## 3 Results and Discussion
### Pot Assays  
Pot experiments were conducted to evaluate the toxicity of Cd and the effects of HANPs on the germination, growth, and medium-term development of quinoa (Figure 1). The main results obtained are summarized in Table 5.  
Germination rates in port experiments differed from those observed in phytotoxicity assays. In pots, quinoa seed germination decreased with increasing Cd concentration, regardless of HANP application, from 10 mg kg\({}^{-1}\) Cd. This difference might be due to direct contact between seeds and soil components in pot experiments. In contrast, in the phytotoxicity assays, the black filter acted as a barrier, isolating the seeds from direct interaction with the soil. Consequently, in phytotoxicity assays, only the soil solution and its ions influenced germination rates. Regarding fresh and dry biomass (stems and leaves), no significant differences were observed between individuals grown in soils treated with and without HANPs at the same Cd concentrations. However, biomass decreased as Cd concentration increased, regardless of HANP application. This indicates that the presence of HANPs did not substantially influence quinoa plant biomass. For plant height, individuals from control soils (0 mg kg\({}^{-1}\) Cd) showed no significant differences between treatments with or without HANPs. However, for 5 and 10 mg kg\({}^{-1}\) Cd with HANPs, plant height was similar to the control height, whereas, for treatments with 25 and 50 mg kg\({}^{-1}\) without HANPs, plant height significantly decreased. In this line, at Cd 25 and 50 mg kg\({}^{-1}\) concentrations with HANPs, plant height was also significantly reduced, underscoring their limited effectiveness under high Cd contamination levels. This suggests that HANPs may mitigate  
Figure 1: Pot assay with quinoa (examples). (**A1**): Control soil; (**A2**): Control soil + HANPs; (**B1**): Soil + Cd (5 mg kg\({}^{-1}\)); (**B2**): Soil + Cd (5 mg kg\({}^{-1}\)) + HANPs; (**C1**): Soil + Cd (10 mg kg\({}^{-1}\)); (**C2**): Soil + Cd (10 mg kg\({}^{-1}\)) + HANPs; (**D1**): Soil + Cd (25 mg kg\({}^{-1}\)); (**D2**): Soil + Cd (25 mg kg\({}^{-1}\)) + HANPs; (**E1**): Soil + Cd (50 mg kg\({}^{-1}\)); (**E2**): Soil + Cd (50 mg kg\({}^{-1}\)) + HANPs. Cd toxicity at moderate contamination concentrations (\(\leq\)10 mg kg\({}^{-1}\)) but are less effective at higher Cd concentrations (>10 mg kg\({}^{-1}\)). The decrease in leaf area and leaf number at higher Cd concentrations shows the negative effects of Cd on the photosynthetic activity and health of quinoa. Cadmium toxicity is known to affect chlorophyll synthesis, affect water transport, and alter enzymatic activities involved in carbon assimilation [53]. The presence of HANPs mitigated these effects at Cd concentrations between 5 and 25 mg kg\({}^{-1}\), possibly by providing essential calcium and phosphorus ions that ameliorate Cd-induced nutrient deficiencies. However, at 50 mg kg\({}^{-1}\) Cd, the mitigation capacity of HANPs was limited, showing the need for more robust remediation strategies at high contamination levels. Root Cd concentrations were below the detection limit for all treatments, while individuals from control soils with or without HANPs showed no Cd accumulation in shoots. Cd content in quinoa shoots was lower in soils with HANPs than soils without HANPs at the same soil Cd concentration. The reduction in Cd content in shoots observed in this study is consistent with the ability of HANPs to immobilize Cd by forming stable phosphate complexes, which reduce its bioavailability. This mechanism aligns with findings indicating that HA effectively reduces the availability of exchangeable and soluble fractions of Cd in contaminated soils [49]. Recent studies have demonstrated the efficacy of HANP to immobilize Cd in contaminated soils, favoring the growth of different plants and improving the yield of several crops. For example, the application of HANPs significantly reduced Cd availability (\(\approx\)90%) in soils, enhancing the germination and early growth of _Sinapis alba_ L. [13].