Table 2.

Effects of engineered metal oxide nanoparticles on plants

Nanoparticle	Size (nm)	Plant	Concentration	Effect	References
Al2O3		Corn, cucumber, lettuce, radish, rapeseed, ryegrass	2,000 mg L-1	No effect on germination	[44]
	13	Carrots, cabbage, cucumber, maize	2,000 mg L-1	Reduced root growth	[146]
		Corn	2,000 mg L-1	Reduced root length	[44]
CeO2	7	Alfalfa	1,000 and 2,000 mg L-1	Slightly reduced shoot growth	[147]
		Tomato	2,000 mg L-1	Reduced shoot growth	[147]
		Cucumber	2,000 mg L-1	Reduced shoot growth	[147]
		Maize	500, 1,000 and 2,000 mg L-1	Reduced shoot growth	[147]
		Alfalfa	500 mg L-1	Reduced biomass	[147]
		Maize	500 to 2,000 mg L-1	Reduced germination	[147]
		Maize	4,000 mg L-1	Reduced root growth	[147]
		Tomato, cucumber	2,000 mg L-1	Reduced germination	[147]
		Tomato	1,000 to 2,000 mg L-1	Reduced root growth	[147]
		Alfalfa	2,000 to 4,000 mg L-1	Reduced root growth	[147]
		Soybean	2,000 mg L-1	Reduced germination	[147]
	7	Alfalfa, corn, soybean	500, 1,000, 2,000 and 4,000 mg L-1	Increased root and stem growth	[147]
	<25	Wheat	100 mg L-1		[148]
	8.0 ± 1.0	Coriander	125 mg kg-1	Increased shoot and root length, increased biomass, increased catalase activity in shoots and increased ascorbate peroxidise activity in roots	[149]
	231 ± 16	Rice	62.50 and 125 mg L-1	Reduced H2O2 generation in shoots and roots	[150]
			500 mg L-1	Increased electrolyte leakage and lipid peroxidation in shoots	[150]
FeO	10.2 ± 2.6	Clover	3.2 mg kg-1	Reduced aboveground and belowground biomass	[49]
Fe3O4	20	Pumpkin	500 mg L-1	No toxic effect	[29]
	7	Cucumber, lettuce	62, 100 and 116 mg L-1	Low to zero toxicity	[47]
Magnetite (iron oxide)		Soybean	0.2, 0.4, 1.0 and 2.0 mg L-1	Increased chlorophyll levels	[151]
Mixture of SiO2/TiO2		Soybean		Increased germination and shoot growth, increased nitrate reductase activity, increased absorption and utilization of water/fertilizer and enhanced antioxidant system	[129]
Ni(OH)2	8.7	Mesquite	2 mg L-1	No effect	[152]
Nanosized TiO2	21	Wheat	10 ppm	Reduced germination	[153]
			2 and 10 ppm	Increased shoot and seedling lengths
			100 and 500 ppm	Reduced shoot and seedling lengths
			100 ppm	Increased root dry matter production
Nanoanatase (TiO2)	4 to 6	Spinach	0.25%	Enhanced rca mRNA expressions, protein levels, activity of Rubisco activase, Rubisco carboxylation, the rate of photosynthetic carbon reaction, single plant dry weight and chlorophyll content	[154]
	5	Spinach	0.25%	Improved spinach growth related to N2 fixation by TiO2	[155]
	5	Spinach	0.25%	Improved light absorbance, transformation from light energy to electron energy, and active chemical energy and promoted carbon dioxide assimilation	[156]
Rutile (TiO2)		Spinach (naturally aged)	0.25% to 4%	Increased germination and germination and vigour indices, plant dry weight, chlorophyll formation, ribulose bisphosphate carboxylase/oxygenase activity and photosynthetic rate	[10]
		Spinach	0.25% to 4%	Promoted photosynthesis, the rate of evolution of oxygen in the chloroplasts was accelerated	[130]
TiO2/inorganic bentonite clay	30/1 to 60	Maize	300 and 1,000 mg L-1	Inhibited hydraulic conductivity, leaf growth and transpiration	[157]
ZnO	8	Soybean	500 mg L-1	Increased root growth	[147]
	9 to 37 (mean 19 ± 7)	Ryegrass	1,000 mg L-1	Reduced biomass, shrank root tips, epidermis and root cap were broken, highly vacuolated and collapsed cortical cells	[44]
		Corn	2,000 mg L-1	Reduced germination	[44]
		Corn, cucumber, lettuce, radish, rapeseed, ryegrass	2,000 mg L-1	Reduced root growth and elongation	[44]
	5	Zucchini	1,000 mg L-1	Reduced biomass	[46]
	8	Soybean	2,000 and 4,000 mg L-1	Decreased root growth	[147]
3-Amino-functionalized SiO2		Lettuce	0.013% to 0.066% (w/w)	No effect on germination, improved shoot/root ratio	[13]