Adsorption of methyl mercaptan on activated carbons

Activated carbons of different origins were studied as methyl mercaptan adsorbents in wet, dry, and oxidizing conditions. The materials were characterized using adsorption of nitrogen, Boehm titration, and thermal analysis. Investigation was focused on the feasibility of the removal of methyl mercaptan on activated carbons and on the role of surface chemistry and porosity in the adsorption/oxidation processes. The results showed relatively high capacities of carbons for removal of CH3SH. The amount adsorbed depends on the surface features. Methyl mercaptan, in general, is oxidized to disulfides, which, depending on the chemistry of the carbon surface, can be converted to sulfonic acid due to the presence of water and active radicals.     

Kinetics and mechanisms of photocatalytic degradation of (CH3)nNH(4-n)+ (0 < or = n < or = 4) in TiO2 suspension: the role of OH radicals

The photocatalytic degradation of a series of (CH3)nNH(4-n)+ (0 < or = n < or = 4) was systematically studied in the UV-illuminated TiO2 aqueous suspensions at pH ranges of 3-11. By investigating the pH-dependent kinetics and analyzing intermediates and products, we elucidated the mechanistic pathways and the role of OH radicals in the photocatalytic oxidation. The deprotonated neutral species more rapidly degraded than their protonated counterparts for these homologous compounds because the OH radicals favorably reacted with the lone-pair electron on the nitrogen atom. Therefore, the photocatalytic degradation was highly enhanced at alkaline solutions for all substances except (CH3)4N+. The H-atom abstraction (from (CH3)4N+) by OH radicals initiated successive demethylation processes to generate tri-, di-, and monomethylammonium/amine as an intermediate and NH3/NH4+ as a final product. On the other hand, the OH-addition to the N-atom with the lone-pair electron led to NO2-/NO3- whose production was highly favored at alkaline conditions. The photocatalytic degradation rates of (CH3)4N+ were comparable at both acidic and alkaline conditions, which could not be explained by a simple electrostatic surface charge model. By using OH-scavenging tert-butyl alcohol as a diagnostic probe into the mechanism, it is suggested that the photocatalytic oxidation of (CH3)4N+ at acidic conditions proceeds through free OH radicals in the solution bulk, not on the surface of TiO2.     

PBCDD and PBCDF from incineration of waste-containing brominated flame retardants

Brominated organic flame retardants comprise a large, heterogeneous group of compounds that are useful but also potentially damaging to the environment. In this investigation, three common brominated flame retardants were co-combusted with an artificial municipal solid waste in a pilot-scale fluidized bed incinerator. Combustion conditions ensured degradation of the flame retardants, but stable brominated organic compounds such as polybrominated dibenzo-p-dioxins and polybrominated dibenzofurans were formed in the cooling flue gases. The incineration of fuels that contain both chlorine and bromine leads to the formation of a complex mixture of polybrominated/chlorinated dibenzo-p-dioxins and dibenzofurans. More bromination than chlorination was observed in these experiments, and the chlorination levels increased when bromine was added to the fuel. The most favored reactions led to the formation of dibromodichlorodibenzo-p-dioxin and dibromodichlorodibenzofuran. Theoretical calculations show that there is more Br2 than Cl2 in the flue gas when the two halogens are present at equimolar levels, because chlorine is mainly found in the form of HCl. This may explain the higher bromination level. BrCl is also present, which drives the chlorination observed when bromine is added.     

First paralytic shellfish poison (PSP) infestation of bivalves due to toxic dinoflagellate Alexandrium tamiyavanichii, in the southeast coasts of the Seto Inland Sea, Japan

The mussel Mytilus edulis and the cultured ark shell Anadara broughtonii in the southeast coasts of the Seto Inland Sea were contaminated with paralytic shellfish poison (PSP) following the appearance of the dinoflagellate Alexandrium tamiyavanichii in early December 1999. A. tamiyavanichii plankton collected around the Straits of Naruto on December 3, 1999 showed PSP toxicity, of which 83 mol% was accounted for by GTX2, GTX3 and GTX4. Its specific toxicity was 112.5 fmol/cell, and one MU was equivalent to 7,200 cells. Toxicity values at the beginning of toxification were 4.7 MU/g for the ark shell and 7.3 MU/g for the mussel. In the former, the value remained at almost 4 MU/g, resulting in prohibition of marketing for about two months. In the latter, it sharply decreased to less than 4 MU/g. These bivalves collected during the toxification period were dissected into five tissues, mantle, adductor muscle, hepatopancreas, gills and "others", and submitted to high-performance liquid chromatography (HPLC). The cultured ark shell accumulated GTX2, GTX3 and STX as major components and GTX1, GTX4, GTX5, neoSTX, dcSTX and PX1-3 (C1-C3) as minor ones. The amount of GTX3 decreased with time, while STX tended to increase. At the early stage of PSP toxification, toxins were accumulated in the gills and "others", most of which were quickly detoxified. On the other hand, PSP of the toxified mussel consisted of GTX4 as a main component, and GTX1, GTX2, GTX3, GTX5, STX and PX1-2 (C1-C2) as minor ones. Its toxin composition pattern was similar to that of the ingested causative plankton. Its total toxin decreased soon after disappearance of the dinoflagellate. During the decrease of toxicity, PSP tended to be retained in the hepatopancreas, resulting in accumulation of 50 mol% of total toxin.     

A Novel Function of the Triterpene Squalene in a Tritrophic System

Changes in apple leaf chemistry after infestation by leafminers and their effect on both host location and host habitat location of the generalist parasitoid Pholetesor bicolor were investigated. Chemical analysis of leaf solvent extracts from healthy and leafminer-damaged leaves revealed that herbivory increased the amount of the triterpene squalene (C₃₀H₅₀), whereas quantities of all other identified compounds were similar in both plant treatments. To assess the response of parasitoids to host location cues, contact bioassays were conducted with naïve females. Results showed that parasitoids performed a characteristic ovipositional probing more often on the mine-damaged than on the healthy leaf. This behavior was triggered by a hexane extract of the mine-damaged leaf, but not by a healthy leaf extract. A synthetic mixture of the compounds identified in the extract triggered a similar response. A mixture devoid of squalene was not active, whereas squalene alone elicited the probing behavior. To assess the use of the identified compounds in habitat location, Y-tube olfactometer experiments were conducted with naïve and experienced females. Results showed that squalene is not involved in habitat location and has no priming effect on P. bicolor. While other triterpenes are known to mediate habitat location of parasitoids, this is the first report in which a plant triterpene is shown to mediate host location of a parasitoid. The biological and ecological functions of squalene on all three trophic levels are discussed.     

Selenium levels in biological matrices in adult population of Mumbai, India

Selenium (Se) levels in whole blood, serum, urine, muscle and saliva of Mumbai adults have been estimated by differential pulse cathodic stripping voltammetry (DPCSV); the detection limit of Se is 0.05 ng ml(-1). The reliability of estimation is further assessed through the analysis of Standard Reference Materials. The Se levels in whole blood (n = 35) and blood serum (n = 201) of the Mumbai adult population is 99.6 and 100 ng ml(-1); approximately 34.8% of the population have serum Se levels between 80 and 100 ng ml(-1). The blood serum levels of Se for Mumbai adults are comparable to those of whole blood. The mean concentration of Se in urine on a 24-h basis is 5.2 ng ml(-1). Muscle and saliva of the Mumbai adult population contain 195.4 ng g(-1) and 2 ng ml(-1) of Se, respectively. A good correlation between serum Se and dietary Se is observed with a correlation coefficient of 0.89.     

Advanced oxidation and adsorption technologies for organic micropollutant removal from lake water used as drinking-water supply

The goal of this research is to evaluate the effectiveness of innovative drinking-water treatments designed to remove toxic and mutagenic organic micropollutants from lake waters used for human consumption. The widely used adsorption on granular activated carbon (GAC) filter technique was compared with the more innovative resin column techniques (XAD4 and Ambersorb-563) and with the advanced oxidation processes (AOPs) with UV/O3 and UV/O3/ H2O2. The water samples, collected from lake Como, treated with these techniques were analysed for mutagenic activity using Ames assay, toxicity using bioluminescent bacteria and organic compound were characterized using the GC-MS technique. The results found a decrease of the mutagenic and toxic activities of the lake water after adsorption on GAC and resins, while the AOP process generally increased these parameters. The absence of mutagenic activity was found only when a GAC adsorption step was performed in addition to the AOP process. Similar results were obtained by the toxicological and chemical analyses. In addition, the GC-MS analysis identified some possible mutagenic agents.     

Determination of seventeen pesticide residues in agricultural products by LC/MS

Residues of 17 pesticides in agricultural products were determined by LC/MS with an atmospheric pressure chemical ionization (APCI) interface in both positive and negative ion modes. Pesticides were extracted with acetonitrile, and the extracts were cleaned-up with a primary and secondary amine (PSA) mini-column eluted with acetone-hexane (1:1). Rice, orange and potato were spiked with the 17 pesticides at 0.1 microgram/g and analyzed by the proposed method. The average recoveries of these pesticides usually ranged from 70 to 98% and the relative standard deviations were usually around 10%. These results suggested that LC/MS with APCI could be used to determine the residue levels of the 17 pesticides in these crops.     

Comparison of electromyographic pattern of sensory experts and untrained subjects during chewing of Mahon cheese

Use of electromyography (EMG) to monitor mastication is a relatively new concept in assessing food physical and sensory properties. Although expert assessment of cheese characteristics is widely used, the effect of training in sensory analysis on mastication patterns, as assessed using EMG is not well known. Nine samples of the same Mahon cheese (60 days ripening) were given to 24 subjects (8 experts, 16 untrained) and EMG recorded for each chewing sequence. Three samples were tested in a single session by each subject, and three sessions carried out on different days. EMG was recorded from four masticatory muscles for each subject. From EMG records the following was extracted: number of chews, chewing time, mean and maximum voltage of EMG bursts (i.e. chews) across chewing sequence, chewing work and chewing rate. No gender bias was found for the EMG parameters considered, therefore, as regards gender, each group was considered to be homogeneous. Variability within-subjects across samples was greater for experts than untrained subjects. Significant differences in chewing time, chewing work and chewing rate were found between the expert and untrained groups. Data analysis of the three sessions showed an influence of cognitive constructs, mediating states, on the chewing process. The experts were found to be goal driven as to their mastication process. Experts showed no significant differences between sessions, untrained subjects were found to vary their EMG output in successive sessions for number of chews, chewing time, mean voltage, and chewing work.