ABSTRACT Advancing an Understanding of Ecological Risk Assessment Approaches for Ionizable Contaminants in Aquatic Systems. Theodore W. Valenti Jr., Ph.D. Committee Chairperson: Bryan W. Brooks, Ph.D. Freshwater is increasingly becoming a finite resource in many regions of the world. Gaps between estimated water supply and demand continue to narrow and the prospects of acquiring additional sources of freshwater remain limited. Furthermore, economically efficient water resource management practices are perplexed by increasing urbanization and changing land-use in semi-arid regions. Although repeated use of water is a practical and effective means for easing strain on water supplies, there is concern that unnecessary contamination may diminish future value of this important resource. Some surface waters in semi-arid regions of the U.S. are effluent-dominated as flow is comprised of >90% treated wastewater. Ionizable compounds are chemicals often associated with urban development and examples include pharmaceuticals, agrochemicals, natural toxins, and other common contaminants (e.g. ammonia). Because continued population growth and urbanization are likely to increase contaminant release and alter dilution capacity of receiving systems, it is important that best management approaches are developed at the watershed scale to limit water quality degradation associated with ionizable compounds. Current methods for prospective and retrospective ecological risk assessments of ionizable compounds seldom consider site-specific conditions during the analysis of effects of phase. Ionization state is largely controlled by the acid/base dissociation constant (pKa) and pH of the solution where a compound resides. Stream water quality can therefore influence ionization state, which is important because the unionized forms a more lipophilic and have a greater propensity to cross cellular membranes. Consequently, the unionized forms are hypothetically more toxic. I completed toxicity tests in the laboratory using various contaminants as model ionizable compounds over a gradient of environmentally-relevant surface water pH and then related measured toxicological endpoints to observed pH of surface waters using both discrete and probabilistic ecological risk assessment approaches. The result of my studies clearly demonstrated that site-specific pH may influence the toxicity of ionizable contaminants. Potential modifications to conceptual frameworks of ecological risk assessment for ionizable contaminants are suggested so that uncertainty can be reduced. Advancing an Understanding of Ecological Risk Assessment Approaches for Ionnizable Contaminants in Aquatic Systems by Theodore W. Valenti Jr., B.S., M.S. A Dissertation Approved by the Institute of Ecological, Earth, and Environmental Science ___________________________________ Joseph W. White, Ph.D., Chairperson Submitted to the Graduate Faculty of Baylor University in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy Approved by the Dissertation Committee ___________________________________ Bryan W. Brooks, Ph.D., Chairperson ___________________________________ C. Kevin Chambliss, Ph.D. ___________________________________ Robert D. Doyle, Ph.D. ___________________________________ Ryan S. King, Ph.D. ___________________________________ Joseph C. Yelderman Jr., Ph.D. Accepted by the Graduate School August 2010 ___________________________________ J. Larry Lyon, Ph.D., Dean Page bearing signatures is kept on file in the Graduate School. Copyright © 2010 by Theodore W. Valenti Jr. All rights reserved TABLE OF CONTENTS LIST OF FIGURES ......................................................................................................... viii LIST OF TABLES .............................................................................................................. x ACKNOWLEDGMENTS ................................................................................................ xii DEDICATIONS ............................................................................................................... xiii CHAPTER ONE ................................................................................................................. 1 Introduction ......................................................................................................................... 1 General Overview ........................................................................................................... 1 Why is Site-Specific pH Important to Ecological Risk Assessment? ............................. 2 Factors that Influence Site-Specific pH ....................................................................... 5 Scope of Dissertation ................................................................................................... 7 CHAPTER TWO ................................................................................................................ 8 Aquatic Toxicity of Sertraline to Pimephales promelas at Environmentally Relevant Surface Water pH ............................................................. 8 Introducti ..................................................................................................................... 8 Materials and Methods .............................................................................................. 11 Experimental Conditions ...................................................................................... 11 Pimephales promelas Bioassays ........................................................................... 12 Statistical Analyses ............................................................................................... 15 Analytical Methods ............................................................................................... 15 Continuous Water Quality Monitoring Data......................................................... 17 Predictions of Ecotoxicological Responses .......................................................... 18 Results ....................................................................................................................... 19 Analytical Results ................................................................................................. 19 Acute Studies ........................................................................................................ 19 Short-term Chronic Experiments .......................................................................... 21 Continuous Water Quality Monitoring Data......................................................... 22 Predictions of Ecotoxicological Responses .......................................................... 22 v Discussion .................................................................................................................. 24 Behavioral Responses To SSRIs ........................................................................... 31 Importance Of Site-Specific pH............................................................................ 34 CHAPTER THREE .......................................................................................................... 36 Sublethal Effects of the Selective Serotonin Reuptake inhibitor (SSRI) Sertraline on Fathead Minnow Under Potential Worst-case Environmental Exposure Scenarios. .... 36 Introduction ............................................................................................................... 36 Materials and Methods .............................................................................................. 42 Test Organisms ..................................................................................................... 42 Experimental Design ............................................................................................. 42 Behavioral Trials ................................................................................................... 43 Analytical Quantification of Sertraline ................................................................. 48 Comparing Measured Versus Predicted Fish Plasma Concentrations .................. 49 Statistical Analysis ................................................................................................ 50 Results ....................................................................................................................... 51 Analytical Quantification of Sertraline ................................................................. 51 SERT Binding Study............................................................................................. 52 Behavioral Trials ................................................................................................... 53 Discussion .................................................................................................................. 56 CHAPTER FOUR ............................................................................................................. 61 A Mechanistic Explanation for pH-Dependent Ambient Aquatic Toxicity of Prymnesium parvum Carter ........................................................................................... 61 Introduction ............................................................................................................... 61 Material and Methods ................................................................................................ 64 Bioassays with Samples Obtained from Reservoirs Experiencing Blooms .......... 64 Laboratory Culture Preparation