Ionizing radiation-induced destruction of benzene and dienes in aqueous media.

Pulse radiolysis with spectrophotometric and conductometric detection was utilized to study the formation and reactions of radicals from benzene and dienes in aqueous solutions. The benzene OH adduct, *C6H6OH, reacts with O2 (k = 3 x 10(8) L mol(-1) s(-1)) in a reversible reaction. The peroxyl radical, HOC6H6O2*, undergoes O2*- elimination, bimolecular decay, and reaction with benzene to initiate a chain reaction, depending on the dose rate, benzene concentration, and pH. The occurrence of the chain reaction is demonstrated in low-dose-rate gamma radiolysis experiments where the consumption of O2 was monitored. 1,4-Cyclohexadiene, 1,4-hexadiene, and 1,4-pentadiene form OH-adducts and undergo H-abstraction by O*- radicals. The OH-adducts react with O2 to form peroxyl radicals. These peroxyl radicals, however, do not undergo unimolecular O2*- elimination but rather decay by second-order processes, which lead to subsequent steps of O2*- elimination.

Comparison of powered and manual toothbrushes for plaque removal by 4- to 5-year-old children.

PURPOSE: This study compared the small head Oralgiene 60 Second Time Machine powered toothbrush, used for 60 seconds, with the Braun Oral-B Mickey Mouse powered toothbrush and a manual toothbrush (Oral-B Rugrats 20), each used for 2 minutes, for efficacy in plaque removal and reduction of gingival inflammation in young children. METHODS: Fifty-eight children, ages 4 to 5 years old, were randomly assigned to one of the 3 toothbrush groups. At visit 1, plaque and gingival indices were recorded for all subjects. Then, the children did not brush for 24 hours. At visit 2, 24 hours later, plaque indices were recorded, the children brushed with their assigned toothbrush, and plaque indices were recorded again. Six weeks later, plaque and gingival indices were recorded again. The data was analyzed to detect plaque reduction after a one-time use (visit 2, prebrushing and postbrushing) as well as plaque and gingival inflammation reduction after 6 weeks of use. RESULTS: The Oralgiene toothbrush removed significantly more plaque during the one-time trial and reduced significantly more gingival inflammation during the 6-week trial. The Braun Oral B powered toothbrush removed significantly more plaque than the other toothbrushes during the 6-week trial. However, no clinically meaningful differences were found between any of the toothbrushes with regard to plaque removal or gingival scores. CONCLUSIONS: There were no clinically meaningful differences found between any of the toothbrushes tested during either of the trials with regard to plaque removal or improvement in gingival health.

Degradation of PCBs in a marine sediment treated with ionizing and UV radiation.

Radiolytic (electron beam) and photolytic (ultraviolet, UV) dechlorination of polychlorinated biphenyls (PCBs) in a marine sediment are described. Samples of a PCB-laden marine sediment, Standard Reference Material (SRM) 1944, NewYork/New Jersey Waterway Sediment, have been mixed with aqueous alcohol solutions and irradiated with an electron beam or photolyzed. Additives, such as alcohol, enhance the radiolytic yield and PCB dechlorination. In the electron beam irradiated samples, the concentrations of 29 PCB congeners decrease with irradiation dose. At the highest dose (500 kGy), the total concentration of PCBs is decreased by 83%. Photolysis leads to little dechlorination, but photolysis with added triethylamine leads to dechlorination (about 60%). It is likely that photolysis under optimal conditions (other additives, exposure time) may be as effective as electron beam radiolysis for the dechlorination of PCBs in sediment.

Dechlorination of polychlorinated biphenyls in industrial transformer oil by radiolytic and photolytic methods.

Used electrical transformer oils containing low or high concentrations of polychlorinated biphenyls (PCBs) were treated using electron, gamma, and ultraviolet radiation, and the conditions for complete dechlorination were developed. Dechlorination was determined by analysis of the inorganic chloride formed and the concentrations of remaining PCBs. Transformer oil containing approximately 95 microg g(-1) PCB (approximately 3.5 mmol L(-1) Cl) is completely dechlorinated by irradiation with 600 kGy after the addition of 10% triethylamine (TEA). Transformer oil containing >800,000 microg g(-1) PCB (17.7 mol L(-1) Cl) requires an additional solvent to prevent solidification. When this oil is diluted with 2-propanol (2-PrOH) and TEA (v/v/v, 1/79/20), complete dechlorination is achieved with a dose of 2500 kGy. Ultraviolet photolysis of the same oil/2-PrOH/TEA solutions led to 90% dechlorination after exposure for 120 h in our experimental setup. Such yields were obtained by radiolysis with a dose of 2000 kGy (300 h in our Gammacell). Replacing TEA with KOH in 2-PrOH solutions greatly increases the yield of dechlorination in both the radiolytic and the photolytic experiments, demonstrating that a chain reaction plays a role in both of these treatment methods and suggesting that both methods deserve further consideration for large-scale application.