Ppm Hg Research Articles

Functionalized sol–gels for mercury(II) separation: a comparison of mesoporous materials prepared with and without surfactant templates

Granular silica gels 1b (7.0 mol% ligand) and 1c (17.0 mol% ligand) containing different amounts of tethered mercapto ligand HS(CH 2) 3Si(O–) 3 were prepared in one step from the co-hydrolysis of HS(CH 2) 3Si(OMe) 3 and Si(OMe) 4. Analyses of 1b revealed that it was mesoporous (pore diameter: ca. 50 Å) with a large surface area (471 m 2/g). In 0.5, 5.0, 50, and 500 ppm Hg 2+ solutions, 1b was found to have Hg 2+ uptake capacities comparable to those of sub-micron mesoporous powders prepared with two different surfactants in the current studies. 1b and 1c removed Hg 2+ ions to be below 5 × 10 −5 ppm (the detection limit of atomic absorption) from 0.368 and 50 ppm solutions, respectively. The granular 1b and 1c are easier to prepare and handle, and may offer an alternative to sub-micron powders prepared with surfactants for Hg(II) uptake.

Gestational exposure to methylmercury retards choice in transition in aging rats

Developmental exposure to methylmercury has behavioral effects that extend into adulthood and aging. In this study, methylmercury's prolonged effects on the acquisition of choice and sensitivity to changes in reinforcement rates were studied. Pregnant female rats were exposed to drinking water containing 0, 0.5, or 6.4 ppm Hg as methylmercury, resulting in about 40 and 500 μg/kg/day of mercury intake. Maternal exposure began at least 4 weeks before mating, and continued to postnatal day 16. Then all mercury exposure ended. The behavior of 1.7- and 2.3-year-old offspring was maintained under various concurrent schedules of reinforcement. Thus, one reinforcement schedule maintained left-lever responding and a separate one maintained right-lever responding. The animal could switch (“changeover”) between the two levers at any time. For the first 30 min of a 3-h session, the left and right levers each produced reinforcement at the same rate and left:right response ratios were about 1:1. After 30 min, either the left lever became richer than the right; the right lever became richer than the left, or there was no change. Terminal reinforcer ratios (left:right) used were 9:1, 4:1, 3:1, 1:1, 1:3, 1:4, and 1:9. Response rates on the two levers were tracked continuously through a session. This novel procedure for examining choice, and its acquisition, in a single session, was validated through many comparisons with the extant literature. Both response rates and changeover rates were influenced by the reinforcer ratios for the 1.7-year-olds. Changeover rates were not influenced by reinforcement rate for their 2.3-year-old littermates. For the 1.7-year-olds, there was no effect of methylmercury on changeover or response rates and there was no interaction between exposure and reinforcer ratio. In controls and most methylmercury-exposed rats, response ratios (the measure of choice) approximately matched reinforcer ratios by the end of the single session. This is commonly interpreted as reflecting sensitivity to reinforcement rates. Methylmercury exposure did not affect this measure systematically. The single-session transition from baseline (response ratios about 1:1) to terminal performance was retarded in many methylmercury-exposed rats relative to controls, especially in the older rats. The 2.3-year-old control rats required about 20 to 25 reinforcers to complete one half of the 9:1 and 4:1 transitions, respectively, and exposed rats required about twice as many. Thus, prenatal methylmercury exposure specifically retarded the acquisition of choice in older rats. Methylmercury did not interfere with the final expression of choice. Moreover, two rate measures, lever-press rates and changeover rates, were not systematically affected by methylmercury. The acquisition of choice appears to be very sensitive to subtle consequences of developmental methylmercury exposure. The specific tactics greatly reduced the time required to study behavior in transition from a month in previous reports to a single session here.

Photocatalytic reduction of Hg(II) on two commercial TiO 2 catalysts

The photocatalytic reduction of Hg(II) in air-equilibrated aqueous suspensions of TiO 2 under UV-illumination were studied. The amount of Hg(II) photo-reduced is affected by the pH of solution, the amount of the hole-scavengers, the concentration of chloride, mass of the catalyst, and incident light intensity. Hg(0) was detected during the photocatalytic reduction of Hg(II). The reduction rate of Hg(II) was controlled by the amount of Hg(II) adsorbed onto the TiO 2 powders. About 100 ppm Hg(II) is efficiently removed within 30 min from air-equilibrated solution at pH 4. The separation for Cr(VI)/Hg(II) mixtures can be achieved via UV/TiO 2 photocatalysis. Photocatalytic activities of two commercially available TiO 2 (Degussa P25 and Hombikat UV100) were also compared for different light intensities and catalyst loadings.

Selective Determination of Mercury(II) Ion by Solvent Extraction with N‐(Dithiocarboxy)sarcosine, Diammonium Salt Followed by Ligand Exchange and Reversed‐Phase HPLC with Photometric Detection

Mercury(II) ion was reacted with N‐(dithiocarboxy)sarcosine (DTCS), diammonium salt and then extracted into 1‐hexanol as Hg‐DTCS chelate at pH 1. The organic layers of 15 and 60 µL of 10‐mmol/L hexamethyleneammonium hexamethylenedithiocarbamate (HMA‐HMDC) were injected into a C18 column. The Hg‐DTCS chelate was converted to Hg‐HMDC chelate on the column and detected at 280 nm. The correlation coefficient of the calibration curves obtained with 5 mL of mercury standard was more than 0.999 over the range of 10 ng/mL (ppb) to 10 µg/mL (ppm). The detection limit of Hg ion in 5 mL solution was 1.1 ppb, which corresponded to three times the standard deviation of the blank peak area. Reproducibilities for 5, 0.5, and 0.05 ppm were 1.7%, 1.6%, and 3.3%, respectively (N = 5). Recovery tests were carried out by the HPLC method presented and ICP‐AES with spiked river water samples. The recoveries by the HPLC method for 5 ppm, 0.5 ppm, and 0.05 ppm Hg were 99%, 98%, and 95%, respectively. Effects of foreign ions on the method were investigated with 54 metal ions. Almost all ions did not interfere except for Co(II), Cu(II), Te(IV), and V(V).

Arsenic and Mercury Partitioning in Fly Ash at a Kentucky Power Plant

Coal and fly ash samples were collected from a 500-MW unit at a Kentucky power plant, with the objective of studying the distribution of arsenic, mercury, and other trace elements in fly ash. The coal feed was low-sulfur, high volatile A bituminous central West Virginia coal. The plant produced a relatively low-carbon fly ash. In contrast to power plants with high-mercury feed coal, the fly ashes from the lower-mercury feed coal had low mercury values, generally not exceeding 0.01 ppm Hg. Mercury capture by fly ash varies with both the amount and type of carbon and the collection temperature; mercury capture is more efficient at lower temperatures. Arsenic in the feed coal and in the flue gas is of concern to the utility, because of the potential for catalyst poisoning in the selective catalytic reduction system (in the planning stage at the time of the sampling). Arsenic is captured in the fly ash, increasing in concentration in the more-distant (from the boiler) reaches of the electrostatic precipitator system.

A first insight into mercury distribution and speciation in soils from the Almadén mining district, Spain

Almost no environmental data on mercury distribution and speciation in soils have been published so far for the Almadén mining district (central Spain), despite its huge size and historic importance. The mercury distribution in soils of the district reveals the existence of high and extremely high mercury values (up to ∼9000 ppm Hg). The Hg-thermodesorption curves for soils from a decommissioned metallurgical precinct (Almadenejos) and a phytoremediation site show that mercury occurs in the forms of cinnabar and as mercury bound to organic matter. The TEM-EDX study of the highly contaminated anthrosols from Almadenejos (samples with Hg >5000 ppm) shows the existence of cinnabar particles adsorbed to the surface of chlorite grains. Given the generally pyrite-poor character of the ores, and the presence of carbonates in the host rocks, cinnabar solubilization is limited, which in turn mitigates environmental hazards in the district. The only by-product of cinnabar leaching in the mineral dumps is schuetteite (Hg 3SO 4O 2). Preliminary results on local plants ( Asparagus acutifolius, Dittrichia graveolens, Marrubium vulgare) show that mercury gets incorporated to roots, stems and leaves, with values of up to about 300 ppm Hg.

Unusual rise in mercury-resistant bacteria in coastal environs.

A sharp rise in mercury-resistant bacteria (MRB) capable of tolerating very high concentration of Hg was observed over the last 3-4 years in the coastal environs of India. While none or negligible colony-forming units (CFU) of bacteria were counted on seawater nutrient agar with 0.5 ppm ( 2.5 microM) Hg (II) as HgCl2 until 1997, from 13 to over 75% of the CFU grew on 20 times higher, 50 microM, Hg concentrations from almost every recently examined marine sample. Although exceptionally high counts of MRB (96% of CFU) were recorded from samples collected from the polluted zones off Mumbai, the MRB capable of growth on seawater nutrient agar with 50 microM Hg were quite abundant in most samples collected from many locations with few or no pollution effects. We noticed for the first time the occurrence of aerobic heterotrophic bacterial isolates capable of growth with 250 microM Hg. Such MRB grew with higher concentrations of many other toxic xenobiotics than the Hg sensitive ones. Based on the unusually high populations of viable MRB and some simple experiments, we propose that many marine bacterial species are selected, possibly through acquisition of plasmids and/or transposable elements and modifying Hg, whose concentration, according to recent studies, is on the rise in marine habitats.

The effect of selenium on phenyl mercury toxicity and mercury retention in chicken

Phenylmercuric chloride in a dose 30 ppm of mercury alone and the same dose supplemented with 4 ppm of selenium were fed to chickens of both sexes for 8 weeks. Body weight, mortality rate, pathological changes and the level of mercury in the muscle, liver, and kidneys of the laying hens and cocks were analysed. After the dosage period, the mean body weight of the hens was unaffected, while in the group of cocks fed 30 ppm Hg without selenium addition, a decrease occured. In the group with Se addition no significant change in body weight of either sex was observed. Differences in the affinity of some organs to bind Hg were observed. Moreover, supplementation with 4 ppm of selenium resulted in significantly increased mercury levels in the organs analysed. The highest increase was found in the liver, but there was the same increasing tendency in the muscle and kidneys.

Stabilization/Solidification of High Mercury Wastes with Reactivated Carbon

This paper presents the study results for a novel stabilization/solidification (S/S) process for high mercury wastes (Hg >260 ppm). In this study, a low-cost powder reactivated carbon (PAC) was used to stabilize mercury in contaminated soils. Two types of contaminated soils were used: (1) a mercury-doped pure sand, used as a waste surrogate so as to minimize competitive adsorption by substances in real soils; and (2) a mercury-contaminated soil with about 2,300 ppm Hg from a mercury cell chlor-alkali plant. To improve the mercury adsorption capacity, PAC was impregnated with sulfides. It was found that sulfurized PAC significantly lowered mercury mobility. After stabilization, wastes were subjected to cement solidification. Results of toxicity characteristic leaching procedure and constant pH leaching tests showed that the S/S process successfully immobilized mercury in the treatment matrix. Even under attack from high chloride concentration, little mercury was leached from the matrix. Optimal S/S treatment parameters and treatment process flows are discussed for possible commercial implementation of the process. Based on the experimental data, it can be concluded that the S/S process by reactivated carbon and cement is a robust and effective technology for immobilization treatment of high mercury wastes.

Methylmercury poisoning in common marmosets--MRI findings and peripheral nerve lesions.

Common marmosets were used as model animals for methylmercury (MeHg) poisoning. Six marmosets were given MeHg of 5 ppm Hg in drinking water. The animals were divided into 3 groups of 2 each. The first group was examined for acute symptomatic MeHg poisoning. They were given MeHg for 70 and 90 days, respectively, to manifest severe symptoms. The second group was sacrificed after 38 days of MeHg exposure, when they had acute-subclinical MeHg poisoning. The third group of animals was exposed for 21 days, and then observed for 2.5 years without MeHg exposure. One of them showed typical symptoms of MeHg poisoning after MeHg exposure had ended, but the other one showed only slight symptoms without ataxia. This experiment demonstrated that MeHg causes pathological changes in neural tissues including the peripheral nerves in common marmosets. Furthermore, common marmosets were found to show MeHg-induced pathological changes similar to those in humans in the cerebrum and cerebellum.

Evaluation of changes in methylmercury accumulation in the developing rat brain and its effects: a study with consecutive and moderate dose exposure throughout gestation and lactation periods

Methylmercury (MeHg) can be transferred to the fetus through the placenta and to newborn offspring through breast milk. The higher mercury (Hg) accumulation and susceptibility to toxicity in the fetus than in the mother during the gestation period is well known. However, the contribution of MeHg exposure through breast milk to the brain Hg concentration in offspring is not clear. The purposes of this study were to evaluate the changes in Hg concentration in the brain of offspring and its effects on the developing rat brain, based on consecutive and moderate doses of MeHg throughout gestation and lactation. Adult female rats were given a diet containing 5 ppm Hg (as MeHg) for 8 weeks. The administration level was thought not to cause adverse effects in adult rats. The rats were then mated and subsequently given the same diet throughout gestation and after parturition. The newborn offspring were placed with the mothers until postnatal day 30. The offspring were exposed to MeHg throughout their intrauterine life through the placenta, and during the postnatal developing phase via contaminated milk. Furthermore, they were given the same diet containing MeHg for 2 months following weaning. On the day of parturition, the concentration of Hg in the brains of newborns was 1.4 times higher than that in the mothers. During the suckling period the concentration in the brain of the offspring rapidly declined to 1/5 of that at birth, suggesting that MeHg transport by milk was limited while the brain and body volumes increased rapidly. The concentration increased gradually again after the offspring started the contaminated diet. In behavioral tests performed at 5 and 6 weeks of age, MeHg-exposed rats showed a significant deficit in motor coordination in the rotarod test and a learning disability in the passive avoidance response test, compared with controls. Histopathologically, focal cerebellar dysplasia, including the heterotopic location of Purkinje cells and granule cells, was observed. These abnormalities may be induced by the effect of highly accumulated MeHg in the brain during the gestation period. Thus, although offspring are subjected to consecutive and moderate dose MeHg exposure throughout both the gestation and suckling periods, the risk is especially high during gestation but may decrease during lactation.

Field, laboratory, and X-ray absorption spectroscopic studies of mercury accumulation by water hyacinths.

We have studied water hyacinth (Eichhornia crassipes), a non-native nuisance plant found in the in San Francisco Bay Delta region, for its potential to phytoremediate mercury. Mercury is a common contaminant in San Francisco Bay Area waters because of gold mining activities. In this study, speciation of mercury in hyacinth roots and shoots, rates of mercury uptake by hyacinths in the laboratory, and mercury levels near the Big Break Region in the Delta were studied. In the speciation studies, Hg L3 edge X-ray absorption spectroscopic analysis of Hg model compounds and water hyacinth roots and shoots revealed that Hg was initially bound ionically to oxygen ligands in roots, most likely to carboxylate groups, and was bound covalently to sulfur groups in shoots. In laboratory uptake studies, we found that water hyacinths grown in 1 ppm Hg and one-quarter strength Hoagland's solution accumulated a maximum of 0.20 ppm in shoots and 16.0 ppm in roots, both reaching maximum concentrations after approximately 16 days. Mercury concentrations were found to be 0.26 +/- 0.20 ppm in the water and 0.86 +/- 1.70 ppm in sediment at Big Break. It was proposed that water hyacinths have the potential to phytoremediate mercury in the water at Big Break if the current herbicide treatments are replaced by physical removal.

The suitability of locally produced milk for human consumption: Investigations into quantity, composition and quality profiles of milk at Njoro, Kenya

The basic premise of this paper is that the supply of milk and milk products from the Guildford Dairy Institute (GDI) at Egerton University (EU) in Kenya decreased drastically over the recent past as a result of a nearly six-fold increase in the human population in the area. A drop of 40 % of milk production from the university farms also added more impetus to the study. These developments resulted in a significant shortfall of milk to the GDI factory for processing and for sale to the university and surrounding communities. The results of the study carried out at some randomly selected neighbouring farms as possible source of additional milk to GDI factory showed 3.8 ± 0.5 % BF, 12.6 ± 0.8 % TS, 0.16 ± 0.02 LA, 1.029 ± 0.003 Sp Gr; - 0.55 ± 0.02 Fr Pt; 0.03 ± 0.004 Fg Pb and 0.04 ± 0.003 ppm Hg and sensory results indicated 'Liked Moderately' for all samples, which were within the Kenya Bureau of Standards (KBS) guidelines. Milk was available but the logistics to collect and pay for the milk need to be put in place. The Journal of Food Technology in Africa Volume 6 Number 2 (April-June 2001), pp. 41-43

Assessment of Fe, Zn, Cd, Hg, and Pb in the Jordan and Yarmouk River Sediments in Relation to Their Physicochemical Properties and Sequential Extraction Characterization

Forty-six surface sediment samples taken along the beds of boththe Jordan and Yarmouk Rivers were analysed for Pb, Cd, Zn, Fe andHg by atomic absorption spectrophotometer. Extraction techniqueswere used to establish the association of the total concentrations of Pb, Cd, Zn and Fe in the sediment samples withtheir contents in the exchangeable, carbonate, Fe/Mn oxides, organic and residual fractions.In the sediments of the Jordan River the recorded heavy metalsconcentrations were as follow: 8.1 ppm for Pb, 0.63 ppm for Cd, 20.3 ppm for Zn, 6 ppm for Hg and 1265.6 ppm for Fe; whereas in the sediment of Yarmouk River were 8.4 ppm for Pb, 0.67 ppm for Cd, 26.4 ppm for Zn, 6.2 ppm for Hg and 1370 ppmfor Fe. Pb, Cd, Zn, and Fe concentrations in the sediments ofboth rivers reflect the natural background value in shale, whereas Hg is moderately enriched. I-geo (geo-accumulation index) of metals in the sediments under study indicates thatthey are uncontaminated with Pb, Zn and Fe; contaminated tomoderately contaminated with Cd; and strongly contaminated with Hg. Heavy metal content in the sediments were found to be significantly influenced by different physico-chemical parameters. The effect of these physico-chemical parameters canbe arranged in the following order: clay fraction > organicmatter fractions > carbonate fraction > silt fraction. As sequential extraction procedure shows that the total concentration of the heavy metals are largely bound to the residual phase (retained 79.5% of Pb, 38% of Cd, 54.4% of Zn and 51.6% of Fe in Jordan River Sediments; and 88.6% of Pb, 48.2% of Cd, 37.6% of Zn and 59.5% of Fe in the YarmoukRiver sediments). The following sequence of mobility are suggested: Fe > Cd > Zn > Pb in Jordan River sediments, and Fe > Zn > Cd > Pb. in Yarmouk River sediments.

Statistical optimization of bioluminescence of Photobacterium phosphoreum KCTC2852

In this study, media optimization by statistically designed experiments stimulated an increase in the intensity and stability of bioluminescence of Photobacterium phosphoreum KCTC 2852 during continuous cultivation. The Plackett-Burman design method selected two components (NaCl, yeast extract) among nine components of the seawater complete (SC) medium. The response-surface design method calculated the optimum concentration of NaCl (31.1 g/ l) and yeast extract (5.1 g/ l). In the optimized medium, bioluminescence per cell increased twofold. During continuous cultivation in a stirred tank reactor, bioluminescence decreased rapidly in the SC medium, whereas the optimized medium could maintain bioluminescence for more than 80 h, resulting in an increased bioluminescence. Upon contact with 0.1 ppm Hg 2+, a sharp decrease in bioluminescence was observed, which was reproducible in the measuring chamber. This shows the possibility that P. phosphoreum could be cultivated continuously with enhanced bioluminescence stability and that on-line water toxicity could be monitored continuously.

Automated Microwave Digestion of Certifiable Color Additives for Determination of Mercury by Cold Vapor Atomic Absorption Spectrometry

A procedure using an automated microwave flow digestion technique was developed and validated for the digestion of samples of certifiable color additives before mercury determination by cold vapor atomic absorption spectrometry. Recovery studies were performed by spiking most of the color additives subject to batch certification by the U.S. Food and Drug Administration with inorganic mercury (HgNO3) and with organic mercury (CH3HgCl). Successful recoveries of 72-113% Hg added at the 1 microg/g level were obtained. A method detection limit of 0.2 microg Hg/g was estimated from a Hg-spiked FD&C Yellow No. 6 sample. At the specification level of 1 ppm Hg (1 microg Hg/g), the 95% confidence interval was +/- 0.2 ppm (0.2 microg Hg/g).

Chronic Low-Dose Methylmercury Administration Decreases Mitochondrial Enzyme Activities and Induces Myopathic Changes in Rats.

Methylmercury (MeHg)-induced neurotoxicity includes skeletal muscle symptoms (muscle weakness and wasting, muscle cramp). In this study the effects of long-term low dose exposure to MeHg on skeletal muscle were investigated using rats which had received food containing MeHg (5 ppm Hg; the average intake: 200 μg Hg/kg/day). From six months after the first MeHg administration, total mercury levels in the skeletal muscle remained almost stable at 3.5-5.5 μg/g, about one tenth of the levels achieved in the acute MeHg-intoxicated model receiving 5 mg MeHgCl/kg/day for 12 days. However low-dose, long-term administration of MeHg induces histochemical changes similar to those in the acute model with decreases in mitochondrial electron transport system enzyme activities. The results indicate that even low dose MeHg administration causes disturbances in mitochondrial enzyme activities if the administration continues long term. In rats treated with MeHg for 21 months, mild myopathic changes appeared: variations in fiber size, increases in central nuclei and an increase of acid phosphatase activity. The declining function of the redox system in skeletal muscle during aging may accentuate the effects of chronic MeHg intoxication on skeletal muscle.

Effect of Salinity on the Toxicity of Mercury in Mangrove Clam, Polymesoda erosa (Lightfoot 1786)

The present study reports the effect of salinity on the toxicity of mercury in mangrove clam Polymesoda erosa. The toxic effect was found to be influenced by different salinities and mortality increased with an increase in salinity. The 96 hour LC50 were 0.58, 0.35 and 0.26 ppm Hg in 10, 20 and 30 ppt salinity, respectively at room temperature. The LT50 values also suggested high mortality with increasing Hg concentration. Accumulation of Hg in the tissue of the clam was greater in the gills than in any other parts. The amount of Hg in the tissues was dependent on the concentration in the medium and length of exposure. This behavior of Hg was related to affinity to certain body organs and changing rate of adsorption after methylation and chemical speciation. Accumulation was maximum in higher salinity (30 ppt).

Aging unmasks adverse effects of gestational exposure to methylmercury in rats

The consequences of developmental exposure to methylmercury on behavior in aged animals were investigated. Methylmercury exposure was arranged by placing 0, 0.5 or 6.4 ppm Hg in the drinking water of female rats at least 4 weeks before mating and continuing until post-natal (PN) day 16. Brain Hg concentrations in cohorts of low- and high-dose offspring were 0.5 and 9.1 ppm at birth and 0.04 and 0.52 ppm at weaning (described in another report). Lever pressing of female offspring was maintained under a Multiple Differential Reinforcement of High Rate 9:4 Extinction schedule of food reinforcement (Mult DRH 9:4 EXT). Under the DRH 9:4 schedule, a food reinforcer was delivered when nine responses occurred within 4 s. Under the Extinction schedule, responding had no programmed consequences. No exposure-related differences in reinforcement rate under the DRH schedule or discrimination between the DRH and extinction components were apparent initially. At 950 days of age, the overall response rates of controls had shown a gradual decline over the previous 500 days to about 80% of their beginning levels, but, otherwise, most controls were healthy. A gradual decline in the reinforcement rate began to appear in low- and high-dose rats at about 500 and 800 days of age, respectively. Microanalyses of the nine-response burst maintained by the DRH schedule revealed that the lever-press duration increased, the inter-response time (IRT) was unaffected, and the time between response bursts increased. Overall, the nine-response burst remained intact as a coherent response unit. The increased time between response bursts caused the decline in reinforcement rate. All rats displayed these effects as they aged, but the mercury-exposed rats did so sooner.

Mercury detection in air using a coated piezoelectric sensor

Three different methods to produce standardized vapors of mercury were tested and compared for posterior determination of metal, using a piezoelectric sensor (QCM). The generation techniques employed were: saturation, syringe dilution and permeation tube. Gold-coated piezoelectric crystals, without any substrate, were initially tested as sensor, based on the selective affinity of gold by mercury. Later, using a permeation tube as source of metal, some substances were investigated as possible substrates capable of interaction with mercury vapor. The best material found was a mixture (1 : 1 v/v) of palladium-II chloride solution (saturated in acetone) and tetrahydroxyethylethylenediamine (THEED) 50% v/v in acetone. The analytical curve is linear in the concentration range from 2.0 to 7.0 ppm of Hg. Good linearities ( r = 0.9952 and 0.9979) and sensitivities (102 and 149 Hz/ppm) were found for exposure times of 20 and 40 s, respectively. It was shown that the technique has potential application as a small, rugged, sensible and portable mercury vapor sensor.