Date of Award


Degree Name

Doctor of Philosophy



First Advisor



Previous monitoring studies by federal agencies such as the United States Geological Survey have shown that environmental contaminants rarely occur as single compounds but, rather, as mixtures. In aquatic ecosystems, mixtures of these compounds are often complex, sometimes containing dozens of compounds across a number of different chemical classes. Non-target aquatic organisms are frequently exposed to varying levels of contaminants based upon the physical properties of the chemicals, such as water solubility, and life-cycle habits of the individual organisms. In addition to this, past research has indicated that the presence of one class of contaminant may have an influence on the toxicities of other chemical classes. Water-only toxicity testing has historically provided a means by which researchers can rapidly determine the toxic effects of water-soluble compounds such as triazine herbicides and organophosphate insecticides. However, many legacy pesticides, such as organochlorine, and some current-use pesticides, such as pyrethroids, are strongly hydrophobic, and suspended or bedded sediments, rather than water, would generally be more appropriate matrices for monitoring. Yet sampling of sediments and quantification of residues of these pesticides is often lacking. Similarly, there have been few studies examining the toxicity of mixtures of these compounds in sediment. The first goal of this research was to examine the effects of select triazine herbicides on organophosphate insecticide toxicity utilizing water-only toxicity test with the aquatic amphipod Hyalella azteca. The second goal was to analyze an existing database of chemical concentrations using a toxicity-based screening approach in order to estimate the environmental hazard posed by mixtures of pyrethroid, organochlorine, and organophosphate insecticides in sediment to H. azteca. The third goal of this research was to examine the toxic effects of mixtures of different pyrethroid insecticides to H. azteca using compounds identified as most relevant from the screening phase of the study. The fourth goal of this research was to examine how pyrethroid and organochlorine insecticides partition between different size fractions within sediment and detritus, as well as between sediments with differing organic carbon content, and the resulting effects to compound toxicity and bioavailability. The final goal of this research was to examine potential modifications to bifenthrin sediment partitioning, toxicity, and bioaccessibility resulting from various dissolved salt concentrations in overlying water using H. azteca and Chironomus dilutus as reference organisms. Together, the individual objectives of this study provide a thorough and multi-tiered approach to determining the occurrence, environmental fate, biological effects, and bioavailability of frequently detected and co-occurring environmental contaminants in both agricultural and urban landscapes.




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