Source: M. G. J. Rikken and R. P. G. Van Rijn. 1993. Soil pollution with heavy metals---an inquiry into spatial variation, cost of mapping and the risk evaluation of copper, cadmium, lead and zinc in the floodplains of the Meuse west of Stein, the Netherlands. Doctoraalveldwerkverslag, Dept. of Physical Geography, Utrecht University.