Table 2. Top twenty keywords by strength.

Years 2011–2013		Years 2008–2010		Years 2005–2007
Node	Strength	Node	Strength	Node	Strength
Nanoparticle	292	Risk Assessment	247	Risk Assessment	100
Risk Assessment	260	Nanotechnology	246	Nanotechnology	87
Nanomaterial	233	Nanoparticle	225	Nanoparticle	69
Nanotechnology	152	Nanomaterial	199	Nanomaterial	54
Nanotoxicology	116	Exposure	69	Fullerenes	30
Toxicity	77	Toxicity	66	Pulmonary Toxicity	26
Risk Management	61	Carbon nanotube	64	Toxicity	25
Engineered Nanomaterial	58	EHS (Environmental, Health, and Safety)	57	Environment	24
Silver Nanoparticle	53	Nanotoxicology	56	Dermal Toxicity	24
Titanium Dioxide	48	Multi-wall Carbon Nanotube	55	Genotoxicity	24
Nanotoxicity	42	Risk Management	53	Carbon nanotube	21
Carbon nanotube	37	Risk	48	Ultrafine Particles	20
Risk	37	Titanium Dioxide	42	Occupational Health	18
Genotoxicity	37	Regulation	39	Nanostructured Materials	17
Oxidative Stress	36	Exposure Assessment	38	Quantum Dots	17
Environment	32	Environment	36	Nanowires	17
Silver	31	Toxicology	36	Nanorod	17
Gold Nanoparticle	28	Health	33	Nanocluster	17
Nanosilver	25	Cytotoxicity	32	Nanocrystal	17