“…This effect was previously reported for mine soils (Madrid, Spain) enriched in the same elements, amended with sheep/horse manure, wood compost, Sphagnum peat and pine bark [40]. These opposite responses have been already documented by other studies [41][42][43], in which plants (Catharanthus roseus G. Don, B. napus, Alocasia macrorrhiza L. and Sedum alfredii (Hance) cultivated on pure SS showed enhanced growth compared to those grown on control soil, due to the abundance of organic matter, N, P and other micronutrients, such as Mn, Cu, and Zn. On the other hand, SS can also suppress plant growth due to its toxicity, as was reported by Suchkova et al [44], who did not record any natural plant species (i.e., Amaranthus albus L., Cynodon dactylon (L.) Pers., Portulaca oleracea L.) growing on 100% municipal sludge from Sindos (Greece), compared to sludges from other WWTPs.…”