Principles for characterizing the potential human health effects from exposure to nanomaterials: elements of a screening strategy

Table 2 Recommendations on material characterization

Characterization (Off-line)	Human exposure	Toxicity Screening Studies
		Supplied material	Administered material	Material *in vivo* / *in vitro*
Size distribution (primary particles)	E (Combine with agglomeration state)	E	D	D
Shape	E	E	O	O
Surface area	D	E	D	O
Composition	E	E	O	O
Surface chemistry	D	E	D	D/O
Surface contamination	D	N	D	N
Surface charge – suspension/solution	O	E	E	O
Surface charge – powder (use bio fluid surrogate)	O	E	N	O
Crystal structure	O	E	O	O
Particle physicochemical structure	E	E	D	D
Agglomeration state	E	N	E	D
Porosity	D	D	N	N
Method of production	E	E	--	--
Preparation process	--	--	E	--
Heterogeneity	D	E	E	D
Prior storage of material	E	E	E	--
Concentration	E	--	E	D

E: These characterizations are considered to be essential.
D: These characterizations are considered to provide valuable information, but are not recommended as essential due to constraints associated with complexity, cost and availability.
O: These characterizations are considered to provide valuable but non-essential information.
N: These characterizations are not considered to be of significant value to screening studies.