Aquatic toxicity of hydroquinone and catechol following metal oxide treatment to Ceriodaphnia dubia and Pimephales promelas.

Metal oxides comprise a large group of chemicals used in water treatment to adsorb organic pollutants. The ability of titanium dioxide (TiO2) and iron (III) oxide (Fe2O3) to reduce the chronic toxicity of (phenolic) C6H6(OH)2 isomers, namely hydroquinone (HQ) and catechol (CAT) to Ceriodaphnia dubia and Pimephales promelas (less than 24 h-old) were investigated. The toxic endpoints following metal oxide treatment were compared to endpoints of untreated CAT and HQ. In chronic toxicity testing, HQ resulted in greater toxicity than CAT for both test organisms; the median lethal concentrations (LC50) for CAT were 3.66 to 12.36 mg.L-1 for C. dubia and P. promelas, respectively, while LC50 for HQ were 0.07 to 0.05 mg.L-1, respectively. Although both treated solutions presented lower toxic endpoints than those in the untreated solutions, Fe2O3 had a better potential to reduce the toxic effects of CAT and HQ than TiO2.

Mole Ratio Dependence of the Mutual Deliquescence Relative Humidity of Aqueous Salts of Atmospheric Importance.

The response of the mutual deliquescence relative humidity (MDRH) of several mixed salt systems to changes in mole ratio is presented here. The MDRH values of NH4Cl-NaCl, NH4Cl-(NH4)2SO4, and, for the first time, the NaCl-NaBr systems were acquired as a function of mole ratio. These changes were studied using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. The MDRH values of 1:1 salt mixtures were consistently found to be lower than the values of the individual deliquescence relative humidity (iDRH) of NH4Cl-NaCl and NH4Cl-(NH4)2SO4. The exception was the MDRH of the NaCl-NaBr system, which was found to be higher than the iDRH of NaBr particles, but lower than the iDRH of NaCl particles. When the mole ratio of the mixed system was varied, the MDRH of the mixtures showed a slight dependence on the mole ratio.