, their responses can vary in function of multiple variables, such as the environment, plant physiology, and other elements in plant (plant ionome). These sources of variability are commonly unreported, which could limit bioassays' utility. Thus, the present study aimed to assess and integrate the mentioned sources of variability on Cu phytotoxicity. Lettuce was used as plant model. Lettuces were grown in growth chambers with contrasting light and air humidity conditions and on two different field-contaminated soils (sandy and loamy soils). Results showed that environmental conditions significantly affected foliar Cu and plant growth, but this effect differed in the two studied soils. Foliar Cu was not a good biomarker of plant growth. In contrast, integrating the potential phytotoxicity effect with the plant's nutritional status allowed a better understanding of plant growth. We remarked on using a structural equation modeling approach (SEM) to integrate plant physiology and plant ionome as moderators of plant growth. Results showed that plant growth was primarily related to plant nutritional status rather than Cu phytotoxicity. Also, the foliar Cu concentration would affect plant nutritional status due to photosynthesis-related plant processes and cation balance. Finally, this research invites to state and include sources of variability when assessing phytotoxicity. This way, it is possible to advance toward understanding complex linked processes occurring in field conditions.

Protein Malnutrition During Juvenile Age Increases Ileal and Colonic Permeability in Rats.

Protein malnutrition can lead to morphological and functional changes in jejunum and ileum, affecting permeability to luminal contents. Regarding the large intestine, data are scarce, especially at juvenile age. We investigated whether low-protein (LP) diet could modify ileal and colonic permeability and epithelial morphology in young rats. Isocaloric diets containing 26% (control diet) or 4% protein were given to male rats between postnatal days 40 and 60. LP-diet animals failed to gain weight and displayed decreased plasma zinc levels (a marker of micronutrient deficiency). In addition, transepithelial electrical resistance and occludin expression were reduced in their ileum and colon, indicating increased gut permeability. Macromolecule transit was not modified. Finally, LP diet induced shortening of colonic crypts without affecting muscle thickness. These data show that protein malnutrition increases not only ileum but also colon permeability in juvenile rats. Enhanced exposure to colonic luminal entities may be an additional component in the pathophysiology of protein malnutrition.

Pentavalent antimony uptake pathway through erythrocyte membranes: molecular and atomic fluorescence approaches.

Previous studies by our group have shown that Sb(V) is able to enter red blood cells in a dynamic process and is reduced to Sb(III) by glutathione. The present study aims to investigate a possible entry pathway for Sb(V) through the erythrocyte membrane. Applying fluorescence spectroscopy studies with Laurdan and diphenylhexatriene (DPH) probes, it was found that there was no interaction between Sb(V) and membrane lipids. By comparing the Sb(V) entry percentages through lipid vesicles and sealed erythrocyte membranes, it was found that Sb(V) required protein channels to pass through the membrane. The competitive inhibition results using HCO3 (-) and Cl(-) showed that the Sb(V) uptake rate through the membrane fell approximately 50-70 % until full inhibition was reached, which was possibly due to the inhibition of the anion exchanger 1 (AE1) channel. Finally, the fluorescence measurements with the 5-iodoacetamidofluorescein (5-IAF) probe showed that Sb(V) interacted with membrane protein SH groups during this process.

Distribution, metabolism, and toxicity of antimony species in wistar rats. A bio-analytical approach.

This work studied the distribution, reactivity, and biological effects of pentavalent or trivalent antimony (Sb(V), Sb(III)) and N-methylglucamine antimonate (NMG-Sb(V)) in Wistar Rats. The expression of fibrosis genes such as α - SMA, PAI-1, and CTGF were determined in Liver, and Kidney tissues. Wistar rats were treated with different concentrations of Sb(V), Sb(III), As(V) and As(III), and MA via intra-peritoneal injections. The results indicated a noteworthy elevation in mRNA levels of plasminogen activator 1 (PAI-1) in the kidneys of rats that were injected. The main accumulation site for Sb(V) was observed to be the liver, from which it is primarily excreted in its reduced form (Sb(III)) through the urine. The generation of Sb(III) in the kidneys has been found to induce damage through the expression of α-SMA and CTGF, and also lead to a higher creatinine clearance compared to As(III).

Development of an analytical method for antimony speciation in vegetables by HPLC-hydride generation-atomic fluorescence spectrometry.

A new method for antimony speciation in terrestrial edible vegetables (spinach, onions, and carrots) was developed using HPLC with hydride generation-atomic fluorescence spectrometry. Mechanical agitation and ultrasound were tested as extraction techniques. Different extraction reagents were evaluated and optimal conditions were determined using experimental design methodology, where EDTA (10 mmol/L, pH 2.5) was selected because this chelate solution produced the highest extraction yield and exhibited the best compatibility with the mobile phase. The results demonstrated that EDTA prevents oxidation of Sb(III) to Sb(V) and maintains the stability of antimony species during the entire analytical process. The LOD and precision (RSD values obtained) for Sb(V), Sb(III), and trimethyl Sb(V) were 0.08, 0.07, and 0.9 microg/L and 5.0, 5.2, and 4.7%, respectively, for a 100 microL sample volume. The application of this method to real samples allowed extraction of 50% of total antimony content from spinach, while antimony extracted from carrots and onion samples ranged between 50 and 60 and 54 and 70%, respectively. Only Sb(V) was detected in three roots (onion and spinach) that represented 60-70% of the total antimony in the extracts.

Total mercury bias in soil analysis by CV-AFS: causes, consequences and a simple solution based on sulfhydryl cotton fiber as a clean-up step.

This study examines the matrix effect over the trueness for determining total mercury (THg) using CV-AFS. We demonstrate that matrix interferences in soils and sediment samples cannot be eliminated by acid digestion and establish the use of sulfhydryl cotton fiber (SCF), a malleable, cheap and easy to synthesize fiber, as a mandatory solution capable to overcome this bias. Using the classic CV-AFS approach, an overestimation bias for THg recovery values of >140% in a certified reference material was reported. Interference metals test was conducted, thus discarding any influence of metals in the overestimation bias. Therefore, a clean-up step using SCF was proposed, and tests with synthesized fiber did not present a dispersion of >0.08 ng L-1. Moreover, validation was performed by analyzing three certified reference material and yielding mean recovery percentages of 100% ± 1%. A validated methodology was applied to ten environmental soil samples; THg values obtained varied from 129 to 384 ng g-1. Finally, a comparison between sample results obtained and reference method did not show any significant differences (p > 0.05), thus highlighting the efficacy of SCF-CV-AFS for THg quantification in environmental solid samples.

Heavy weight vehicle traffic and its relationship with antimony content in human blood.

Brake pads systems are nowadays considered as one of the most important sources of antimony in airborne particulate matter. One way that antimony can enter the body is through the lungs and specially by the interaction of antimony with -SH groups present in erythrocyte membrane cells. In spite of that, there are no studies about antimony enrichment in blood of workers exposed to high vehicle traffic. Port workers are generally exposed to heavy weight vehicle traffic. In Chile the biggest marine port is found in Valparaíso City. In this study antimony in whole blood and its fractions (erythrocytes-plasma and erythrocytes membranes-cytoplasm) of 45 volunteers were determined. The volunteers were port workers from Valparaíso city, and two control groups, one from Valparaíso and another from Quebrada Alvarado, the latter being a rural area located about 100 Km away from Valparaíso. The results demonstrate that port workers are highly impacted by antimony emissions from heavy weight vehicle traffic showing an average concentration of 27 +/- 9 ng Sb kg(-1), 5-10 times higher than the concentration of antimony in the blood of control groups. These are the highest antimony levels in blood ever reported in the literature. The highest antimony percentages (>60%) were always found in the erythrocyte fractions. However, the exposure degree to vehicle traffic is significant over antimony distribution in plasma, erythrocytes and cytoplasm. This results shows that the antimony mass in the erythrocyte membranes, was approximately constant at 1.0 +/- 0.1 ng Sb g(-1) of whole blood in all blood samples analyzed.

Butyltin compounds and their relation with organic matter in marine sediments from San Vicente Bay-Chile.

Tributyltin and its degradation products, mono-and dibutyltin have been determined in sediments collected in some representative sites in San Vicente Bay, Chile. The organic matter contents of sediments and water collected simultaneously from the same sampling sites were also determined. High levels of total organic carbon were found in sediments, especially in those from the northern part of the bay (1.80-8.87%). Good correlations were found between total organic carbon and the oxidizable and refractory carbon fractions. Among the butyltin species determined, TBT presented the highest levels, ranging from 14 to 1,560 ng Sn g(-1) dry weight. Concentration ratios of TBT to DBT ranged between 1.33 and 3.10, showing a high degree of contamination in sediments of this Chilean bay. All data obtained were analysed by the chemometric method of principal components analysis. A strong correlation was found between TBT and DBT concentrations in sediments, the different organic matter contents in sediments and water. In marine organisms only TBT was detected, containing the filterer organism Semele solida higher level than Perumytilus purpuratus and Pyura chilensis (220, 150 and 120 ng Sn g(-1) dry weight, respectively). For the alga Rodoficea iridae the TBT concentration was 60 ng Sn g(-1) dw. Comparatively, these values are higher than those reported for the same kind of marine organisms worldwide. The different samples from San Vicente Bay were found to be contaminated by TBT. This contamination can be attributed to the different anthropogenic activities taking place in the bay.

Critical evaluation of distillation procedure for the determination of methylmercury in soil samples.

In the present work, the efficiency of distillation process for extracting monomethylmercury (MMHg) from soil samples was studied and optimized using an experimental design methodology. The influence of soil composition on MMHg extraction was evaluated by testing of four soil samples with different geochemical characteristics. Optimization suggested that the acid concentration and the duration of the distillation process were most significant and the most favorable conditions, established as a compromise for the studied soils, were determined to be a 70 min distillation using an 0.2 M acid. Corresponding limits of detection (LOD) and quantification (LOQ) were 0.21 and 0.7 pg absolute, respectively. The optimized methodology was applied with satisfactory results to soil samples and was compared to a reference methodology based on isotopic dilution analysis followed by gas chromatography-inductively coupled plasma mass spectrometry (IDA-GC-ICP-MS). Using the optimized conditions, recoveries ranged from 82 to 98%, which is an increase of 9-34% relative to the previously used standard operating procedure. Finally, the validated methodology was applied to quantify MMHg in soils collected from different sites impacted by coal fired power plants in the north-central zone of Chile, measuring MMHg concentrations ranging from 0.091 to 2.8 ng g-1. These data are to the best of our knowledge the first MMHg measurements reported for Chile.

Study of conformational changes and protein aggregation of bovine serum albumin in presence of Sb(III) and Sb(V).

Antimony is a metalloid that affects biological functions in humans due to a mechanism still not understood. There is no doubt that the toxicity and physicochemical properties of Sb are strongly related with its chemical state. In this paper, the interaction between Sb(III) and Sb(V) with bovine serum albumin (BSA) was investigated in vitro by fluorescence spectroscopy, and circular dichroism (CD) under simulated physiological conditions. Moreover, the coupling of the separation technique, asymmetric flow field-flow fractionation, with elemental mass spectrometry to understand the interaction of Sb(V) and Sb(III) with the BSA was also used. Our results showed a different behaviour of Sb(III) vs. Sb(V) regarding their effects on the interaction with the BSA. The effects in terms of protein aggregates and conformational changes were higher in the presence of Sb(III) compared to Sb(V) which may explain the differences in toxicity between both Sb species in vivo. Obtained results demonstrated the protective effect of GSH that modifies the degree of interaction between the Sb species with BSA. Interestingly, in our experiments it was possible to detect an interaction between BSA and Sb species, which may be related with the presence of labile complex between the Sb and a protein for the first time.

Mechanisms underlying the toxic effects of antimony species in human embryonic kidney cells (HEK-293) and their comparison with arsenic species.

Antimony cytotoxicity was assessed in human embryonic kidney cells (HEK-293). Uptake, mitochondrial respiratory activity, ROS generation and diffusional kinetics were measured using fluorescence recovery after photobleaching (FRAP). Furthermore, the toxic effect induced by Sb was compared with As toxicity in regard to ROS generation and diffusional kinetics, which provides information on the protein aggregation process. Our results show a favored uptake of Sb(III) and a more severe effect, decreasing the mitochondrial activity more than in the presence of Sb(V). In comparison with As, the Sb species did not generate a significant increase in ROS generation, which was observed with As(III) and As(V). FRAP analysis yielded important information on the diffusion and binding dynamics of live cells in presence of these metalloids. The mobile fraction showed a strong decrease with the As species and Sb(III). The diffusion rate and the koff-rate were significantly decreased for the As and Sb species but were more strong in the presence of As(III).

Simultaneous speciation analysis of Sb(III), Sb(V) and (CH3)3SbCl2 by high performance liquid chromatography-hydride generation-atomic fluorescence spectrometry detection (HPLC-HG-AFS): application to antimony speciation in sea water.

This paper presents an improvement for the simultaneous separation of Sb(V), Sb(III) and (CH3)3SbCl2 species by high performance liquid chromatography (HPLC) and its detection by hydride generation-atomic fluorescence spectrometry (HG-AFS). The separation was performed on an anion exchange column PRP-X100 using a gradient elution program between EDTA/KHP (potasium hydrogen phtalate) as first mobile phase and phosphate solutions solution as the second one. The chromatographic separation and the HG-AFS parameters were optimized by experimental design. The best results were obtained by using an elution program with 20 mmol l(-1) EDTA + 2 mmol(-01) KHP solution at pH 4.5, during 1.15 min, then change to 50 mmol l(-1) (NH4)2HPO4 solution at pH 8.3, switching back after 4.0 min to the first mobile phase, until 5 min, with a constant flow rate of 1.5 ml min(-1). Retention time of Sb(V), Sb(III) and trimethylantimony species were 1.22, 2.31 and 3.45 min and the detection limits were 0.13; 0.07 and 0.13 microg l(-1), respectively. Studies on the stability of this antimony species in sea water samples on the function of the elapsed time of storage in refrigerator at 4 degrees C was performed employing the optimized method. Results revealed that Sb(III) is easily oxidized within some hours to Sb(V) in sea water stored at 4 degrees C. However, when the sea water was immediately mixed with EDTA no oxidation of Sb(III) was observed up to 1 week of storage. The proposed methodology was then applied to the antimony speciation in sea water samples.

Distribution and pollution assessment of trace elements in marine sediments in the Quintero Bay (Chile).

The aim of this study was to assess the levels of heavy metal pollution in the clay/silt fraction (<63 µm fraction) of marine sediments from Quintero Bay, Chile. For this, sediment samples were collected from 14 sites from the bay and analyzed for major and minor element determination. The metal concentrations found suggest an anthropogenic origin related with Cu, Se, Mo, As, Sb and Pb. The mineralogical characteristics of the samples were determined by XRD and selected samples were examined by SEM to determine morphological differences. The results showed heavy metal-bearing particles such as Cu, Zn, As and Pb, which are most likely associated with by the copper smelter.

Sb(V) reactivity with human blood components: redox effects.

We assessed the reactivity of Sb(V) in human blood. Sb(V) reactivity was determined using an HPLC-HG-AFS hyphenated system. Sb(V) was partially reduced to Sb(III) in blood incubation experiments; however, Sb(III) was a highly unstable species. The addition of 0.1 mol L(-1) EDTA prevented Sb(III) oxidation, thus enabling the detection of the reduction of Sb(V) to Sb(III). The transformation of Sb(V) to Sb(III) in human whole blood was assessed because the reduction of Sb(V) in human blood may likely generate redox side effects. Our results indicate that glutathione was the reducing agent in this reaction and that Sb(V) significantly decreased the GSH/GSSG ratio from 0.32 ± 0.09 to 0.07 ± 0.03. Moreover, the presence of 200 ng mL(-1) of Sb(V) increased the activity of superoxide dismutase from 4.4 ± 0.1 to 7.0 ± 0.4 U mL(-1) and decreased the activity of glutathione peroxidase from 62 ± 1 to 34 ± 2 nmol min(-1) mL(-1).

Speciation analysis of organotin compounds in human urine by headspace solid-phase micro-extraction and gas chromatography with pulsed flame photometric detection.

A new headspace solid-phase micro-extraction (HS-SPME) method followed by gas chromatography with pulsed flame photometric detection (GC-PFPD) analysis has been developed for the simultaneous determination of 11 organotin compounds, including methyl-, butyl-, phenyl- and octyltin derivates, in human urine. The methodology has been validated by the analysis of urine samples fortified with all analytes at different concentration levels, and recovery rates above 87% and relative precisions between 2% and 7% were obtained. Additionally, an experimental-design approach has been used to model the storage stability of organotin compounds in human urine, demonstrating that organotins are highly degraded in this medium, although their stability is satisfactory during the first 4 days of storage at 4 °C and pH=4. Finally, this methodology was applied to urine samples collected from harbor workers exposed to antifouling paints; methyl- and butyltins were detected, confirming human exposure in this type of work environment.

Distribution of trace elements in particle size fractions for contaminated soils by a copper smelting from different zones of the Puchuncaví Valley (Chile).

Metal contents in soil samples are commonly used to evaluate contamination levels. However, the distribution of metals is dependent on particle size. We investigated the distribution of metals in various particle size fractions of the soil from four sites of the Puchuncaví Valley (Central Chile). The soil samples were segregated into size fractions ranging from 0.3 to 20µm and analyzed using inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). The results of the statistical analysis of the total metal concentrations indicated that the soil samples from Greda and Maitenes, the sites nearest the industrial sources, are the most contaminated. For these sites, the size-fractionated samples containing higher concentrations of Cu, Zn, As, and Pb were found in the finer fractions, suggesting anthropogenic depositions from smelter facilities. In addition, a high Ca concentration was observed in the finer fractions, which could be attributed to the technological approaches used to reduce the SO2 emissions from the roasting process of copper sulfide. The mineral composition of fine particles permitted the identification of Tenorite and Calcium oxide, which are most likely associated with smelting activities, confirming emission of enriched particulate matter from the copper smelter.

Sb(V) and Sb(III) distribution in human erythrocytes: speciation methodology and the influence of temperature, time and anticoagulants.

In this research a new method was developed and optimized for the determination of Sb(V) and Sb(III) in human erythrocytes fractions (plasma and cytoplasm) by high performance liquid chromatography with hydride generation atomic fluorescence spectrometry. The method considers the first step of samples cleaning by protein precipitation by salting out followed by C18 solid phase extraction, EDTA elution, and finally a chromatographic separation by using anion exchange PRPX-100 (100 mm × 4.1mm) and EDTA 20 mmol L(-1) as mobile phase. The method was optimized by experimental design with a recovery of 90% for Sb(V) and 55-75% for Sb(III) approximately. The analytical method was applied to study the distribution of Sb(V) and Sb(III) in human erythrocytes considering temperature and time of incubations and with special attention about the influence of the anticoagulant. Results showed that both Sb(V) and Sb(III) are capable to enter the red blood cell in a proportion of approximately 40-60%. On the other hand, both species are then excreted from the interior of the cell, where the percentage considerably decreased from approximately 60 to less than 30% within the cell. An increase in the culture temperature increases the capacity of Sb(V) and Sb(III) to penetrate the membrane barrier and reach the cytoplasm. In order to preserve the original distribution of Sb in blood, heparin seems to be the best anticoagulant for sample preservation.

Critical evaluation of fiber coatings for organotin determination by using solid phase microextraction in headspace mode.

In the present work three different SPME fibers have been investigated for simultaneous determination of methyl-, butyl- and phenyltins by using gas chromatography-pulsed flame photometer detection (GC-PFPD). The optimal experimental conditions for each fiber were determined and the respective figures of merit were evaluated. All fiber evaluated presented similar limit of detection (sub ng L⁻¹) and requires two internal standards to reach an acceptable repeatability. However, the CAR-PDMS fiber offers the best compromise between selectivity and sensibility for determination of organotins selected. The developed method was validated for analysis of certified reference material and spiked samples, obtaining satisfactory results. Finally, some contaminated samples were analyzed demonstrating the applicability of developed method for determination of organotin compounds in the environment and for monitoring their biochemical cycle.

Variation in patterns of metal accumulation in thallus parts of Lessonia trabeculata (Laminariales; Phaeophyceae): implications for biomonitoring.

Seaweeds are well known to concentrate metals from seawater and have been employed as monitors of metal pollution in coastal waters and estuaries. However, research showing that various intrinsic and extrinsic factors can influence metal accumulation, raises doubts about the basis for using seaweeds in biomonitoring programmes. The thallus of brown seaweeds of the order Laminariales (kelps) is morphologically complex but there is limited information about the variation in metal accumulation between the different parts, which might result in erroneous conclusions being drawn if not accounted for in the biomonitoring protocol. To assess patterns of individual metals in the differentiated parts of the thallus (blade, stipe, holdfast), concentrations of a wide range of essential and non-essential metals (Fe, Cr, Cu, Zn, Mn, Pb, Cd, Ni and Al) were measured in the kelp Lessonia trabeculata. Seaweeds were collected from three sampling stations located at 5, 30 and 60 m from an illegal sewage outfall close to Ventanas, Chile and from a pristine location at Faro Curaumilla. For the majority of metals the highest concentrations in bottom sediment and seaweed samples were found at the site closest to the outfall, with concentrations decreasing with distance from the outfall and at control stations; the exception was Cd, concentrations of which were higher at control stations. The patterns of metal concentrations in different thallus parts were metal specific and independent of sampling station. These results and the available literature suggest that biomonitoring of metals using seaweeds must take account of differences in the accumulation of metals in thallus parts of complex seaweeds.