O'Connor, Lauren Elizabeth2024-01-242024-01-242023https://udspace.udel.edu/handle/19716/33871Pesticides are widely used and are ubiquitously distributed in aquatic environments. Legacy pesticides are chemicals that are no longer used but still recognized as threats to ecosystems and human health due to their refractory nature. Current-use pesticides (CUPs) were introduced to replace legacy pesticides, under the assumption that they are both highly effective and possibly safer. However, the effects of CUPs on ecosystem health have not been thoroughly assessed. ☐ Chlorpyrifos (CLP) was the most commonly used consumer crop pesticide in the 2010s. Despite being banned in the United States and European Union, it continues to be used globally. Much of the research to date has focused on detecting CLP in ecosystems but have not focused on its effect on aquatic ecosystems in a holistic fashion. Further, the interaction between organic pollutants and dissolved organic matter (DOM), which is ubiquitous to all natural waters is a crucial but often overlooked mechanism for understanding the fate of these contaminants. ☐ DOM is an important source of carbon in water bodies and plays important ecosystem roles ranging from being an important substrate for heterotrophic activity to complexing toxic substances (metals and hydrophobic organic substances like CLP) rendering them less bioavailable. This dissertation studies the role that DOM plays in CLP fate in aquatic ecosystems ranging from Arctic lakes to artificial streams. In one chapter DOM-CLP partition coefficients (KDOM) were measured for a diverse pool of dissolved organic matter, mostly isolated from the Arctic at the Toolik Lake Field Station as well as reference materials obtained from the International Humic Substances Society (IHSS). Further, I calculated a theoretical KDOM using a polyparameter linear free energy relationship model (pp-LFER) calibrated to a reference IHSS fulvic acid derived from the Suwannee River, GA, USA. My results surprisingly show that CLP has a stronger affinity for lacustrine relative to fluvial DOM. The latter is derived from higher plant precursors that are more aromatic and presumably less polar than lacustrine DOM, which has a higher percentage of autochthonous components that are more polar in nature. While the pp-LFER values accurately estimated KDOM for Suwannee River fulvic acid it underestimated CLP partitioning to lacustrine DOM by as much as an order of magnitude. ☐ To better understand DOM’s role in the fate and effect of CLP on aquatic ecosystems, an 18-day experiment was conducted in the Artificial Stream Facility at the Cary Institute of Ecosystem Studies. This unique experimental facility allowed me to study the whole stream ecosystem response to the addition of DOM and CLP. Environmentally relevant concentrations of CLP and Suwannee River DOM (as well as background controls) were introduced to artificial streams. DOM composition and ecosystem metrics, e.g., gross primary production, chlorophyll A, dissolved oxygen, etc. were monitored throughout the 18-day experiment. ☐ I also measured the DOM composition, which was characterized by light absorbance and fluorescence spectroscopy. Specific UV absorbance or SUVA at 280 nm is a proxy for DOM aromaticity and surprisingly did not change during the experiment with the exception of an initial decrease on Day 1. Fluorescence measurements were conducted in excitation-emission matrix (EEM) mode and the data analyzed by parallel factor analysis (PARAFAC) to elucidate fluorescent components (based upon the excitation and emission of known substances), the fluorescence index (FI: a proxy for DOM precursor composition) and the redox index (RI: an indicator of the oxidation state of quinones, which are an important component of DOM). The model elucidated five components with three of them identified as autochthonous-derived, while the other two are considered allochthonous in nature. Unlike SUVA, autochthonous-like components increased over time, while allochthonous-like components decreased. This could be the result of heterotrophic activity degrading the added Suwannee River DOM combined with increase autochthonous components added to the DOM pool from in stream primary production. Comparisons were made also between DOM-only streams and DOM+CLP treated streams and revealed no significant differences in DOM concentration and composition but did show changes in the FI to RI relationship. ☐ Ecosystem health, often used as a proxy for water quality, was assessed by monitoring insect emergence. Streams treated with CLP showed an immediate treatment effect whereby no to little emergence of macroinvertebrates occurred. The streams treated with DOM did not attenuate CLP toxicity to macroinvertebrates. Biofilm metabolism as measured by gross primary production, ecosystem respiration and net ecosystem production remained consistent over time in all streams. Autotrophic biomass was highest on day 10, gradually decreasing by day 18, with greater biomass in CLP-treated streams compared to reference and DOM-only streams. It is believed that this was caused by macroinvertebrate mortality, which limited the grazing of the biofilms in the streams impacted by CLP. ☐ Bioaccumulation of the target pesticide in the biofilms was also examined to determine to assess CLP fate in my streams. It was found that CLP exhibited a high affinity for the biofilms, a finding not terribly surprising given its high octanol-water partition coefficient. CLP concentrations in the stream water was below detection limits of our high-pressure liquid chromatograph mass spectrometer further corroborating CLPs propensity to bioaccumulate. ☐ Overall, there was a significant treatment effect with the streams treated with chlorpyrifos and added DOM did not offer protection to the rest of the ecosystem as I had hypothesized. Statistical analyses of all the parameters measured in the streams showed that the presence of chlorpyrifos at environmentally relevant levels alter certain trends between ecosystem parameters relative to the streams without chlorpyrifos i.e RI, FI, and more. This study provides insights into the ecosystem changes that occur as a result of chlorpyrifos contamination in stream ecosystems.EcosystemAquatic ecosystemsChlorpyrifosHeterotrophic activityCrop pesticideThesis1428155114https://doi.org/10.58088/wxgp-16342024-01-22en