Toxicity of Silver Manufactured Nanomaterials to the Model Terrestrial Invertebrate, Caenorhabditis Elegans.

Since 2006 there has been an increase in the number of products containing manufactured nanomaterials (MNMs), with over 1500 products on the market.  Experimental evidence, along with a life-cycle inspired risk analysis indicates that the many MNM classes are entering the terrestrial environment through waste water streams and application of the resulting biosolids to agricultural soils. One of the MNM of principle concern is nano silver (Ag). In the wastewater treatment process, the Ag MNMs undergo transformations, with fully or partially sulfidized aged Ag MNMs (sa-Ag MNMs) being shown to be an important transformation product. We are interested in understanding the toxicity mechanisms of Ag MNMs and sa-AgMNMs to soil organisms and are employing ecotoxicological and toxicogenomic approaches utilizing the model organism Caenorhabditis elegans. We hypothesize that the responses of C. elegans to pristine Ag MNMs and sa-Ag MNMs will be distinct and that toxicity will also be determined by dissolution and release of Ag⁺. We assessed the impacts of 60 nm pristine polyvinylpyrrolidone (PVP) capped Ag MNMs (PVP-Ag MNMs) and sa-Ag MNMs referenced to Ag ions on mortality, growth, and reproduction of C. elegans.   We have found that Ag ions, pristine PVP-Ag MNMs and sa-AgMNMs are toxic to C. elegans for all three ecologically relevant endpoints analyzed, with reproduction being the most sensitive.  Ag ions are most toxic with an LC₅₀ and EC₅₀ of 0.075 mg/L and 0.020 mg/L, respectively. Among the Ag MNMs tested, PVP-Ag MNMs are more toxic than the sa-AgMNMs, with a LC₅₀ and an EC₅₀ of 3.5 and 0.625 mg/L and 10.0 and 4.0 mg/L, respectively. Greater toxicity of pristine PVP-Ag MNMs can only be partially explained by greater release of ions (~ 20 fold). Toxicogenomic responses of C. elegans exposed to Ag MNMs and Ag ions are being evaluated via whole genome microarrays.

Keywords: Nanomaterials, Nanotechnology, Toxicity, Caenorhabditis elegans, Silver