A new medium for Caenorhabditis elegans studies using silver and silver nanoparticles

Many of the well established media used for C. elegans studies are unsuitable for work involving silver ions and silver nanoparticles. The use of silver with such media may lead to precipitation of silver salts, or aggregation of silver nanoparticles, due to high chloride and/or phosphate concentrations, and high ionic strength. The use of solid (agar) media is complicated by the antimicrobial effects of silver, which make the growth of the E. coli nutrient source impossible at high exposure concentrations. We have developed a new liquid medium of low ionic strength with no chloride and very low phosphate concentrations. The medium contains major ions at environmentally realistic concentrations, and fulvic acid may be added to simulate natural organic matter. The concentration of the ions and fulvic acid can be adjusted to explore the influence of medium composition on toxicity.The medium has been successfully used in trials with silver nitrate and silver nanoparticles. Control responses of C. elegans compared favourably with those seen in the standard M9 medium. The levels of variation among replicates in these trials was low, allowing subtle differences such as potential hormesis effects to be detected and analysed with a high degree of statistical rigour.