First of a kind real-time study of nanosilver in fish embryos raises hopes and concerns - NanoWerk, USA

The nanoparticles show concentration-dependent toxicity – as nanoparticle concentration increases, the number of normally developed zebrafish decreases, while the number of dead zebrafish increases.

This study raises environmental concerns. It represents the first direct observation of passive diffusion of nanoparticles into an in vivo system, suggesting that the release of large amounts of silver nanoparticles into aquatic ecosystems (e.g., rivers) may have drastic environmental consequences should the sizes of nanomaterials remain unchanged during environmental transport.

Copper nanoparticles harm zebrafish - NanoWerk, USA
Researchers have found that nanosized copper particles affect fish gills through a different and as-yet-unknown mechanism than dissolved copper ions do.
Copper nanomaterials are currently used mostly in microelectronics, says Boxall, and "the release to the environment is therefore likely to be minimal." But if such nanoparticles become more widely used in personal-care products, for example, they may end up in water bodies or passing through wastewater treatment plants that cannot strain them out. Nanoparticles that sorb to treated biosolids later applied to agricultural fields could then get into the environment.