Ferrate(VI) oxidation of ß-lactam antibiotics: reaction kinetics, antibacterial activity changes, and transformation products.

Oxidation of ß-lactam antibiotics by aqueous ferrate(VI) was investigated to determine reaction kinetics, reaction sites, antibacterial activity changes, and transformation products. Apparent second-order rate constants (kapp) were determined in the pH range 6.0-9.5 for the reaction of ferrate(VI) with penicillins (amoxicillin, ampicillin, cloxacillin, and penicillin G), a cephalosporin (cephalexin), and several model compounds. Ferrate(VI) shows an appreciable reactivity toward the selected ß-lactams (kapp for pH 7 = 110-770 M(-1) s(-1)). The pH-dependent kapp could be well explained by considering species-specific reactions between ferrate(VI) and the ß-lactams (with reactions occurring at thioether, amine, and/or phenol groups). On the basis of the kinetic results, the thioether is the main reaction site for cloxacillin and penicillin G. In addition to the thioether, the amine is a reaction site for ampicillin and cephalexin, and amine and phenol are reaction sites for amoxicillin. HPLC/MS analysis showed that the thioether of ß-lactams was transformed to stereoisomeric (R)- and (S)-sulfoxides and then to a sulfone. Quantitative microbiological assay of ferrate(VI)-treated ß-lactam solutions indicated that transformation products resulting from the oxidation of cephalexin exhibited diminished, but non-negligible residual activity (i.e., ∼24% as potent as the parent compound). For the other ß-lactams, the transformation products showed much lower (<5%) antibacterial potencies compared to the parent compounds. Overall, ferrate(VI) oxidation appears to be effective as a means of lowering the antibacterial activities of ß-lactams, although alternative approaches may be necessary to achieve complete elimination of cephalosporin activities.

Decabromodiphenyl ether in indoor dust from different microenvironments in a university in the Philippines.

This study was conducted to develop a method for the determination of decabromodiphenyl ether (BDE-209) in indoor dust from different microenvironments in a university in the Philippines. BDE-209 was extracted from dust samples by ultrasonication and determined by HPLC-UV. The determination was performed using external calibration and internal standard calibration. Internal standard calibration was shown to be more precise and sensitive than external calibration. The linearity for the concentration range of 0-300 µg L(-1) BDE-209 was good (R(2)=0.993). The % absolute recovery and the % RSD for n=8 spiked dust analysis based on a 0.2 g dust sample was 57% and 19%, respectively. The method detection limit was 285 ng g(-1). All dust samples showed detectable levels of BDE-209 with some at levels below the quantification limits. The concentrations of BDE-209 in the quantified samples are within the range of 1103-4117 ng g(-1) with an average concentration of 2172 ng g(-1). The levels of BDE-209 found in the dust samples are comparable to those reported in house and workplace dusts from other Asian countries. Although not conclusive, it has been shown empirically that BDE-209 concentrations are higher in sampling sites containing more possible BDE-209 sources like electrical and electronic equipment.

Occurrence and sources of bromate in chlorinated tap drinking water in Metropolitan Manila, Philippines.

Significant levels of potentially carcinogenic bromate were measured in chlorinated tap drinking water in Metropolitan Manila, Philippines, using an optimized ion-chromatographic method. This method can quantify bromate in water down to 4.5 µg l⁻¹ by employing a postcolumn reaction with acidic fuchsin and subsequent spectrophotometric detection. The concentration of bromate in tap drinking water samples collected from 21 locations in cities and municipalities within the 9-month study period ranged from 7 to 138 µg l⁻¹. The average bromate concentration of all tap drinking water samples was 66 µg l⁻¹ (n = 567), almost seven times greater than the current regulatory limit in the country. The levels of bromate in other water types were also determined to identify the sources of bromate found in the distribution lines and to further uncover contaminated sites. The concentration of bromate in water sourced from two rivers and two water treatment plants ranged from 15 to 80 and 12 to 101 µg l⁻¹, respectively. Rainwater did not contribute bromate in rivers but decreased bromate level by dilution. Groundwater and wastewater samples showed bromate concentrations as high as 246 and 342 µg l⁻¹, respectively. Bromate presence in tap drinking water can be linked to pollution in natural water bodies and the practice of using hypochlorite chemicals in addition to gaseous chlorine for water disinfection. This study established the levels, occurrence, and possible sources of bromate in local drinking water supplies.