The effect of nitroaromatics' composition on their toxicity in vivo: novel, efficient non-additive 1D QSAR analysis

Novel 1D QSAR approach that allows analysis of non-additive effects of molecular fragments on toxicity has been proposed. Twenty-eight nitroaromatic compounds including some well-known explosives have been chosen for this study. The 50% lethal dose concentration for rats (LD50) was used as the estimation of toxicity in vivo to develop 1D QSAR models on the framework of Simplex representation of molecular structure. The results of 1D QSAR analysis show that even the information about the composition of molecules provides the main trends of toxicity changes. The necessity of consideration of substituents' mutual impacts for the development of adequate QSAR models of nitroaromatics' toxicity was demonstrated. Statistic characteristics for all the developed partial least squares QSAR models, except the additive ones are quite satisfactory (R2=0.81-0.92; Q2=0.64-0.83; R2 test=0.84-0.87). A successful performance of such models is due to their non-additivity i.e. possibility of taking into account the mutual influence of substituents in benzene ring which plays the governing role for toxicity change and could be mediated through the different C-H fragments of the ring. The correspondence between observed and predicted by these models toxicity values is good. This allowing combine advantages of such approaches and develop adequate consensus model that can be used as a toxicity virtual screening tool.     

Estimating naphthenic acids concentrations in laboratory-exposed fish and in fish from the wild

Naphthenic acids (NAs) are the most water-soluble organic components found in the Athabasca oil sands in Alberta, Canada, and these acids are released into aqueous tailing waters as a result of bitumen extraction. Although the toxicity of NAs to fish is well known, there has been no method available to estimate NAs concentrations in fish. This paper describes a newly developed analytical method using single ion monitoring gas chromatography-mass spectrometry (GC-MS) to measure NAs in fish, down to concentrations of approximately 0.1mgkg(-1) of fish flesh. This method was used to measure the uptake and depuration of commercial NAs in laboratory experiments. Exposure of rainbow trout (Oncorhynchus mykiss) to 3mg NAsl(-1) for 9d gave a bioconcentration factor of approximately 2 at pH 8.2. Within 1d after the fish were transferred to NAs-free water, about 95% of the NAs were depurated. In addition, the analytical method was used to determine if NAs were present in four species of wild fish - northern pike (Esox lucius), lake whitefish (Coregonus clupeaformis), white sucker (Catostomus commersoni), walleye (Sander vitreus) - collected from near the oil sands. Flesh samples from 23 wild fish were analyzed, and 18 of these had no detectable NAs. Four fish (one of each species) contained NAs at concentrations from 0.2 to 2.8mgkg(-1). The GC-MS results from one wild fish presented a unique problem. However, with additional work it was concluded that the NAs concentration in this fish was <0.1mgkg(-1).     

Discriminating the pH toxicity to Poecilia reticulata Peters, 1859 in the Dunas Lake (Camaçari, BA, Brazil)

Toxic potential of the pH reduction to fingerlings of Poecilia reticulata, through acute toxicity bioassays, as well as the influence of increased pH on the toxicity were assessed. Acid lake samples (Dunas Lake) were collected during 19 months, and assessed with following treatments: water at local pH (+/-3.0) and samples with modified pH to 3.5, 3.8, 4.0, 4.3, 4.6, 5.0, 5.5, 6.0, and 6.5. Culture water samples with pH reduced to 3.0 were also assessed. Newborn P. reticulata were exposed during 96h, and dead/immobile organisms were counted at various time intervals during exposure (short intervals in the beginning and long towards the end). Mean results of LT(50) and confidence intervals from the Dunas Lake and control water with reduced pH were 1.36 (+/-0.48)h, and 1.03 (+/-0.50)h, respectively, with no statistical difference. Samples with increased pH showed a significant reduction in toxicity, with no toxicity detected at pH 6.0 and higher. Relationship between pH and lethal toxicity for fingerlings of P. reticulata demonstrated that pH exerted a strong effect on the survival of this species at the Dunas Lake, explaining about 80% of the toxicity observed.     

Biochemical effects of clomazone herbicide on piava (Leporinus obtusidens)

This study aims to verify the effects of the clomazone concentration used in rice fields on acetylcholinesterase (AChE), thiobarbituric acid reactive substances (TBARS), protein carbonyl and catalase activity in tissues of piava (Leporinus obtusidens). LC(50)-96h was 5.0 mg L(-1) and the fish were exposed to 1/10 of LC(50)-96 h: 0.5 mg L(-1) of clomazone for 96 and 192h. The same parameters were also assayed after a recovery period of 192 h in clean water. AChE activity was reduced only in the brain and heart of fish exposed for 96 h. AChE activity was decreased in the brain, muscle and heart tissues after 192 h of exposure. After 192 h of recovery period, AChE activity remained diminished in brain and muscle and showed a decrease in eye. However, after 192 h of recovery, AChE activity in heart was recovered. Fish showed increased TBARS levels in brain at all experimental periods. TBARS levels decreased in liver and muscle tissues after 192 h of exposure. The increase in muscle TBARS persisted in fish transferred to clean water. Protein carbonyl in the liver was increased in all periods studied including the recovery period. Catalase activity was reduced during all periods. The present study demonstrates the occurrence of disorders in AChE, TBARS, protein carbonyl and catalase activity in piava. The results also show changes in fish after exposure to an environmentally relevant concentration of clomazone. Most effects observed persisted after the recovery period. Thus, these parameters may be used to monitor clomazone toxicity in fish.     

Regio- and stereoselective isomerization of hexabromocyclododecanes (HBCDs): kinetics and mechanism of gamma- to alpha-HBCD isomerization

Hexabromocyclododecanes (HBCDs) are high production volume chemicals (>20000 ty(-1)) used as flame retardants for plastics and textiles. Lately, we reported on the stereoselective isomerization of beta-HBCDs. Herein we present insights into the mechanism and kinetics of (+)gamma- to (+)alpha- and of (-)gamma- to (-)alpha-HBCD isomerization. Only two of the six bromine atoms migrated, indicating that rearrangements of gamma- to alpha-HBCDs are regio- and stereoselective as well. The apparent first-order isomerization rate constants increased from 0.0013 to 0.0031 to 0.0070 min(-1) at 120, 130, and 140 degrees C, respectively, corresponding to half-lives of 540, 230, and 99 min. Thus, a thermal treatment of materials containing gamma-HBCDs at temperatures >100 degrees C may induce the formation of alpha-HBCDs and, hence, may alter the diastereomeric ratio of a HBCD mixture. The inversion of vicinal dibromides in like-configurations (RR/SS) prevailed, whereas unlike-configurations (RS/SR) were not affected. An intramolecular, stereoselective migration of neighboring bromine atoms via a four-center transition state would explain the observed stereoisomer pattern and first-order kinetics. Despite the fact that vicinal dibromides in HBCDs prefer synclinal (gauche) conformations, antiperiplanar (staggered) conformations are assumed to facilitate concerted 1.2-shifts of both bromine atoms. A conformation analysis revealed that under kinetic control, only those bromine atoms in the more flexible part of the molecules are migrating, whereas those in the conserved triple-turn motive were not affected. Thus, this structural motive, common to all alpha-, beta-, and gamma-HBCDs, is more rigid and less reactive than the flexible part, containing the reacting dibromides in like-configurations.     

Long-term geochemical evolution of the near field repository: insights from reactive transport modelling and experimental evidences

The KBS-3 underground nuclear waste repository concept designed by the Swedish Nuclear Fuel and Waste Management Co. (SKB) includes a bentonite buffer barrier surrounding the copper canisters and the iron insert where spent nuclear fuel will be placed. Bentonite is also part of the backfill material used to seal the access and deposition tunnels of the repository. The bentonite barrier has three main safety functions: to ensure the physical stability of the canister, to retard the intrusion of groundwater to the canisters, and in case of canister failure, to retard the migration of radionuclides to the geosphere. Laboratory experiments (< 10 years long) have provided evidence of the control exerted by accessory minerals and clay surfaces on the pore water chemistry. The evolution of the pore water chemistry will be a primordial factor on the long-term stability of the bentonite barrier, which is a key issue in the safety assessments of the KBS-3 concept.In this work we aim to study the long-term geochemical evolution of bentonite and its pore water in the evolving geochemical environment due to climate change. In order to do this, reactive transport simulations are used to predict the interaction between groundwater and bentonite which is simulated following two different pathways: (1) groundwater flow through the backfill in the deposition tunnels, eventually reaching the top of the deposition hole, and (2) direct connection between groundwater and bentonite rings through fractures in the granite crosscutting the deposition hole. The influence of changes in climate has been tested using three different waters interacting with the bentonite: present-day groundwater, water derived from ice melting, and deep-seated brine. Two commercial bentonites have been considered as buffer material, MX-80 and Deponit CA-N, and one natural clay (Friedland type) for the backfill. They show differences in the composition of the exchangeable cations and in the accessory mineral content. Results from the simulations indicate that pore water chemistry is controlled by the equilibrium with the accessory minerals, especially carbonates. pH is buffered by precipitation/dissolution of calcite and dolomite, when present. The equilibrium of these minerals is deeply influenced by gypsum dissolution and cation exchange reactions in the smectite interlayer. If carbonate minerals are initially absent in bentonite, pH is then controlled by surface acidity reactions in the hydroxyl groups at the edge sites of the clay fraction, although its buffering capacity is not as strong as the equilibrium with carbonate minerals. The redox capacity of the bentonite pore water system is mainly controlled by Fe(II)-bearing minerals (pyrite and siderite). Changes in the groundwater composition lead to variations in the cation exchange occupancy, and dissolution–precipitation of carbonate minerals and gypsum. The most significant changes in the evolution of the system are predicted when ice-melting water, which is highly diluted and alkaline, enters into the system. In this case, the dissolution of carbonate minerals is enhanced, increasing pH in the bentonite pore water. Moreover, a rapid change in the population of exchange sites in the smectite is expected due to the replacement of Na for Ca.     

A system dynamics approach for hospital waste management

Healthcare services provided by hospitals may generate some infectious wastes. Although a large percentage of hospital waste is classified as general waste, which has similar nature as that of municipal solid waste and, therefore, could be disposed in municipal landfills, a small portion of infectious waste has to be managed in the proper manner in order to minimize risk to public health. Many factors involved in the hospital waste management system often link to one another, which require a comprehensive analysis to determine the role of each factor in the system. In this paper, we present a hospital waste management model based on system dynamics to determine the interaction among factors in the system using a software package, Stella. A case study of the City of Jakarta, Indonesia is selected. The hospital waste generation is affected by various factors including the number of beds in the hospitals and the NIMBY (not in my back yard) syndrome. To minimize the risk to public health, we found that waste segregation, as well as infectious waste treatment prior to disposal, has to be conducted properly by the hospital management, especially when scavenging takes place in landfill sites in developing countries.     

Numerical simulation of hydrogen–air detonation for damage assessment in realistic accident scenarios

An accidental hydrogen release within an equipment enclosure may result in the presence of detonable mixture in a confined environment. From a safety standpoint, it is then useful to assess the potential for damage. In that context, numerical simulation of the sequence of events subsequent to detonative ignition provides a useful tool, although with obvious limitations. This article describes the procedure, summarizes two case studies, and reviews the limitations. First, a hydrogen dispersion pattern is obtained from numerical simulation of dispersion, using a commercial package designed primarily for incompressible flow. This dispersion cloud is then used as the initial condition in an inviscid, compressible, reactive flow simulation. To force detonative ignition, a sufficiently large amount of energy is deposited in a small region that corresponds to the ignition location. Chemistry is modeled using a single step Arrhenius model. Because the wave thickness is small compared with the computational domain, a fine mesh is needed, limiting the practicality of the process to two-dimensional geometries. This is the most significant limitation; it is conservative. The two cases described in the paper include an electrolyzer, in which a small release occurs, leading potentially to some damage to the enclosure, and a reformer, in which the consequences are potentially more serious.     

On the implementation of an International Curriculum on Hydrogen Safety Engineering into higher education

This paper describes the implementation of an International Curriculum on Hydrogen Safety Engineering into higher education. The curriculum is being developed as part of the educational and training activities of the European Network of Excellence Safety of Hydrogen as an Energy Carrier (HySafe) and has been implemented into a 1-year Postgraduate Certificate Course in Hydrogen Safety Engineering by the University of Ulster. The course is taught in the distance learning mode and comprises of two 30 CATS-point modules, namely, ‘Principles of Hydrogen Safety’ and ‘Applied Hydrogen Safety’. The first delivery of this course began in January 2007 and the second delivery will commence in September 2007.     

Mechanical Property Characterization of Plasticized Sugar Beet Pulp and Poly(Lactic Acid) Green Composites Using Acoustic Emission and Confocal Microscopy

Sorbitol and glycerol were used to plasticize sugar beet pulp-poly(lactic acid) green composites. The plasticizer was incorporated into sugar beet pulp (SBP) at 0%, 10%, 20%, 30% and 40% w/w at low temperature and shear and then compounded with poly(lactic acid) (PLA) using twin-screw extrusion and injection molding. The SBP:PLA ratio was maintained at 30:70. As expected, tensile strength decreased by 25% and the elongation increased. Acoustic emission (AE) showed correlated debonding and fracture mechanisms for up to 20% w/w plasticizer and uncorrelated debonding and fracture for 30–40% sorbitol and 30% glycerol content in SBP–PLA composites. All samples had a well dispersed SBP phase with some aggregation in the PLA matrix. However, at 40% glycerol plasticized SBP–PLA composites exhibited unique AE behavior and confocal microscopy revealed the plasticized SBP and PLA formed a co-continuous two phase system.