HEAVY-METAL UPTAKE OF VEGETABLES

In a field experiment lettuce, mangold, seleriac, and carrots were planted on the waste water fields of Freiburg Br. where the soil is contaminated by heavy metals. A control plot was established on a neighbouring field (Ackerland Hardt) which is not contaminated. The aim of the investigation was to test the influence of NPK-fertilization, liming and atmospheric deposition on the heavy metal contents of the plants. Lead contents of the plants were generally low. Due to the higher contents in the soil, vegetables from the waste water field contained more Zn than those from the uncontaminated field. However, Cd-contents on both sites were often at the same high level. NPK-fertilization stimulated plant growth, which reduced the heavy metal contents by maximum 1/3. Additional liming further decreased the heavy metal contents by 20-30%. Atmospheric deposition hardly affected Cd- and Zn-contents, however Pb-contents were strongly influenced. NPK-fertilization and liming are not sufficient to reduce the Cd-contents of lettuce, mangold and seleriac in the waste water field to meet the ZEBS-standards. The increased Cd-contents in the vegetables from the uncontaminated field were primarily caused to sub-optimal growth conditions. Thus for this site for the production of vegetables complying with the standards, a sufficient nutrient supply must be guaranteed. This can be achieved through NPK-fertilization and liming.