Document Type

Theses, Ph.D

Rights

This item is available under a Creative Commons License for non-commercial use only

Disciplines

Environmental sciences

Publication Details

Successfully submitted for the award of Doctor of Philosophy (Ph.D) to the Dublin Institute of Technology 2004.

Abstract

Sediments, as a repository for persistent anthropogenic contaminants, have the potential to cause deleterious effects in the aquatic environment. Particular attention to the quality of sediment is, therefore, warranted in the ecotoxicological risk assessment of aquatic systems. An assessment methodology combining chemical, ecotoxicological and ecological evaluations in a hierarchial test strategy, where toxicological significant and complexity increases with the tiers, is recommended for a thorough appraisal of sediment toxicity. The aim of the present study was to assess the potential of in vitro bioassays to be employed as screening tools got Tier 1 ecotoxicity evaluation of Irish estuarine sediments. Chemical analysis was conducted on all sediment samples to assist in interpreting any observed cytotoxicity. The potential toxicity of various exposure phases (solid phase, porewater and elutriate) from three estuarine sediment samples was evaluated using representative organisms from a number of trophic levels. The potential impact of the differing salinities of the sediment aqueous extracts, on the sensitivity of the bioassays, was also addressed. The selective sensitivities of the assays employed, demonstrated the value of using a multi-trophic, multi phase battery approach to sediment toxicity testing. Inhibition of bacterial bioluminescence and algal growth, were identified as sensitive bioassays for Tier 1 screening purposes. Immortal cell lines and primary epidermal cell cultures were used as representative vertebrate model systems. Initial studies were carried out using zinc metal salts as model environmental contaminants, to establish reference values which could be employed as test validity criteria for the sediment toxicity tests. This work also permitted an evaluation of the sensitivity of the cell cultures and the multiple endpoints utilised. The high sample osmolality of porewater extracts precluded their assessment using the cell culture assays. Of the three cell lines utilised in this study, RTG-2 cells were the most suitable for the testing of estuarine elutriate samples on the basis of their tolerance to osmolality effects. While significant cytotoxic effects were not detected following exposure to any of the three elutriate samples examined, it was notable that these samples did not elicit any significant reduction in bacterial bioluminescence either when assessed using the Microtox system, a widely accepted regulatory bioassay for the screening of environmental samples. Cellular responses detected in primary epidermal cultures following exposure to elutriate extracts were used to discriminate between samples of different contaminant burden. These responses included increases in apoptosis and necrosis, reduction in goblet cell area and increased acidification of mucin glycoproteins. Parallel exposures with osmolality controls ensured that the toxicity observed was due to sample contaminants and not osmotic stress. The ability of low levels of contaminants in these aqueous extracts to elicit a toxic response in this model system indicates the potential of these cultures to be employed in ecotoxicological assessments. Finally, this research demonstrated the functional activity of a multixenobiotic resistance mechanism in in vitro cultures of fish epidermis. While further research is needed to validate these findings in vivo, the presence of an inducible P-gp phenotype and an mdr1-like efflux mechanism in the epidermal cell cultures indicate that this in vitro model could be used to elucidate the significance of P-gp mediated transport as a protective mechanism against environmental toxicants in fish. Furthermore, as this mechanism was inhibited following exposure to elutriate prepared from the most contaminated sediment sample, the modulation of its activity could potentially be used as a marker of contaminant exposure

DOI

10.21427/D70K6B

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