The concentration of selenium in the soil is reflected in the plants and the animals that feed on these plants. Reproductive failure as a consequence of selenium deficiency has been demonstrated in a number of animal and agricultural studies. Soil selenium levels differ between countries and local studies in herbivores have demonstrated that the selenium concentration in South African soils is low. Humans obtain selenium through their diet. Studies from the UK have demonstrated that selenium concentrations are highest in foods like Brazil nuts (245 ug/100 g), kidney (146 ug/100 g), crab meat (84 ug/100 g) and liver (42 ug/100 g). Other sources of selenium include bread, cereals, meat, poultry and fish.