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Biomedical subjects

J Uhnák

Publications and source records attributed to J Uhnák.

At least 19 recordsLinked to original sources
PubMed1997

Analytical methods for the determination of organochlorine compounds. Application to environmental samples in the Slovak Republic.

The paper deals with the isolation of chlorinated phenols, benzenes and insecticides from water, soil and vegetable samples. A review of the current procedures is presented. Solid-phase extraction on Empore extraction discs was experimentally evaluated for isolation of the compounds from surface and ground waters. For the isolation of chlorophenols from soil and vegetable samples, a method of simultaneous steam distillation/extraction was elaborated which proved to be also applicable for waste waters and sludges. Chlorinated insecticides and benzenes were extracted from soil and vegetable samples with the Soxhlet procedure. Final determinations were carried out by GC-electron-capture detection. The recoveries of the methods were well over 70%, with relative standard deviations below 14%. Samples of surface and ground waters, soil and vegetables, mostly from the vicinity of chemical and municipal waste dumping sites, were analysed. The highest contamination levels were found for chlorinated phenols in surface water from the vicinity of a former chemical waste dumping place where the concentrations of 2,6-dichlorophenol and pentachlorophenol were 4.3 and 3.9 micrograms l-1, respectively.

Benzene↗
PubMed1996

Chlorinated phenols in human milk.

The paper deals with the contamination of human milk with chlorinated phenols. The average and median concentrations of the chlorophenols investigated ranged from 0.75 to 9.74 micrograms.kg-1 and from being not detectable to 5.62 micrograms.kg-1, respectively, for the different compounds. The highest average and median levels were found for pentachlorophenol and 2,4,5-trichlorophenol. The concentrations determined were below the permissible levels.

Agriculture↗
PubMed1994

Determination of chlorinated phenols and cresols in human urine using solid-phase extraction and gas chromatography.

A method is described for the isolation, derivatization, separation and determination of chlorinated phenols and cresols in urine. After acid hydrolysis, solid-phase extraction on Separcol SI C18 was used. Quantification was based on the internal standard method using 2,6-dibromophenol. Before GC determination the isolated compounds were derivatized with pentafluorobenzyl bromide. The separation of interfering substances followed on a Ekosorb column using elution with dichloromethane-toluene (15:85). The recovery of the method ranged from 72.3 +/- 9.9 to 109.9 +/- 6.3% and the limit of determination varied from 0.0005 to 0.002 micrograms ml-1. Using this method, 52 persons from occupationally and non-occupationally exposed groups were examined for the presence of chlorinated compounds in urine. The levels of chlorinated phenols and cresols were several times higher in the group of occupationally exposed workers, especially for 2,4-dichlorophenol.

Chemical Industry↗
PubMed1994

Polychlorinated phenols in total diet.

A method has been developed for the isolation, separation and determination of chlorinated phenols in total diet. The isolation takes place following acid hydrolysis of the conjugates and is performed by simultaneous extraction and distillation with water vapour and toluene. The isolated chlorophenols are removed by clean-up on a Florisil column using a mixture of 15% dichloromethane in toluene for elution. The separation and determination is carried out by capillary gas chromatography with electron capture detection. The recovery of the method ranged between 70.1 +/- 5 and 96.8 +/- 4.9% for the individual chlorophenols. The determination limits were 0.5 to 1.0 microgram.kg-1. The method was applied in a study aimed at estimating the chlorophenol burden in two population groups (children up to the age of 6 years and students up to the age of 18 years). In two successive years, 80 total diet samples were analysed. Average contents of the individual chlorophenols were from 0.7 to 33.5 micrograms.kg-1 and were higher for the dichlorophenol isomers. The calculated average daily intake ranged from 0.04 to 1.69 micrograms.kg-1 body weight for the individual phenols.

Calibration↗
PubMed1994

Polychlorinated biphenyls in mother milk and adapted cow's milk.

In the present study, 50 samples of mother milk and 20 samples of adapted cow's milk produced for bottle feeding supplied from the lactarium of the Pediatric Hospital were examined for presence of 6 indicator congeners of polychlorinated biphenyls (IUPAC No. 28, 52, 101, 138, 153, and 180). Congeners No. 138, 153, and 180 were predominant in all samples, the highest mean as well as the maximum level was found for No. 138 for both type of samples. The average daily intake based on the sum of indicator congeners was found to be 2.56 micrograms. (kgb.w..day)-1 for mother milk, and 0.85 microgram.(kgb.w..day)-1 for adapted cow's milk.

Adult↗
PubMed1990

[Xenobiotics in the food chain].

The problem of xenobiotics is presented by nitrate, cadmium, DDT and PCBs. Data are given especially for vegetables, supplemented by residue determinations in human breast milk.

Cadmium↗
PubMed1986

Dynamics of hexachlorobenzene residues in the food chain.

Epidemiological studies of food contamination in an area of intensive agriculture for the years 1975-1983 showed that hexachlorobenzene (HCB) was present in all food-chain links, although HCB has not been used in Czechoslovakian agriculture since 1980. Samples of potatoes, wheat, milk fat, eggs, meat and human milk were analysed by gas-liquid chromatography with electron-capture detector. Levels of HCB residues ranged from 0.02 (potatoes) to 2.5 mg/kg (human milk, fat basis). A study of HCB accumulation in eggs from a poultry experiment showed that HCB levels in eggs can reach about twice the level given in feed at 7-10 weeks.

Animals↗
PubMed1983

Criteria for evaluating pesticide residues in children's diet.

By studying the exposure of the human organism to chlorinated pesticide residues, revealed on the basis of ecological studies in the food chain in Czechoslovakia, the authors proved that the exposure was relatively low for the adult population (except for HCB), but with regard to the children's organism the acceptable daily intake (ADI) was in some cases overpassed. As the ADI's in DDT and gamma-HCH would be overstepped 1, 2 times and in HCB 7 times approximately even when observing the standing maximum residual limits (MRL's), the authors arrived at the conclusion that these MRL's should be reduced 15 times. The reasonability of such considerations in Czechoslovakia is supported by the assessment of the actual daily intake of pesticide residues, determined on the basis of both the actually found residue levels by 10 Czechoslovak institutes and in that of the daily consumption of fundamental foodstuffs. The intake in sigma DDT, sigma HCH, gamma-HCH and HCB reached the values of 0.424; 1.376; 1.145 and 3.085 micrograms per 1 kg of body weight a day, respectively.

Child, Preschool↗
PubMed1980

[Ecotoxicological study of chlorinated pesticides].

The authors describe a model for the ecotoxicological investigation of pesticide residues guided by the analysis of various links of the food chain and of human materials. It is pointed to the possibility of studying the dynamics of the exposure to human beings by analyzing gynaecological material (prenatal stage) and samples obtained at necropsy from human beings of varying age (different durations of exposure). The observations of the relative accumulation of hexachlorobenzene, beta-BHC and DDT in butter, human milk and human fat in a region with intensive cultivation revealed a considerble accumulation of hexachlorobenzene which reaches the level of DDT. The conclusion drawn from ecotoxicological studies indicates that a reduction of the tolerances of pesticide residues in raw materials for baby foods is imperative. The analyses of gynaecological material (202 samples of the available content of the uterus and 24 placental and embryonic specimens) permitted to evidence a significant difference between two regions and a specific relationship of the observed substances and their metabolites to the fat-dissolving power of the analyzed materials.

Adipose Tissue↗
PubMed1980

[Dynamics of hexachlorobenzene residues in meat and eggs from chickens].

In a feeding experiment with poultry a more than twofold cumulation of hexachlorobenzene (HCB) in eggs and in meat and a 7.5-fold cumulation in fat, in comparison with the concentration in the feed, have been demonstrated. With the aid of a combined identification by gas chromatography (before and after a conversion into anisole derivatives) and by thin layer chromatography the presence of pentachlorophenol in the liver, in fat and in muscles after feeding the birds with HCB as well as BHC-isomers has been proved. 2,4,6-trichlorophenol and 2,4-dichlorophenol were found by thin layer chromtography (without derivatisation). While 2,4,6-trichlorophenol was found after feeding with HCB only, 1,2,4,5-tetrachlorobenzene has been demonstrated by gas chromatography after feeding with HCB as well as with BHC-isomers.

Adipose Tissue↗