Abstract
Toxicity laboratory tests are used world-wide to manage environmental resources such as water
quality and are considered to be the first step in a tiered approach in establishing guidelines for
setting maximum acceptable concentrations of specific pollutants. The aim of this study was to
evaluate the aquatic toxicology of gold nanoparticles (nAu) using a combination of acute and
chronic ecotoxicological bioassays. Particle distribution and agglomeration in the reconstituted
water medium was evaluated using several microscopy techniques as well as characterization
tools which included dynamic light scattering and Fourier transform infrared spectrometery.
Range finding exposure tests were done to determine the LC50 of nAu in Pseudokirchneriella
subcapitata, Daphnia pulex, Daphnia magna and 14 day old Danio rerio using standard OECD
protocols where ionic gold and solvent controls were also included. The acute toxicity showed a
bimodal response for nAu and an LC50 was only calculated for D. pulex at 75.314mg/l while
ionic gold concentrations had an LC50 with a 95% confidence level at 0.01mg/l and 4.85mg/l
daphnia and 14 day old zebrafish respectively. The in vivo nAu distribution and mechanical
effect was observed using several microscopy techniques which showed the attachment of nAu
to the surface of algae and daphnia, uptake via the gills and storage in cartilage and muscle
tissue in zebrafish as well as nAu ingestion of agglomerates visible to the naked eye (40mg/l
and 45mg/l). A reproductive study in D. magna to determine the effect of nAu on molting
patterns related to reproduction showed that as exposure concentrations increased daphnia
molting also increased and a lower correlation was seen between reproduction and molting as
concentrations increased. Sub lethal testing was done by exposing adult zebrafish (D. rerio) to
nAu for 96 hours at a concentration range of 5mg/l to 45mg/l with a 5mg/l interval between
concentrations. Male fish livers were stored in RNA later and grouped samples were used for
DNA microarray. Real time polymerase chain reactions (RT-PCR) were used to determine
changes in gene expression in the liver comparing male fish to female fish. The results obtained
from scanning the gene chip gave an indication of events in the cell based on 15 618 genes
being regulated. The gene ontology was further investigated using ArrayStar® to show pathway
interactions as well as the clustering of genes. The 20mg/l and 25mg/l nAu concentrations
showed similar genetic clustering and these were related to 40mg/; and 45mg/l respectively. By
using a process of elimination genes were narrowed down to 75, genes that are not yet properly
understood in the zebra fish genome and genes that had a fold change less than threefold were
eliminated. Pathways were then looked at and the following genes were focused on and used...
D.Phil. (Aquatic Health)