Barrett, The Honors College Thesis/Creative Project Collection

Plasticizers are plastic additives used to enhance the physical properties of plastic and are ubiquitous in the environment. A class of plasticizer compounds called phthalate esters that are not fully eliminated in wastewater treatment facilities are relevant to the ecological health of downstream ecosystems and urban areas due to their ecotoxicity, tendency for soil accumulation, and the emerging concern about their effects on public health. However, plasticizer concentrations in a constructed wetland environment have rarely been studied in the United States, prompting the need for a method of plasticizer quantification in the Tres Rios Constructed Wetlands which are sustained by the effluent of the 91st Avenue Wastewater Treatment Plant in Phoenix, Arizona. The concentrations of four common plasticizer compounds (dimethyl: DMP, diethyl: DEP, di-n-butyl: DnBP, and bis(2-ethylhexyl): DEHP phthalate) at five sites across the wetland surface water were quantified using solid-phase extraction followed by gas chromatography coupled with mass spectrometry (GC/MS). The sampling period included four sample sets taken from March 2022 to September 2022, which gave temporal data in addition to spatial concentration data. Quantification and quality control were performed using internal standard calibration, replicate samples, and laboratory blanks. Higher molecular weight phthalates accumulated in the wetland surface water at significantly higher average concentrations than those of lower molecular weight at a 95% confidence level, ranging from 8 ng/L to 7349 ng/L and 4 ng/L to 27876 ng/L for DnBP and DEHP, respectively. Concentrations for dimethyl phthalate and diethyl phthalate were typically less than 50 ng/L and were often below the method detection limit. Average concentrations of DnBP and DEHP were significantly higher during periods of high temperatures and arid conditions. The spatial distribution of phthalates was analyzed. Most importantly, a method for successful ultra-trace quantification of plasticizers at Tres Rios was established. These results confirm the presence of plasticizers at Tres Rios and a significant seasonal increase in their surface water concentrations. The developed analytical procedure provides a solid foundation for the Wetlands Environmental Ecology Lab at ASU to further investigate plasticizers and contaminants of emerging concern and determine their ultimate fate through volatilization, sorption, photodegradation, hydrolysis, microbial biodegradation, and phytoremediation studies.

Humans can influence wildlife populations and behavior through structural and behavioral disturbances, which can be particularly pronounced along the gradient of urbanization. Importantly, although anthropogenetic structural characteristics are relatively static along the gradient of urbanization for a given period of time, the presence of humans can be dynamic on daily and seasonal scales, which can affect wildlife activity patterns. The rapid onset of the COVID-19 pandemic created a unique opportunity to evaluate how a sudden change in human behavior can affect wildlife activity along the urbanization gradient. Specifically, we used a before-after-control-impact (BACI) study design to compare human presence and coyote daily activity patterns from before the COVID-19 pandemic to after COVID-19 stay-at-home orders and shutdowns were put in place in areas of low and high levels of urbanization. We predicted that human detection rates would increase in low levels of urbanization and decrease in high levels of urbanization due to the COVID-19 pandemic shutdowns. We also predicted that coyote daily activity patterns would shift in response to human detection rates, where coyotes would become more nocturnal in areas of low levels of urbanization where human presence was expected to increase and become more diurnal in areas of high levels of urbanization where human presence was expected to decrease. We used data from wildlife cameras across the gradient of urbanization from 2019 to 2020 within the Phoenix Valley of Arizona. Across 8 sites in low levels of urbanization and 12 sites in high levels of urbanization, we did not find a statistical difference in human detection rates or coyote activity patterns in response to the COVID-19 pandemic. However, low sample size likely led to low power to detect differences and next steps for this research (as part of my M.S. thesis project) will be incorporating additional wildlife camera locations and wildlife species (e.g., bobcat, cottontail rabbit, gray fox, etc.), into future analyses. This project and future studies can help us better understand how structural and behavioral characteristics of humans can shape wildlife populations along the gradient of urbanization, which has important conservation implications for wildlife and people.