Dortmund, Universiẗat, Diss., 2001.

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The aim of this thesis is to understand how mining and processing of polymetallic ores in areas Kombat and Berg Aukas of Namibia may affect the geochemistry and behavior of hazardous elements (selenium and molybdenum), especially then their mobility and bioavailability in the soil environment and consequently assess their potential hazardous properties and factors affecting them.

This dissertation thesis deals with uptake, accumulation and transformation of arsenic and selenium in plants growing on soils with different chemico-physical soil properties. The contents of arsenic were investigated in 99 wild plant species, coming from 27 different families and 6 different vegetables growing in arsenic contaminated soils. The results suggest that there are species-specific mechanisms which protects certain plants from the excessive uptake of arsenic from the soil. On the other hand, there are plants using a strategy of accumulation, which theoretically may increase the risk of arsenic entry into the food chain, whether through grazing cattle and wildlife or through consumption of vegetables growing on arsenic contaminated soils. The most prevalent arsenic compounds are AsV and AsIII. Other arsenic compounds occure as minor species. An important finding was detection of arsenobetaine in Plantago lanceolata L. and Carex praecox Schreb .. The contents of selenium were examined in 73 species of wild plants, coming from 29 different families. The results suggest that naturally low levels of selenium in the soil of selected locations along with a low capability of selenium uptake via collected plant species lead to the low content of selenium in plant biomass which may contribute to selenium deficient throughout the food chain. Foliar application of selenate on wild plant communities and on some types of vegetables in our case Brassica oleracea var. italica can have a positive impact on increasing the selenium content in the aboveground biomass of these plants and by extension, increase the selenium content in the human diet. Dominant selenium compounds in the aboveground biomass of the analyzed plants were SeVI and selenomethionine, with variable proportion of other commonly occurring organic selenium compounds, which is mainly affected by plant species.

Aim of this thesis was to evaluate influence of inorganic selenium given, in a form of mineral supplement compound, to cows and their calves in order to supply their organism with selenium and also for the utilitarian traits. These were divided into two groups of six and supplemented with two different forms of selenium: group A was given inorganic sodium selenite, group B was given organic selenomethionine. Cows that were examined before the start of supplementation had average activity GPX in blood samples from group A 847,06 +- 170,77 ukat/l and group B 791,30 +- 91,20 ukat/l and concentration of Se of group A: 136,70 +- 27,97 ug/l and group B 95,77 +- 20,05 ug/l. It was found that cows postpartum had higher activity of GPx by 26% in group A and by 45% in group B. Difference between groups was statistically inconclusive (p < 0,28). Increase in concentration of selenium in blood of cows in group A was 7,5% and in group B 5%. In blood of newborn calves of both groups was not found conclusive difference of GPx (p < 0,43). Concentration of selenium in group calves A 160,18 +- 18,07 ug/l and group B 105,30 +- 24,26 ug/l. Difference in concentration of selenium in blood of cows and calves was statistically conclusive (p < 0,05), but because this difference was conclusive already before the supplement compound was given both inorganically and organically bound selenium, this result cannot be interpreted as conclusive influence of different forms of selenium supplemented. Weight and weight gain of calves were balanced between groups and statistically did not differ (p < 0,39). It can be concluded that both forms of selenium had analogical biological effect on focused parameters.In blood of newborn calves no conclusive difference in GPx was found

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