Biochar as a tool to optimise Miscanthus sinensis resilience and phytoremediation efficiency: Case study of contamination by mixture of Ni and 4.4′-DDE

This study investigated the effects of 1 % commercial sewage sludge-based biochar on the physiological, biochemical, and phytoremediation parameters of Miscanthus sinensis And. ( M. sinensis ) under greenhouse conditions. Biochar was applied to soils subjected to mono- and combined contaminations involving 4.4′-DDE and Ni ions. Biochar incorporation led to (a) a significant increase in plant yield (up to 121 %), (b) enhanced free proline (up to 366 %) and total protein content (up to 135 %), (c) increased levels of the auxiliary pigment chlorophyll b (up to 154 %), (d) partially restored electron transport in photosystem II (up to 36.9 %), and (e) reduced antioxidant enzyme activity in M. sinensis leaves. However, when applied to control soil, biochar induced plant stress, highlighting its suitability primarily for contaminated environments. Post-vegetation analysis confirmed that biochar sorbed Ni and Cr ions from the soil, desorbed Cu and Zn, and had no effect on Pb across all treatments. Furthermore, biochar incorporation significantly reduced plant uptake of 4.4′-DDE, decreasing its bioavailability by 38.9 % and 59.1 % under combined and mono-DDE contamination, respectively, compared to the respective unamended treatments. Under combined contamination, biochar exhibited selective sorption activity, enhancing 4.4′-DDE adsorption while reducing Ni ion retention, indicating that Ni stabilisation depends on both biochar properties and the nature of contamination. Additionally, biochar’s ability to desorb Cu and Zn suggests its potential use in agricultural soils with Cu and/or Zn deficiencies. These findings underscore biochar’s dual role in promoting M. sinensis growth and reducing pollutant bioavailability, demonstrating its potential to enhance the phytoremediation of complexly contaminated soils. • 1 % SSB enhanced M. sinensis biomass under organic and complex soil contamination. • SSB negatively affected M. sinensis morpho-physiology in non-spiked control soil. • SSB showed higher affinity for organic contaminants in complex contamination. • Due to biochar selectivity, Ni adsorption under complex contamination was inhibited. • To validate suitability of biochar in pot trials, granular particles are required.