This review is concerned with evaluating the toxicity associated with human exposure
to silver and gold nanoparticles (NPs), due to the relative abundance of toxicity
data available for these particles, when compared to other metal particulates. This
has allowed knowledge on the current understanding of the field to be gained, and
has demonstrated where gaps in knowledge are. It is anticipated that evaluating the
hazards associated with silver and gold particles will ultimately enable risk assessments
to be completed, by combining this information with knowledge on the level of human
exposure. The quantity of available hazard information for metals is greatest for
silver particulates, due to its widespread inclusion within a number of diverse products
(including clothes and wound dressings), which primarily arises from its antibacterial
behaviour. Gold has been used on numerous occasions to assess the biodistribution
and cellular uptake of NPs following exposure. Inflammatory, oxidative, genotoxic,
and cytotoxic consequences are associated with silver particulate exposure, and are
inherently linked. The primary site of gold and silver particulate accumulation has
been consistently demonstrated to be the liver, and it is therefore relevant that
a number of in vitro investigations have focused on this potential target organ. However,
in general there is a lack of in vivo and in vitro toxicity information that allows
correlations between the findings to be made. Instead a focus on the tissue distribution
of particles following exposure is evident within the available literature, which
can be useful in directing appropriate in vitro experimentation by revealing potential
target sites of toxicity. The experimental design has the potential to impact on the
toxicological observations, and in particular the use of excessively high particle
concentrations has been observed. As witnessed for other particle types, gold and
silver particle sizes are influential in dictating the observed toxicity, with smaller
particles exhibiting a greater response than their larger counterparts, and this is
likely to be driven by differences in particle surface area, when administered at
an equal-mass dose. A major obstacle, at present, is deciphering whether the responses
related to silver nanoparticulate exposure derive from their small size, or particle
dissolution contributes to the observed toxicity. Alternatively, a combination of
both may be responsible, as the release of ions would be expected to be greater for
smaller particles.