Uptake routes of silver nanoparticles in earthworms

This study aims at quantifying the contribution of dermal and oral uptake of silver nanoparticles (AgNP) in earthworms. With the greater production and incorporation into consumer products, it is expected that increasing amounts of AgNPs will be released to the environment. These NPs will end up in soil through wastewater and sewage sludge or may directly be deposited on land, thus being of environmental relevance for terrestrial ecosystems. To assess their risk in soil, besides their dissolution and speciation it is important to investigate the mechanisms by which the different metal species (single nanoparticles, aggregates and metal ions) interact with biological membranes and enter the body of the organisms exposed. Earthworms are representative test organisms for ecological risk assessment. They will be exposed to contaminants in soil both through the skin (dermal) and by ingestion (oral). To assess bioavailability of metal nanoparticles in soil to earthworms, it is necessary to know the contribution of each pathway. For that reason, experiments will be performed with the earthworm Lumbricus rubellus, applying oral sealing with medical histoacryl glue to block the ingestion of soil particles. Glued and unglued earthworms will be exposed to Lufa 2.2 soil spiked with 100 and 500 mg kg-1 dry soil AgNPs for 7 days. An exposure of glued and unglued earthworms to soil spiked with 20 and 100 mg kg-1 AgNO3 will also be included to address the interaction of silver ions with earthworm tissues. By measuring total silver body concentrations at different sampling times in both exposure scenarios it will be possible to assess the contribution of the different routes of exposure. The distribution of silver in tissues of exposed earthworms will be mapped by transmission electron microscopy (TEM) and synchrotron X-ray microanalysis.