Benefits of Ryegrass on Multicontaminated Soils Part 1: Effects of Fertilizers on Bioavailability and Accumulation of Metals

Abstract

Effects of three phosphorus fertilizers on the shoot biomass and on the accumulation of alkali, alkaline earth, and transition metals in the shoots and roots of ryegrass were studied with two contaminated garden soils. Phosphates were added in sustainable quantities in order to reduce the environmental availability of carcinogenic metals (e.g., Cd and Pb) and to enhance the bioavailability of alkali and alkaline earth metals as well as micronutrients needed by plants. Addition of Ca(H2PO4)2 was the most convenient way to (i) limit the concentration of Cd and Pb, (ii) keep constant the transfer of macro- and micronutrient from the soil to the ryegrass shoots, (iii) decrease the availability of metals, and (iv) increase the ratio values between potential Lewis acids and Cd or Pb in order to produce biosourced catalysis. For instance, the real phytoavailability was reduced by 27%–57% and 64.2%–94.8% for Cd and Pb, respectively. Interestingly, the real phytoavailability of Zn was the highest in the least contaminated soils. Even if soils were highly contaminated, no visual toxicity symptoms were recorded in the growing ryegrasses. This indicates that ryegrass is suitable for the revegetation of contaminated gardens. To promote the sustainable ryegrass production on contaminated soils for production of new organic fragrance and drugs in green processes according to REACH (Registration, Evaluation, Authorisation, and Restriction of Chemicals) regulation, two processes should be recommended: assisted phytostabilization of the elements, and then assisted phytoextraction by using chelators.