The seasonal variations of arsenic species in lake water were studied in the mesotrophic northern and eutrophic southern basins of Lake Biwa in Japan. Within the euphotic zone, arsenite [As(III)] increased in spring and fall, and dimethylarsinic acid [DMAA(V)] became the dominant form in summer. Measurable concentrations of monomethylarsonic acid [MMAA(V)] and trivalent methylarsenic species [monomethylarsonous acid, MMAA(III), and dimethylarsinous acid, DMAA(III)] also appeared, although they were always minor fractions. The total arsenic concentration in the euphotic zones remained constant in the northern basin throughout the year. However, it was increased by 2−4 times in the southern basin in summer. The enhancement was caused by the increase of As(V), which was accompanied by the increase of iron, manganese, and phosphorus. The concentration of methylarsenicals per chlorophyll a was lower in the southern basin. These results indicate that the variations of arsenic species in lake water largely depend on biological processes, such as the metabolism of phytoplankton, decomposition of organic matter by bacteria, and microbial reduction of iron and manganese oxides in sediments. Moreover, they show that eutrophication affects the concentration and speciation of arsenic in the lake water.
The effects of salts, acids, and phenols on the hydrogen-bonding structure of water in 20% (v/v) EtOH−H2O solution were investigated on the basis of 1H NMR chemical shifts of the OH of water and ethanol. It was found that many salts caused structure breaking of water while a few metal salts, such as MgCl2 and KF, had a strengthening effect. The OH proton chemical shifts caused by the presence of alkali-metal and alkaline-earth-metal ions or anions (halides, NO3 -, ClO4 -, SO4 2-) from strong acids were related to the sizes and charges of the ions. Not only acids (H+ and HA, undissociated acids) but also bases (OH- and A-, conjugate-base anions from weak acids) had the effect of strengthening the structure of water; the degree of the effect was dependent on the acid strength (pK a). The proton exchange between water and ethanol molecules in 60% (v/v) EtOH−H2O solution was examined, on the basis of the coalescence of two signal peaks of water and ethanol as well as the further low-field shift in 1H NMR spectra with increasing concentration of solutes. Although it has been already reported that the proton exchange between water and ethanol molecules is promoted by strong acids and bases, a distinct proton exchange was also observed in the neutral solution, i.e., by the addition of phosphate pH buffer solution (pH 6.86). It was also discovered that NaCl had the effect of breaking the structure of water in 20% (v/v) EtOH−H2O solution; however, in 60% (v/v) EtOH−H2O solution the same salt at lower concentrations strengthened the water−ethanol structure, promoting the proton exchange between water and ethanol molecules. Hydrogen bond donors as well as acceptors seemed to cause the intimate (or tight) interaction between H2O and EtOH molecules even in alcoholic beverages.
Electrochemical reduction of elemental sulfur (S8) has been carried out in acetonitrile using a platinum electrode. The products were identified by means of spectrophotometry and ESR. Sulfur is reduced voltammetrically in two steps: S_8+2e→S_8^2-, S_8^2-+2e→2S_4^2- These products turns into more stable species by the succeeding chemical reactions in a bulk solution as follows: 2&S_8^2\oversetK\ightleftarrowsS_6^2-+1/4S_8& &(K=1.6×10^-2) &S_6^2-\oversetK_d\ightleftarrows2S_3^\ewdot& &(K_d=1.2×10^-3) The S42− species was enough active to react with S8 into S82−, which was regarded as the cause of a current maximum on the current-time curve in a controlled potential coulometry of S8 at a potential of the second reduction step.
A new approach is described for the speciation of arsenic species including trivalent methyiarsenicals in natural waters. Arsenious acid [As(m)], monomethylarsonous acid [MMAA(III)], and dimethylarsinous acid [DMAA(III)] are separated from pentavaient species by solvent extraction using diethyiammonium diethyldithiocarbamate (DDDC) and determined by hydride generation atomic absorption spectrometry (HG-AAS) after cold trapping and chromatographic separation. The
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.