Impact of emerging and low cost alternative amendments on the (im)mobilization and phytoavailability of Cd and Pb in a contaminated floodplain soil

• Impact of amendments on (im)mobilization of Cd, Pb and plant uptake were studied.
• Nano-hydroxyapatite and cement dust showed the highest decreasing rate of plant Pb.
• Organo-clay increased the solubility and the uptake of Cd and Pb.
• Liming materials decreased soluble Cd but increased its uptake by rapeseed.
• Lead in rapeseed was reduced by 35–99% in the amended soil compared to control.

Contamination of wetland ecosystems by cadmium (Cd) and lead (Pb) is a serious concern because of its high health risk via the food chain. Therefore, an ecological solution is required to effectively remediate contaminated floodplain soils by toxic metals. This study aimed to assess the effects of various emerging amendments (e.g., nano-hydroxyapatite, biochar, chitosan, and organo-clay) and several of low cost amendments (e.g., activated carbon, bentonite, cement kiln dust, fly ash, lime stone, sugar beet factory lime, and zeolite) on the (im)mobilization of Cd and Pb and their uptake by rapeseed (Brassica napus) in a contaminated floodplain soil. Application of the amendments (except for OC, HA, and FA) increased the rapeseed dry biomass yield significantly compared to control. The amendments (except organo-clay and zeolite) decreased soluble + exchangeable Cd (4–60%) compared to the control. Although the cement kiln dust, sugar beet factory lime, and lime stone showed the highest decreasing rate of soluble + exchangeable Cd, they increased the carbonate fraction and Cd in plants, which might be due to dissolving of carbonates and release of Cd in the rhizosphere. The zeolite, bentonite, activated carbon, biochar, and chitosan decreased Cd in plants (22–36%). The amendments (except organo-clay and zeolite) decreased soluble + exchangeable Pb by 6–87% and decreased Pb in the plant by 35–99% compared to the control. The sugar beet factory lime, cement kiln dust, and lime stone showed the highest decreasing rate of soluble Pb and nano-hydroxyapatite showed the highest decreasing rate of Pb uptake which highlights the high potential of these amendments for Pb immobilization in the soil and reduce Pb accumulation by plants.