Electron microscopy of gold nanoparticle intake in the gut of Daphnia magna

Few studies have described aquatic organisms interacting with manufactured nanoparticles. One key factor in determining these materials potential toxicity is the extent to which these particles accumulate in tissues. This may be most important for aquatic organisms as they contact large quantities of water through their feeding behavior. We examined the uptake and release of gold particles in filter-feeding Daphnia magna. Daphnia were exposed to sublethal concentrations of gold nanoparticles for 1, 6, 12, or 24 hours. Transmission Electron Microscopy was used to examine the presence and distribution of gold in gut tissue. The highest concentration of nanoparticles was found after 12 h. Particle clearance was investigated by placing organisms in fresh water and observing particles retention in the gut tissue over time. The initial trend of high gold concentration in the mouth with low levels in the tail region was reversed, suggesting clearance of particles with time.