Mercury Determination

Laboratory respirometry experiments were conducted on mixtures of soil and oily sludge to estimate biodegradation rates by CO2 production rates and determine optimum conditions for biodegradation of high-strength hydrocarbon waste products. These experiments were used to determine a suitable range of total petroleum hydrocarbon (TPH) concentration for biological treatment and to optimize for nutrient addition and moisture content. CO2 production rates from biological respiration of hydrocarbon-contaminated soil were maximized at concentrations of 3-9% TPH (30,00090,000 mg/kg TPH). CO2 production rates decreased dramatically at concentrations above 9% TPH, indicating that either these concentrations are lethal to microbes present, or this high sludge content inhibits aeration of the soils. Addition of 120 mg/kg nitrogen, 40 mg/kg phosphorous, and 40 mg/kg potassium to the soils resulted in a three fold increase in CO2 production rates. No significant increase in CO2 production was ob...

A liquid-liquid extraction procedure (L-L) based on room temperature ionic liquid (RTIL) was developed for the preconcentration and determination of mercury in different water samples. The analyte was quantitatively extracted with 1-butyl-3-methylimidazolium hexafluorophosphate ([C 4 mim][PF 6 ]) under the form of Hg-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Hg-5-Br-PADAP) complex. A volume of 500 l of 9.0 mol L −1 hydrochloric acid was used to back-extract the analyte from the RTIL phase into an aqueous media prior to its analysis by flow injection-cold vapor atomic absorption spectrometry (FI-CV-AAS). A preconcentration factor of 36 was achieved upon preconcentration of 20 mL of sample. The limit of detection (LOD) obtained under the optimal conditions was 2.3 ng L −1 and the relative standard deviation (RSD) for 10 replicates at 1 g L −1 Hg 2+ was 2.8%, calculated with peaks height. The method was successfully applied to the determination of mercury in river, sea, mineral and tap water samples and a certified reference material (CRM).

Combustion of solid fuels is one of the main sources of mercury in the environment. To reduce the amount of mercury emitted to the atmosphere, it is necessary to modify or optimize old purification technologies or introduce the new ones. Effective reduction of mercury level in the flue gas requires the use of speciation systems for mercury form determination. This paper describes tests and provides comparison of two industrial portable and continuous systems for mercury speciation in the flue gas: Durag HM-1400 TRX with a speciation module and the Portable Continuous Mercury Speciation System based on the SGM-8 mercury speciation set, made by Nippon Instruments Corporation. Additionally, the paper describes a few analytical problems that were encountered during a two-year period of using the systems.

Combustion of solid fuels is one of the main sources of mercury in the environment. To reduce the amount of mercury emitted to the atmosphere, it is necessary to modify or optimize old purification technologies or introduce the new ones. Effective reduction of mercury level in the flue gas requires the use of speciation systems for mercury form determination. This paper describes tests and provides comparison of two industrial portable and continuous systems for mercury speciation in the flue gas: Durag HM-1400 TRX with a speciation module and the Portable Continuous Mercury Speciation System based on the SGM-8 mercury speciation set, made by Nippon Instruments Corporation. Additionally, the paper describes a few analytical problems that were encountered during a two-year period of using the systems.

Biodegradation of spent engine oil (SEO) by bacteria isolated from the rhizosphere of Cajan cajan and Lablab purpureus was investigated. It was with a view to determining most efficient bacterial species that could degrade SEO in phytoremediation studies. Hydrocarbon degrading bacteria were isolated and identified by enrichment culture technique using oil agar supplemented with 0.1% v/v SEO. Total heterotrophic and oil utilizing bacterial count showed the occurrence of large number of bacteria predominantly in the rhizosphere soil, ranging between 54×108 - 144×108 CFU/g and 4×108- 96×108 CFU/g respectively. Percentage of oil utilizing bacteria ranged between 0% (uncontaminated non rhizosphere soil) to 76% (contaminated rhizosphere). Turbidimetrically, five bacterial species namely Pseudomonas putrefacience CR33, Klebsiella pneumonia CR23, Pseudomonas alcaligenes LR14, Klebsiella aerogenes CR21, and Bacillus coagulans CR31 were shown to grow maximally and degraded the oil at the rate...

Spatial characterization of the contamination is a fundamental component of any remediation approach. Compared to conventional investigation methods, the laser-induced fluorescence (LIF) is a faster screening tool and provides the detection of hydrocarbon contamination in real-time. This investigation was conducted at a hydrocarbon-contaminated site in Pennsylvania, US. The presence of light nonaqueous-phase liquids (LNAPL) was detected in 6 of 17 LIF borings, with the reference emitter responses ranging between 45% and 225%. The depth of the response was highly accurate and valuable and provided insight into the spatial distribution of contamination. The results indicated that no substantial amount of LNAPL existed along the LIF borings profile, thus excluding this area as a preferential LNAPL migration pathway. The obtained results contributed to the characterization and remediation of this industrial site.

A novel approach of head-space single-drop micro-extraction applied to the determination of ethanol in wine is presented. For the first time, the syringe of an automated syringe pump was used as an extraction chamber of adaptable size for a volatile analyte. This approach enabled to apply negative pressure during the enrichment step, which favored the evaporation of the analyte. Placing a slowly spinning magnetic stirring bar inside the syringe, effective syringe cleaning as well as mixing of the sample with buffer solution to suppress the interference of acetic acid was achieved. Ethanol determination was based on the reduction of a single drop of 3mmol L(-1) potassium dichromate dissolved in 8mol L(-1) sulfuric acid. The drop was positioned in the syringe inlet in the head-space above the sample with posterior spectrophotometric quantification. The entire procedure was carried out automatically using a simple sequential injection analyzer system. One analysis required less than 5m...

A novel method combining headspace single-drop microextraction with a paper-based colorimetric assay was developed. Headspace single-drop microextraction using a microdrop containing unmodified gold nanoparticles (AuNPs) as both the extractant and the colorimetric probe was used for the sensitive and selective determination of Se(IV). The method relies on the color change of the microdrop solution caused by the adsorption of in situ-generated hydrogen selenide on the surface of AuNPs. Following extraction, the microdrop was spotted onto cellulose paper, and scanometric-assisted digital image analysis was used for selenium quantification. The analytical variables affecting the method sensitivity, including the drop volume, the concentrations of KBH 4 , HCl, and AuNP solutions, and the extraction time, were studied. Under the optimal conditions, a linear correlation between the colorimetric signal and Se(IV) concentration in the range from 15-100 μg L −1 with a limit of quantification of 12 μg L −1 was achieved. The repeatability of the method was studied by the calculation of intraday and interday precision for the standard solutions at concentrations of 20 and 70 μg L-1. The batch-to-batch reproducibility of the AuNPs synthesized under the same conditions was also assessed. The relative standard deviations were less than 7%. The method provided satisfactory results for the determination of selenium in real samples.

Remediation of soils polluted with heavy metals or petroleum hydrocarbons is one of the environmental problems. This research aimed to evaluate the effect of carbon nanotubes, zeolite and AMF on triticale Ni concentration in a soil co-contaminated with diesel fuel and Ni. Treatments consisted of applying multi walled carbon nanotubes (MWCNs) and zeolite at the rates of 0 , 1 and 2 % (W/W) in a Ni-polluted soil (0, 75 and 150 mg Ni/kg soil) which was naturally polluted with diesel fuel under cultivation of triticale plant inoculated with AMF. After 70 days, plants were harvested and soil and plant Ni concentration was measured using atomic absorption spectroscopy (AAS). Soil microbial respiration and degradation of diesel fuel were also measured. Applying 2 % (W/W) zeolite and MWCNs significantly increased the diesel fuel degradation in soil by 12.3% and 14.5 %, respectively, while the plant Ni concentration was decreased by 8.9 % and 13.1%, respectively. Increasing soil pollution with Ni from 0 to 75 mg/kg soil significantly decreased the degradation of diesel fuel in the soil under cultivation of plant inoculated with AMF by 14.4%. In addition, the soil microbial respiration was also decreased by 11.8%. The results of this study showed that application of zeolite and MWCNs had significant effect on increasing diesel fuel degradation in heavy metal polluted soil that is a positive point in environmental studies.

Chronic petroleum discharges resulting from underground storage tank (UST) system failures may continue for months or years, whereas catastrophic releases result from structural failures or overfills that occur over shorter time periods. A forensic analytical framework is useful for distinguishing between chronic and catastrophic releases and identifying responsible parties. However, the forensic program must account for the petroleum type because identifying release modes relies on understanding the chemical evolution of petroleum through time within the context of site conditions. Here we discuss key petroleum components that aid in reconstructing the release and identifying potential responsible parties when subsurface conditions are known.

This study involves the greenhouse assessment of the effect of oil on Chromolaena odorata ability to remove PCB from soil treated with transformer oil co-contaminated with Aroclor 1260. Plants were transplanted into one kilogram of soil contained in 1L pots differently containing 100, 200, and 500 ml of transformer oil (T/O), co-contaminated with 100 ppm of Aroclor. Treatment was done in two microcosm; direct contamination and soil culture method. Measured plant growth parameters showed that C. odorata growth was differently affected by the different concentrations of transformer oil. Inhibition of the oil to plant growth increased with concentration. At the end of six weeks of growth, plants showed a diminished effect in T/O amended soil to the parameters tested. Plants size was increased by 1.4, 0.46 and -1.0 % in direct treatment and 17.01, 6.09 and 1.08 % in soil culture at the 100, 200 and 500 ppm respectively. Untreated control showed 43.07 % increase. Slight PCB recovery was ...

A novel approach of head-space single-drop micro-extraction applied to the determination of ethanol in wine is presented. For the first time, the syringe of an automated syringe pump was used as an extraction chamber of adaptable size for a volatile analyte. This approach enabled to apply negative pressure during the enrichment step, which favored the evaporation of the analyte. Placing a slowly spinning magnetic stirring bar inside the syringe, effective syringe cleaning as well as mixing of the sample with buffer solution to suppress the interference of acetic acid was achieved. Ethanol determination was based on the reduction of a single drop of 3mmol L(-1) potassium dichromate dissolved in 8mol L(-1) sulfuric acid. The drop was positioned in the syringe inlet in the head-space above the sample with posterior spectrophotometric quantification. The entire procedure was carried out automatically using a simple sequential injection analyzer system. One analysis required less than 5m...

Two basic requirements of each individual are sanitation and water supply (Ikhlaq et al., 2014). Some elements are supplied by water but when water is contaminated, it becomes the source of such substances which cause diseases in human beings. Most common diseases caused by polluted water are different kinds of cancer, teeth decay, cardiovascular, reproductive and neurological diseases. It has been observed that the rate of effects of toxic metals is greater in children than adults (Johnson and Hallberg, 2005). Arsenic (As) and its compounds i.e., arsenicals are hazardous to human beings. Anthropogenically, they come in water from ceramic, glassware, metallurgic products, fertilizers, pesticide, petroleum and other industries. Some sources of arsenic are also natural like soil (Tareen et al., 2014). As arsenic belongs to nonessential group of elements, so its exposure for long time results in lungs, skin and bladder cancer (Modal and Suzuki, 2002; Morales et al., 2000). Sources of lead are polluted water, soil and air. Water becomes polluted with lead when it passes through lead solder, lead containing pipes and brass fixtures (Tareen et al., 2014). Lead (Pb) effects on normal functions of circulatory system, kidneys, reproductive and nervous system (Singh et al., 2010; Duruibe et al., 2007; Jarup, 2003). The sources of chromium (Cr) [i.e. Cr(III) and Cr(VI)] and its compounds in air, soil and water are natural as well as anthropogenic. They come in water from sewage and industrial effluents of leather and steel industries. Their compounds also come from procedures like electroplating and pigmentation (Venkateswaran et al., 2007; Nath et al., 2005). It has been shown from several studies that exposure to chromium (VI) compounds for longer time may result in lung cancer, ulcers, liver and kidney damage, convulsions, upset stomach and even death (Barceloux and Barceloux, 1999). Arsenic poisoning is observed in

A trapping technique was developed for the determination of mercury traces in blood serum by graphite furnace Ž. atomic absorption spectrometry GFAAS. The mercury was converted to metallic vapour in a reaction cell by tin chloride solution, swept by nitrogen into a gold-plated graphite tube and subsequently atomized. The influence of four experimental factors on the sensitivity of mercury determination was examined using two level factorial designs. It was found that the solution volume is the most significant parameter.

A simple, rapid and green ion-pair single-drop microextraction procedure followed by attenuated total reflectance-Fourier transform infrared technique has been developed for the analysis of phosphate in water samples. This method is based on the extraction of the phosphate-cetyltrimethylammonium bromide ion-pair by the singledrop extraction procedure. The linear range for calibration plot of phosphate is 1-900 ng mL, with good correlation coefficient (r = 0.998). The limit of detection, limit of quantification, standard deviation and relative standard deviation of six replicate measurements are respectively 0.34 ng mL, 1.12 ng mL, 0.001 and 0.94-3.36%. The significant parameters such as selection of solvent, their volume, ion-pair reagent and their concentration, extraction time, stirring rate, sample pH, extraction temperature and effect of salt concentration are studied and optimized. The present method is successfully applied for the quantification of phosphate in water samples w...

In this work, a novel room temperature ionic liquids 1-butyl-imidazolium di(2-ethylhexyl) phosphate [BIm + ] [D2EHP-] and 1-methyl-imidazolium di(2-ethylhexyl) phosphate [MIm + ][D2EHP-] were synthesized and tested as extractants in the batch removal of mercury (II) from aqueous solution. The influence of contact time, aqueous to organic phase's volume ratio, initial concentration of Hg (II), IL concentration, pH levels, ionic strength, and temperature was evaluated. The extraction equilibrium was established in 30 min for [MIm + ][D2EHP-] and in 15 min for [BIm + ][D2EHP-]. The maximum mercury extraction was obtained at pH 5.81. For the extraction of mercury, [([MIm + ] [D2EHP-]) 5 (HgCl 2)] org , [([MIm + ][D2EHP-]) 5 (HgClOH)] org , [([BIm + ][D2EHP-]) 3/2 (HgCl 2)] org and [([BIm + ][D2EHP-]) 3/2 (HgClOH)] org species were formed. Regarding the ionic strength for [MIm + ][D2EHP-], the results show a significant improvement of the mercury extraction yield (100%) upon the addition of sodium acetate to the aqueous phase in a Na + /Hg 2+ mass ratio ranging from 0.1 to 2.0. The relationship between the percentages of the extracted species and the extraction yield was established by calculations using CHEAQS V. L20.1 software. The results revealed a decrease in the extraction yield of Hg (II) with decreasing proportions of HgCl 2aq from 65.15 to 40.31% and of HgClOH aq from 31.31 to 0.1%, when NaCl was added. The very important optimal sorption capacities for ([BIm + ][D2EHP-]) and ([MIm + ][D2EHP]) were 58.39 mg/g and 93.23 mg/g respectively. With a longer alkyl chain on the imidazolinic ring, the decreasing of extraction yield was observed.

A simple and sensitive method for using electrothermal atomic absorption spectrometry (ET AAS) with Rh as permanent modifier determination of Sb(III) and total Sb after separation and preconcentration by N-benzoyl-N-phenylhydroxylamine (BPHA)-chloroform single drop has been developed. Parameters, such as pyrolysis and atomization temperature, solvent type, pH, BPHA concentration, extraction time, drop size, stirring rate and sample volume were investigated. Under the optimized experimental conditions, the detection limits (3σ) were 8.0 ng L −1 for Sb(III) and 9.2 ng L −1 for total Sb, respectively. The relative standard deviations (R.S.Ds.) were 6.6% for Sb(III) and 7.1% for total Sb (c = 0.2 ng mL −1 , n = 7), respectively. The enrichment factor was 96. The developed method has been applied successfully to the determination of Sb(III) and total Sb in natural water samples.

A novel method for trace inorganic mercury (Hg 2+) and methylmercury (MeHg) speciation was developed utilizing two-step hollow fiber liquid phase microextraction (two-step HF-LPME) procedures with two/three phases combined with electrothermal atomic absorption spectrometry (ETAAS). This allowed for consecutive determination of MeHg and Hg 2+ in water and fish samples. MeHg was firstly extracted into a polypropylene hollow fiber containing toluene by HF(3)-LPME, Na 2 S 2 O 3 was then injected inside the fiber lumen as an acceptor phase to trap the analyte, while Hg 2+ still existed in the aqueous solution. For Hg 2+ determination, HF(2)-LPME procedure was subsequently applied after Hg 2+ was chelated with diethyldithiocarbamate (DDTC) and then Hg 2+-DDTC was extracted using 1-octanol. The key parameters and ETAAS profiles were investigated and optimized. This method was then applied to mercury speciation in several real-world samples and the recoveries of these samples including a standard reference material (SRM-1566b). This led to LODs of 0.14 and 0.06 μg L −1 with 2.3 and 3.7% RSD (n = 6) achieved with enrichment factors of 103 and 95 for Hg 2+ and MeHg, respectively. The developed method was then evaluated and compared to other analytical techniques for mercury determination in water and fish samples.

The risk assessment procedure for identifying the remediation actions which may be adopted at a mercury contaminated site, when the plants are upgraded in the future, is proposed. The potentially active exposure/migration pathways in the future arrangement of the area will be due to Hg contaminated subsoil as a primary source (vapor inhalation and groundwater leaching) and to groundwater as a possible secondary source (transport to the point of compliance). The data of mercury concentration in the soil were acquired through environmental monitoring campaigns, and were processed to establish the three-dimensional distribution of contamination in subsoil, to locate sources and to define their geometrical and chemical characteristics. Speciation tests of mercury in the soil indicated that the most abundant species present were poorly leachable under the site-specific environmental conditions, confirming the coefficient distribution value obtained by the leaching tests. Analytical and numerical fate and transport modeling tools were used to locate digging zones in the contaminated subsoil, so as to reduce the possible groundwater contaminant loading and to avoid the down-gradient exceeding the concentration limit according to regulations. Remediation actions additional to civil works were required, which consists of soil digging within one contamination source, for about 22,200 m 3 of soil. In order to evaluate the Hazard Index (HI) for human receptors due to Hg vapor inhalation, the air concentration of volatile mercury at the exposure point was estimated, based on direct measurements carried out at the site. Simulation gave HI values below 1 for all tested scenarios, suggesting that public health is protected without any additional actions to the already scheduled plant upgrading and digging for groundwater protection.

Partially oxidized graphene flakes (po-Gr) were obtained from graphite electrode by an electrochemical exfoliation method. As-produced po-Gr flakes were dispersed in water with the assistance of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS). The po-Gr flakes and the po-Gr/PEDOT:PSS nanocomposite (po-Gr/PEDOT:PSS) were characterized by Raman spectroscopy, Fourier transform-infrared spectroscopy (FT-IR), UV-Vis spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM). In addition, we demonstrated the potential use of po-Gr/PEDOT:PSS electrode in electrochemical detection of mercury ions (Hg 2+) in water samples. The presence of po-Gr sheets in PEDOT:PSS film greatly enhanced the electrochemical response for Hg 2+. Cyclic voltammetry measurements showed a well-defined Hg 2+ redox peaks with a cathodic peak at 0.23V, and an anodic peak at 0.42V. Using differential pulse stripping voltammetry, detection of Hg 2+ was achieved in the range of 0.2-14 µM (R 2 = 0.991), with a limit of detection of 0.19 µM for Hg 2+. The electrode performed satisfactorily for sensitive and selective detection of Hg 2+ in real samples, and the po-Gr/PEDOT:PSS film remains stable on the electrode surface for repeated use.Therefore, our method is potentially suitable for routine Hg 2+ sensing in environmental water samples.

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O estudo introduz um método para microextração por headspace (HS-SME) de hidreto de estanho em uma microgota aquosa contendo Pd(II) e tributil fosfato (TBP) como uma estratégia de enriquecimento e de modificação de matriz previamente à determinação por ETAAS. O hidreto de estanho foi gerado pela adição de um volume fixo de solução de borohidreto de sódio na amostra. Os efeitos de vários parâmetros, tais como volume da amostra, quantidade de NaBH 4 , Pd(II) e TBP na gota, tipo de ácido e concentração na amostra, tempo de extração e volume da gota, foram cuidadosamente estudados. Possíveis interferências causadas por concomitantes foram testadas e nenhum efeito significativo foi gerado por hidretos formados por outros elementos. Concentrações salinas de até 0,3 mol L-1 foram toleradas pelo método HS-SME, porém aumentos drásticos nos sinais de absorbância e de fundo ocorreram em um método de injeção direta. O HS-SME mostrou-se um método sensível para determinação de estanho com um limite de detecção de 2,09 ng mL-1 e uma precisão melhor do que 4,04% (RSD). O método foi aplicado com sucesso para a determinação de estanho em águas residuais e suspensões. The study introduces a method for headspace solvent microextraction (HS-SME) of tin hydride into an aqueous microdrop containing Pd(II) and tributyl phosphate (TBP) as an enrichment and matrix modification method prior to ETAAS determination. The tin hydride was generated by injection of a fixed volume of sodium tetrahydroborate solution into the sample. Effects of several parameters including sample volume, amount of added NaBH 4 , Pd(II) and TBP concentrations in the drop, acid type and concentration in the sample, extraction time and drop volume were carefully studied. Possible interferences from a number of elements were tested and no significant interference from hydrides of other elements was observed. Salt concentrations up to 0.3 mol L-1 was tolerated by the HS-SME method while it drastically increased the background and signal absorbances in a direct injection method. The HS-SME resulted in a relatively sensitive tin determination method with a detection limit of 2.09 ng mL-1 and a precision better than 4.04% (RSD). The method was successfully applied to the determination of tin in waste water and slurry samples.

Biodegradation of spent engine oil (SEO) by bacteria isolated from the rhizosphere of Cajan cajan and Lablab purpureus was investigated. It was with a view to determining most efficient bacterial species that could degrade SEO in phytoremediation studies. Hydrocarbon degrading bacteria were isolated and identified by enrichment culture technique using oil agar supplemented with 0.1% v/v SEO. Total heterotrophic and oil utilizing bacterial count showed the occurrence of large number of bacteria predominantly in the rhizosphere soil, ranging between 54×108 - 144×108 CFU/g and 4×108- 96×108 CFU/g respectively. Percentage of oil utilizing bacteria ranged between 0% (uncontaminated non rhizosphere soil) to 76% (contaminated rhizosphere). Turbidimetrically, five bacterial species namely Pseudomonas putrefacience CR33, Klebsiella pneumonia CR23, Pseudomonas alcaligenes LR14, Klebsiella aerogenes CR21, and Bacillus coagulans CR31 were shown to grow maximally and degraded the oil at the rate...

Human food chain toxicity has been shown to be influenced by application of inorganic fertilizers. Three samples of commercial inorganic fertilizers marketed in Nigeria were analysed for their heavy metal contents. The fertilizer samples used were N 15 P 15 K 15 (CF1), N 20 P 10 K 10 (CF2) and N 27 P 13 K 13 (CF3). Molybdenum (Mo) levels were the highest and Vanadium (V), Arsenic (As), Mercury (Hg) and Silver (Ag) were not detected by our analytical method. The concentrations of Mo in the CF1 (2, 570.0 mg/kg), CF2 (2,3000.0 mg/kg) and CF3 (1,340.0 mg/kg), were above the maximum acceptable concentration (20mg/kg) while CF1 (0.129 mg/ha/yr) and CF2 (0.115 mg/ha/yr) were above the maximum annual metal addition to soil (0.079 mg/ha/yr), as established by Canadian standard for fertilizers. Only CF1 (5.805 kg/ha) was above long-term cumulative assessment of metal addition to soil (3.57 kg/ha). Other heavy metals detected were Magnesium(Mg), Iron(Fe), Nickel(Ni), Zinc(Zn), Cadmium(Cd), Manganese(Mn), Cupper(Cu), Cobalt(Co), Lead(Pb), Chromium(Cr) and Boron(B). Cd and Pb mean concentrations of the fertilizer samples examined ranged from 2.84 to 11.32 mg/kg and 7.43 to 9.02 mg/kg respectively. Cd followed significantly (p<0.05) with phosphate percentage by weight of the inorganic fertilizers. Though the concentrations of these non-nutrient/toxic metals were below the recommended levels, it is important to encourage manufacturers to indicate their concentrations on the fertilizer labels in view of their health implications.

Neste trabalho, bifenila e óxido de bifenila foram extraídos por microextração em headspace com única gota (HS-SDME) e analisados por cromatografia gasosa com detector de ionização em chama (GC-FID). A extração ocorreu a partir da ponta de uma microsseringa, pela suspensão de uma gota de tolueno, de 3,5 µL, como solvente extrator, contendo acetonaftona como padrão interno. O efeito de diferentes parâmetros como a natureza do solvente de extração, temperaturas da amostra e da microgota, velocidade de agitação, volumes da amostra e da microgota, força iônica e tempo de extração na eficiência da extração dos analitos foram investigados e otimizados. Sob condições ótimas, os limites de detecção (S/N = 3) da bifenila e óxido de bifenila foram 0,40 ± 0,03 e 0,30 ± 0,06 µg mL -1 , respectivamente. Boas linearidades foram obtidas para ambos analitos com os coeficientes de correlação superiores a 0,997 e desvios-padrão relativos (R.S.D.) de 1 a 3%. As recuperações dos analitos a partir das amostras de água enriquecida foram próximas a 100%. In this work, biphenyl and biphenyl oxide were extracted by headspace single drop microextraction (HS-SDME) and analyzed by gas chromatography-flame ionization detection (GC-FID). The extraction occurred from the tip of a microsyringe by suspending a 3.5 µL drop of toluene, as extracting solvent, containing acetonaphton, as internal standard. The effect of different parameters such as the nature of extraction solvent, microdrop and sample temperatures, stirring rate, microdrop and sample volumes, ionic strength and extracting time on the extraction efficiency of the analytes were investigated and optimized. Under optimized conditions the limits of detection (S/N = 3) of biphenyl and biphenyl oxide were 0.40 ± 0.03 and 0.30 ± 0.06 µg mL -1 , respectively. Good linearities were obtained for both analytes with the correlation coefficients higher than 0.997 and the relative standard deviations (R.S.D.) were in the range of 1-3%. The recoveries of analytes from spiked water samples were near to 100%.

Neste trabalho, bifenila e óxido de bifenila foram extraídos por microextração em headspace com única gota (HS-SDME) e analisados por cromatografia gasosa com detector de ionização em chama (GC-FID). A extração ocorreu a partir da ponta de uma microsseringa, pela suspensão de uma gota de tolueno, de 3,5 µL, como solvente extrator, contendo acetonaftona como padrão interno. O efeito de diferentes parâmetros como a natureza do solvente de extração, temperaturas da amostra e da microgota, velocidade de agitação, volumes da amostra e da microgota, força iônica e tempo de extração na eficiência da extração dos analitos foram investigados e otimizados. Sob condições ótimas, os limites de detecção (S/N = 3) da bifenila e óxido de bifenila foram 0,40 ± 0,03 e 0,30 ± 0,06 µg mL-1 , respectivamente. Boas linearidades foram obtidas para ambos analitos com os coeficientes de correlação superiores a 0,997 e desvios-padrão relativos (R.S.D.) de 1 a 3%. As recuperações dos analitos a partir das amostras de água enriquecida foram próximas a 100%. In this work, biphenyl and biphenyl oxide were extracted by headspace single drop microextraction (HS-SDME) and analyzed by gas chromatography-flame ionization detection (GC-FID). The extraction occurred from the tip of a microsyringe by suspending a 3.5 µL drop of toluene, as extracting solvent, containing acetonaphton, as internal standard. The effect of different parameters such as the nature of extraction solvent, microdrop and sample temperatures, stirring rate, microdrop and sample volumes, ionic strength and extracting time on the extraction efficiency of the analytes were investigated and optimized. Under optimized conditions the limits of detection (S/N = 3) of biphenyl and biphenyl oxide were 0.40 ± 0.03 and 0.30 ± 0.06 µg mL-1 , respectively. Good linearities were obtained for both analytes with the correlation coefficients higher than 0.997 and the relative standard deviations (R.S.D.) were in the range of 1-3%. The recoveries of analytes from spiked water samples were near to 100%.

Human food chain toxicity has been shown to be influenced by application of inorganic fertilizers. Three samples of commercial inorganic fertilizers marketed in Nigeria were analysed for their heavy metal contents. The fertilizer samples used were N 15 P 15 K 15 (CF1), N 20 P 10 K 10 (CF2) and N 27 P 13 K 13 (CF3). Molybdenum (Mo) levels were the highest and Vanadium (V), Arsenic (As), Mercury (Hg) and Silver (Ag) were not detected by our analytical method. The concentrations of Mo in the CF1 (2, 570.0 mg/kg), CF2 (2,3000.0 mg/kg) and CF3 (1,340.0 mg/kg), were above the maximum acceptable concentration (20mg/kg) while CF1 (0.129 mg/ha/yr) and CF2 (0.115 mg/ha/yr) were above the maximum annual metal addition to soil (0.079 mg/ha/yr), as established by Canadian standard for fertilizers. Only CF1 (5.805 kg/ha) was above long-term cumulative assessment of metal addition to soil (3.57 kg/ha). Other heavy metals detected were Magnesium(Mg), Iron(Fe), Nickel(Ni), Zinc(Zn), Cadmium(Cd), Man...

Single drop microextraction has become a widespread liquid/liquid microextraction technique owing to its simplicity, high preconcentration factor and low consumption of organic solvents in the extraction due to direct introduction of the very low volume of extract into the analytical system. Crucial features ensuring excellent repeatability of single drop microextraction include: solvent volume, solvent type, sample agitation, salts addition, and pH. The influence of sample quality on the microdrop volume and agitation type was studied. Effect of the sample matrix, such as water, acid content samples (orange juice), sample containing alcohol (plum brandy) and protein content sample (milk), on the microdrop hold-up was also investigated. For water analysis, several organic solvents such as chloroform, dichloromethane, tetrachloromethane, tetrachloroethane and chlorobenzene were tested; last three mentioned were suitable for SDME experiments. For milk samples analysis, chlorobenzene m...

Mercury is one of the most dangerous pollutants. Its presence in living organisms is associated with cancer, birth defects, and other undesirable outcomes [1]. The toxic effects of divalent mercury can be prevented to some extent either by chelating or enhancing antioxidant defense mechanisms. Vitamin E is a lipid soluble antioxidant, which plays an important role in stabilizing the cell membranes by scavenging free radicals [2]. One of the routes of incorporation mercury into the human body is drinking water. Hence, control of mercury is becoming increasingly important, especially in water sources [3]. Mercury is also one of the most poisonous elements for humans and animals [4, 5].

In this research, a microfunnel-assisted headspace liquid-phase microextraction technique has been used in combination with hydride generation to determine arsenic (As) by UV-Vis spectrophotometry. The method is based on the reduction of As to arsine (AsH 3) in acidic media by sodium tetrahydroborate (NaBH 4) followed by its subsequent reaction with silver diethyldithiocarbamate (AgDDC) to give an absorbing complex at 510 nm. The complexing reagent (AgDDC) has been dissolved in a 1:1 (by the volume ratio) mixture of chloroform/chlorobenzene microdroplet and exposed to the generated gaseous arsine via a reversed microfunnel in the headspace of the sample solution. Several operating parameters affecting the performance of the method have been examined and optimized. Acetonitrile solvent has been added to the working samples as a sensitivity enhancement agent. Under the optimized operating conditions, the detection limit has been measured to be 0.2 ng mL −1 (based on 3s b /m criterion, n b =8), and the calibration curve was linear in the range of 0.5-12 ng mL −1. The relative standard deviation for eight replicate measurements was 1.9 %. Also, the effects of several potential interferences have been studied. The accuracy of the method was validated through the analysis of JR-1 geological standard reference material. The method has been successfully applied for the determination of arsenic in raw and spiked soft drink and water samples with the recoveries that ranged from 91 to 106 %.

The presence of free phase petroleum fuels in the subsurface (often called light nonaqueous phase liquids/LNAPL) is a hazard in almost every town and city in the modern world. Leaking underground storage tanks and the resulting contamination and hazards have proven to be a challenge to investigate and remediate. One issue is adequately characterizing the presence and spatial extent of LNAPLs in the subsurface. Experience has shown that conventional soil coring methods and groundwater monitoring methods are fraught with limitations that can lead to significant errors in the estimation of the amount and spatial distribution of LNAPLs in the subsurface. This leads to the development of inaccurate conceptual site models and costly errors in remedial actions. A new direct push logging tool, the optical image profiler (OIP), has been developed to obtain high resolution site characterization data to more accurately define the presence and extent of LNAPLs in unconsolidated materials. The OIP system uses a downhole ultraviolet light-emitting diode to induce fluorescence of fuel LNAPL. A small complimentary metal-oxide-semiconductor camera mounted inside the probe behind a sapphire window captures photographic images of visible range fluorescence as the probe is advanced by direct push methods. In situ images of subsurface fuel fluorescence have not previously been available to the investigator and may further the understanding of LNAPL behavior. The OIP software also provides a log of percent area fluorescence (%AF) based on analysis of the images. An electrical conductivity (EC) dipole on the probe provides a log of bulk formation EC that is often a good indicator of formation lithology. The information presented here explains the basic design and operation of the OIP system in the field. Bench tests confirm the capability of the OIP system to detect a range of petroleum fuels. Field studies with the tandem EC and %AF logs are used to identify LNAPL and its migration pathways in the subsurface. These capabilities can improve the management and remediation of LNAPL-impacted sites and reduce long-term costs associated with cleanup and closure.

Gas-phase limitations during HS-SDME sampling exist. HS-SDME sampling under vacuum removes interfacial gas constraints. Vacuum can improve extraction rates even when analyte uptake by the drop is slow. Vacuum removes 96% of gas phase constraints at the gas-drop interface for organic analytes. Extraction accelerations are discussed as functions of K H and H OA .

Gas-phase limitations during HS-SDME sampling exist. HS-SDME sampling under vacuum removes interfacial gas constraints. Vacuum can improve extraction rates even when analyte uptake by the drop is slow. Vacuum removes 96% of gas phase constraints at the gas-drop interface for organic analytes. Extraction accelerations are discussed as functions of K H and H OA .

A time based injection system used in conjunction with cold vapor generation atomic absorption spectrometry and microwaveaided heating oxidation with potassium persulfate has been developed for the determination of total and inorganic mercury in urine samples. Inorganic mercury is determined after reduction with SnCl 2 while total mercury is determined after an on-line oxidation step with persulfate prior to the reduction step to elemental mercury with SnCl 2. The difference between total and inorganic mercury determines the organomercury content in samples. Experimental parameters were optimized by the univariate optimization method. A linear calibration graph was obtained in the range 0.2±20 mg l À1 of Hg 2 by using injection times from 0 to 12 s of a solution of 20 mg l À1 of either inorganic or organic mercury. The detection limit based on 3' of the blank signal was 0.1 mg Hg l À1 regardless of the mercury species under evaluation. The relative standard deviations for ®ve independent measurements were 1.5% and 1.0% for total and inorganic mercury. The recoveries of different amounts of inorganic and organic mercury added to urine samples ranged from 98.5% to 102.2% and from 97.0% to 103%, respectively. Good agreement with certi®ed values of the total mercury containing urine reference materials were also obtained. With the proposed procedure, 20 urine samples of unexposed subjects from Me Ârida city were measured; and the values lay in the range between 1.8 and 6.7 mg l À1. In addition, the use of a mercury standard solution as the carrier converts the¯ow injection manifold used in this work to an on-line standard addition system which permits a rapid and simple test for monitoring the mercury levels in these samples.

A novel automatic sequential injection (SI) single-drop micro-extraction (SDME) system is proposed as versatile approach for on-line metal preconcentration and/or separation. Coupled to electrothermal atomic absorption spectrometry (ETAAS) the potentials of this SI scheme are demonstrated for trace cadmium determination in water samples. A non-charged complex of cadmium with ammonium diethyldithiophosphate (DDPA) was produced and extracted on-line into a 60 L micro-drop of di-isobutyl ketone (DIBK). The extraction procedure was performed into a newly designed flow-through extraction cell coupled on a sequential injection manifold. As the complex Cd(II)-DDPA flowed continuously around the micro-droplet, the analyte was extracting into the solvent micro-drop. All the critical parameters were optimized and offered good performance characteristics and high preconcentration ratios. For 600 s microextraction time, the enhancement factor was 10 and the sampling frequency was 6 h −1. The detection limit was 0.01 g L −1 and the precision (RSD at 0.1 g L −1 of cadmium) was 3.9%. The proposed method was evaluated by analyzing certified reference material.

A microextraction methodology based on a room temperature ionic liquid (IL) as an ion-pairing reagent for determination of trace Cr(III) and Cr(VI) species is proposed. First, an ion-pair was formed between Cr(VI) species and the hydrophobic IL trihexyl(tetradecyl)phosphonium chloride (CYPHOSâ IL 101). A simple and rapid microextraction procedure named ultrasound-assisted emulsification-microextraction (USAEME) was then developed for Cr species separation and preconcentration. Determination of Cr was performed by direct injection of the organic phase into an electrothermal atomic absorption spectrometer (ETAAS). Parameters that affect the efficiency of the microextraction step were investigated using a Plackett-Burman screening design. Then, the variables showing significant effects on the analytical response were considered within a further central composite design to optimize the experimental conditions. For 10 mL of water sample, the optimized USAEME procedure used 40 mL of tetrachloroethylene as extraction solvent, 5 min of extraction and 5 min of centrifugation at 1700 rpm. Selectivity among Cr species was obtained through pH selection. The concentration of Cr(III) species was calculated from the difference of total Cr and Cr(VI) concentrations. Under optimum conditions, the analyte extraction recovery was higher than 99% and yielded a preconcentration factor of 250. The limit of detection (LOD) obtained was 14.8 ng L À1 and the relative standard deviation for 10 replicate determinations at the 0.05 mg L À1 Cr(VI) level was 3.8%, calculated at peak areas. A correlation coefficient of 0.9983 was achieved. The method was successfully applied for Cr species determination in tap and river water samples.

This paper describes the development of a method for the determination of mercury in honey. Analyte pre-concentration/matrix separation is carried out by cloud point extraction (CPE), while cold vapouroptical emission spectrometry (CV-ICP OES) is used to detect the analyte. A careful analytical work was carried out in order to evaluate precision and accuracy of the method. Mercury was complexed with ammonium diethyldithiophosphate (DDTP) and Triton X-114 was used as surfactant. Parameters such as type and concentration of acid (HCl or HNO 3 + KCl), concentrations of complexant, surfactant and reductant (NaBH 4), dilution of the surfactant-rich phase and the mass of honey were evaluated. Two procedures of sample preparation were investigated: sonication in presence of L-cysteine and acid decomposition in closed vessel. Sonication was very effective for extraction of inorganic mercury (Hg 2+), but it was observed the sample should be decomposed to ensure the quantification of total mercury. Certified dog fish liver, analyte recovery and comparison with an independent technique (cold vapour-inductively coupled plasma mass spectrometry) were used to evaluate the method. Analyte recovery close to 100% was observed when up to 2.0 g of honey were subjected to sonication or up to 1.0 g of honey was decomposed with acid. The enrichment factor (EF) obtained was 13 and the limit of detection (LOD) was 2.2 ng g À1. The Hg concentration in the analyzed samples was lower than the LOD.

Under many oil field sites, shallow soils and groundwater are contaminated with benzene, toluene, ethylbenzene, and xylene compounds. I propose using phytoremediation, specifically Liriodentdro tulipifera , Yellow Poplar, in the cleanup of the site. Phytoremediation processes include enhanced rhizosphere biodegradation, hydraulic control, phytodegradation and phytovolatilization. Plant roots supply nutrients to the microorganisms within the soil, increasing microbial activity, which includes biodegradation of organic contaminants. Root growth and degeneration loosen soils, providing aeration and water transport pathways. Water uptake and transpiration processes move large quantities of water through the contaminated zones, allowing trees to become sinks for contaminants and providing for some hydraulic control. Initial core sampling will provide information on the hydraulic conductivity, thus refining the solute transport models. Phytoremediation processes and groundwater parameters must be understood to refine the remediation effort. Once collected, data will be analyzed to obtain the following:

Under many oil field sites, shallow soils and groundwater are contaminated with benzene, toluene, ethylbenzene, and xylene compounds. I propose using phytoremediation, specifically Liriodentdro tulipifera , Yellow Poplar, in the cleanup of the site. Phytoremediation processes include enhanced rhizosphere biodegradation, hydraulic control, phytodegradation and phytovolatilization. Plant roots supply nutrients to the microorganisms within the soil, increasing microbial activity, which includes biodegradation of organic contaminants. Root growth and degeneration loosen soils, providing aeration and water transport pathways. Water uptake and transpiration processes move large quantities of water through the contaminated zones, allowing trees to become sinks for contaminants and providing for some hydraulic control. Initial core sampling will provide information on the hydraulic conductivity, thus refining the solute transport models. Phytoremediation processes and groundwater parameters must be understood to refine the remediation effort. Once collected, data will be analyzed to obtain the following:

Propõe-se uma nova maneira de gerar vapor de mercúrio em altos valores de pH pela adição de NaOH ou de outra base a uma solução contendo íons de mercúrio, sem utilizar redutor, como NaBH 4 ou SnCl 2. Após dissolução total da amostra em sistema de microondas fechado, empregando HNO 3 e H 2 O 2 , o pH da solução da amostra é elevado para 13 com NaOH. Após 90 min de repouso, o vapor frio é transportado até o plasma por um fluxo de gás argônio. O Hg é determinado em 253,652 nm em um espectrômetro de emissão óptica com plasma indutivamente acoplado com configuração axial. O procedimento foi aplicado a cinco amostras biológicas certificadas obtendose um limite de detecção (3s, n = 10) de 0,04 g g-1 para uma massa da amostra de 0,5 g em um volume final de 50 mL. A calibração foi realizada com soluções padrão aquosas em NaOH 0,1 mol L-1. O procedimento foi eficiente, com recuperações dos valores certificados entre 85 e 113%, demonstrando concordância entre o valor encontrado e o certificado para um nível de 95% de confiança (teste-t). A precisão apresentou resultados aceitáveis com desvios padrão relativos de 7 a 9%. Mercúrio a partir de espécies orgânicas em solução, não foi detectado; somente Hg 2+ em solução produz sinal. O procedimento é novo, simples, pode permitir estudos de especiação e serve para demonstrar liberação de vapor de mercúrio de soluções aquosas em altos valores de pH. A novel approach to the generation of mercury vapor at high pH by the simple addition of NaOH or other base to a solution containing mercury ions is described. Subsequent addition of another reducing agent, such as NaBH 4 or SnCl 2 , is unnecessary. Following total dissolution of sample using HNO 3 and H 2 O 2 in a closed microwave vessel, the pH of the sample solution is increased to 13 by the addition of NaOH. After standing for 90 min in a closed vessel, the Hg 0 is directed to the plasma by a flow of argon. Emission from mercury is measured at 253.652 nm by an axial view inductively coupled plasma optical emission spectrometer (ICP OES). The procedure was applied to five certified biological samples, yielding a detection limit (3s, n = 10) of 0.04 g g-1 based on a nominal sample mass of 0.5 g in a final volume of 50 mL. Calibration was achieved using simple aqueous standard solutions containing 0.1 mol L-1 NaOH. The procedure was efficient, with determined values lying in the range of 85-113 % of the certified values, showing good agreement at the 95% confidence level (t-test). The precision was fit for purpose, with relative standard deviations ranging from 7 to 9%. Organomercury species in solution were not detected; only Hg 2+ in solution produces a signal. This new procedure provides for a simple approach to quantitation (and potentially speciation).

Single drop microextraction (SDME) nowadays earns an increasing attention by scientists due to its simplicity, low cost and the need for only common laboratory equipment. This microextraction technique combines sample cleanup and pre-concentration of analytes in one step. Furthermore, a significant reduction in the amount of organic solvents needed comparing to standard LLE techniques places SDME into the position of environmental friendly extraction techniques. SDME is a straightforward technique in which a micro-drop of solvent is suspended from the tip of a conventional micro-syringe and then it is in a direct contact with a sample solution in which it is immiscible or it could be suspended in the headspace above the sample. The paper overviews developments of the state-of-the-art SDME techniques for the extraction of harmful organic compound and pollutants from environmental, food and biological matrices. Key extraction parameters essential for SDME performance were described an...

A time based injection system used in conjunction with cold vapor generation atomic absorption spectrometry and microwaveaided heating oxidation with potassium persulfate has been developed for the determination of total and inorganic mercury in urine samples. Inorganic mercury is determined after reduction with SnCl 2 while total mercury is determined after an on-line oxidation step with persulfate prior to the reduction step to elemental mercury with SnCl 2. The difference between total and inorganic mercury determines the organomercury content in samples. Experimental parameters were optimized by the univariate optimization method. A linear calibration graph was obtained in the range 0.2±20 mg l À1 of Hg 2 by using injection times from 0 to 12 s of a solution of 20 mg l À1 of either inorganic or organic mercury. The detection limit based on 3' of the blank signal was 0.1 mg Hg l À1 regardless of the mercury species under evaluation. The relative standard deviations for ®ve independent measurements were 1.5% and 1.0% for total and inorganic mercury. The recoveries of different amounts of inorganic and organic mercury added to urine samples ranged from 98.5% to 102.2% and from 97.0% to 103%, respectively. Good agreement with certi®ed values of the total mercury containing urine reference materials were also obtained. With the proposed procedure, 20 urine samples of unexposed subjects from Me Ârida city were measured; and the values lay in the range between 1.8 and 6.7 mg l À1. In addition, the use of a mercury standard solution as the carrier converts the¯ow injection manifold used in this work to an on-line standard addition system which permits a rapid and simple test for monitoring the mercury levels in these samples.

The determination of Hg in gasoline by cold vapor atomic absorption spectrometry, after direct aqueous NaBH 4 reduction in a threecomponent (microemulsion) medium, was investigated. Microemulsions were prepared by mixing gasoline with propan-1-ol and 50% v / v HNO 3 at a 20 : 15 : 1 volume ratio. A long-term homogeneous system was immediately formed this way. After reduction, the Hg vapor generated in a reaction flask was transported to an intermediate K 2 Cr 2 O 7 /H 2 SO 4 trap solution in order to avoid poisoning of the Au-Pt trap by the gasoline vapors. A second reduction step was then conducted and the generated Hg vapor transported to the Au-Pt trap, followed by thermal release of Hg 0 and atomic absorption measurement. Purified N 2 was used as purge and transport gas. After multivariate optimization by central composite design calibration graphs showed coefficients of correlation of 0.9999 and a characteristic mass of 2 ng was obtained. Typical coefficients of variation of 5% and 6% were found for ten consecutive measurements at concentration levels of 1 and 8 Ag L À1 of Hg 2+ , respectively. The limit of detection was 0.10 Ag L À1 (0.14 Ag kg À1) in the original sample. A total measurement cycle took 11 min, permitting duplicate analysis of 3 samples per hour. The results obtained with the proposed procedure in the analysis of commercial gasoline samples were in agreement with those obtained by a comparative procedure. Gasoline samples of the Rio de Janeiro city have shown Hg concentrations below 0.27 Ag L À1 .

The determination of Hg in gasoline by cold vapor atomic absorption spectrometry, after direct aqueous NaBH 4 reduction in a threecomponent (microemulsion) medium, was investigated. Microemulsions were prepared by mixing gasoline with propan-1-ol and 50% v / v HNO 3 at a 20 : 15 : 1 volume ratio. A long-term homogeneous system was immediately formed this way. After reduction, the Hg vapor generated in a reaction flask was transported to an intermediate K 2 Cr 2 O 7 /H 2 SO 4 trap solution in order to avoid poisoning of the Au-Pt trap by the gasoline vapors. A second reduction step was then conducted and the generated Hg vapor transported to the Au-Pt trap, followed by thermal release of Hg 0 and atomic absorption measurement. Purified N 2 was used as purge and transport gas. After multivariate optimization by central composite design calibration graphs showed coefficients of correlation of 0.9999 and a characteristic mass of 2 ng was obtained. Typical coefficients of variation of 5% and 6% were found for ten consecutive measurements at concentration levels of 1 and 8 Ag L À1 of Hg 2+ , respectively. The limit of detection was 0.10 Ag L À1 (0.14 Ag kg À1) in the original sample. A total measurement cycle took 11 min, permitting duplicate analysis of 3 samples per hour. The results obtained with the proposed procedure in the analysis of commercial gasoline samples were in agreement with those obtained by a comparative procedure. Gasoline samples of the Rio de Janeiro city have shown Hg concentrations below 0.27 Ag L À1 .

A rapid ultrasound-assisted extraction procedure for the determination of total mercury, inorganic and methyl mercury (MM) in various environmental matrices (animal tissues, samples of plant origin and coal fly ash) has been developed. The mercury contents were estimated by cold vapour atomic absorption spectrometry (CVAAS). Inorganic mercury (IM) was determined using SnCl 2 as reducing agent whereas total mercury was determined after oxidation of methyl mercury through UV irradiation. Operational parameters such as extractant composition (HNO 3 and thiourea), sonication time and sonication amplitude found to be different for different matrices and were optimized using IAEA-350 (Fish homogenate), IM and MM loaded moss and NIST-1633b (Coal fly ash) to get quantitative extraction of total mercury. The method was further validated through the analysis of additional certified reference materials (RM): NRCC-DORM2 (Dogfish muscle), NRCC-DOLT1 (Dogfish liver) and IAEA-336 (Lichen). Quantitative recovery of total Hg was achieved using mixtures of 5% HNO 3 and 0.02% thiourea, 10% HNO 3 and 0.02% thiourea, 20% HNO 3 and 0.2% thiourea for fish tissues, plant matrices and coal fly ash samples, respectively. The results obtained were in close agreement with certified values with an overall precision in the range of 5-15%. The proposed ultrasound-assisted extraction procedure significantly reduces the time required for sample treatment for the extraction of Hg species. The extracted mercury species are very stable even after 24 h of sonication. Closed microwave digestion was also used for comparison purposes. The proposed method was applied for the determination of Hg in field samples of lichens, mosses, coal fly ash and coal samples