Nikolay Panichev

Determination of total mercury in fish and sea products by direct thermal decomposition atomic absorption spectrometry

A Zeeman Mercury analyzer Model RA-915(+) (Lumex, St. Petersburg, Russia), based on the direct thermal evaporation of Hg from solid samples was used for developing a method for the determination of Hg in fish and other seafood. The method does not require any chemical pretreatment of samples. This greatly simplifies the analytical procedure and minimises potential sources of contamination. The limit of detection (3s criteria) and limit of quantification (10 s criteria) for the determination of Hg in wet fish samples with a mass of 250 mg was found to be 0.6 ng g(-1) and 2.0 ng g(-1), respectively. Time taken for the analysis of one sample is about 3 min. The accuracy of the method was confirmed by the analysis of certified reference materials of different types and by comparative analysis of fish samples using the accepted method of cold vapour generation. Excellent correspondence to the certified values was obtained. It was found that the mercury concentration in most fish species purchased from the Tshwane fish market were below the 0.5 mg kg(-1) (500 ng g(-1)), wet weight, recommended by the FAO/WHO. It was also found that the direct thermal decomposition method for the determination of mercury is a more environmentally friendly alternative since it does not generate chemical waste.

Solid phase extraction of trace amount of mercury from natural waters on silver and gold nanoparticles

Silver (Ag) and gold (Au) nanoparticles impregnated in nylon membrane filters have been proposed as a new solid phase for preconcentration of mercury from natural waters. Water samples were treated with KMnO4 to convert all mercury species to inorganic Hg(2+) and this was followed by the reduction of Hg(2+) with NaBH4 to elemental Hg(0). The determination of Hg was carried out by thermal evaporation of mercury from membrane filters using Zeeman mercury analyzer RA-915+ (Lumex, Russia). This process does not involve any additional sample treatment and sharply reduces risk of samples contamination. The limit of detection (LOD) was found to be 0.04 ng (absolute mass). Relative LOD was 0.4 ng L(-1) for 100 mL of water. The method was validated through the analysis of CRM NRCC Tort-2 (Lobster hepatopancreas) and the found value (0.30±0.07 μg g(-1)) was in good agreement with the certified value (0.27±0.06 μg g(-1)). High efficiency of Hg accumulation from aqueous phase to membrane filters can be attributed to a large surface area of nanoparticles.

Speciation of Cr(VI) in environmental samples in the vicinity of the ferrochrome smelter

The impact of ferrochrome smelter on the contamination of its environment with toxic hexavalent chromium, Cr(VI), was assessed by analyzing smelter dusts, soil, grass and tree barks. For the separation of Cr(VI) from Cr(III), solid samples were treated with 0.1M Na(2)CO(3) and filtered through hydrophilic PDVF 0.45 microm filter prior to the determination of Cr(VI) by electrothermal atomic absorption spectrometry (ET-AAS). Ferrochrome smelter dust was found to contain significant levels of Cr(VI), viz. 43.5 microg g(-1) (cyclone dust), 2710 microg g(-1) (fine dust), and 7800 microg g(-1) (slimes dust) which exceeded the maximum acceptable risk concentration (20 microg g(-1)). The concentration of Cr(VI) in environmental samples of grass (3.4+/-0.2), soil (7.7+/-0.2), and tree bark (11.8+/-1.2) collected in the vicinity of the chrome smelter were higher as compared with the same kind of samples collected from uncontaminated area. The results of the investigation show that ferrochrome smelter is a source of environmental pollution with contamination factors of Cr(VI) ranging between 10 and 50.

The leaching of vanadium(V) in soil due to the presence of atmospheric carbon dioxide and ammonia.

The natural leaching of vanadium(V) with CO2 from soil-water in the presence of ammonia, a known precursor to atmospheric aerosols, has been tested by bubbling carbon dioxide through soil suspension with varying amount of ammonia. It was found that the leaching of V(V) is enhanced in the presence of ammonia. From the results of the investigation, it could be concluded that atmospheric CO2 in the presence of ammonia (the only atmospheric gas that increases the pH of soil-water) could naturally leach V(V) from soil. Furthermore, it was also shown that the presence of (NH4)2CO3 in soil could enhance the leaching of toxic V(V) species thereby making it bioavailable for both plants and animals.

Speciation analysis of plants in the determination of V(V) by ETAAS

Vanadium(IV) and vanadium(V) were easily separated from each other in the same plant sample and be determined independently by ETAAS (electrothermal atomic absorption spectrometry). This was achieved by treating the sample with 1M (NH(4))(2)HPO(4) which transfer only insoluble V(V) species into solution leaving V(IV) species in the solid part of the sample solution. V(IV) was then transferred into solution by ashing the precipitates and dissolving them in dilute acid. Statistical evaluations indicate that the sum of the concentrations of V(IV) and V(V) species is the same as the total concentration of vanadium determined by an independent method from the same plant sample at 95% level of confidence. The maximum concentrations for V(V) and total vanadium in plants around the vanadium mine were found to be 24.3 and 350mugg(-1), respectively.

Monitoring mercury in two South African herbaria.

Mercury [Hg] emissions from old plant collections treated with mercuric chloride (HgCl(2)) may present a high health risk for staff working in certain herbaria. The present study evaluated Hg concentrations in ambient air, plant specimens and biological samples from staff working in the Pretoria National Herbarium (PRE) and the H.G.W.J. Schweickerdt Herbarium (PRU), University of Pretoria. Biological samples from a group of 15 people exposed to HgCl(2) in herbaria and a non-exposed control group of five people were studied. Additionally, plant samples from herbarium specimens treated and non-treated with HgCl(2) were analysed. Plant materials treated with HgCl(2) had persistent high concentrations of Hg in the range of 114-432 microg g(-1), whereas untreated materials were in the range of 0.20-0.45 microg g(-1). The HgCl(2)-treated plant specimens induced elevated concentrations of Hg into the herbarium rooms near storage cabinets, where up to 1 microg m(-3) of Hg was measured in the air of both herbaria. However, no significant difference in mean Hg concentrations in hair was found between herbarium workers and members of the control group, 0.46 and 0.64 microg g(-1) respectively (p0.05, Students t-test). For both groups, Hg concentrations were lower than that indicated by the World Health Organization [WHO] for non-exposed adults, namely 2 microg g(-1). The mean concentration of total Hg in urine from the mercury-exposed herbarium group, 2.28 microg g(-1) creatinine, was significantly higher than in the control group, 1.05 microg g(-1) of creatinine. For both populations, the concentrations of Hg in their urine were below the threshold Hg values set by the WHO, i.e., 5 microg g(-1) creatinine. We concluded that there was no strong response by individual herbarium staff from long-term exposure to Hg concentrations in the range of 0.28-1.1 microg m(-3).

Distribution of mercury in the sediments of some freshwater bodies in Ethiopia

Sediment samples were collected from Tinishu Akaki River (TAR), Lake Awassa, and Lake Ziway, Ethiopia for determination of mercury. The air-dried samples were analyzed for mercury with a differential atomic absorption spectrometer after thermal evaporation of bound mercury converting it to its atomic form. Certified reference materials (CRMs) of sediments and soils were used to validate the method. The recovery of mercury from CRMs and sediments was in the range of 95–100%. The limit of detection for the determination of mercury was 50 ng kg−1. The concentration of total mercury in the sediments varied from 3.9 to 110 µg kg−1 for TAR, 14 to 67 µg kg−1 for Lake Awassa, and 17 to 110 µg kg−1 for Lake Ziway. It was found that the total mercury concentrations in all samples were below the United States Environmental Protection Agency guideline of 200 µg kg−1.

Analysis of soil reference materials for vanadium(+5) species by electrothermal atomic absorption spectrometry

Solid Certified Reference Materials (CRMs) with known vanadium(+5) content are currently not commercially available. Because of this, vanadium species have been determined in solid CRMs of soil, viz. CRM023-50, CRM024-50, CRM049-50, SQC001 and SQC0012. These CRMs are certified with only total vanadium content. Vanadium(+5) was extracted from soil reference materials with 0.1M Na(2)CO(3). The quantification of V(+5) was carried out by electrothermal atomic absorption spectrometry (ET-AAS). The concentration of V(+5) in the analyzed CRMs was found to be ranging between 3.60 and 86.0 microg g(-1). It was also found that SQC001 contains approximately 88% of vanadium as V(+5) species. Statistical evaluation of the results of the two methods by paired t-test was in good agreement at 95% level of confidence.