Concentrations Of MBT Research Articles

Corrosion resistance and antibacterial activity of 2-mercaptobenzothiazole for 7B04 aluminium alloy in 3.5%NaCl solution

In this paper, the inhibition effect of 2-mercaptobenzothiazole (MBT) on microorganisms in the fuel system and corrosion inhibition of 7B04 aluminum alloy are studied, and the mechanism is discussed. The antibacterial activity of MBT is studied by microbial experiments. The agar diffusion test demonstrates the significant antibacterial efficacy of MBT against Lysinibacillus sphaericus (L. sphaericus) and Acinetobacter lwoffii (A. lwoffii) strains isolated from aircraft fuel systems, and the bacteriostatic effect on L. sphaericus is better. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curve (PDP) results show that MBT inhibits the corrosion of 7B04 aluminum alloy by forming a protective film on the aluminum alloy surface and inhibiting the cathode reaction. In this study, the most effective corrosion inhibition concentration of MBT is 200 mg∙L−1, with a maximum corrosion inhibition rate of 99.27%. Langmuir adsorption isotherm results further indicate that MBT acts on the aluminum alloy surface by physical adsorption and chemical adsorption. The scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) results confirm that MBT form a protective adsorption film on the aluminum alloy surface, which effectively shield the corrosive media on the surface. Furthermore, density functional theory (DFT), Monte Carlo simulation (MC), and molecular dynamics simulation (MD) are employed to identify the active sites of MBT as N and S atoms and to demonstrate that MBT adsorb onto the aluminum alloy surface in a horizontal orientation.

Occurrence of organotin compounds in food: increasing challenge of phenyltin compounds

Concentrations and distribution for 16 organotin compounds were studied in all kinds of foods, including seafood, agricultural products, and wine. Meanwhile, the degradation of the TBT or TPhT was also evaluated. Concentrations of total organotins in seafood, agricultural products, and wine were 1047.2, 469.4, and 13.5 μg Sn/kg. Meanwhile, the most frequently detected organotin in three kinds of samples were TPhT, MPhT, and MPhT, respectively. The results demonstrated that phenyltin may probably become an emerging organotin pollutant. Regarding seafood, organotin concentrations of fish and mollusks were much higher than those of crustaceans. At the same time, a significant positive correlation was observed between the concentrations of TBT and MBT (p < 0.05), and between DBT and MBT(p < 0.0001). Moreover, TPhT was significantly and positively associated with DPhT (p < 0.0001), suggesting that TPhT was the precursor of DPhT. Apart from the likely illegal use of OTs as biocides in antifouling paints for ships, anthropogenic activity like agricultural activity or industrial activity also caused organotin contamination. Further research and more effective measures should be formulated to protect the food safety. Meanwhile, monitoring of the organotin contamination should not only in Qinhuangdao, but also expand to the cities along Bohai Bay.

Monitoring and modelling of butyltin compounds in Finnish inland lake

In this study we measured the total concentration of BTCs using grab water sampling, dissolved concentration with passive samplers, and particle-bound fraction with sedimentation traps in a Finnish inland lake. The sampling was conducted from May to September over two study years. In grab water samples the average concentration of MBT at sampling sites varied between 4.8 and 13 ng L−1, DBT 0.9–2.4 ng L−1, and TBT 0.4–0.8 ng L−1 during the first study year and 0.6–1.1 ng L−1, DBT 0.5–2.2 ng L−1 and TBT &amp;lt; LOD-0.7 ng L−1 during the second year. The average BTC concentrations determined with passive samplers varied between 0.08 and 0.53 ng L−1 for MBT, 0.10–0.14 ng L−1 for DBT and 0.05–0.07 ng L−1 for TBT during the first study year and 0.03–0.05 ng L−1 for MBT, 0.02–0.05 ng L−1 for DBT and TBT 0.007–0.013 ng L−1 during the second year. The average BTC concentrations measured in sedimented particles collected with sedimentation traps were between 1.5 and 9.0 ng L−1 for MBT, 0.61–22 ng L−1 for DBT and 0.05–1.8 ng L−1 for TBT during the first study year and 3.0–12 ng L−1 for MBT, 1.7–9.8 ng L−1 for DBT and TBT 0.4–1.2 ng L−1 during the second year. The differences between sampling techniques and the detected BTCs were obvious, e.g., tributyltin (TBT) was detected only in 4%–24% of the grab samples, 50% of the sedimentation traps, and 93% of passive samplers. The BTC concentrations measured with grab and passive sampling suggested hydrological differences between the study years. This was confirmed with flow velocity measurements. However, the annual difference was not observed in BTC concentrations measured in settled particles which suggest that only the dissolved BTC fraction varied. The extreme value analysis suggested that grab sampling and sedimentation trap sampling results contain more extreme peak values than passive sampling. However, all high concentrations are not automatically extreme values but indicates that BTCs are present in surface water in trace concentrations despite not being detected with all sampling techniques.

CS2 mediated synthesis of corrosion-inhibiting mercaptobenzothiazole molecule for industrial zinc: Experimental studies and molecular dynamic simulations

In this study, 2-mercaptobenzothiazole (MBT) was synthesized from a CS2 mediated formation scheme involving a catalyzed reaction between aminophenyl disulfide with metal sulfide under N2 atmosphere. The formation mechanism of MBT involved the development of a C–S bond under relatively less reaction time and milder thermal conditions, as an alternative route to organic thiols. The tendency of MBT toward Zn-surface adsorption and corrosion inhibition was investigated in chloride-enriched (1 M HCl) acidizing solution. MBT acted as a corrosion inhibitor within this acid medium and this was consistent with molecular adsorption and formation of mercaptobenzothiazole films on Zn substrate. Corrosion investigations were performed using electrochemical impedance spectroscopy and Tafel polarization techniques. Surface analytical techniques, e.g. Scanning Electron Microscopy, Atomic Force Microscopy and X-ray Photoelectron Spectroscopy, were also utilized to probe metal-surface changes as well as adhering corrosion inhibiting MBT films on Zn substrates. Inhibition of Zn corrosion increased with MBT concentration due to formation of passive MBT protective films on the metallic surface; this was consistent with increase in charge transfer resistance (Rct) and reduced magnitudes of corrosion current density (jcorr). Magnitude of Rct up to 156.8, 225.8, 420.7 and 753.5 Ω cm2 were recorded for 0, 100, 300 and 500 ppm MBT while the trend of jcorr reduced in the order: 500 ppm (89 μA cm−2) < 300 ppm (230 μA cm−2) < 100 ppm (340 μA cm−2) < 0 ppm (955 μA cm−2) MBT. The MBT heterocyclic molecular structure may have been the greater edge toward Zn surface adsorption, hence corrosion inhibition. The extent of interfacial interactions between MBT and the Zn layer has also been theoretically investigated by molecular dynamic simulations. Zn corrosion resulted in chloride-induced pits with a predominantly anodic kinetics. Since molecular structure is an important aspect of sustainable corrosion inhibition design, the present study reflects a modern design for alleviating corrosion in industrial metallic Zn.

A self-healing coating based on facile pH-responsive nanocontainers for corrosion protection of magnesium alloy

• Mesoporous silica core@layered double hydroxide shell nanocontainers were obtained. • The preparation process is facile, low cost and environmentally-friendly. • The acidic-responsive feature of the nanocontainers was demonstrated. • The corrosion protection of nanocontainers-embedded coating is enhanced remarkably. • The corrosion protection mechanism of nanocontainers-embedded coating is proposed. The preparation of pH-responsive nanocontainers by typical silane modification of the mesoporous silica nanoparticle (MSN) surface is usually high-cost, complex, and time-consuming, which remains a great challenge for effective corrosion protection of magnesium alloy. Here, a new strategy to construct pH-responsive nanocontainers (MSN-MBT@LDH) is demonstrated. The nanocontainers consist of corrosion inhibitor (2-mercaptobenzothiazole, MBT) loaded MSN core and layered double hydroxide (LDH) nanosheet shell serving as gatekeepers. The successful loading of MBT and encapsulation by LDH nanosheets were confirmed by a series of characterization such as scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (STEM-EDS) and N 2 adsorption/desorption isotherms. The pH-responsive feature of the nanocontainers was demonstrated by determination of the MBT concentration in buffer solutions with different pH values. A smart corrosion protection system on Mg alloy is obtained by incorporating the synthesized nanocontainers into a self-assembled nanophase particle (SNAP) coating. The electrochemical tests and visual observations show that the hybrid coating has the best barrier properties and robustness in corrosion protection in NaCl corrosive solutions in comparison with the control coatings. The present method simplifies the synthesis processes of nanocontainers and eliminates the potential detrimental effect of excess gatekeepers on the coating. The findings provide new insights into the preparation of scalable nanocontainers. The self-healing coatings are expected to have widespread applications for corrosion protection of Mg alloy and other metals.

Assessment of the organotin pollution in the coastal sediments of the Western Arabian Gulf, Saudi Arabia

Organotin compounds (OTCs) are persistent pollutants and are considered as chemicals of environmental concern. They enter the marine environment from the antifouling paints containing organotin compounds on the hulls of ships and boats. We report the results of a study conducted in 2015 on the level of butyltins (TBT, DBT, and MBT) and phenyltins (TPhT, DPhT, and MPhT) in the sediments collected from three fishing harbors (Jubail, Khobar, and Qatif) and a reference site (Half Moon Bay). The concentrations of OTCs in the sediments vary widely among the different sampling locations. Overall, the phenyltins contribute more than the butyltins and the order of the abundance is: MPhT > DPhT > MBT > DBT > TPhT. In most stations, the concentrations of MBT are higher than DBT. The sediments from Khobar and Qatif are moderately polluted, whereas those from the Jubail are ranked as highly polluted. The concentrations of TBT at all study sites are less than the detection limit, and hence, the environmental and ecotoxicological risks are low.

PH-Responsive Nanostructured Polyaniline Capsules for Self-Healing Corrosion Protection: The Influence of Capsule Concentration

Nanostructured hollow polyaniline (PANI) capsules are good candidates for encapsulation of corrosion inhibitors and pH-responsive release when incorporated into organic coatings. In previous work the corrosion protection performance of PANI capsules containing organic inhibitor 2-Mercaptobenzothiazole (MBT) was demonstrated. The present work studies the influence of capsule concentrations (i.e. 0.3, 1 and 2 wt.%) on the corrosion protection properties of the coating system. Anti-corrosion properties of different coatings were compared by means of Electrochemical Impedance Spectroscopy (EIS), and Scanning Vibrating Electrode Technique (SVET). MBT loaded PANI capsules in epoxy ester coating on AA2024-T3 substrate allows for a self-healing effect to be obtained during the corrosion process. The results showed that the concentration of MBT loaded PANI capsules greatly influence the corrosion protection properties of the coatings, and the best corrosion protection performance was observed for the coating system containing 1 wt% PANI capsules. The impedance value of the scratched area of this coating after 7 days of immersion was one order of magnitude higher than that of the control sample.

Distribution of butyltin species in sediment samples collected from Saigon habours in Ho Chi Minh city

In this study, the distribution of tributyltin (TBT) and its degradation products, dibutyltin –DBT and monobutyltin – MBT in sediment sample collected adjacent Saigon habours was studied using gas chromatographic separation/ mass spectrometric detection. Sediment samples at 12 sites along the Saigon river were taken during dry and raining seasons in 2014 and 2015. Butyltin species were extracted from sediment matrix using HBr-tropolone into dichloromethane followed by ethylation with NaB(C2H5)4 in hexane. The reliability of the analytical method for butyltin species was evaluated by the use of the certified reference BCR-646 material. The concentrations of TBT, DBT and MBT in sediment samples were &lt;0.1–2.81 ng/g, &lt;0.1–4.3 ng/g and &lt;0.2–8.4 ng/g (as Sn, dw). Butyltin species in sediment samples at sites within the habour area were higher than those at sites far upstreams or down-streams of the habours. Low values in TBT/(DBT+MBT) ratios revealed that the discharge of TBT from fouling paint was low at recent years.

Mechanism of mixed dithiophosphate and mercaptobenzothiazole collectors for Cu sulfide ore minerals

The species adsorbed on Cu sulfide ore minerals from alkaline or near neutral solutions of blends of the flotation collectors dibutyl dithiophosphate (BDTP) and 2-mercaptobenzothiazole (MBT) have been established by X-ray photoelectron spectroscopy. Adsorption on air-exposed Cu metal, cuprite, chalcocite, covellite, chalcopyrite and pyrite was investigated from relatively high concentration solutions to simulate processing of variably oxidised ores or slug addition of collector under plant conditions, as well as from solutions of lower concentration. For air-exposed Cu metal, it was found that for a typical BDTP-MBT blend in which di-n-butyl DTP predominated, negligible BDTP was adsorbed at high concentration unless the pH was below 7. By contrast, at low concentrations but under non-starvation conditions, BDTP adsorption predominated even in the alkaline pH range. Both BDTP and MBT species were adsorbed following sequential conditioning in the two collectors. The dithiolate (MBT)2 was not adsorbed from high concentrations of the blend, whereas it was adsorbed from similar concentrations of MBT collector alone. Most of the observed behaviour can be explained by collector solution species reactivity with Cu decreasing in the order MBT−>BDTP−>HMBT. There was no evidence to suggest any surface chemical synergism between the two collectors. For the minerals, competitive chemisorption broadly similar to that for Cu metal was observed, but the formation and adsorption of multilayer molecular CuBDTP or CuMBT was lower, and that of (MBT)2 and HMBT was higher, when the surface availability of Cu was lower than at a native oxide layer. Open circuit potentials for Cu metal, chalcocite and covellite electrodes in 10−3M solution of the collector blend were lower than for the corresponding values in MBT collector alone. For all concentrations in the alkaline pH range, surfaces conditioned in either BDTP alone or the blend were obviously hydrophobic, whereas surfaces conditioned in high concentrations of MBT were not obviously hydrophobic. Some surfaces conditioned sequentially in the two collectors, or in high concentrations of the blend at a pH below 7, were only moderately hydrophobic. Thus, depending on the collector concentration and pH, direct (albeit ex-situ) surface chemical characterisation established the adsorption of different species from a BDTP-MBT blend compared with sequential conditioning in the individual collectors, and hence potentially different hydrophobicities.

Impaired anterior swim bladder inflation following exposure to the thyroid peroxidase inhibitor 2-mercaptobenzothiazole part II: Zebrafish

Disruption of the thyroid hormone (TH) system, an important mode of action, can lead to ecologically relevant adverse outcomes, especially during embryonic development. The present study characterizes the effects of disruption of TH synthesis on swim bladder inflation during zebrafish early-life stages using 2-mercaptobenzothiazole (MBT), a thyroid peroxidase (TPO) inhibitor. Zebrafish were exposed to different MBT concentrations until 120/168h post fertilization (hpf) and 32days post fertilization (dpf), in two sets of experiments, to investigate the effects of TPO inhibition on posterior and anterior swim bladder inflation respectively, as well as whole body thyroid hormone concentrations (triiodothyronine (T3) and its prohormone, thyroxine (T4)). At 120hpf, MBT did not directly impair posterior chamber inflation or size, while anterior chamber inflation and size was impaired at 32dpf. As previously shown in amphibians and mammals, we confirmed that MBT inhibits TPO in fish. Whole-body T4 decreased after MBT exposure at both time points, while T3 levels were unaltered. There was a significant relationship between T4 levels and the anterior chamber surface at 32dpf. The absence of effects on posterior chamber inflation can possibly be explained by maternal transfer of T4 into the eggs. These maternally derived THs are depleted at 32dpf and cannot offset TPO inhibition, resulting in impaired anterior chamber inflation. Therefore, we hypothesize that TPO inhibition only inhibits swim bladder inflation during late development, after depletion of maternally derived T4. In a previous study, we showed that iodothyronine deiodinase (ID) knockdown impaired posterior chamber inflation during early development. Our findings, in parallel with similar effects observed in fathead minnow (see part I, this issue) suggest that thyroid disruption impacts swim bladder inflation, and imply an important distinction among specific subtypes of TH disrupting chemicals. However, the existence of another – yet unknown – mode of action of MBT impacting swim bladder inflation cannot be excluded. These results can be helpful for delineating adverse outcome pathways (AOPs) linking TPO inhibition, ID inhibition and other TH related molecular initiating events, to impaired swim bladder inflation in fish during early life stages. Such AOPs can support the use of in vitro enzyme inhibition assays for predicting reduced survival due to impaired posterior and anterior chamber inflation.

Influence of organic corrosion inhibitors on the corrosion performance of organic–inorganic hybrid coatings applied on aluminium alloy

The proposed work aims to develop and study sol–gel derived anticorrosion films for aluminium. To further improve performance of these films, organic corrosion inhibitors were incorporated into the films. The organic–inorganic hybrid films with and without corrosion inhibitors were deposited on an aluminium substrate by dip coating. The films were characterized by electrochemical impedance spectroscopy (EIS), DC polarisation techniques, and neutral salt spray test to evaluate their anticorrosion properties. This study shows that very low and very high MBT concentrations deteriorate the corrosion performance of coatings, and consequently, there is an optimum concentration of MBT. EIS results revealed a higher corrosion inhibitive activity of 2-mercaptobenzothiazole (MBT) compared to that of 2-amino-5-methylthiazole and 1,2,3 benzotriazole.

Degradation of 2-mercaptobenzothiazole in aqueous solution by gamma irradiation

Industrial wastewaters containing 2-mercaptobenzothiazole (MBT), a widely used chemical additive, usually cannot be treated properly by conventional biological methods, thus cause an environmental risk. Ionizing radiation was proposed as a method for abatement of several refractory pollutants from water. The paper investigated MBT degradation using irradiation technology. The decomposition kinetics was described, and the transformation and the change of biodegradability were discussed. The results of gamma radiation experiments on MBT-containing aqueous solutions indicated that reactive radicals resulting from water radiolysis effectively degrade MBT and improve the biodegradability of the solutions. At a 20mg/L MBT concentration, the removal of 82% was achieved at the absorbed dose of 1.2kGy. The results of specific oxygen uptake rate (SOUR) test showed that MBT was decomposed into biodegradable products, after irradiation at 20kGy. Radicals attacked the sulfur atoms of the studied molecule leading to the release of sulfate ions, but the mineralization of organic carbons was rather weak. Initial concentration significantly affected the degradation efficacy of MBT by gamma radiation.

Scintigraphic demonstrations of a retrosternal goiter

Determining the effects of chemicals on the thyroid system is an important aspect of evaluating chemical safety from an endocrine disrupter perspective. Since there are numerous chemicals to test and limited resources, prioritizing chemicals for subsequent in vivo testing is critical. 2-Mercaptobenzothiazole (MBT), a high production volume chemical, was tested and shown to inhibit thyroid peroxidase (TPO) enzyme activity in vitro, a key enzyme necessary for the synthesis of thyroid hormone. To determine the thyroid disrupting activity of MBT in vivo, Xenopus laevis larvae were exposed using 7- and 21-day protocols. The 7-day protocol used 18–357 μg/L MBT concentrations and evaluated: metamorphic development, thyroid histology, circulating T4, circulating thyroid stimulating hormone, thyroidal sodium-iodide symporter gene expression, and thyroidal T4, T3, and related iodo-amino acids. The 21-day protocol used 23–435 μg/L MBT concentrations and evaluated metamorphic development and thyroid histology. Both protocols demonstrated that MBT is a thyroid disrupting chemical at the lowest concentrations tested. These studies complement the in vitro study used to identify MBT as a high priority for in vivo testing, supporting the utility/predictive potential of a tiered approach to testing chemicals for TPO activity inhibition. The 7-day study, with more comprehensive, sensitive, and diagnostic endpoints, provides information at intermediate biological levels that enables linking various endpoints in a robust and integrated pathway for thyroid hormone disruption associated with TPO inhibition.

Potential of 5-methyl 1-H benzotriazole to suppress the dissolution of α-aluminum bronze in sulfide-polluted salt water

This work investigates the inhibition effect of 5-methyl 1-H benzotriazole (MBT) on the dissolution behavior of α-aluminum bronze in clean and sulfide-polluted salt water using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), electrochemical frequency modulation (EFM) and scanning electron microscopy (SEM) techniques. The inhibition efficiency increases with the increasing MBT concentration and decreases with the increasing temperature. The adsorption process of MBT is spontaneous and follows Langmuir adsorption isotherm model. MBT possesses excellent inhibiting effect for the corrosion of α-Al-bronze, which acts as a mixed type inhibitor. Thermodynamic and kinetic parameters for the adsorption process were determined. The presence of sulfide ions (2 ppm) decreases the inhibition efficiency of MBT against the corrosion of Al-bronze alloy in chloride solutions from 94.7% to 89% as also confirmed via SEM images. The results obtained from the different techniques were in good agreement, which prove the validity of these tools in the measurements of the tested inhibitor.

Seasonal changes in organotin compounds in water and sediment samples from the semi-closed Port of Gdynia

The effect of seasonal changes on the distribution of organotin compounds (OTC) in the sediments and seawater from the docks of the Port of Gdynia was investigated. Sediment and seawater samples were collected from four industrial docks in February (winter) and June (summer) in 2009. The samples were analyzed for butyltin, phenyltin, octyltin, and tricyclohexyltin (total of 9 OTC derivatives). The fine fraction (<0.063mm) accumulated the highest concentration of OTC, although it was not the dominant fraction in the sediment samples from the Port of Gdynia. The average concentration of TBT, DBT and MBT in collected samples were as follows: 4400; 2188; 730ngcationg−1d.w. (February) 3638; 1590; 474ngcationg−1d.w. (June) in the fine sediment samples, 2805; 1266; 485ngcationg−1d.w. (February) in <2.00mm sediment fractions and 118.6; 39.2; 25.3ngcationL−1 (February) and 46.5; 12.6; 8.2ngcationL−1 (June) in the water samples. Higher concentrations of butyltin derivatives (BT) were observed in samples collected in February than in those collected in June. Seasonal changes in BT correlate well with changes in the water pH and concentrations of organic matter and can be attributed to sorption/desorption to sediments, photodegradation and biodegradation. Although the Port of Gdynia does not represent the natural features of a marine environment, seasonal variations recorded in the pH values as well as BT, organic carbon and biogenic element concentrations seem to be influenced by temperature and microbial activity.

Inhibition of the thyroid hormone pathway in Xenopus laevis by 2-mercaptobenzothiazole

Determining the effects of chemicals on the thyroid system is an important aspect of evaluating chemical safety from an endocrine disrupter perspective. Since there are numerous chemicals to test and limited resources, prioritizing chemicals for subsequent in vivo testing is critical. 2-Mercaptobenzothiazole (MBT), a high production volume chemical, was tested and shown to inhibit thyroid peroxidase (TPO) enzyme activity in vitro, a key enzyme necessary for the synthesis of thyroid hormone. To determine the thyroid disrupting activity of MBT in vivo, Xenopus laevis larvae were exposed using 7- and 21-day protocols. The 7-day protocol used 18–357μg/L MBT concentrations and evaluated: metamorphic development, thyroid histology, circulating T4, circulating thyroid stimulating hormone, thyroidal sodium-iodide symporter gene expression, and thyroidal T4, T3, and related iodo-amino acids. The 21-day protocol used 23–435μg/L MBT concentrations and evaluated metamorphic development and thyroid histology. Both protocols demonstrated that MBT is a thyroid disrupting chemical at the lowest concentrations tested. These studies complement the in vitro study used to identify MBT as a high priority for in vivo testing, supporting the utility/predictive potential of a tiered approach to testing chemicals for TPO activity inhibition. The 7-day study, with more comprehensive, sensitive, and diagnostic endpoints, provides information at intermediate biological levels that enables linking various endpoints in a robust and integrated pathway for thyroid hormone disruption associated with TPO inhibition.

Butyltin Compounds in Fish Commonly Sold in North of Iran

Levels of tributyltin (TBT) and its degradation products, mono (MBT) and dibutyltin (DBT), were monitored in fish commonly consumed in Iran. Samples were purchased from fish markets at seasonal intervals in 2010 along the North coast of Iran. Concentration of MBT, DBT and TBT in the muscle of these fish were in the range of n.d. -1.01±0.84, n.d. -0.33±0.26 and n.d. -4.31±0.95 ngg(-1) (wet weight), respectively. Residue levels of butyltins were found lower than the tolerable average residue level of 100 ngg(-1) (wet weight).

Construction and evaluation of self-cloning bottom-fermenting yeast with high SSU1 expression

To construct a self-cloning brewer's yeast that can minimize the unfavourable flavours caused by oxidation and certain kinds of sulfur compounds. DNA fragments of a high-expression promoter from the TDH3 gene originating from Saccharomyces cerevisiae were integrated into the promoter regions of the S. cerevisiae-type and Saccharomyces bayanus-type SSU1 genes of bottom-fermenting brewer's yeast. PCR and sequencing confirmed the TDH3 promoter was correctly introduced into the SSU1 regions of the constructed yeasts, and no foreign DNA sequences were found. Using the constructed yeasts, the concentration of sulfite in fermenting wort was higher when compared with the parent strain. In addition, the concentrations of hydrogen sulfide, 3-methyl-2-buten-1-thiol (MBT) and 2-mercapto-3-methyl-1-butanol (2M3MB) were lower when compared with the parent strain. We successfully constructed a self-cloning brewer's yeast with high SSU1 expression that enhanced the sulfite-excreting ability and diminished the production ability of hydrogen sulfide, MBT and 2M3MB. The self-cloning brewer's yeast with high SSU1 expression would contribute to the production of superior quality beer with a high concentration of sulfite and low concentrations of hydrogen sulfide, MBT and 2M3MB.

Relationship between oxidative degradation of 2-mercaptobenzothiazole and physicochemical properties of manganese (hydro)oxides

Environmental context. Manganese (hydro)oxide is one kind of the most important natural minerals that are capable of oxidising organic contaminants with a wide range of functionality. However, the oxidative reactivity of manganese (hydro)oxides for organic pollutant degradation may depend on their individual physicochemical properties. It is important to determine a relationship between their oxidative reactivity and physicochemical properties. Abstract. The oxidative reactivity of manganese (hydro)oxides is important for geochemical transformation of organic pollutants. Here, 2-mercaptobenzothiazole (MBT) degradation by six manganese (hydro)oxides, including γ-MnOOH, β-MnO2, α-MnO2, γ-Mn2O3, δ-MnO2, and MO-700, were investigated with different initial MBT concentrations, manganese (hydro)oxide dosages and pH values. The results show the oxidative reactivity of manganese (hydro)oxides towards MBT degradation strongly depends on their physicochemical properties. Specific surface area and reduction potential of manganese (hydro)oxides were positively correlated with MBT degradation rates, whereas pH at the point of zero charge (pHPZC) of manganese (hydro)oxides and apparent activation energy (Ea) were negatively correlated. A high average oxidation state with the same chemical valence always corresponds to high oxidative reactivity. Such findings provide some insights into understanding the transport and fate of organic pollutants in the presence of different manganese (hydro)oxides in the natural environment.

MONITORING OF BUTYLTIN COMPOUNDS IN THE AQUATIC ENVIRONMENTS OF THE PHILIPPINES

This article provides a comprehensive review of the contamination by Butyltin compounds (BTs) and its possible implications on the marine and coastal environments of the Philippines. Butyltin compounds were detected in mussels from all the sampling locations investigated as part of the monitoring surveys under the Asia-Pacific Mussel Watch (APMW) Program conducted in the late 1990s. BTs were detected in green mussels collected from all the aquaculture sites in the country, suggestive of considerable widespread pollution by BTs in the coastal waters. Among BTs, TBT was detected at all locations at relatively higher concentrations, whereas the concentrations of DBT and MBT were lower. This could be indicative that green mussels have limited ability of metabolize TBT to DBT and MBT. In addition, this result may be suggestive of fresh TBT inputs into the aquatic environments and the presence of recent sources along the coastal waters. Concentrations of 0 BT in green mussels were reported up to 790 ng/g wet weight in a site where intensive maritime activities are occurring. Mussels from rural areas contained TBT at lower proportions indicating that TBT usage as antifouling agents is minimal. Tolerable average residue level (TARL) for seafood in the Philippines was estimated at 173 ng/g wet weight for an average person weighing 60kg. Concentrations of TBT or the sum of TBT and DBT in some green mussels analysed revealed that some values exceeded TARL level, which could suggest that humans consuming this seafood from areas with high BTs contamination could be at risk from elevated exposure to BTs. Similarly, BTs were detected in all the skipjack tuna collected, suggestive of the widespread contamination even in offshore waters and open seas on a global scale. Skipjack tuna collected from the offshore waters of the Philippines revealed considerable levels (up to 220 ng/g wet weight), with high percentages of BTs in total tin (0Sn: inorganic tin + organic tin) in the liver tissues. This finding seems to suggest that the anthropogenic BTs represent the major source of Sn accumulation in skipjack tuna. On the other hand, relatively low concentrations of BTs were found in the liver of cetaceans from the coastal waters of the Philippines, which ranged 42-98 ng/g wet weight. Significantly lower hepatic BT concentrations in cetaceans in tropical waters were noted compared with those inhabiting temperate waters proximal to developed nations. This result could imply smaller usage of BTs in the Philippines at least at the present.