Title page for ETD etd-04112005-145019

Type of Document Dissertation
Author Gust, Kurt A.
Author's Email Address kgust1@lsu.edu
URN etd-04112005-145019
Title Ecotoxicology of Metal-Hydrocarbon Mixtures in Benthic Invertebrates
Degree Doctor of Philosophy (Ph.D.)
Department Biological Sciences
Advisory Committee
Advisor Name Title
John W. Fleeger Committee Chair
Joseph Siebenaller Committee Member
Kevin Carman Committee Member
Ralph Portier Committee Member
Huiming Bao Dean's Representative
  • polynuclear aromatic hydrocarbons
  • metals
  • contaminant mixtures
  • environmental pollution
  • sediment toxicity
  • ecotoxicology
  • bioaccumulation
  • benthic invertebrates
Date of Defense 2004-12-01
Availability unrestricted
Metal-hydrocarbon mixtures are becoming increasingly prevalent in natural environments due to expanding industrial activity and urbanization. The ecotoxicology of metal-hydrocarbon mixtures in benthic environments is of particular concern because both classes of contaminants partition to sediments and can thereby exert toxic effects in benthic organisms. Mixtures of dissimilar chemicals (including metals and hydrocarbons) are broadly hypothesized to elicit independent toxic effects however; this hypothesis has little supporting data. The purpose of this dissertation was to test this hypothesis for metal-hydrocarbon mixtures using environmentally relevant exposures and to determine mechanisms for observed interactive effects. Sediment and water-only bioassays were conducted employing the toxic heavy metal cadmium (Cd) and the polynuclear aromatic hydrocarbon phenanthrene (Phen) as model toxicants. Lethal and sublethal effects of singular and combined contaminants were examined in two freshwater species, the epibenthic amphipod Hyalella azteca and the bulk deposit-feeding benthic oligochaete Ilyodrilus templetoni. When interactive toxicity was observed, mixture effects on contaminant bioavailability, bioaccumulation and elimination were tested. As well, mixture effects on bioenergetics parameters were investigated and kinetic modeling was conducted to establish the source of mixture-mediated changes in contaminant bioaccumulation in I. templetoni. Cadmium-Phen mixtures caused independent effects in water-only exposures, but when incorporated into sediments, elicited synergistic lethal effects in H. azteca and antagonistic lethal effects in I. templetoni. Interactive effects were likely caused by Phen-mediated alterations in Cd bioaccumulation that resulted from changes in exposure via feeding.

The current basis for assessing ecotoxicological effects of contaminant mixtures in natural environments relies heavily on models derived from dosage-based mixture toxicology with considerably less emphasis on environmental science and biology. Understanding how contaminants interact toxicologically is important, but does not provide all the information necessary for assessing effects in natural populations that encounter contaminant mixtures in a diversity of natural environments. My experiments indicate that exposure source may be more important than dosage-based toxicological interactions in determining contaminant mixture effects in sediment environments. If this trend is widespread, understanding how species are exposed, determining the route of uptake and understanding how environmental characteristics affect exposure may be more important in determining mixture effects than mixture toxicology.

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