The increasing use of nanoparticles is causing a threat to the environment and humans. The aim of this work was to evaluate the effects of the quenching procedure of biochar production on the biochar capacity to retain the CeO2 nanoparticle (CeO2NP) in soil. The effects on Lepidium sativum L. (watercress) were considered. Two biochars were produced from fir wood pellets under the same pyrolysis conditions but with different quenching procedures: dry quenching and wet quenching. The two biochars (BCdryQ and BCwetQ) were separately added to a CeO2NP-spiked soil (1000 mg kg−1) at the dose 5%DW and placed in 12 lysimeters under controlled conditions. Lepidium sativum L. seeds were sowed on each lysimeter. The lysimeters were irrigated once a week for 7 weeks, and the leachates were collected. At the end of the experiment, the aboveground biomass was harvested; the total number of plants and the number of plants at the flowering stage were counted, and the height of the tallest plant and the total dry biomass were measured. The data showed that the quenching procedure influences the CeO2NP retention in soil, and BCdryQ can reduce the leaching of the nanoparticles. Biochar significantly increased the flowering in plants, and BCwetQ reduced the biomass production. This work highlights the importance of the biochar production process for soil applications. The production settings are crucial in determining the efficacy of the product for its ultimate use.
