[en] Food safety has recently become a prominent public concern in Southern Belgium since excessive levels of Cd and Pb were measured in vegetables grown in private and market gardens, even in areas with slight to moderate soil contaminations. Addition of amendments to soil has been reported in the literature as a cost-effective remediation approach to decrease trace elements bioavailability in contaminated soils.
A multi-year field trial with lettuce and Swiss chard was installed in several market gardens presenting different contamination levels. The effects of two organic amendments, biochar and green waste compost, and lime addition on soil pH, CaCl2 extractible metals and uptake by the plants were studied. In parallel, pots trials were conducted with the same amendments under controlled greenhouse or outdoors conditions.
After one growing season, marked by severe drought conditions, our results showed that longer periods of time were needed for amendments to fully interact with soil. No significant trend in soil evolution was observed during the first months of trial on the field and uptake of Cd by plants was influenced by initial soil pH. The effects of amendments on soil pH under pot experimental conditions were higher than that under field conditions, due to irrigation.
Our study emphasizes the importance of comparing results obtained in pots with field experiments. These should be repeated over longer periods of time in order to monitor the bioavailability of trace elements following the addition of amendments. The importance of soil pH in controlling Cd mobility and trace elements uptake by plants is widely recognized. However, despite a neutral soil in some gardens, the vegetables grown in these gardens still do not comply with EU legislation. Therefore, further studies are still needed to identify remediation strategies for these impacted areas and it may be necessary to consider site-specific remediation solutions.
