The presence of engineered nanoparticles (ENPs) in soil systems can modify their properties and the availability of nutrients. This study evaluated the effect of 1% CuO or ZnO ENPs on the physicochemical properties and on the phosphorus (P) adsorption–desorption processes of a volcanic ash soil (Lautaro; LAU). The dynamics of P were conducted through kinetic and isotherm batch experiments. The results showed that LAU soil with 1% CuO or ZnO ENPs increased pH_H2O (from 5.67 to 6.03 and 6.82, respectively), electrical conductivity (from 0.119 to 0.143 and 0.150 dS m⁻¹, respectively), Zn availability (597.7 times higher for LAU with 1% ZnO ENPs in relation to soil without ENPs), and Cu availability (41.8 times higher for LAU with 1% CuO ENPs in relation to soil without ENPs). Moreover, the presence of ENPs decreased Brunauer, Emmett, and Teller specific surface area. The adsorption kinetic studies of P on LAU soil without and with 1% ENPs fitted well to the Elovich model (r² ≥ 0.923), which indicated a chemiadsorption mechanism, whereas the adsorption isotherms were described by Langmuir–Freundlich model (r² ≥ 0.939). The desorption percentage was LAU > LAU + 1% CuO–ENPs > LAU + 1% ZnO–ENPs, demonstrating an increased stability of the P–soil surface binding with 1% ENPs. Co–existing NO₃⁻, SeO₄²⁻, and SO₄²⁻ anions did not generate a steric hindrance between P and LAU soil binding. Finally, both ENPs could alter the quality of the soil due to changes in their physicochemical properties and decrease the availability of P in volcanic ash soils.

Excessive release of ammonium (NH₄⁺) into aquatic ecosystems can promote eutrophication. In this study, the natural adsorbents, coal (C) prepared from Hawthorn (Acacia caven) and coal fly ash obtained from C, were used to remove NH₄⁺ from aqueous systems through batch adsorption–desorption studies. Both adsorbents were physically and chemically characterized, while Fourier-transform infrared spectroscopy and zeta potential were used to understand the surface functional groups and surface charge characteristics. CFA showed a higher pH, BET specific surface area, electrical conductivity and higher % values for CaO and MgO than C. Kinetic studies of NH₄⁺ adsorption at pH = 4.5 for both materials fitted the pseudo-second-order model giving the r² of 0.970–0.983 and the χ² of 0.008–0.005 and at pH = 6.5 only for C with the r² of 0.986 and the χ² of 0.013. Meanwhile, the adsorption isotherm data at pH = 4.5 for both materials and 6.5 for CFA complied with the Freundlich model (r² > 0.965 and χ² < 0.012), suggesting that NH₄⁺ adsorption onto both adsorbents at those pH values occurred through the formation of a multilayer adsorption on heterogeneous surfaces. This indicates that the dominant adsorption of both adsorbents was physisorption with no site-specific interaction. Based on these results, CFA is proposed as a promising and economical material for the removal of NH₄⁺ from aqueous systems.

Excessive release of engineered nanoparticles (NPs) into the environment can affect the biological and chemical properties of soils. This study evaluated the effects of two commercial metallic copper nanoparticles (Cu-NPs 25 nm; CuNPs/25, and Cu-NPs 40–60 nm; CuNPs/40–60) on enzymatic activity and nutrient bioavailability in an agricultural soil. An incubation experiment was conducted using Ultisol soil treated with 500 mg kg⁻¹ CuNPs/25 or CuNPs/40–60, simulating a high-exposure scenario, in the presence and absence of 200 mg kg⁻¹ P (K₂HPO₄). Acid phosphatase, alkaline phosphatase, and β-glucosidase enzymatic activities along with P bioavailability were measured at 0.14, 1, 3, 5, and 8 weeks. The results showed that in most instances, 500 mg kg⁻¹ CuNPs/25 or CuNPs/40–60 significantly decreased the activities of acid phosphatase, alkaline phosphatase, and β-glucosidase. The P bioavailability in soil was lower in the presence of CuNPs/25 than Cu-NPs/40–60. In addition, the Cu²⁺ concentrations in the water-extractable fraction were higher than in the CaCl₂ fraction, and the increase in water-extractable Cu²⁺ concentrations in the soil solution was correlated with a decrease in enzyme activities. Eight weeks of exposure to NPs did not cause any marked changes in organic matter content or electrical conductivity. However, the Cu²⁺-(DTPA) bioavailability in soil treated with 500 mg kg⁻¹ CuNPs/25 and CuNPs/40–60 for 8 weeks increased over 90 times, regardless of the presence or absence of P. However, these findings should be interpreted in the context of a high-exposure scenario for CuNPs and should not be directly extrapolated to environmentally realistic exposure levels.