Self-dispersion of mercury metal into aqueous solutions

Enhancement of the Negative Capacitance Associated with the Dissolution of Silver by Salt Concentrations by Means of Anodic Stripping Voltammetry

The amount of anodically dissolved charge of silver by linear sweep stripping voltammetry has been observed to be smaller than that of the potentiostatically deposited charge. The imbalance in the charge is opposite to the participation in the double-layer capacitance. This can be explained in terms of the negative capacitive current, which is caused by dipoles of generated redox charge (Ag+) with counterions (NO3−). Lower concentrations of counterions may suppress the capacitance to retain the equality of the charge. This prediction is examined in this work by the oxidation of silver film at various concentrations of NO3− by anodic stripping voltammetry. The capacitance decreased with a decrease in the salt concentrations less than 0.05 mol dm−3. Low concentrations of salts prevent loss of the anodic charge in electroanalysis. This dependence was related with the lifespan of generated silver nitrate dipoles and is described theoretically.

Parallel Combination of Inner Capacitance and Ionic Capacitance, Apparently Inconsistent with Stern’s Model

A double layer capacitance (DLC) has mainly been brought about in the Helmholtz layer rather than in the diffuse layer, as was demonstrated with the invariance of DLC to salt concentration, c, less than 0.5 M (M = mol dm−3). The DLC measured here increased with concentrations of KCl and HCl solutions as high as 1 M at a platinum electrode by the ac impedance method. It was represented as a sum of the Helmholtz capacitance and the ionic one which had 0.7 power of the concentrations. The simple addition implies that the Helmholtz contribution and the ionic one should be represented by a parallel combination rather than a series one such as in the Stern model. The disagreement of the experimental values of the DLC with the Gouy–Chapman theory at high concentrations has been conventionally attributed to the effects of packing of ions over their sizes. In this paper, a model of avoiding the packing was introduced, in which ions were distributed in the direction normal to the electrode in the balance of electric motive force and the thermal energy, keeping the uniform distribution on a plane projected to the electrode. The energy balance was taken by using the grand canonical ensemble in statistical mechanics. The ionic contribution had a linear relation with the applied voltage rather than exponential dependence. When a series combination was applied to the Helmholtz capacitance and the ionic one under the condition of difference between the locally anionic DLC and the cationic one, we obtained approximately a parallel combination of the two capacitances because either the anionic or the cationic DLC works predominantly.

Mercury levels in birds and small rodents from Las Orquideas National Natural Park, Colombia

Mercury (Hg) is a heavy metal known as one of the most toxic elements on the planet. The importance of Hg on living organisms resides on its biomagnification ability. Artisanal gold extraction activities release substantial amounts of this metal, polluting the ecosystems. To assess the impact of gold mining in Las Orquideas National Natural Park (Colombia), total Hg (T-Hg) levels were evaluated from 37 bird and 8 small rodent species collected at two sites within the boundaries of the Natural Park (Abriaqui and Frontino municipalities) that have experienced some gold-extraction history. The mean concentration of T-Hg in bird feathers from both sites was 0.84 ± 0.05 μg/g fw. Differences between species were found according to diet. Total Hg levels were greater on insectivorous (1.00 ± 0.08 μg/g fw), followed by nectarivorous (0.73 ± 0.07 μg/g fw) and frugivorus (0.57 ± 0.09 μg/g fw) species. These Hg levels were greater than those found in feathers from a control sample belonging to the species Penelope perspicax (0.53 ± 0.03 μg/g fw), a frugivorous species living at the Otun Quimbaya Fauna and Flora Sanctuary, a forest without known gold mining. Mercury concentrations in the livers of small rodents were greater in specimens from Frontino (0.15 ± 0.01 μg/g fw) than those from Abriaqui (0.11 ± 0.01 μg/g fw), but levels were not different between species. These results indicate that Hg in birds depends mainly on their diet, but geographical location may affect Hg concentration in rodents. Moreover, Hg sources in natural parks of Colombia may not rely solely on gold mining, atmospheric deposition, among others factors, could be influencing its accumulation in biota.