The substrate (22) for vegetation contains material (26) with carbon content converting contaminant-absorbing substances and or contaminant-degradable substances and or contaminants into harmless materials. Micro-organisms (287) are added to,or mixed with, the vegetation-substrate which decompose certain selected contaminants and or convert them into harmless substances. The material is placed as a layer on top of, inside, or underneath the vegetation-substrate and is wood, charcoal or lignite based. The vegetation system contains a drainage and ventilation layer (16) at least 1 centimetre thick. IMAGE
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