The environmental toxicology of zinc oxide nanoparticles to the oligochaete

Abstract

This thesis investigated the potential toxicity of zinc oxide nanoparticles (NPs) and bulk particles (both with and without organic matter (HA)) to the Californian Blackworm, Lumbriculus variegatus. The NPs and bulk particles in this thesis were characterised using numerous techniques. ZnO NPs were found to be 91 (13364) nm (median (interquartile range)) and ZnO bulk particles were found to be 237 (322165) nm (median (interquartile range)) by TEM. In the acute behavioural study (96 hour), ZnO NPs had a dose-dependent toxic effect on the behaviour of the worms up to 10mg/L whereas the bulk had no significant effect. This result, however, was mitigated by the addition of 5mg/L HA in the NP study whereas a similar addition enhanced the toxicity of the bulk particles at 5mg/L ZnO. In the chronic study (28 days), ZnO NPs and bulk particles were found to have a dose-dependent significant effect on the behaviour of the worms after 28 days, with NPs causing a significantly greater negative response than bulk particles at 12.5, 25 and 50mg/L ZnO. HA had no effect on the toxicity of either particle type in the chronic study. Acute (96 hour) oxidative stress in L. variegatus in response to ZnO NP and bulk particle (with and without 5mg/L HA) exposure was evaluated by examining the changes in glutathione (GSH) content of cells, since NPs are expected to have potential for toxicity via mechanisms such as oxidative stress. Neither ZnO NPs nor bulk particles (with and without 5mg/L HA) were found to induce significant changes in the GSH content of L. variegatus cells after 96 hours of exposure. The uptake, accumulation and depuration of ZnO NPs and bulk particles in L. variegatus over a 48 hour period of uptake and a 48 hour period of depuration were also investigated. This study found a high level of variability and it was concluded that the protocol employed was not suitable for investigating the uptake, bioaccumulation and depuration of ZnO NPs and bulk particles. Finally, histological techniques and a number of fixatives were evaluated for use with L. variegatus. Bouin’s solution was found the most suitable fixative for use with these worms, with no histological damage observed in the morphology of the worms after a 96 hour exposure to ZnO NPs and bulk particles (with and without 5mg/L HA). When considering the toxicology results from all experiments within this thesis it is concluded that ZnO NPs can cause both acute and chronic toxicity in terms of behavioural response, but do not cause acute oxidative stress in L. variegatus.