## 4 Discussion  
### Ce in Plants  
The data regarding Ce plant uptake was in accordance with the observations by other authors [32; 33; 34], studying CeO\({}_{2}\) nanoparticle uptakes of corn, lettuce, soybeans and zucchini grown in a soil amended with biochar from pecan shells, observed that, in most cases, there were no effects on the Ce accumulation in plant tissues. In fact, Ce accumulation occurred mostly at the highest CeO\({}_{2}\) level (2000 mg kg\({}^{-1}\)). The authors of [33] confirmed that a 2000 mg CeO\({}_{2}\)NPs L\({}^{-1}\) concentration in hydroponic conditions negatively affected _Triticum aestivum_ L. growth and its photosynthesis-related processes. The application of biochar from the pyrolysis of bamboo leaves at 500 \({}^{\circ}\)C considerably reduced about nine-fold the Ce in plants through the surface complexation process, alleviating the phytotoxic effects; they also observed that the biochar application showed a positive effect on plant growth at all CeO\({}_{2}\)NPs exposure levels. The authors of [34], in a study where AgNPs were accounted for, concluded that the exposure to plants induced dose-dependent phytotoxicity with negative effects on the plant growth, photosynthesis, gas exchange and nutrients assimilation. The addition of biochar reduced the toxic effects of AgNPs by reducing four to eight times the uptake and Ag tissue accumulation.  
Although not the main objective of the present study, a phonological shift observed in _L. sativum_ induced by the BC application (regardless of the quenching type) was observed. According to [35], biochar can have a full range of responses in terms of germination and plant development, thereby influencing some growth traits but not some others, and have an impact on the hormone pathways. The experiments performed by [36] using three types of biochar and _L. sativum_ (other than lentils, lettuce, cucumbers and tomatoes) revealed that differences were observed for cresc seeds with which two biochars (paper sludge and wheat husks biochar and sewage sludge biochar) showed a phytostimulant effect.  
A greater height of the plants as a response after biochar application was observed by several authors, such as in rice [37], in corn [38] and in cotton [39]. Recently, several studies have been performed to observe the nanoceria accumulation in plants from contaminated soils, considering a wide spectrum of concentrations and no evidence of accumulation was observed at the lowest concentrations (from 1.3 to 62.5 mg kg\({}^{-1}\)) [40]. According to the authors, evidence of CeO\({}_{2}\)NPs uptake was found for concentrations above 100 mg kg\({}^{-1}\). However, the processes that influence the nanoparticles' bioavailability are still unknown. The same authors, examining the effect of the soil properties on the CeO\({}^{2}\)NPs' phytoavailability and uptake by rescue and tomatoes, observed that one of the main influencing factors (second only to the initial concentration of Ce in soil) was the soil type in terms of texture, the clay soils being the ones for which the phytoavailability was lower than the sandy soils within the range 70-80%. This was another important observation that could explain the low plant uptake, since the clay content of the soil used in this experiment had a high clay content (67.7%).