Urine and hair was collected from 128 mothers and 129 children, so that the pollutants they contain could be measured. In Belgium, children were recruited in schools from three regions : in two sparsely populated regions in Flanders and Wallonia (around Braken en Ellezelles/Frasnes) and in the densely populated Brussels-Capital Region.
The sparsely populated regions met the selection criteria of the European study, namely < 15000 inhabitants, <295 inhabitant/km², absence of important emission sources and industries, <5% industrial zone and school situated >=500m from main roads. Both rural regions are located 10 to 15 km from each other, 50 to 65 km south west of the capital Brussels. The Brussels-Capital Region was chosen as an urban area because it has more that 150 000 inhabitants and a density of population of at least 5000 inhabitants/km².
Illustration: overview of the number of participants in each region where recruiting took place.