Maria Pythias B. Espino

Ferrate(VI) Oxidation of β-Lactam Antibiotics: Reaction Kinetics, Antibacterial Activity Changes, and Transformation Products

Oxidation of β-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 β-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 β-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 β-lactams was transformed to stereoisomeric (R)- and (S)-sulfoxides and then to a sulfone. Quantitative microbiological assay of ferrate(VI)-treated β-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 β-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 β-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.

Heavy metals in lake water: a review on occurrence and analytical determination

ABSTRACT Many lakes especially in Asia are source of livelihood for the surrounding communities. With increased urbanisation and industrialisation, however, these lakes are threatened with emerging environmental contaminants, including heavy metals. Some heavy metals are harmful to human health and the environment. This review aims to describe the different sampling, sample preparation and pretreatment, and instrumental methods of analysis for heavy metals in lake water. Filtration and acid digestion are common sample treatment methods used prior to analytical determination. Atomic absorption spectroscopy and inductively-coupled plasma – mass spectrometry (ICP-MS) are typical analytical techniques but nowadays ICP-MS is frequently used. This review also describes the sources and extent of heavy metals contamination in different lakes. Although some lakes still have natural levels of heavy metals in the water, many have elevated concentrations due to anthropogenic sources, such as vehicular, household, agricultural, industrial and mining activities.