Impact of exposure to environmentally-relevant concentrations of ionic silver and nanosilver on thyroid hormone-dependent postembryonic development of the North American bullfrog (Rana catesbeiana)

Nanoparticles (<100 nm) are engineered to have unique physico-chemical properties compared to their larger counterparts. Nanosilver (nAg) is the most prevalent nanoparticle in consumer products due to its strong antimicrobial action. While nAg toxicity at high concentrations has been well described, the potential for sublethal effects at or below regulatory guidelines is relatively unknown. Amphibian metamorphosis is mediated by thyroid hormone (TH) and can be precociously induced by the addition of exogenous hormone. Low concentrations of nAg have been shown to disrupt TH-dependent responses in cultured premetamorphic Rana catesbeiana tadpole tail fin. The present study examined the effects of exposure to an environmentally relevant concentration (6 µg/L) of either nAg or ionic silver (iAg) on premetamorphic tadpoles in the absence and presence of exogenous TH. Disruption of thyroid hormone-mediated signalling in brain and liver transcriptomes was evaluated using the MAGEX cDNA microarray. Six premetamorphic tadpoles were randomly selected from each treatment condition (n=12) and the status of brain and liver transcriptomes determined by MAGEX cDNA array analysis.