Geographical overview of Se content in the Netherlands. Notice that all four premises with affected foals are indeed located in Se deficient areas. Panel a: Results on top soil (0–20 cm) on 358 locations in forests, agricultural and natural areas, representing total Se content. Panel b: representing “maximum available Se content” (analysis with ICP-MS after 0.43 HNO3 extraction). Mark the important difference between “total” and “maximum available” Se content. The grey circles indicate the locations with Se concentrations exceeding the 95 percentile. Reprinted from Mol et al.