Exploring the mechanism of diphenylmethanol oxidation: A combined experimental and theoretical approach

Selective accumulation of pharmaceutical residues from 6 different soils by plants: a comparative study on onion, radish, and spinach

The accumulation of six pharmaceuticals of different therapeutic uses has been thoroughly investigated and compared between onion, spinach, and radish plants grown in six soil types. While neutral molecules (e.g., carbamazepine (CAR) and some of its metabolites) were efficiently accumulated and easily translocated to the plant leaves (onion > radish > spinach), the same for ionic (both anionic and cationic) molecules seems to be minor to moderate. The maximum accumulation of CAR crosses 38,000 (onion), 42,000 (radish), and 7000 (spinach) ng g-1 (dry weight) respectively, in which the most majority of them happened within the plant leaves. Among the metabolites, the accumulation of carbamazepine 10,11-epoxide (EPC - a primary CAR metabolite) was approximately 19,000 (onion), 7000 (radish), and 6000 (spinach) ng g-1 (dry weight) respectively. This trend was considerably similar even when all these pharmaceuticals applied together. The accumulation of most other molecules (e.g., citalopram, clindamycin, clindamycin sulfoxide, fexofenadine, irbesartan, and sulfamethoxazole) was restricted to plant roots, except for certain cases (e.g., clindamycin and clindamycin sulfoxide in onion leaves). Our results clearly demonstrated the potential role of this accumulation process on the entrance of pharmaceuticals/metabolites into the food chain, which eventually becomes a threat to associated living biota.

Transformation of diazepam in water during UV/chlorine and simulated sunlight/chlorine advanced oxidation processes

Psychoactive drug diazepam is one of benzodiazepines widely used in human medicine. It has been found to be relatively resistant to chlorination and photolysis. Here we investigated the transformation mechanism of diazepam in aqueous solution through UV/chlorine and simulated sunlight/chlorine treatments. The results showed that the UV/chlorine and sunlight/chlorine processes significantly increased the degradation of diazepam in water. These observed degradations can be elucidated by in-situ generation of reactive species including hydroxyl radical (HO), reactive chlorine species (RCS) and ozone (O₃) during photolysis of chlorine. In the UV/chlorine treatment, the degradation efficiency of diazepam for HO, chlorine, UV and RCS reaction at 90 min was calculated to be 62.1%, 3.8%, 11.9% and 12.3%, respectively. In the simulated sunlight/chlorine treatment, the calculated degradation of 53.1%, 8.1% and 11.2% was attributed to HO, chlorine and RCS reaction, with negligible loss by O₃ reaction and sunlight irradiation. In the UV/chlorine and sunlight/chlorine treatments, a total of 70 transformation products was detected using a high-resolution TripleTOF mass system. Six transformation pathways have been tentatively proposed for the diazepam, which includes hydroxylation, chlorination, hydrolyzation, N-demethylation, loss of phenyl group, benzodiazepine ring rearrangement and contraction. Most of the obtained transformation products were less toxic to aquatic organisms including fish, daphnia and green algae than diazepam itself according to the toxicity prediction tool, and did not cause significant changes in toxicity to luminescent bacteria.

Sonochemical degradation of benzenesulfonic acid in aqueous medium

Degradation of benzenesulfonic acid (BSA), the simplest aromatic sulfonic acid with extreme industrial importantance, by sonochemically generated hydroxyl radical (OH) have been thoroughly investigated. A reasonable reduction (∼50%) in the total organic carbon (TOC) was achieved only after prolonged irradiation (∼275 min, 350 kHz) of ultrasound, although a short irradiation of less than an hour is enough to degrade significant amount of BSA. The degradation efficiency of ultrasound has been reduced in lower and extremely higher frequencies, and upon increasing the pH. An irregular, but continuous, release of sulfate ions was also observed. Further, the release of protons upon the oxidation of BSA consistently reduces the experimental pH to nearly 2. High resolution mass spectrometric (HRMS) analyses reveals the formation of a number of aromatic intermediates, including three mono (I_a-c) and two di (II_a&b) hydroxylated BSA derivatives as the key products in the initial stages of the reaction. Pulse radiolysis studies revealed the generation of hydroxycyclohexadienyl-type radicals, characterized by absorption bands at 320 nm (k₂ = (7.16 ± 0.04) × 10⁹ M^-1 s^-1) and 380 nm, as the immediate intermediates of the reaction. The mechanism(s) leading to the degradation of BSA under sonolytic irradiation conditions along with the effect of various factors, such as the ultrasound frequency and reaction pH, have been explained in detail. The valuable mechanistic aspects obtained from our pulse radiolysis and HRMS studies are essential for the proper implementation of sonochemical techniques into real water purification process and, thus, receives extreme environmental relevance.