Determination of mercury and methylmercury in hair samples by neutron activation

Mercury and methylmercury in hair samples were determined by neutron activation analysis. Samples were digested in 10M NaOH, and methylmercury was then isolated by solvent extraction with toluene. The isolated methylmercury was then absorbed onto cysteine paper. The dried cysteine paper was activated for six hours in a TRIGA reactor and methylmercury was analysed via 279.2 keV of²⁰³Hg. Methylmercury and total mercury in some standard reference materials were also analysed, and the results were in good agreement with those reported in the literature. Results for hair samples showed that the methylmercury concentration ranged 14–40% of the total mercury. Gas chromatogram showed that methylmercury was only present in the samples analysed. In samples where methylmercury and other organic mercury are presented, the NAA method is good for the determination of the total organic mercury only.     

Concentration levels of total and methylmercury in mussel samples collected along the coasts of Sardinia Island (Italy)

This paper reports the assessment of the total mercury (T-Hg) and methylmercury (MeHg) contamination of mussel samples collected by two sampling campaigns from along the coastline of Sardinia (Italy). T-Hg has been determined by a direct mercury analyser (DMA) whereas MeHg has been determined by gas chromatography-mass spectrometry (GC-MS) after acid extraction, and employs a novel NaBPh₄ derivatization method. The evaluation of the quality of measurements was carried out by analysing candidate certified reference material (CRM) BCR 710, for MeHg and T-Hg, and CRM IAEA-350 for T-Hg. In the analysed samples, the T-Hg concentrations range from 35 to 115 μg kg⁻¹ and from 40 to 830 μg kg⁻¹, for the two sampling campaigns, respectively, whereas the MeHg concentrations range from l5 to 51 μg kg⁻¹ and from 17 to 116 μg kg⁻¹. Consequently, the MeHg/T-Hg ratios range from 0.33 to 0.91 and from 0.14 to 0.98, respectively. Despite the increasing trend of Hg concentration from the first to the second sampling campaign, the T-Hg concentration of all the samples was much below the 0.5 μg g⁻¹ WHO limit, and the MeHg values ranged between 2.2 and 17.2 μg kg⁻¹, not exceeding the 43.5 μg kg⁻¹ tolerable daily residue level calculated for Italy.     

Hollow fiber liquid phase microextraction combined with graphite furnace atomic absorption spectrometry for the determination of methylmercury in human hair and sludge samples

Two methods, based on hollow fiber liquid–liquid–liquid (three phase) microextraction (HF-LLLME) and hollow fiber liquid phase (two phase) microextraction (HF-LPME), have been developed and critically compared for the determination of methylmercury content in human hair and sludge by graphite furnace atomic absorption spectrometry (GFAAS). In HF-LPME, methylmercury was extracted into the organic phase (toluene) prior to its determination by GFAAS, while inorganic mercury remained as a free species in the sample solution. In HF-LLLME, methylmercury was first extracted into the organic phase (toluene) and then into the acceptor phase (4% thiourea in 1 mol L^− 1 HCl) prior to its determination by GFAAS, while inorganic mercury remained in the sample solution. The total mercury was determined by inductively coupled plasma-mass spectrometry (ICP-MS), and the levels of inorganic mercury in both HF-LLLME and HF-LPME were obtained by subtracting methylmercury from total mercury. The factors affecting the microextraction of methylmercury, including organic solvent, extraction time, stirring rate and ionic strength, were investigated and the optimal extraction conditions were established for both HF-LLLPME and HF-LPME. With a consumption of 3.0 mL of the sample solution, the enrichment factors were 204 and 55 for HF-LLLPME and HF-LPME, respectively. The limits of detection (LODs) for methylmercury were 0.1 μg L^− 1 and 0.4 μg L^− 1 (as Hg) with precisions (RSDs (%), c = 5 μg L^− 1 (as Hg), n = 5) of 13% and 11% for HF-LLLPME–GFAAS and HF-LPME–GFAAS, respectively. For ICP-MS determination of total mercury, a limit of detection of 39 ng L^− 1 was obtained. Finally, HF-LLLME–GFAAS was applied to the determination of methylmercury content in human hair and sludge, and the recoveries for the spiked samples were in the range of 99–113%. In order to validate the method, HF-LLLME–GFAAS was also applied to the analysis of a certified reference material of NRCC DORM-2 dogfish muscle, and the determined values were in good agreement with the certified values.     

A new neutron activation technique for simultaneous determination of inorganic and total mercury contents in human hair

A simple method for simultaneous determination of inorganic and total mercury contents in human hair by neutron activation analysis (NAA) has been developed. The method is based on the selective extraction of methylmercury from hair by hydrochloric acid. Thus, the residual phase containing inorganic mercury can be determined by NAA. Further, the methylmercury contents in hair samples are easily calculated by subtracting the inorganic mercury contribution from the total Hg simultaneously given by INAA. Several reference materials of human hair, including IAEA hair RM 085 and 086, Chinese hair RMs GBW 09101 and 07601, were analyzed by this method. Our results show that the method is reliable.     

Mercury content of hair from normal and poisoned persons

Several hundred samples of human head hair were analyzed to establish the range and variation of mercury concentration in “normal” people and in persons ingesting organic mercury compounds. Instrumental neutron activation analysis was used. The 77 keV line of¹⁹⁷Hg was counted on a Ge(Li) detector. The pattern of concentration variation along hair was shown to be a more reliable criterion for hair individualization than average concentration values. The hair mercury contents of “normal” people in uncontaminated areas were 0.1–4 and 1–12 ppm, respectively. People who had ingested a mercury compound but showed no symptoms had hair mercury concentrations of from a few ppm to 300 ppm. Mild symptoms appeared with a 120–600 ppm hair mercury level, moderate with 200–800 ppm, and severe with 400–1600 ppm. There was no correlation with sex or age, except that infants showed more severe symptoms than expected, and people over 55 had mild or no symptoms with hair mercury levels of 1000 ppm and higher.     

Determination of methylmercury and estimation of total mercury in seafood using high performance liquid chromatography (HPLC) and inductively coupled plasma-mass spectrometry (ICP-MS): Method development and validation

A method was developed for determination of methylmercury and estimation of total mercury in seafood. Mercury (Hg) compounds were extracted from 0.5 g edible seafood or 0.2 g lyophilized reference material by adding 50 ml aqueous 1% w/v l-cysteine·HCl·H₂O and heating 120 min at 60 °C in glass vials. Hg compounds in 50 μl of filtered extract were separated by reversed-phase high performance liquid chromatography using a C-18 column and aqueous 0.1% w/v l-cysteine·HCl·H₂O + 0.1% w/v l-cysteine mobile phase at room temperature and were detected by inductively coupled plasma-mass spectrometry at mass-to-charge ratio 202. Total Hg was calculated as the mathematical sum of methyl and inorganic Hg determined in extracts. For seafoods containing 0.055-2.78 mg kg⁻¹ methylmercury and 0.014-0.137 mg kg⁻¹ inorganic Hg, precision of analyses was ≤5% relative standard deviation (R.S.D.) for methylmercury and ≤9% R.S.D. for inorganic Hg. Recovery of added analyte was 94% for methylmercury and 98% for inorganic Hg. Methyl and total Hg results for reference materials agreed with certified values. Limits of quantitation were 0.007 mg kg⁻¹ methylmercury and 0.005 mg kg⁻¹ inorganic Hg in edible seafood and 0.017 mg kg⁻¹ methylmercury and 0.012 mg kg⁻¹ inorganic Hg in lyophilized reference materials. Evaluation of analyte stability demonstrated that l-cysteine both stabilized and de-alkylated methylmercury, depending on holding time and cysteine concentration. Polypropylene adversely affected methylmercury stability. Total Hg results determined by this method were equivalent to results determined independently by cold vapour-atomic absorption spectrometry. Methylmercury was the predominant form of Hg in finfish. Ratios of methylmercury/total Hg determined by this method were 93-98% for finfish and 38-48% for mollusks.     

Determination of Mercury and Selenium in Hair Samples of Brazilian Indian Populations Living in the Amazonic Region by NAA

Biomonitoring of mercury contamination of Brazilian Indian population groups living in the Xingu Park, a reservation situated in the Amazonic region, has revealed very high levels of mercury in hair samples as compared to controls. Total mercury was determined by INAA in most of the tribes living in the Park and methylmercury was determined by CVAAS in samples with total mercury above 10 mg/kg. Due to the fact that selenium seems to protect animals against the toxic effects of methylmercury, it was considered also of interest to determine its concentrations in the hair samples with very high mercury levels. Selenium was determined by INAA via the short-lived radionuclide ⁷⁷mSe (T _1/2 = 17.45 s). The correlations between selenium and mercury concentrations in Brazilian controls and in the Indian population groups are discussed.     

Methylmercury in marine fish from Malaysian waters and its relationship to total mercury content

The study evaluated methylmercury concentrations, the methylmercury to total mercury ratio (%MeHg) and their correlations in ten fish species from different trophic levels. Methylmercury levels in fish studied were in the range of 0.007 to 0.914 µg g^?1 wet wt. Muscle tissue of predatory fish contained significantly (p < 0.05) higher content of methylmercury than non-predatory fish. The methylmercury to total mercury ratio ranged from 49.1% to 87.5%, with the highest ratio in predatory fish. This ratio was always higher in muscle tissue compared to the liver tissues, indicating tissue-specific binding and accumulation of methylmercury in the muscle. All the fish species showed strong positive correlation between methylmercury and total mercury levels (R ²> 0.86). Except for long tail tuna and short-bodied mackerel, all fish species showed lower methylmercury levels and estimated weekly intake as compared to the maximum values established by US FDA (of 0.5 µg g^?1) and by FAO/WHO (1.5 µg kg^?1 bodyweight), respectively. This study showed that the percentage of methylmercury is rather high in fish and fish represents the major source of this toxic mercury form to the local population.     

Assessment of daily dietary intake of Hg and some essential elements in diets of children from the Amazon region

Summary Daily dietary intake of Hg and some essential elements in diets of children from communities in the Jaú National Park, Amazon region, were assessed. Diet samples were analyzed for total Hg content using cold vapor atomic absorption spectrometry and Ca, Fe, K, Na, Se and Zn contents by instrumental neutron activation analysis. The weekly tolerable provisional intake for Hg in the communities studied varied from 13 to 57 mg of Hg per kg of body weight, exceeding the limit of 5 mg ^. kg^-1 set by the WHO. Comparison of the daily dietary intake values to the new Dietary Reference Intakes (4-8 years), showed prevalence of inadequacy.     

The determination of total mercury in biological tissues by a modified potassium permanganate procedure.

A simple cold-tube atomic absorption method with a silver-mercury amalgam trap and potassium permanganate as oxidizing agent is described for the determination of total mercury in tissue homogenates. Results are presented for animals fed inorganic (HgCl₂) and organic (CH₃HgOH) mercury orally at a level of 1 mg Hg kg^?1. Data are presented which compare potassium permanganate oxidation of tissue homogenates with whole tissue analysed by cold-tube atomic absorption after digestion with acid, or by neutron activation. For kidney tissue there is good agreement between all three methods for animals fed inorganic and organic mercury. For liver, however, homogenization produced an average loss of about 50 % of the mercury in rats fed mercury(II) chloride. Factors such as adsorption of mercury on sample container walls, bacterial action on the tissue and inadvertent introduction of reducing agents which could reduce the mercury to its elemental state, are not significant. Despite the loss of mercury in the liver by homogenization, rank ordering of mercury values for potassium permanganate—homogenate versus direct neutron activation analyses was essentially the same.     

Determination of total and methyl mercury in human permanent healthy teeth by electrothermal atomic absorption spectrometry after extraction in organic phase

A simple and sensitive method has been developed for determination of inorganic and methyl mercury in biological samples by ETAAS. For determination of methyl mercury; it was transferred to toluene phase by acid leaching extraction method. For total mercury after digestion of samples; it was extracted to toluene phase by means of the chelating agent diethyldithiocarbamate. Formation of complex between MeHg and diethyldithiocarbamate enhance the MeHg signal and increases the reproducibility. Furthermore, Pd-DDC was used as modifier for both mercury and methyl mercury determinations. The optimization performance was independently carried out by modifying the parameters such as temperature of mineralization, atomization and gas flow rate for methylmercury and inorganic mercury in ETAAS. The limits of detection were 0.15 and 0.12 μg g⁻¹ for methyl mercury and total mercury, respectively. The repeatability of the measurements of whole procedure were 15.8% for methyl mercury and 16.9% for total mercury determination. The accuracy of the method has been investigated by means of spiking different amounts of methylmercury and inorganic mercury to the samples. The recoveries were found within the range of 88-95% for methyl mercury and 85-92% for total mercury. For determination of total mercury, the method was validated by CVAAS. The obtained results by the present procedure were in good agreement with those of the CVAAS. The proposed method was applied for 30 human permanent healthy teeth (without filling) which significant positive correlations were found among number of amalgam filling and total mercury and MeHg.     

Determination of cadmium using radiochemical neutron activation analysis

A method has been developed for the determination of cadmium in samples of food and biological materials using neutron activation analysis with radiochemical separation. The irradiated sample is digested in presence of cadmium carrier, with a nitric-perchloric mixture, evaporated to dryness, dissolved in 6M HCl and placed onto an ion exchange column loaded with Dowex 1-X8 resin in chloride form and conditioned with HCl 6M. The cadmium is retained in the resin. After a washing procedure with several portions of HCl of decreasing concentration, the cadmium is eluted with an ammonia-ammonium chloride buffer. The activity of ^115mIn which is in equilibrium with ¹¹⁵Cd, is measured using a NaI(Tl) well type detector. The method has been evaluated by analyzing certified reference materials with cadmium concentrations covering a range of 0.020 to 200 mg^.kg^-1. The agreement of the results with the certified values is within 95%, which gives an indication of the sensitivity and accuracy of the proposed method.     

Uranium and phosphate behavior in the vadose zone of a fertilized corn field

Phosphate fertilizers contain approximately 200 mg^.kg^-1 of uranium. The uranium and phosphate can move through the vadose zone and reach groundwater. Therefore, the knowledge of the ways in which these two elements are distributed, their partition relationships and their mobility behavior is of great interest. In order to study the latter, suction cup samplers, intended to collect soil water at different depths, were installed in an experimental site in a high plain of Mexico, where corn is cultivated and phosphate fertilizers are systematically applied. It was observed that the vadose zone contains high concentrations of uranium (1-50 mg^.kg^-1) and phosphates (22-33 mg^.kg^-1), which decrease at greater depths. Uranium concentration in the soil water varies between 10 and 3 mg^.l^-1 and phosphates between 1 and 0.3 mg^.l^-1. Their evolution throughout the profile of the vadose zone is determined by the decrease in concentrations, due to the physico-chemical processes involved.     

Gas chromatography–tandem mass spectrometry analysis of 52 monohydroxylated metabolites of polycyclic aromatic hydrocarbons in hairs of rats after controlled exposure

A method based on gas chromatography–tandem mass spectrometry after derivatization with N-tert-butyldimethylsilyl-N-methyltrifluoroacetamide was developed for the analysis of monohydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) in hair. The method focused on 52 target compounds corresponding to two- to six-ring monohydroxylated metabolites of polycyclic aromatic hydrocarbons (PAHs). The limits of quantification ranged from 0.2 to 50 pg mg^?1. The method was then applied to the analysis of hair samples collected from rats exposed to 12 PAHs at 0.01, 0.1, and 1 mg kg^?1, by intraperitoneal injection, for 28 days. The results of this study confirm that these metabolites can be incorporated in hair after intraperitoneal administration of the corresponding parent compound. Only 20 of the 52 metabolites were actually detected in hair samples and corresponded to nine parent PAHs. The mean concentrations of OH-PAHs in rat hair samples exposed to PAHs at 1 mg kg^?1 ranged from 0.6?±?0.2 pg mg^?1 for 8-hydroxybenzo[b]fluoranthene to 6.7?±?1.0 pg mg^?1 for 1-hydroxypyrene. The results also demonstrated that hair pigmentation has no influence on the concentration of most OH-PAHs. This animal experiment confirmed the incorporation of PAH metabolites in hair and demonstrated that the method was sufficiently sensitive to detect low levels of exposure to PAHs. These results confirmed the usefulness of hair analysis in the biomonitoring of human exposure to PAHs.

Analytical approach for routine methylmercury determination in seafood using gas chromatography-atomic fluorescence spectrometry

Two methodologies have been developed for the analysis of mercury species in seafood by capillary gas chromatography coupled to an AFS detector via pyrolysis. The first one is based on the ethylation of both, inorganic and methylmercury species (Method 1), in which clean-up is not necessary because a small amount of sample is required. In the second one, monoalkylated mercury species are extracted into organic phases after forming the corresponding chlorides (Method 2). In this case the elimination of the interfering compounds from the matrix requires a clean-up step, which enables the treatment of higher quantities of sample. Both procedures can be considered complementary because the concentration range applicable for each one of them is different: 0.75-10 μg_Hg g⁻¹, in dry basis for methylmercury (Method 1) and 6-1000 ng_Hg g⁻¹ (Method 2). The range of application for natural samples can be easily selected by a preliminary analysis of total mercury, because most mercury in seafood is present as MeHg. Optimum parameters for both procedures have been evaluated, and the methods were validated with two standard reference materials (BCR-463 and NIST-2977). Finally, the methods have been applied to the analysis of seafood samples. Detection limits of MeHg range from 1.7 to 220 ng_Hg g⁻¹ (dry basis) depending of the methodology selected and the weight of sample. The method can be successfully applied to commercially available seafood samples, and considered for routine analysis.     

Determination of total mercury in nuts at ultratrace level

Total mercury, at μg kg⁻¹ level, was determined in different types of nuts (cashew nut, Brazil nuts, almond, pistachio, peanut, walnut) using a direct mercury analyser after previous sample defatting and by cold vapour atomic fluorescence spectrometry. There is not enough sensitivity in the second approach to determine Hg in previously digested samples due to the strong matrix effect. Mercury levels in 25 edible nut samples from Brazil and Spain were found in the range from 0.6 to 2.7 μg kg⁻¹ by using the pyrolysis of sample after the extraction of the nut fat. The accuracy of the proposed method was confirmed by analysing certified reference materials of Coal Fly Ash-NIST SRM 1633b, Fucus-IAEA 140 and three unpolished Rice Flour NIES-10. The observed results were in good agreement with the certified values. The recoveries of different amounts of mercury added to nut samples ranged from 94 to 101%. RSD values corresponding to three measurements varied between 2.0 and 14% and the limit of detection and quantification of the method were 0.08 and 0.3 μg kg⁻¹, respectively.     

The determination of antimony in nodular cast iron by wavelength-dispersive x-ray fluorescence spectrometry

Antimony is determined in cast irons by wavelength-dispersive x-ray fluorescence spectrometry. Excitation and detection conditions are evaluated for the three most intense x-rays of antimony, i.e., the K_α, L_α and L_β lines. Standard samples were obtained by precise determination of the antimony content of some specimen cast irons by neutron activation analysis. Calibration graphs are linear from 0 to 200 mg kg^?1. The precision of the determination by means of the most sensitive Sb L_α line, using a chromium tube and a 5-min measuring time, ranges from 6% for samples containing 20 mg kg^?1 antimony, to 1% for samples containing 200 mg kg^?1.     

Mercury speciation in hair by headspace injection-gas chromatography-atomic fluorescence spectrometry (methylmercury) and combustion-atomic absorption spectrometry (total Hg)

The speciation of Hg in human hair was carried out with combustion-atomic absorption spectrometry for total Hg (THg) and headspace-gas chromatography-atomic fluorescence spectrometry (HS-GC-AFS) for methylmercury (MMHg).The determination of total Hg in hair was carried out with the AMA analyzer (Advanced Mercury Analyser 254). Accuracy and reproducibility were assessed on a Certified Reference hair sample (IAEA-086 CRM), yielding, respectively, a recovery of 97.5% and a RSD of 3.2%. Analyses of 10 blank measurements resulted in a detection limit of 1.5 ng g⁻¹ of THg for a 20 mg sample of human hair.MMHg concentrations in hair were assessed with HS-GC-AFS in a single analysis step. Either acid or alkaline extraction can be applied because they yielded very similar results on a IAEA-086 CRM: we observed a recovery of 103% and a RSD of 7% with acid extraction and a recovery of 110% and a RSD of 9% with alkaline extraction. Optimization of the headspace vial, injection and GC parameters is described. The detection limit of the MMHg determination in human hair, which amounts to 0.04 ng g⁻¹ for a 20 mg sample, is far below the concentrations observed in natural samples.The number of samples that can be analyzed per hour, respectively, amounts to 8 for THg and 4 for MMHg. Finally, Hg speciation in natural human hair samples was carried out by combining both AMA and HS-GC-AFS analysis methods. THg levels were at the μg g⁻¹, level, with an average MMHg fraction of about 70%.     

Comparison of selenium content in human hair from different individuals in different countries,by76Se(n,γ)77mSe reaction

Samples of hair from 370 subjects were analysed by neutron activation. The samples were taken from residents of nine different countries: Japan, France, Ivory Coast, Brasil, Paraguay, Canary Islands, Papua New Guinea, Italy and New Zealand. The selenium determination was made using the⁷⁶Se(n,)^77mSe reaction.It was found that the average selenium concentration in the hair of Japanese subjects, both those living in Japan and those living in foreign countries was higher (total average: 0.59±0.14 mg/kg) than those of subjects from other countries (total average: 0.42±0.13 mg/kg).Our results from the determination of the selenium concentration in the hair of individuals from different countries show significant differences between different countries, nevertheless, the selenium content in human hair was small amounts. Since this is likely due to differences in diet. This method was able to analyze quickly for many samples.     

Determination of methylmercury and inorganic mercury in water samples by slurry sampling cold vapor atomic absorption spectrometry in a flow injection system after preconcentration on silica C18 modified

A novel method for preconcentration of methylmercury and inorganic mercury from water samples was developed involving the determination of ng l⁻¹ levels of analytes retained on the silica C₁₈ solid sorbent, previous complexation with ammonium pyrrolidine dithiocarbamate (APDC), by slurry sampling cold vapor atomic absorption spectrometry (SS-CVAAS) in a flow injection (FI) system. Several variables were optimized affecting either the retention of both mercury species, such as APDC concentration, silica C₁₈ amount, agitation times, or their determination, including hydrochloric acid concentration in the suspension medium, peristaltic pump speed and argon flow-rate. A Plackett-Burman saturated factorial design permitted to differentiate the influential parameters on the preconcentration efficiency, which were after optimized by the sequential simplex method. The contact time between mercury containing solution and APDC, required to reach an efficient sorption, was decreased from 26 to 3 min by the use of sonication stirring instead of magnetic stirring. The use of 1 mol dm⁻³ hydrochloric acid suspension medium and 0.75% (m/v) sodium borohydride reducing agent permitted the selective determination of methylmercury. The combination of 5 mol dm⁻³ hydrochloric acid and 10⁻⁴% (m/v) sodium borohydride was used for the selective determination of inorganic mercury. The detection limits achieved for methylmercury and inorganic mercury determination under optimum conditions were 0.96 and 0.25 ng l⁻¹, respectively. The reliability of the proposed method for the determination of both mercury species in waters was checked by the analysis of samples spiked with known concentrations of methylmercury and inorganic mercury; quantitative recoveries were obtained.