Date of Award
Doctor of Philosophy (PhD)
John W. Fleeger
Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous contaminants in aquatic environments. Because of their hydrophobicity, PAHs accumulate in bed sediments and pose a risk to the benthos. Information on the toxicity of sediment-associated PAHs is, however, limited and more information is needed to improve sediment quality-criteria and ecological-risk assessments. My research focused on improving our current knowledge of the acute and, especially, the sublethal effects of sediment-associated PAHs to aquatic invertebrates. Representatives of two phylogenetically distinct benthic invertebrate groups, freshwater tubificid oligochaetes and estuarine meiobenthic harpacticoid copepods, were used. Organisms were exposed to a range of concentrations of sediment-amended contaminants in laboratory bioassays. Individual PAH congeners (pyrene, fluoranthene, and phenanthrene) and a complex mixture (diesel fuel) were employed. The tubificid oligochaete Limnodrilus hoffmeisferi was tolerant to PAH effects on survival in 10-d exposures. Because of its feeding mode (head-down, bulk-deposit feeder), egestion rates were used as surrogates for ingestion rates. PAHs significantly reduced sediment ingestion at concentrations much lower than lethal. This impact had direct effects on the flux of contaminants from sediments to the water column. Offspring production was also decreased at relatively low PAH concentrations, whereas burrowing avoidance did not occur. Harpacticoid copepods display many traits desirable for sediment-toxicity testing. The estuarine species Schizopera knatreni, Nirocra locustris and Coullana sp. were used. Adult harpacticoids were relatively tolerant to PAHs in 10-d exposures. Species-specific differences in sensitivity were detected. Early life stages were much more sensitive than adults in some species, but not others. Low concentrations of PAHs decreased copepod-offspring production, egg hatching-success, and embryonic and early-stage-development rate, demonstrating the high sensitivity of life-history related endpoints. In addition, grazing on microalgae was significantly impaired at low concentrations after short exposures ($<$30 h). Finally, it was demonstrated that harpacticoids can actively avoid contaminated sediments. Harpacticoids were shown to uptake and eliminate PAHs efficiently. Lethal and sublethal effects were related to the tissue concentration of PAH. Lethal doses were within the range predicted to cause death by narcosis in animals. Low tissue concentrations were associated with significant reductions in reproduction and feeding.
Lotufo, Guilherme R., "Toxicity of Polycyclic Aromatic Hydrocarbons to Benthic Invertebrates." (1996). LSU Historical Dissertations and Theses. 6357.