Influences of spatio-temporal variability during aquatic assessments of ionizable contaminants.

Urbanization and evolving land-use is challenging water management strategies in semi-arid regions of the United States, where stream flows are often dominated by treated wastewater effluent discharges. Effluent-dominated and dependent surface waters are becoming common in urbanized watersheds, where physical and chemistry factors can influence exposure and toxicity of many down-the-drain chemicals and contaminants of emerging concern (CECs). In these effluent-dominated systems, effective exposure increases when rate of chemical introductions to surface waters exceed chemical degradation rates in receiving systems. In fact, many consumer chemicals (e.g., pharmaceuticals) and other contaminants (e.g., ammonia, algal toxins) are ionizable across surface water pH. Here I examined aquatic biota in tidally influenced urban estuaries, where dynamic salinity and pH gradients may challenge prospective and retrospective risk assessments. In several of these urban systems, the ionizable pharmaceutical diltiazem was initially observed to exceed human therapeutic plasma doses in plasma from several fish species, which indicate risks to aquatic life in these dynamic systems. Dickinson Bayou, an urban estuary influenced by onsite (e.g., septic) and centralized effluent discharges, was then examined, in which influences of tides on spatiotemporal hazards of select ionizable contaminants were identified under conditions not typically included in routine surface water quality assessments. A third study employed the Gulf killifish, a common euryhaline species in the Gulf of Mexico, to define influences of salinity and pH conditions on uptake of representative ionizable weak bases (e.g., diltiazem, diphenhydramine) to fish plasma and body burden. Though pH, but not salinity, altered fish uptake, body burdens of diphenhydramine were elevated at low pH and apparent volumes of distribution were lower than studies with freshwater fish. The fourth chapter of this dissertation examined pH influences on toxicity of Prymnesium parvum, a harmful algal bloom (HAB) species in riverine and transition zones of a moderately saline inland reservoir. Combined with climatological and geological influences, anthropogenic changes in some Texas reservoirs support HAB of this typically estuarine alga, which appears to bloom in response to site-specific water chemistry, including pH and salinity. Observations suggest that fatty acid amides are not responsible for P. parvum related fish kills and identified locations of elevated risks for HABs of this emerging threat to water quality. Findings from these studies collectively, highlight the importance of characterizing site-specific influences on bioaccumulation and toxicity of ionizable contaminants, and integrating such information during prospective and retrospective risk assessments.