Thesis (Ph. D.)--University OF MICHIGAN.

Thesis (Ph. D.)--University OF MICHIGAN.

Thesis (Ph. D.)--University OF MICHIGAN.

Thesis (Ph. D.)--University OF MICHIGAN.

Thesis (Ph. D.)--University OF MICHIGAN.

Thesis (Ph. D.)--University OF MICHIGAN.

Thesis (Ph. D.)--University OF MICHIGAN. / CHAIRMAN: STEVEN P. LEVINE.

Pesticides are used primarily for agricultural purposes in the US and while these chemicals provide many benefits, the inherent toxicity of the compounds pose a substantial risk to the environment. These chemicals may enter water bodies in areas with a high proportion of agricultural land use through surface run off, ground water discharge, and erosion, and negatively impact non-target aquatic organisms. As a result, Louisianas estuaries may be vulnerable to a variety of compounds, including the herbicide atrazine. Atrazine is used extensively throughout the Midwest and has been known to enter the Mississippi River through surface runoff and ground water discharge. The River transports the compound downstream to the delta, where it is discharged into Louisianas coastal estuaries. Due to the high amount of sugarcane production in the southeastern part of the state, atrazine also has the potential to enter these systems indirectly through agricultural runoff, and adversely affect native aquatic organisms. Because it is a photosynthesis inhibitor, phytoplankton communities may be especially susceptible to atrazine exposure. The phytoplankton stress response in these systems may be critical because phytoplankton form the base of the food web and are essential to the production of the entire ecosystem. The purpose of this study was to determine the extent of atrazine contamination in Louisianas estuaries, and its effect on local phytoplankton stress response. Field samples were taken under low and high flow and nutrient conditions from Breton Sound and Barataria Estuary. The results showed that atrazine was consistently present in these systems at low levels. Local phytoplankton from Barataria Estuary were also grown in microcosm and exposed to an atrazine dilution series under low and high nutrient conditions to determine the phytoplankton stress response. The treatment groups that received 5 ppb and 50 ppb atrazine treatments under high nutrient conditions exhibited an extended lag phase and entered into the exponential growth phase several days after the control groups. Overall, communities in nutrient enriched treatment groups exhibited higher growth response, oxygen production, and were healthier than non-enriched groups, indicating that atrazine exposure may induce a stress response in phytoplankton communities under low nutrient conditions.

Approximately 4.9 million barrels of crude oil along with natural gas were released into the Gulf of Mexico (GoM) from April to July 2010 (Deepwater Horizon, DWH, spill). Impacts of this magnitude seldom occur in the GoM (Ixtoc I was the last spill close to this magnitude occurring in 1979), and one cannot predict when they will happen. Major constituents of concern found in crude oil are Polycyclic Aromatic Hydrocarbons (PAHs), which often have low volatility that allows for prolonged existence in the environment. PAHs are compounds of concern according to the United States Environmental Protection Agency (USEPA), with one characteristic being that they have the potential to accumulate within adipose tissue. Several PAHs are listed as mutagenic and carcinogenic, making their presence in commercial fishery populations of major environmental concern. Gulf menhaden fishery was chosen for use as an indicator for impact of crude oil exposure in the years following the spill event. Total whole body PAH concentrations along with both benzo[a]pyrene, toxic and mutagenic equivalents (BaP-TEQ and BaP-MEQ respectively), were used to determine overall impact on the species. Proposed standard weight equations and length categories for Gulf menhaden were developed to assess morphological changes in the species. Lipid content was also used as a metric for determining overall health of the Gulf menhaden. Results are outlined in each chapter abstract.

The Deep Water Horizon oilrig explosion led to the release of 6.8 ± 1.7 x 108 kg or 4.9 million barrels of petroleum hydrocarbons into the Gulf of Mexico. The spill persisted from the end of April to mid July 2010 affecting a significant portion of the Gulf coast. The effects of this spill are being studied in labs across the country, and this thesis investigated high-energy water accommodated fractions (HEWAFs) as a potential tool for use in this effort. Water accommodated fractions (WAFs) are mediums containing only the fraction of petroleum that remains in aqueous phase after a mixing energy has been removed, and after a period sufficient for phase separation. HEWAF was the exposure medium of choice because this type of WAF is created by vigorous mixing of seawater with crude oil, similar to what occurs in the environment. The effects of plankton (a zooplankton and phytoplankton species) on the toxicity of HEWAFs were also investigated because the spill occurred at a time of year when plankton populations are especially high in the Gulf of Mexico. Dr. Sarah Webb looked at how the HEWAFs and inclusion of plankton affected the test species, Anchoa mitchilli. The inclusion of plankton was also meant to more closely resemble the natural environment, and give a more accurate indication of oil spill dynamics in the Gulf ecosystem. The trials conducted throughout this experiment demonstrated that concentrations of aromatics and alkanes increased steadily with increases in HEWAF loadings. At high HEWAF loadings (33.3% HEWAF and above), alkane and aromatic concentrations in samples containing plankton were elevated; however, this effect dropped off in lower HEWAF concentrations (15% HEWAF and below). HEWAF shows potential as a tool in exposures simulating GoM conditions, but much more work needs to be done before the results they yield are reliable. The species responsible for the planktonic effect seen in the high HEWAF loading studies was not determined in this study; however, the results do show that plankton might play a significant role in crude oil partitioning in the environment. This would make plankton important in exposures for determining real world oil toxicities.