Engineered Nanomaterials Impact Biological Carbon Conversion in Soils

Engineered nanomaterials (ENMs) increasingly used in commercial products can accumulate in biosolids. Land application of biosolids potentially leads to consequent exposure of ENMs to soils. This article examines the impact of ENM-amended biosolids on biological carbon dioxide production in soils. ENMs, including nano-silver (Ag), zinc oxide (ZnO), titanium dioxide (TiO₂), and cerium oxide (CeO₂), were applied to soils with dosages of 1 and 1,000 mg/kg, simulating the normal and high concentration exposure scenarios, respectively. Under dark conditions, 1,000 mg/kg of nano-Ag and ZnO exhibited inhibitory effects on aerobic carbon conversion in both a 28-day basal respiration test and a modified 24-h substrate-induced respiration (SIR) test. At 1 and 1,000 mg/kg levels, nano-TiO₂ was found to be inert to carbon conversion in both respiration tests. Nano-CeO₂ at 1,000 mg/kg exhibited an increased basal respiration rate (48% higher than in the control soil), but having a minimum inhibitory effect in the SIR test. Single particle-inductively coupled plasma-mass spectrometry was used to determine the presence of nano-sized particles in water extracted from soils after 28 days of respiration test. Soils treated with nano-TiO₂, CeO₂, and Ag released<1% of nanoparticles into the extracted water, while the majority of ENMs were still retained in the soil. Nano- and micron-sized particles containing zinc were not detected even in soils treated with 1,000 mg/kg of nano-ZnO. The findings of this article will inform scientific and regulatory communities about the potential effects of ENMs on microbial respiration in biosolid-amended soils.