Fragmentation of mercury compounds under ultraviolet light irradiation.

Ultraviolet light induced photofragmentation of mercury compounds is studied experimentally with electron energy resolved photoelectron-photoion coincidence techniques and theoretically with computational quantum chemical methods. A high resolution photoelectron spectrum using synchrotron radiation is presented. Fragmentation of the molecule is studied subsequent to ionization to the atomic-mercury-like d orbitals. State dependent fragmentation behaviour is presented and specific reactions for dissociation pathways are given. The fragmentation is found to differ distinctly in similar orbitals of different mercury compounds.

Atmospheric photolytic reduction of Hg(ii) in dry aerosols.

A laboratory reactor system was developed to examine the role of light and aerosol composition in the reduction of oxidized mercury (Hg(ii)) in laboratory-generated aerosols. Aerosolized sodium chloride, doped with mercury chloride, was exposed to light in a fixed-bed flow-through reactor. Three spectral ranges (UV, visible and a simulated solar spectrum) were examined, along with dark experiments, to investigate the role of light conditions in mercury reduction. In addition, the role of iron in the aerosol matrix was examined. The effluent from the reactor was analyzed for Hg(0) as evidence of reduction of Hg(ii) in the reactor. Significant reduction of Hg(ii) (1.5-9.9%) was observed for all three light sources and the rate of mercury reduction was proportional to the light irradiance. The presence of iron in the aerosol matrix inhibited the reduction rate and the degree of inhibition was dependent on the chemical form of the iron in the aerosol. The observed reduction reactions may be important chemical processes in the atmosphere and could be incorporated in atmospheric transport models that are used to understand the fate of atmospheric mercury.

Effects of methylmercury on electric organ discharges in the weak electric fish Gymnotus sylvius

Methylmercury (MeHg) is present in the environment because of natural and anthropogenic causes. MeHg can reach the central nervous system (CNS) and cause neurological damage in humans and animals. Electric organ discharges (EODs) in the weak electric fish Gymnotus sylvius are produced by the electric organ and modulated by the CNS. These discharges are used for electrolocation and communication. The purpose of the present study was to investigate the effects of dietary MeHg exposure on EOD rate in G. sylvius. An oscilloscope was used to record the EOD rate. Two treatments were investigated: chronic MeHg administration (4 µg/kg MeHg every 2 days, with a total of nine dietary exposures to MeHg) and acute MeHg administration (a single dose of 20 µg/kg MeHg). The control data for both treatments were collected every 2 days for 18 days, with a total of nine sessions (day 1 until day 18). Data of fish exposed to MeHg were collected every 2 days, totaling nine sessions (day 19 until day 36). Chronic treatment significantly increased the EOD rate in G. sylvius (p < .05), especially with the final treatment (day 32 until day 36). Acute treatment resulted in an initial increase in the EOD rate, which was maintained midway through the experiment (day 26 until day 30; p < .05). The present study provides the first insights into the effects of MeHg on EODs in weak electric fish. The EOD rate is a novel response of the fish to MeHg administration.

Effects of methylmercury on electric organ discharges in the weak electric fish Gymnotus sylvius

Methylmercury (MeHg) is present in the environment because of natural and anthropogenic causes. MeHg can reach the central nervous system (CNS) and cause neurological damage in humans and animals. Electric organ discharges (EODs) in the weak electric fish Gymnotus sylvius are produced by the electric organ and modulated by the CNS. These discharges are used for electrolocation and communication. The purpose of the present study was to investigate the effects of dietary MeHg exposure on EOD rate in G. sylvius. An oscilloscope was used to record the EOD rate. Two treatments were investigated: chronic MeHg administration (4 µg/kg MeHg every 2 days, with a total of nine dietary exposures to MeHg) and acute MeHg administration (a single dose of 20 µg/kg MeHg). The control data for both treatments were collected every 2 days for 18 days, with a total of nine sessions (day 1 until day 18). Data of fish exposed to MeHg were collected every 2 days, totaling nine sessions (day 19 until day 36). Chronic treatment significantly increased the EOD rate in G. sylvius (p < .05), especially with the final treatment (day 32 until day 36). Acute treatment resulted in an initial increase in the EOD rate, which was maintained midway through the experiment (day 26 until day 30; p < .05). The present study provides the first insights into the effects of MeHg on EODs in weak electric fish. The EOD rate is a novel response of the fish to MeHg administration.(AU)

Production and separation of no-carrier-added thallium isotopes from proton irradiated (nat)Hg2Cl2 matrix.

For the first time, (nat)Hg2Cl2 target has been used to produce no-carrier-added-NCA (197,198,198m,199,200,201)Tl radionuclides using (nat)Hg(p,xn) reaction. Liquid-liquid extraction technique was employed in order to separate radiothallium from the bulk mercury matrix using liquid anion exchanger trioctylamine (TOA) dissolved in cyclohexane. In order to verify the presence of stable Hg in Tl fraction, the entire process was repeated with stable salts of Hg and Tl and the extent of separation was examined by Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). High separation factors were observed both by radiometric and ICP-OES technique when 0.1 M HNO³ and 0.1M TOA were used as aqueous and organic phase, respectively. The Hg contamination was less than 0.3 ppm in the aqueous phase containing Tl after three times of extraction at the optimal condition.

Practical limit of the accuracy of radiometric measurements using HgCdTe detectors.

The spectral responsivity of HgCdTe detectors operating in the thermal infrared region was observed to drift slowly with time. The characteristics of the drift were investigated and were shown to have a different origin from the drifts previously reported by one of the authors. Those drifts were caused by a thin film of water ice depositing on the active area of the cold detector. The source of the new drift is far more serious because it is fundamental, making the acquisition of accurate radiometric measurements with these detectors very difficult. It is demonstrated that the source of the new drift is the nonlinearity in the response of the HgCdTe detectors, coupled with the fluctuations of the irradiance reaching them. These fluctuations are due to variations in the thermal background caused by changes in the temperature of objects in the field of view of the detectors. This phenomenon is expected to provide a practical limit to the accuracy of radiometric measurements using not only HgCdTe detectors but also other detectors whose linearity is a function of the thermal background.