3. Results
3.1. Gradient of soil pollution
Heavy metal wastes were spread especially on the road surface in a layer about 4 cm deep and were constituted of
coal, scoria and zinc ore. Cadmium, copper and lead were also observed. Starting from the blockhouse, the wastes
were distributed on a 4 × 15 m line, and continued for 100 m through a neighbouring field (Fig. 1a). A sharp
gradient of pollution was observed from the road (maximum 19 000 ppm Zn) to the unpolluted area (171–230: normal
values in the north of France) with a 15 m wide intermediate zone (330–500).