Silver nanoparticle toxicity in Drosophila: size does matter

BACKGROUND Consumer nanotechnology is a growing industry. Silver nanoparticles are the most common nanomaterial added to commercially available products, so understanding the influence that size has on toxicity is integral to the safe use of these new products. This study examined the influence of silver particle size on Drosophila egg development by comparing the toxicity of both nanoscale and conventional-sized silver particles. METHODS The toxicity assays were conducted by exposing Drosophila eggs to particle concentrations ranging from 10 ppm to 100 ppm of silver. Size, chemistry, and agglomeration of the silver particles were evaluated using transmission electron microscopy, X-ray photoelectron spectroscopy, and dynamic light scattering. RESULTS This analysis confirmed individual silver particle sizes in the ranges of 20-30 nm, 100 nm, and 500-1200 nm, with similar chemistry. Dynamic light scattering and transmission electron microscope data also indicated agglomeration in water, with the transmission electron microscopic images showing individual particles in the correct size range, but the dynamic light scattering z-average sizes of the silver nanoparticles were 782 ± 379 nm for the 20-30 nm silver nanoparticles, 693 ± 114 nm for the 100 nm silver nanoparticles, and 508 ± 32 nm for the 500-1200 nm silver particles. Most importantly, here we show significantly more Drosophila egg toxicity when exposed to larger, nonnanometer silver particles. Upon exposure to silver nanoparticles sized 20-30 nm, Drosophila eggs did not exhibit a statistically significant (P < 0.05) decrease in their likelihood to pupate, but eggs exposed to larger silver particles (500-1200 nm) were 91% ± 18% less likely to pupate. Exposure to silver nanoparticles reduced the percentage of pupae able to emerge as adults. At 10 ppm of silver particle exposure, only 57% ± 48% of the pupae exposed to 20-30 nm silver particles became adults, whereas 89% ± 25% of the control group became adults, and 94% ± 52% and 91% ± 19% of the 500-1200 nm and 100 nm group, respectively, reached adulthood. CONCLUSION This research provides evidence that nanoscale silver particles (<100 nm) are less toxic to Drosophila eggs than silver particles of conventional (>100 nm) size.