Adsorption of chromium (VI) from aqueous solutions by cellulose modified with ß-CD and quaternary ammonium groups.

Cellulose powder was grafted with the vinyl monomer glycidyl methacrylate using ceric ammonium nitrate as initiator and was further derived with ß-CD and quaternary ammonium groups to build Cell-g-GMA-ß-CDN(+) adsorbent. Epoxy cellulose was made up of Cell-g-GMA and Cell-hydro-g-GMA, and was found to contain 3.71 mmol g(-1) epoxy groups. The adsorption process of the modified cellulose was described by the Langmuir model of adsorption well, and the maximum adsorption capacity of chromium (VI) reached 61.05 mg g(-1). The adsorption-desorption tests of ß-CDN(+)-type cellulose derivatives exhibited that the reproducibility of the adsorbent was well and the adsorbent could be reused five times at least.

Behavioral changes in metallothionein-null mice after the cessation of long-term, low-level exposure to mercury vapor.

The neurobehavioral changes in wild-type and metallothionein (MT)-null mice after the cessation of long-term, low-level exposure to Hg0 were investigated. MT-null and wild-type females were continuously (24 h/day) exposed to mercury vapor (Hg0) at 0.055 mg/m3 (range: 0.043-0.073 mg/m3), which was similar to the current threshold limit value (TLV), for 29 weeks. The effects on behavior, such as locomotor activity in the open field (OPF), learning ability in the passive avoidance response (PA) and spatial learning ability in the Morris water maze (MM) were examined immediately and 12 weeks after the cessation of exposure. Immediately after the exposure had ceased, total locomotor activity in OPF was decreased in the both strain of mice, although the MT-null mice appeared to show more distinct effect. In the PA test, the exposed animals of both strains showed learning impairment as compared to un-exposed mice. Twelve weeks after the cessation of exposure, the locomotor activity in OPF was elevated in the exposed mice of both strains, while the learning ability in the PA test appeared normal in both strains. Spatial learning ability was not affected at all. Immediately after the exposure had ceased, the brain mercury concentration of the exposed wild-type mice was 1.75 microg/g, twofold of that in the MT-null mice. In 12 weeks, brain mercury levels decreased to approximately 1/20 of those in immediately after the exposure in both of the strains. These results for the first time indicated that long-term, low-level exposure to Hg0 could exert neurobehavioral effects, which were not reversible even after a long exposure-free period. Whereas the effects on learning ability were presumably transient, the effects on spontaneous behavior as evaluated in OPF were persistent. Finally, the MT-null mice seemed more susceptible to Hg0-induced neurotoxicity than the wild-type mice, confirming our previous results.

Measurement of radical-scavenging ability in hepatic metallothionein of rat using in vivo electron spin resonance spectroscopy.

In this study, the ability of metallothionein (MT) to scavenge free radicals was determined by in vivo electron spin resonance (ESR) spectroscopy using a carbamoyl-PROXYL, nitroxyl radical, as a spin probe. Production of metallothionein was induced in the liver of rats with ZnSO(4) (0.2 mol/kg, ip) and the intensity of the carbamoyl-PROXYL ESR signal was measured at the upper abdominal level which is a position of the liver. After the injection of carbamoyl-PROXYL, the peak of ESR signal gradually decreased and showed a linear decay curve. The rate of decay of carbamoyl-PROXYL, the spin clearance rate, was determined over the first 3 min. The spin clearance rate did not differ significantly between ZnSO(4)-treated and control rats. When rats were fasted for 24 h, hepatic glutathione (GSH) concentrations decreased significantly and the spin clearance rate was significantly lower than non-fasted rats. However, the spin clearance rate of the fasted rats treated with Zn returned to the control level. To reduce GSH concentrations in the liver, buthionine sulfoximine (BSO, 2 mmol/kg, ip) was injected into the rats. The spin clearance rate of rats treated with BSO was significantly decreased as compared with that of control rats without BSO treatment. In rats treated with Zn, the decay rate of carbamoyl-PROXYL increased significantly in spite of the depletion of the hepatic GSH caused by BSO treatment, and returned to the control level. These results indicate that when the hepatic GSH concentration was significantly decreased by fasting and the administration of BSO, hepatic MT acted as a scavenger of free radicals. We suggest that GSH and MT act cooperatively as antioxidants to scavenge free radicals produced in response to various forms of stress, and MT serves as a second rather than the first line of defense.

Susceptibility of metallothionein-null mice to the behavioral alterations caused by exposure to mercury vapor at human-relevant concentration.

While recent human studies suggested adverse neurobehavioral outcomes of low-level exposure to mercury vapor (Hg0) as found among those having dental amalgam fillings and dental personnel, past animal experiments only dealt with exposure at much higher mercury concentrations. The present study aimed to examine neurobehavioral effects of prolonged, low-level Hg0 exposure in mice and to evaluate the protective role of metallothionein-I,II (MT-I,II) against Hg0-induced neurotoxicity, using a knock-out strain of mice. Adult female metallothionein-I,II-null (MT-null) and wild-type OLA129/C57BL6 mice were exposed to 0.06 mg/m3 of Hg0 for 8 h per day for 23 weeks. Neurobehavioral effects were evaluated at 12 and 23 weeks of exposure using open-field test and passive avoidance test. Subcellular distribution of mercury and the induction of MT were also assessed. The Hg0 exposure resulted in significantly enhanced locomotion in the open-field test and poorer performance in the passive avoidance test at a brain Hg concentration less than 1 ppm. These effects were slightly exaggerated in MT-null mice, which showed less induction of MT, lower brain Hg concentration, and lower calculated concentration of MT-unbound cytosolic Hg. The results showed, for the first time, that a concentration of Hg0 relevant to human exposure level could cause neurobehavioral effects in adult mice. The higher susceptibility of MT-null mice suggested that MT-I,II have protective roles in the metal-induced neurobehavioral toxicity, which cannot be entirely explained by kinetic mechanisms, thus suggesting an involvement of nonkinetic mechanisms.

Extraction mechanism of Cr(VI) on the aqueous two-phase system of tetrabutylammonium bromide and (NH(4))(2)SO(4) mixture.

An aqueous two-phase system of tetrabutylammonium bromide (TBAB) and (NH(4))(2)SO(4) mixture has been developed for the extractive preconcentration and separation of certain compounds. TBAB concentration in upper phase is much higher than that of bottom solution. This new aqueous two-phase system is proposed for the highly selective extraction of Cr(VI) from large amounts of Cr(3+). The Cr(VI) is found to be extracted into the TBAB-rich upper phase due to ion pair formation such as HCrO(4)(-) . TBAB(+). The Cr(VI) was sufficiently extracted into the upper phase in the pH range from 1 to 5. The proposed method has been applied to the determination of trace of Cr(VI) in wastewater samples with a coefficient of variation less than 3.2%. The recovery obtained was not lower than 90%. The determination limit for the Cr(VI) was found to be 60 mug l(-1) in 10 ml of sample solution.