The ecotoxicology of nanoparticles in Daphnia magna

Manufactured nanoparticles are increasingly being used in the production of consumer products and appliances. A release in the environment, either intended through remediation or unintended through a spill at production sites, through wastewater or product degradation, is most likely to occur. Due to their small size, nanoparticles have a far greater surface area to unit mass ratio than conventional substances, rendering them potentially more reactive. This project aims to obtain key data on the ecotoxicology of nanoparticles in the aquatic environment. Initially, data from acute and chronic toxicity tests were gathered by exposing the invertebrate Daphnia magna to nanoparticles of carbon black, cerium dioxide, silver and titanium dioxide. The endpoints were mortality, moulting frequency, growth and number of offspring. The results indicate that a gradient of toxicity can be drawn, with cerium dioxide being the least toxic, to silver being the most toxic. Also a size dependent increase of toxicity was observed, with exposures to nano sized particles being more toxic than micro sized particles. Uptake and fate of nano sized materials were studied by exposing D. magna to fluorescent polystyrene beads of 20 nm and 1000 nm sizes and the results were compared. Both particle sizes were readily taken up in the gut and relocated in storage droplets within the body of D. magna. A quantification of the results showed that the mass of 1000 nm sized particles taken up was higher at equal exposure concentrations than the 20 nm sized particle but the excretion rate was higher as well for the 1000 nm particles. However, when assessing uptake as surface area or particle number dose, uptake of 20 nm particles exceeds uptake of 1000 nm particles. To assess the effect of nanoparticles on oxidative stress, the total antioxidant capacity was measured as well as the glutathione concentration of exposed D. magna. A decrease in total glutathione in D. magna was detected due to exposure to nano sized carbon black, while measuring the total oxidant capacity proved to be impossible due to interferences with the method used. The results show that, when negative effects are observed, these are more severe in exposures to nanoparticles than their micro sized counterparts and furthermore a clear route of uptake of nanoparticles in the body of D. magna can be observed.