PubMed · 5794003
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Mercury.. https://pubmed.ncbi.nlm.nih.gov/5794003/
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The studies on the analytical procedure for mercury determination in food of plant origin on the level of 5 micrograms/kg, were carried out. For this reason, microwave digestion with HNO3 and cold vapour atomic absorption spectrometry (CVAAS) with tin (II) chloride reduction, were used. Both digestion and determination conditions were experimentally optimized. The procedure was checked using two real food samples: apple juice and preserved carrot with peas both spiked on two levels with mercury. On these results basic statistic parameters that characterized the method as standard deviation, relative standard deviation and recovery, were calculated. The precision was generally better than 10%, and recovery ranged from 96 to 100%. The detection limit of the entire procedure, defined as the mercury concentration corresponding to three times the standard deviation of ten consecutive determinations of blank measurement, was 0.012 microgram/l. Taking into account the amount of a sample and the factor of dilution the detection limit corresponds to 0.3 microgram/kg for 1.0 g, 1.0 microgram/kg for 0.3 g, and 0.15 microgram/l for 2 ml of a sample. Accuracy of the analytical procedure was tested by analysing five certified reference plant materials with the mercury contents ranged from 6 to 280 micrograms/kg. The obtained results were in a good agreement with their certified values. Both analyses of the spiked real samples and certified reference materials allow to suggest that this analytical procedure based on microwave digestion and cold vapour determination using Fully Automated Mercury System is suitable for mercury determination in food products of plant origin on the level of microgram/kg or microgram/l, with a good precision and accuracy.
Metallic mercury has been assumed by several authors as not very reactive and, as a consequence, with little or no toxicity. The toxicity of this element is usually ascribed to alkyl-mercury ions considered to be formed by some microorganisms. In this work, we describe experiments that clearly show that metallic mercury can be easily oxidized by molecular oxygen in aqueous solution in the presence of species such as chloride, which complex Hg(II). The experiments were carried out using metallic mercury in NaCl aqueous solution under 'open air' (temperature and agitation rate maintained constant) and under more controlled conditions (CO2 rate bubbling, i.e. pH = 4.2; air rate bubbling, i.e., O2 constant concentration, temperature, agitation rate). The reactions were monitored spectrophotometricaly at 230 nm (HgCl2-(4)). Significative values of the concentration of Hg(II) in the form of HgCl2-(4) were soon attained in those solutions. For example, in 'open air' conditions, at 25 degrees C and [NaCl] = 30 g/l (0.51 mol/dm3), the maximal concentration of 13 ppm (6.44 x 10(-5) mol/dm3) of Hg(II) in the form of HgCl2-(4) was reached in 120 min; for [NaCl] = 5 g/l at 25 degrees C, (0.085 mol/dm3) the maximal concentration of 0.3 ppm (1.53 x 10(-6) mol/dm3) of Hg(II) in the form of HgCl2-(4) was reached in 10 min. The rate constants, kobs, of the oxidation of the metallic mercury under the studied conditions are pseudo zero-order at 25 degrees C, and under more controlled conditions have ranged from 1.0 x 10(-7) mol/min ([NaCl] = 5 g/l identical to 0.085 mol/dm3) to 20.0 x 10(-7) mol/min ([NaCl] = 300 g/l identical to 5.12 mol/dm3). The rate constant increases with temperature, up to 25 degrees C, from where kobs remains constant up to 40 degrees C. From the analysis of the experimental results it was possible to propose a mechanism of oxidation of metallic mercury by O2 in aqueous solution containing NaCl. This oxidation is proposed as a possible route for the introduction of mercury into biological systems.
Studies were made of the aquatic liverwort Scapania undulata (L.) Dum from streams in the Polish Sudeten Mountains. It was found that this species growing in water with mercury concentrations below the detection limit (10(-3) micrograms/liter) contains from 0.025 to 4.7 mg Hg/kg dry wt. According to the bioassay the lethal concentration of Hg2+ (24-hr LC100) for S. undulata appeared to be 500 or 1000 micrograms/liter, depending on the population the liverworts were chosen from. Exposure to 16 micrograms Hg2+/liter for 14 days may be recognized as harmless for S. undulata. After completion of the experiment S. undulata, treated with 64-512 micrograms Hg2+/liter, accumulated respectively 46-2800 times more mercury than the blank.