1. Ongoing studies Full scale study for assessing bioavailability, uptake, biodistribution and maternal transfer of nano (7nm) vs bulk sized Ag MNMs. Full scale study for assessing bioavailability, uptake, biodistribution and maternal transfer of nano Ag MNMs with different surface coatings. Rhys M. Goodhead 1*, Victoria Jennings 1, Simone Tinguely 1,2, Charles R.Tyler 1. 1 Ecotoxicology and Aquatic Biology Research Group Biosciences, College of Life and Environmental Sciences, University of Exeter, Geoffrey Pope Building, Stocker Road, Exeter, Devon, EX4 4QD, UK. 2 University of Applied Sciences North-western Switzerland, School of Life Sciences, Institute for Ecopreneurship, Gründenstrasse 40, CH-4132 Muttenz, Switzerland. *R.M.Goodhead@ex.ac.uk Pilot data on Ag MNMs A pilot study has been conducted to assess the bioavailability, uptake, biodistribution and maternal transfer of nano vs bulk sized Ag MNMs in X.eiseni Fish were dosed via the diet for the duration of gestation after mating naive females with males. 7nm and >500nm sized Ag particles were dosed via the diet at 1.75 µg Ag/fish/day. On the day of parturition (between 50-60 days), fish and fry were sampled for Ag content. Ag concentration in tissues and water samples were measured by ICP-MS. Introduction It is well documented that early life stages of many species exhibit a greater toxicological sensitivity to contaminants than adult life stages, principally because most developmental processes occur at this time, when much of the genome is activated. Thus developing embryos represent a sub-population potentially at high risk of toxicant effects. This is especially true for live bearing animals due to maternal transfer. Despite many studies on the toxicity of manufactured nanomaterials (MNM), maternal exposure of developing offspring to MNMs has received little research attention,and this is especially true for aquatic organisms. Here we present ongoing pilot work investigating a novel fish model to study the maternal transfer of MNMs and their biological effects on developing offspring. The Fish Model - Xenotoca eiseni Xenotoca eiseni have developed interesting adaptations in their reproductive biology and show matrotrophic viviparity (direct nutrient provisioning to developing embryos and live bearing). There are morphological and functional adaptations in both the female and embryo that facilitate the transfer of nutrients and oxygen from the mother to the embryo, the most conspicuous of which are structures on the embryos, called trophotaeniae, that absorb maternally derived nutrients from a surrounding fluid matrix (histotrophe). Trophotaeniae (Figure 1) Ribbon like nutritive processes that are everted extensions of the hind gut with a surface covered by a modified intestinal like epithelium and an extensive system of microvilli. Provide an extensive surface area for exchange of metabolites between the histotrophe in the ovarian lumen. Rapidly absorbed soon after birth. Histotrophe and Ovary (Figure 2, 3) Histotrophe – the nutritional ovarian fluid bathing the larval trophotaeniae during the intraluminal gestation. Internal ovarian epithelium (IOE) - involved in the transport and exchange of multiple metabolites from the maternal vascular system into the histotrophe. IOE also supports gas exchange and waste transfer Hypothesised that the histotrophe may also have an immunological function Cutaneous gas exchange is likely in the developing larvae which contains a complex capillary network. Maternal transfer of Ag MNMs occurred into the larvae (Figure 4). Initial findings show that Ag partitions to many organs, with the highest concentration in the liver. Ag MNMs (or Ag+ derived from these particles) appeared to be more bioavailable than the bulk counterpart. Figure 4. Ag concentrations in tissues of adult X.eiseni and whole larval body burdens. * Indicates significant difference from bulk treatment tissue, p < 0.05. * * * * Figure 1. Prominent trophotaeniae of larval X.eiseni, 4 weeks post fertilisation. A B Figure 3. (A) Transverse and (B) longitudinal histological section of an adult X.eiseni at 6 weeks post fertilisation and just prior to parturition. Figure 2. Photograph of the ovary of X.eiseni at full term.