Use of sodium borohydride for determination of total mercury in urine by atomic absorption spectrometry

Geochemical modeling of mercury in coastal groundwater

The systematic analysis of groundwater in the Greek island of Skiathos revealed a seasonal increase of total mercury concentrations after the extensive groundwater abstraction during the busy and heavily touristic summer months. This contamination was accompanied by a corresponding increase of the chloride content of groundwater, attributed to seawater intrusion into the freshwater-depleted aquifer within mercury-rich bedrock. The effects of elevated concentrations of chloride anions in the mobilization of mercury and its speciation were addressed by geochemical equilibrium modeling, considering cinnabar (HgS) as the mineral source of mercury. Adsorption onto hydrous ferric oxide (Fe₂O₃·H₂O) was a necessary ingredient of the geochemical model for bringing the calculated concentrations in agreement with field measurements, after optimization of the cinnabar/adsorbent mass ratio to a value of 4.9 × 10^-8. The speciation of mercury was found to depend on the acidity and redox status as well as on the chloride content of groundwater. Mercury concentrations in the groundwater of Skiathos rise above the World Health Organization limit of 1 μg L^-1 for a seawater intrusion higher than 3 %, with HgCl₂ being the dominant species followed by HgClOH, HgCl₃^- and HgCl₄^2-. The assumed concentration of dissolved organic matter in groundwater had a negligible impact on the mercury speciation and its mobilization by chloride.

Mercury content in rat teeth after administration of organic and inorganic mercury. The effects of interrupted exposure and of selenite

Rat molars are indicators of exposure concentration and target organ content in chronic mercury vapor exposure. We wished to study the accumulation and persistence of organic and inorganic mercury in rat teeth and the effect of selenium on mercury retention. Male Wistar rats received either inorganic or organic mercury (with or without addition of selenite), selenite only, or no mercury or selenite (controls) in the drinking water for 4 weeks. Group A was killed after exposure. Group B was killed 20 weeks later. The mercury content was measured by cold-vapor atomic absorption spectrophotometry. The mercury content in the molars in group B was 66% and 77% less than in group A after inorganic and organic exposure, respectively. In the incisors the corresponding reductions were 90% and 97%. Selenite had limited effect on mercury retention in group A and none in group B. We suggest that rat molars and, by inference, human deciduous teeth may serve as indicators of organic and inorganic mercury exposure.

Factors affecting the determination of total mercury in biological samples by continuous-flow cold vapor atomic absorption spectrophotometry

The acidic reduction of Hg using a continuous-flow analytical system was evaluated. With 25% SnCl2 as the reductant, characteristic concentrations (sensitivities) of 0.44 microgram/L (open cell) and 0.29 microgram/L (flow-through cell) were obtained using inorganic Hg2+ standards in 1.5% HCl. When CH3Hg+ standards were used, absorption signals were an order of magnitude lower, indicating that Sn(II) is incapable of producing Hg degree from organic Hg in this acidic reduction system. Addition of CdCl2 to the SnCl2 reductant, as suggested by Magos (1) for the reduction of organomercurials under alkaline conditions, was without beneficial effect. Similarly, combining Sn with another reducing agent (hydroxylamine hydrochloride), or a strong alkaline solution (40% NaOH), in the reaction coil of the flow-through system did not significantly enhance the Hg absorption signal for either inorganic or organic Hg. Recovery of Hg from spiked liver homogenates digested at 70-80 degrees C using a HNO3/H2SO4/HCl procedure and stabilized with 0.5 mM K2Cr2O7 was > 85% using either inorganic Hg2+ or CH3Hg+, indicating that this digestion procedure successfully breaks the C-Hg bond to form readily reducible Hg species. Using L-cysteine to stabilize standards of inorganic Hg2+ in HCl caused significant depressions of the Hg absorption signal at L-cysteine concentrations > 0.001% (approximately 0.5 mM); 0.1% L-cysteine caused total suppression of the Hg signal. These results indicate that: (1) acidic reduction of Hg by Sn in this continuous-flow system requires breakdown of organomercurials prior to analysis; (2) tissue digestion using HNO3/H2SO4/HCl followed by the addition of K2Cr2O7 to stabilize Hg2+ achieves this breakdown and allows good recovery of total Hg; and (3) use of L-cysteine to complex and prevent losses of Hg should be avoided in systems using acidic reduction of Hg. Concentrations of endogenous tissue sulfhydryls are generally lower than those associated with depressed absorbance signals during the acidic reduction of Hg.

Percutaneous absorption of mercury vapor by man

Five volunteer male subjects who were 24 to 78 y of age exposed the skin of their forearm to mercury vapor (203Hg) at concentrations of 0.88-2.14 ng/cm3 for periods of 27-43 min. Approximately 216 to 844 ng was taken up by the skin at rates of 0.0101 to 0.0402 ng Hg per cm2 per min per ng Hg per cm3 air. About half of the mercury taken up was shed by desquamation of epidermal cells during several weeks. The remainder diffused into the general circulation and could be measured as systemic mercury. When the total skin area (of which the forearm skin was assumed to be representative) was compared to the lung as a route of entry for mercury vapor at the same concentration, the rate of uptake was estimated to be 2.2% of the rate of uptake by the lung. A model is proposed that describes the growth and loss of skin-derived systemic mercury.

In vitro oxidation of mercury by the blood

A method is described for studying the in vitro oxidation of mercury vapour by red blood cells at short times and with diminishing mercury vapour concentrations. It is found that for 40% red blood cell suspensions and 37 degrees at concentrations greater than about 6 ng mercury vapour/ml, the oxidation rate is zero order, and that at lower concentrations the rate changes to first order. The effect of temperature and of added hydrogen peroxide are studied. Results are considered in terms of the generally accepted belief that the catalase-compound I system is the main path of oxidation. If the results obtained in vitro in these experiments apply in vivo to man, it follows that inhaled mercury is carried in the blood to the brain and other organs primarily as dissolved vapour rather than as inorganic mercury ions.

Prediction of kidney mercury content by isotope techniques

A 61-year-old female patient accidentally aspirated liquid mercury during a medically ordered diagnostic procedure. To develop animal-based guidelines, liquid mercury was introduced into the lungs of four dogs. Based on the study of these animals, a method of predicting the kidney inorganic mercury burden was developed using radioactive isotope dilution techniques. It was further demonstrated in dogs that oral administration of dimercaptopropane sulfonate (DMPS) increased mercury excretion and reduced the kidney burden. A rat experiment was performed permitting a statistical evaluation of the assumptions basic to the use of the method. The method was applied to the patient with the result that the kidney inorganic mercury burden was predicted to be 28.1 mg, 8 months after the accident. Treatment with DMPS increased urinary excretion and the post-treatment kidney burden was estimated at 19.6 mg Hg. Inasmuch as the radioactive dose to the subject may be kept at a negligible level and because sensitive methods exist for measurement of radioactive and stable mercury concentrations, the technique may be applicable in special cases to the estimation of kidney inorganic mercury burdens incurred by industrial exposure.

The AAS determination of copper and zinc levels in the serum of hemodialysis patients

An electrothermal atomic absorption technique for the determination of subnanogram amounts of copper and zinc in aqueous and blood serum matrices has been evaluated. The technique has been utilized to study the effect of dialysis (artificial kidney) on the levels of these trace elements in the serum of hemodialysis patients. The present results confirm a previous study (1) which was conducted on representative samples that were taken from the continuous flow of the dialysis fluid (dialysate). Matrix effects have been minimized by using serum controls (obtained from a pool made of the tested serum samples), small sample size, and background correction. Before dialysis, values of copper for patients who were dialysed against tap water (tap-water patients) and distilled water (distilled-water patients) were: (mean +/- SD) 1297 +/- 59 and 1064 +/- 137 micrograms/L, respectively; after dialysis: 1539 +/- 98 and 1120 +/- 129 micrograms/L, respectively. Zinc levels were less affected by the dialysis process; before dialysis: tap-water patients, 952 +/- 131 micrograms/L; distilled-water patients, 932 +/- 119 micrograms/L; after dialysis: 1001 +/- 137 micrograms/L, and 934 +/- 121 micrograms/L, respectively. Because the method is sensitive, accurate, and precise, it can be utilized to study trace levels of copper and zinc in serum when limitations of sample volume exist as in the present case or with pediatric patients.