Table 4.

Effect of different ENMs on soil microbial activity.

Type of Nanomaterial	Concentration Range in Soil	Toxic Effects	Ref.
ZnO, TiO2 and CeO2	1000 mg kg−1	NPs hampered thermogenic metabolism and reduced soil Azotobacter, P-solubilizing and K-solubilizing bacteria and enzymatic activities	[231]
TiO2 NPs	5–100 mg kg−1 soil	TiO2 NPs at 100 mg/kg of soil reduced the biomass of total phospholipid fatty acid (PLFA) and microbial load in soil	[232]
Silver (Ag), zinc oxide (ZnO) and fullerene (C60)	100 mg kg−1 dry weight	Nitrogen transformation suppressed by all three NPs via inhibiting Flavobacterium and Nitrospira	[233]
La2O3, Nd2O3 and Gd2O3 nanoparticle	10, 50 and 100 mg kg−1	Altered the ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacterial (AOB) community	[198]
Polyvinylpyrrolidone-coated Ag NPs	1, 10 and 100 mg kg−1 soil	Ag NPs at 100 mg kg−1 reduced dominant Nitrosospira and Nitrosomonas, and Nitrosovibrio even disappeared	[234]
		Ag NPs reduced the dehydrogenase soil enzyme activity
CuO NPs	27, 54, 123, 265 and 627 mg Cu kg−1 soil	Inhibitory effect over dehydrogenase and phosphatase enzyme activities	[235]
		No significant inhibitory effects on the soil microbial growth
Ag NPs	1, 10 and 100 mg kg−1 dry soil	Reduced the urease enzyme and ammonia-oxidizing enzyme activities	[236]