Hg Vapor Research Articles

Study of Surface Morphology Effects on Hg Sorption–Desorption Kinetics on Gold Thin-Films

Mercury (Hg) vapor sorption and desorption kinetics on gold (Au) thin-films of different surface morphologies and at various operating temperatures have been studied by using the quartz crystal microbalance (QCM) technique. The QCM data was used to estimate Hg desorption activation energy (Ea) from Au nanostructured surfaces deposited over optically polished (Au-polished) and mechanically roughened (Au-rough) quartz substrates to better understand Hg adsorption and desorption processes, with the ultimate aim of developing better materials for Hg measurement and/or capturing applications. After accounting for the difference in active surface area, the Au-polished sample was calculated to have a Hg uptake of ∼1030 ng·cm–2 when exposed to 10.55 mg·m–3 of Hg vapor for 1 h. In comparison, the Au-polished film had a Hg uptake 15% higher than that of the Au-rough film at an operating temperature of 28 °C. However, at 132 °C, the difference increased to ∼140% higher uptake for the Au-polished film, thus indicatin...

Investigation of Hg sorption and diffusion behavior on ultra-thin films of gold using QCM response analysis and SIMS depth profiling

Using the quartz crystal microbalance (QCM) technique, we demonstrate that the contribution of Hg adsorption and absorption on the sensor response profile can be distinguished by studying the dynamic response curve of QCM based Hg vapor sensors that employ an ultra-thin film of Au in the range of 10 to 40 nm thickness as the sensitive layer. The response magnitudes of the QCMs were extrapolated to zero thickness (ETZT) in an attempt to determine the contribution of adsorbed Hg on the sensor response magnitude and response profile. In general, the ratio of adsorbed to absorbed Hg on Au films is found to decrease with increased Hg vapor concentration. Furthermore, the same ratio was observed to decrease with increasing Au film thickness. The 10 nm and 40 nm Au films for example were found to contain adsorbed Hg content of 43.8% and 16.4%, respectively, with the balance attributed to absorption/amalgamation, when exposed to Hg vapor concentration of 10.55 mg m−3 for a period of 14 hours and an operating temperature of 28 °C. In addition, the QCMs were characterized using secondary ion mass spectroscopy depth profiling in order to study the diffusion behaviour of Hg in the Au surfaces. It is deduced that in order to reduce Hg accumulation in Au thin films, a non-continuous type film (similar to the 10 nm ultra-thin Au sensitive layer morphology) would be more functional as a Hg sensitive layer where quick absorption and desorption processes are required.

Mercury vapor sensor enhancement by nanostructured gold deposited on nickel surfaces using galvanic replacement reactions

Anthropogenic mercury emission is a serious global environmental problem because of its toxicity to humans, plants and wildlife. In order to control these emissions, accurate and reliable online continuous mercury monitoring systems (CMMs) are critical. Such systems can notify appropriate authorities or provide feedback signals to a process control system in time, thus making them an integral part of monitoring and controlling Hg emissions. We demonstrate how nanostructured gold can easily be deposited in small quantities on nickel electrode based QCMs using galvanic replacement (GR) reactions with the resultant surface having excellent Hg monitoring properties. The developed GR surfaces were observed to have higher sensitivity and selectivity in the presence of interfering gas species (NH3 and H2O), as well as to have ∼80% higher mercury sorption capacity than the most efficient mercury sorbents reported to date. Investigations towards the Hg-sensing capabilities of the resultant Ni–Au surface based Hg sensors showed ∼50% better sensitivity and detection limit over control Au films. Furthermore, the GR based QCMs were found to self-regenerate without changing the operating temperature of the sensor, undergoing Hg desorption with sensor recoveries of 93.7–99.3% following Hg exposure at an operating temperature of 90 °C. Surface depth profile analysis of the Ni–Au electrode surfaces showed that the high recovery rate of the sensors was primarily due to the Ni–Au structures, which unlike continuous Au thin-films more commonly used for Hg sensing applications, do not accumulate Hg at the sensitive-layer–substrate interface. Furthermore, the GR Ni–Au surfaces were found to be highly selective towards Hg vapor in the presence of NH3 and H2O interfering gas species which makes them potentially suitable for operating in harsh industrial effluent environments.

Multivariate optimization of mercury determination by flow injection-cold vapor generation-inductively coupled plasma optical emission spectrometry

In this work a procedure for mercury determination by Flow Injection-Cold Vapor Generation-Inductively Coupled Plasma Optical Emission Spectrometry (FI-CVG-ICP OES) has been developed. The system uses a small homemade glass separator constructed to drive the Hg vapor to the plasma. An evolutionary operation factorial design was used to evaluate the optimal experimental conditions for mercury vapor generation, aiming at the low consumption of reagents, the improvement of the analytical signal and consequently greater sensitivity. The procedure allowed the determination of mercury and showed excellent linearity for the concentration range from 0.50 μg L(-1) to 100.0 μg L(-1), with Limits of Detection (LOD) and Quantification (LOQ) of 0.11 μg L(-1) and 0.36 μg L(-1), respectively, and a sampling rate of 36 analyses per hour. The optimized procedure showed good accuracy and precision, and the method was validated by the analysis of two certified reference materials: Buffalo River Sediment (NIST 2704) and human hair (IAEA 085). A good agreement with the certified values was achieved, with recovery values of 99% and 98% and relative standard deviation close to 2%.

Dielectric barrier discharge-plasma induced vaporization for the determination of thiomersal in vaccines by atomic fluorescence spectrometry

Direct determination of thiomersal in vaccine by atomic fluorescence spectrometry with dielectric barrier discharge (DBD)-plasma induced vaporization was developed. No sample pretreatments other than dilution were needed in the measurement. The evaporation and atomization of thiomersal in vaccine samples was achieved rapidly in one step. The produced mercury vapor was transported to atomic fluorescence spectrometry for analysis. It is a green method that obviates the need of strong oxidization procedure for degradation of thiomersal to inorganic mercury and reduction agents such as sodium tetrahydroborate(III) or tin(II) chloride to generate Hg vapor. The DBD plasma was generated in a quartz tube (i.d. 5 mm and o.d. 6 mm) by a concentric circles model. The operating parameters such as discharge gas type, gas flow rate, and power were optimized. Possible interference by concomitant elements was also investigated. External calibration was achieved with aqueous standards solution of thiomersal. Under the optimal experimental condition, the detection limit was 0.03 μg L−1 for Hg, equivalent to 0.06 μg L−1 of thiomersal in solution. The analytical precision, represented by the relative standard deviation (RSD) from multiple measurements (n = 5) of 5 μg L−1 thiomersal (as Hg), was 2.5%. This method was also applied to measure thiomersal in five commercial vaccines. In the absence of CRMs for thiomersal in vaccine samples, it was validated by comparing with results from inductively coupled plasma mass spectroscopy (ICP-MS), which showed good correlation.

A novel analytical system with a capacitively coupled plasma microtorch and a gold filament microcollector for the determination of total Hg in water by cold vapour atomic emission spectrometry

A novel, miniaturized analytical system of high sensitivity and precision based on atomic emission in a capacitively coupled plasma microtorch (13.56 MHz, 20 W, 200 mL min−1 Ar) equipped with a gold filament microcollector and a microspectrometer was investigated for total Hg determination in water. The method is based on cold vapour generation using SnCl2 and preconcentration on the microcollector followed by thermal desorption for 5 s and emission measurement at 253.652 nm. The microcollector consists of a gold filament of 80 μm diameter, 24 cm length and 43 turns encapsulated in a quartz capillary of 2.5 mm i.d., 4 mm o.d. supplied at 1.5 A. Due to very low thermal inertia, the fast, direct heating of the filament provides a high flow rate of Hg vapour toward plasma and hence sensitivity of the analytical system in the sub-ng L−1 Hg range. The optimal working conditions and figures of merit of the system are presented for Hg determination in drinking and river water, leachate of polyethylene terephthalate bottles and food packaging of biodegradable materials. At concentrations in the range of 0.06–57.4 ng L−1 the precision was 0.9–7.0%. The detection limit in solution was 0.02 ng L−1, while the absolute value was 0.5 pg. Validation of the system was carried out by analyzing a certified groundwater (ERM-CA615) that gave a recovery of 101 ± 2% for the certified concentration of 37.0 ± 0.4 ng L−1. The novel system can be prototyped as a substitute for existing systems based on atomic fluorescence or absorption.

A Simple Approach for Measuring Emission Patterns of Vapor Phase Mercury under Temperature-Controlled Conditions from Soil

In an effort to study the possible effects of climate change on the behavior of atmospheric mercury (Hg), we built a temperature–controlled microchamber system to measure its emission from top soils. To this end, mercury vapour emission rates were investigated in the laboratory using top soil samples collected from an urban area. The emissions of Hg, when measured as a function of soil temperature (from ambient levels up to 70°C at increments of 10°C), showed a positive correlation with rising temperature. According to the continuous analyses of the Hg vapor given off by the identical soil samples, evasion rate diminished noticeably with increasing number of repetitions. The experimental results, if examined in terms of activation energy (Ea), showed highly contrasting patterns between the single and repetitive runs. Although the results of the former exhibited Ea values smaller than the vaporization energy of Hg (i.e., <14 Kcal mol−1), those of the latter increased systematically with increasing number of repetitions. As such, it is proposed that changes in the magnitude of Ea values can be used as a highly sensitive criterion to discriminate the important role of vaporization from other diverse (biotic/abiotic) processes occurring in the soil layer.

XAFS characterization of mercury captured on cupric chloride-impregnated sorbents

X-ray Absorption Near-Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy were used to determine the mercury species formed as a result of the reaction of elemental mercury vapor with cupric chloride impregnated onto activated carbon. Oxidized mercury was found to be a dominant mercury species identified from XAFS analysis. Both XANES and EXAFS spectra indicated that Hg–Cl bonding is present from CuCl2- or HCl-impregnated sorbents, and HgCl2 is most likely to be formed rather than HgCl. In addition, the XAFS analysis results obtained for spent raw activated carbon sorbents prepared in nitrogen or oxygen carrier gas confirmed that chemisorption is likely the dominant adsorption mechanism of Hg(0) vapor. It is currently speculated from results from this and previous studies that if oxidized mercury is formed onto raw activated carbon, Hg(0) vapor is very likely to be bound to sulfur species.

Environmental Release of Mercury from Broken Compact Fluorescent Lamps

This article presents an original study on the releases of mercury (Hg) from broken compact fluorescent lamps (CFLs) under various environmental conditions. Leaching of Hg in liquids was examined using the U.S. Environmental Protection Agency's standard procedures Toxicity Characteristic Leaching Procedure (TCLP) and Synthetic Precipitation Leaching Procedure. Emission of Hg in vapor phase from broken CFLs was detected using an emission monitoring system. CFLs of eight different brands and four different wattages were tested. Results show that Hg contents in CFLs varied significantly with brand. Total amount of Hg contained in each CFL ranged from 0.1 to 3.6 mg, and only <4% of the Hg was TCLP-leachable. Hg concentrations in TCLP extracts of all the new CFLs tested were lower than the regulatory level of 0.2 mg/L and thus the discarded CFLs do not fall into the hazardous waste category. Hg concentrations in Synthetic Precipitation Leaching Procedure extracts were lower than those in the TCLP extracts. Hg vapor emission test revealed that the CFLs continuously release Hg vapor once broken and the release can last over 10 weeks. Total amount of Hg vapor released from a broken CFL can exceeds 1.0 mg, which can cause Hg level in a regular room to exceed the safe human exposure limit under poor ventilation conditions. Results provide useful implications in guiding the handling and treatment of CFLs during and after use.

Stabilization and Solidification of Elemental Mercury for Safe Disposal and/or Long-Term Storage

ABSTRACT A simple and highly effective stabilization/solidification (S/S) technology of elemental mercury using only sulfur with paraffin is introduced. First, elemental mercury is mixed with an excess of sulfur powder and heated to 60 °C for 30 min until elemental mercury is converted into mercuric sulfide (HgS black, metacinnabar) (Step 1). Then, metacinnabar with additional sulfur is poured into liquid paraffin (Step 2). Finally, the mixture is melted at 140 °C and settles to the bottom of the vessel where it cools and solidifies under the layer of liquid paraffin (Step 3). The proposed S/S method with sodium sulfide nonahydrate (Na2S·9H2O) as an additive is also tested for comparison. The average toxicity characteristic leaching procedure test values are 6.72 μg/L (no additive) and 3.18 μg/L (with additive). Theses concentrations are well below the Universal Treatment Standard (25 μg/L). Effective diffusion coefficient evaluated from accelerated leach test and average headspace concentration of Hg vapor after 18 hr are 3.62 × 10−15 cm2/sec, 0.55 mg/m3 (no additive) and 5.86 × 10−13 cm2/sec, 0.25 mg/m3 (with additive). IMPLICATIONS The simple treatment method for elemental mercury by stabilization/solidification introduced in this study will benefit the United Nations Environmental Programme (UNEP) Mercury Programme initiating a project to reduce the global mercury supply and address the safe and long-term storage of mercury. In addition, it will also provide an option and possible solution to the compliance of the recently passed law individually by the European Union and the United States banning the sale of toxic mercury abroad in 2011 and 2013, respectively.

QCM based mercury vapor sensor modified with polypyrrole supported palladium

Polypyrrole (PPy) nanofibers loaded with either palladium (II) acetate (PPy/Pd(O 2CCH 3) 2) or palladium (II) nitrate (PPy/Pd(NO 3) 2) were characterized by TEM, SEM, EDX, Raman and FTIR techniques prior to their use as sensing materials for QCM based mercury vapor sensors. The QCM based sensor loaded with PPy/Pd(O 2CCH 3) 2 nanofibers was observed to perform better over that of the PPy/Pd(NO 3) 2 loaded QCM and is postulated to be due to the lack of Pd salt reduction in the PPy/Pd(O 2CCH 3) 2 matrix. The developed sensor was observed to operate with a response precision of ±5% over a 16 h testing period, and can withstand the presence of different levels of humidity at an operating temperature of 28 °C. Furthermore, the PPy/Pd(O 2CCH 3) 2 based sensor was found to have a response time ( t 90) of ∼45 min towards a Hg vapor concentration of 10.55 mg/m 3 balanced in either dry nitrogen or in streams containing up to 38% RH at near room temperature (28 °C). The stability of the developed sensor over 50 h of continuous testing towards Hg vapor under varying humidity levels indicates that a PPy/Pd(O 2CCH 3) 2 thin layer is a good choice for near room temperature Hg vapor sensing applications.

Hair can be a good biomarker of occupational exposure to mercury vapor: Simulated experiments and field data analysis

Generally, urine mercury (U-Hg) is widely used for assessment of inorganic mercury (I-Hg) exposure in humans. The reliability of scalp hair as an indicator of mercury vapor exposure is contentious. However, significant correlations were found between hair total mercury (T-Hg) and U-Hg and between hair I-Hg and total gaseous mercury (TGM) in ambient air in our previous studies. Simulated experiments were designed to assess the contribution of direct absorption/adsorption of mercury vapor in the hair. Results indicated that the increases of hair T-Hg concentrations were less than 1 μg/g, which was negligible compared with hair T-Hg concentrations in occupationally exposed workers. The β-mercaptoethanol washing can remove 30% of mercury (Hg) in the exposed hair samples. The inhaled Hg constituted the major fraction (97.4%) of I-Hg exposure for the artisanal Hg mining workers. From the simulated experiments and field data analysis, we can conclude that hair I-Hg can be a useful tool for monitoring occupational exposure to Hg vapor.

Mercury exposure and risks from dental amalgam in the US population, post-2000

Dental amalgam is 50% metallic mercury (Hg) by weight and Hg vapour continuously evolves from in-place dental amalgam, causing increased Hg content with increasing amalgam load in urine, faeces, exhaled breath, saliva, blood, and various organs and tissues including the kidney, pituitary gland, liver, and brain. The Hg content also increases with maternal amalgam load in amniotic fluid, placenta, cord blood, meconium, various foetal tissues including liver, kidney and brain, in colostrum and breast milk. Based on 2001 to 2004 population statistics, 181.1 million Americans carry a grand total of 1.46 billion restored teeth. Children as young as 26 months were recorded as having restored teeth. Past dental practice and recently available data indicate that the majority of these restorations are composed of dental amalgam. Employing recent US population-based statistics on body weight and the frequency of dentally restored tooth surfaces, and recent research on the incremental increase in urinary Hg concentration per amalgam-filled tooth surface, estimates of Hg exposure from amalgam fillings were determined for 5 age groups of the US population. Three specific exposure scenarios were considered, each scenario incrementally reducing the number of tooth surfaces assumed to be restored with amalgam. Based on the least conservative of the scenarios evaluated, it was estimated that some 67.2 million Americans would exceed the Hg dose associated with the reference exposure level (REL) of 0.3 μg/m 3 established by the US Environmental Protection Agency; and 122.3 million Americans would exceed the dose associated with the REL of 0.03 μg/m 3 established by the California Environmental Protection Agency. Exposure estimates are consistent with previous estimates presented by Health Canada in 1995, and amount to 0.2 to 0.4 μg/day per amalgam-filled tooth surface, or 0.5 to 1 μg/day/amalgam-filled tooth, depending on age and other factors.

Characterization of a marine-isolated mercury-resistant Pseudomonas putida strain SP1 and its potential application in marine mercury reduction

The Pseudomonas putida strain SP1 was isolated from marine environment and was found to be resistant to 280 μM HgCl₂. SP1 was also highly resistant to other metals, including CdCl₂, CoCl₂, CrCl₃, CuCl₂, PbCl₂, and ZnSO₄, and the antibiotics ampicillin (Ap), kanamycin (Kn), chloramphenicol (Cm), and tetracycline (Tc). mer operon, possessed by most mercury-resistant bacteria, and other diverse types of resistant determinants were all located on the bacterial chromosome. Cold vapor atomic absorption spectrometry and a volatilization test indicated that the isolated P. putida SP1 was able to volatilize almost 100% of the total mercury it was exposed to and could potentially be used for bioremediation in marine environments. The optimal pH for the growth of P. putida SP1 in the presence of HgCl₂ and the removal of HgCl₂ by P. putida SP1 was between 8.0 and 9.0, whereas the optimal pH for the expression of merA, the mercuric reductase enzyme in mer operon that reduces reactive Hg²⁺ to volatile and relatively inert monoatomic Hg⁰ vapor, was around 5.0. LD₅₀ of P. putida SP1 to flounder and turbot was 1.5 × 10⁹ CFU. Biofilm developed by P. putida SP1 was 1- to 3-fold lower than biofilm developed by an aquatic pathogen Pseudomonas fluorescens TSS. The results of this study indicate that P. putida SP1 is a low virulence strain that can potentially be applied in the bioremediation of HgCl₂ contamination over a broad range of pH.

Comparative toxicology of mercurials in Caenorhabditis elegans

Mercury (Hg) is a toxic metal that can exist in multiple chemical species. Humans are commonly exposed to methylmercury and Hg vapor, which are converted to mercuric species in the body. Despite years of research, little information exists on the similarities and differences in the mechanisms of Hg toxicity. The relative toxicity of mercuric chloride (HgCl(2)) and methylmercury chloride (MeHgCl) in Caenorhabditis elegans was determined in assays that measured growth, feeding, reproduction, and locomotion. The effect of HgCl(2) and MeHgCl on the expression of several archetypal stress-response genes was also determined. There was no significant difference between the EC50s of the two mercurials in terms of C. elegans growth. However, MeHgCl was more toxic to C. elegans than HgCl(2) when assessing feeding, movement, and reproduction, all of which require proper neuromuscular activity. Methylmercury chloride exposure resulted in increased steady-state levels of the stress response genes at lower concentrations than HgCl(2). In general, MeHgCl was more toxic to C. elegans than HgCl(2), particularly when assaying behaviors that require neuromuscular function.

Creating gold nanoprisms directly on quartz crystal microbalance electrodes for mercuryvapor sensing

A novel electrochemical route is used to form highly {111}-oriented and size-controlled Aunanoprisms directly onto the electrodes of quartz crystal microbalances (QCMs) which aresubsequently used as mercury vapor sensors. The Au nanoprism loaded QCM sensorsexhibited excellent response–concentration linearity with a response enhancement of up to ∼ 800% over a non-modified sensor at an operating temperature of28 °C. The increased surface area and atomic-scale features (step/defect sites) introduced duringthe growth of nanoprisms are thought to play a significant role in enhancing thesensing properties of the Au nanoprisms toward Hg vapor. The sensors are shownto have excellent Hg sensing capabilities in the concentration range of 0.123–1.27 ppmv (1.02–10.55 mg m − 3), with a detectionlimit of 2.4 ppbv (0.02 mg m − 3) toward Hg vaporwhen operating at 28 °C, and 17 ppbv (0.15 mg m − 3)at 89 °C, making them potentially useful for air monitoring applications or for monitoring theefficiency of Hg emission control systems in industries such as mining and wasteincineration. The developed sensors exhibited excellent reversible behavior (sensorrecovery) within 1 h periods, and crucially were also observed to have high selectivitytoward Hg vapor in the presence of ethanol, ammonia and humidity, and excellentlong-term stability over a 33 day operating period.

Neurobehavioral effects of combined prenatal exposure to low-level mercury vapor and methylmercury

We evaluated the effects of prenatal exposure to low-level mercury (Hg(0)) or methylmercury (MeHg) as well as combined exposure (Hg(0) + MeHg exposure) on the neurobehavioral function of mice. The Hg(0) exposure group was exposed to Hg(0) at a mean concentration of 0.030 mg/m(3) for 6 hr/day during gestation period. The MeHg exposure was supplied with food containing 5 ppm of MeHg from gestational day 1 to postnatal day 10. The combined exposure group was exposed to both Hg(0) vapor and MeHg according to above described procedure. After delivery, when their offspring reached the age of 8 weeks, behavioral analysis was performed. Open field (OPF) tests of the offspring showed an increase and decrease in voluntary activity in male and female mice, respectively, in the MeHg exposure group. In addition, the rate of central entries was significantly higher in this group than in the control group. The results of OPF tests in the Hg(0) + MeHg exposure group were similar to those in the MeHg exposure group in both males and females. The results in the Hg(0) exposure group did not significantly differ from those in the control group in males or females. Passive avoidance response (PA) tests revealed no significant differences in avoidance latency in the retention trial between the Hg(0), MeHg, or Hg(0) + MeHg exposure group and the control group in males or females. Morris water maze tests showed a delay in the latency to reach the platform in the MeHg and Hg(0) + MeHg exposure groups compared with the control group in males but no significant differences between the Hg(0), MeHg, or Hg(0) + MeHg exposure group and the control group in females. The results of OPF tests revealed only slight effects of prenatal low-level Hg(0) exposure (0.03 mg/m(3)), close to the no-observable-effect level (NOEL) stated by the WHO (0.025 mg/m(3)), on the subsequent neurobehavioral function. However, prenatal exposure to 5 ppm of MeHg affected exploratory activity in the OPF test, and, in particular, male mice were highly sensitive to MeHg. The MeHg and Hg(0) + MeHg exposure groups showed similar neurobehavioral effects. Concerning the effects of prenatal mercury exposure under the conditions of this study, the effects of MeHg exposure may be more marked than those of Hg(0) exposure.

Photoluminescence properties and energy-transfer of thermal-stable Ce 3+, Mn 2+-codoped barium strontium lithium silicate red phosphors

A series of thermal-stable Ce 3+, Mn 2+-codoped barium strontium lithium silicate (BSLS) phosphors was synthesized by a high-temperature solid-state reaction. The XRD patterns of this phosphor seem to be a new phase that has not been reported before. BSLS:Ce 3+, Mn 2+ showed two emission bands under 365 nm excitation: one observed at 421 nm was attributed to Ce 3+ emission, and the other found in red region was assigned to Mn 2+ emission through Ce 3 +–Mn 2+ efficient energy transfer. The Mn 2+ emission shifted red along with the replacement of barium by strontium, which was due to the change of crystal field. A composition-optimized phosphor, BSLS:0.10Ce 3+, 0.05Mn 2+ (Ba = 65), exhibited strong and broad red-emitting and supreme thermal stability. The results suggest that this phosphor is suitable as a red component for NUV LED or high pressure Hg vapor (HPMV) lamp.

Seasonal and diel patterns of total gaseous mercury concentration in the atmosphere of the Central Valley of Costa Rica

Abstract Monitoring of Hg in the atmosphere near volcanoes is limited with no previous data for Costa Rica. Seasonal and daily patterns of total gaseous mercury (TGM) were observed at the main sampling location at the Universidad Nacional, Heredia, Costa Rica. The area (lat. 10.000230 long. −84.109499) is located in the Central Valley of Costa Rica and is 27 km SE of the Poas volcano (lat. 10.199486 long. −84.231388). Measurements were made from May 2008 to May 2009 at this location with some additional values obtained at other sites near the Poas volcano including San Luis and Grecia as well as near, Turrialba and Irazu volcanoes. Total gaseous Hg was determined in samples collected at a height of 2 m using the Tekran 2537A (Tekran Inc.) gas-phase Hg vapor analyzer. Meteorological data (temperature, relative humidity, wind speed, wind direction, radiation and precipitation) were obtained from the airport weather station located at Alajuela. Monthly precipitation is typically 85 mm during the dry season (December to April) with winds from the west. The wet season begins in late April and continues to December with monthly rainfall of 328 mm and winds from the NE. The annual mean temperature is 20 °C. With the onset of the wet season TGM increased from typical values near 10 to 905 ng m −3 . Measurements made within 5 km of the Poas volcano were higher than at Heredia at that time. Diel values measured at the university site increased until midday along with temperature and radiation. Relative humidity showed a reciprocal pattern. It was found that high values of TGM were not related to wind velocity or direction. The strong diel pattern increased with sunrise, peaked at midday and was lowest during the night time. It would seem that Hg 0 from the volcano is oxidized and is deposited to the soils during the dry season when winds are blowing from the volcano. With the onset of heavy rains in April, Hg in the soil is reduced and re-volatilized resulting in the high levels in the atmosphere. Values at other volcano sites were provided. The role of atmospheric pollutants such as H 2 O 2 and O 3 should be included in future studies as they may result in oxidation of reduced Hg. The instability in the air masses may also be a factor and local pollution sources may result in high levels that is emitted from the volcanoes of Hg being circulated to ground level as radiation intensity increases.

Human co-exposure to mercury vapor and methylmercury in artisanal mercury mining areas, Guizhou, China

Mercury (Hg) concentrations were determined in human urine and hair samples from Gouxi (GX, n=25) and Laowuchang (LWC, n=18), Tongren, Guizhou, China, to evaluate human exposure from artisanal Hg mining. Geometric means of urinary Hg (U-Hg) were 216 and 560μgg−1 Creatinine (μgg−1 Cr) for artisanal mining workers from GX and LWC, respectively, and clinical symptoms (finger tremor) were observed in three workers. The means of hair Me-Hg concentrations were 4.26μgg−1 (1.87–10.6μgg−1) and 4.55μgg−1 (2.29–9.55μgg−1) for the population in GX and LWC, respectively. Significant relationship was found between estimated rice Me-Hg intake and hair Me-Hg levels (r=0.73, p<0.001). Co-exposure to Hg vapor and Me-Hg may pose health risks for the study population.