Biotransformation of the active ingredients in PAXLOVID, nirmatrelvir and ritonavir, in aerobic soils
Open Access
- Author:
- Vozenilek, Natasha
- Graduate Program:
- Biorenewable Systems
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- February 29, 2024
- Committee Members:
- Michael Mashtare, Thesis Advisor/Co-Advisor
Heather Elise Preisendanz, Committee Member
Suat Irmak, Program Head/Chair
Patrick Joseph Drohan, Committee Member
Clinton Williams, Special Signatory
Ronald Turco, Committee Member - Keywords:
- emerging contaminants
pharmaceuticals
COVID-19
pandemic
SARS-CoV-2
biotransformation
agriculture
nirmatrelvir
ritonavir
PAXLOVID
aerobic soil - Abstract:
- In response to the emergence of SARS-CoV-2, the novel coronavirus that first caused the coronavirus disease in 2019 (COVID-19) and led to the COVID-19 pandemic, the repurposing of existing pharmaceuticals and the development of new pharmaceuticals for the treatment of COVID-19 became necessary. Once taken, these pharmaceuticals are excreted and introduced into wastewater treatment plants. Many wastewater treatment plants do not possess the technologies necessary to completely remove these contaminants from wastewater during the treatment process, and require additional technologies, which may be expensive to implement at the treatment plant scale. The incomplete removal of these compounds during wastewater treatment poses a potential risk to ecosystem health when wastewater residuals are beneficially reused in agroecosystems (i.e., application of contaminated irrigation water or biosolids), or discharged into receiving waters. This study focused on two novel pharmaceuticals used in the treatment of symptoms of COVID-19, nirmatrelvir and ritonavir, the active ingredients in PAXLOVID. PAXLOVID is an oral medication for COVID-19 and was first utilized publicly in December of 2021 following an Emergency Use Authorization by the United States Food and Drug Administration (FDA). It later gained full approval in May of 2023. The use of ritonavir, a human immunodeficiency virus (HIV) protease inhibitor, as a pharmacokinetic enhancer for other pharmaceuticals has been in practice since the drug was approved in 1996 by the FDA; however, our understanding of the environmental fate-transport behavior of this drug is still limited. To date, studies on ritonavir have been limited to its occurrence in hospitals and wastewater effluent. Studies analyzing occurrence in wastewater effluent indicated the presence of ritonavir in effluent posed medium ecotoxicological risk to aquatic species. Risk assessments regarding the behavior of ritonavir in the environment have largely focused on aquatic ecosystems; however, no assessments have been made for nirmatrelvir, due to its novelty. Given the coupling of ritonavir with nirmatrelvir for PAXLOVID, production of ritonavir had been increased to at least 100 million tablets to meet demand associated with COVID-19 in 2022 with a total of 7 million courses distributed by the end of the year in the United States. By October of 2023, 3.4 million courses had been administered in the United States. While demand for PAXLOVID has fluctuated following its approval, quantifying the biodegradable half-lives of nirmatrelvir and ritonavir is necessary to better understand the potential for these chemicals to persist in agroecosystems following the beneficial reuse of wastewater treatment plant residuals (i.e., biosolids application and/or irrigation with treated wastewater) or direct discharge into receiving water. The overarching goal of this study was to assess the potential for persistence of the two active ingredients in PAXLOVID, nirmatrelvir and ritonavir, in aerobic soils. A degradation study was carried out for 126 days in aerobic soil microcosms containing soils with different taxonomic properties to assess the role that soil properties played in differences in loss exhibited by the two compounds. Three soils were collected for this study, two of which were agricultural soils with different cover crops (e.g., PSF2 and PSF3) and one forested soil (i.e., MOR). Abiotic controls were included in this study to investigate whether compound loss was mainly driven by biological processes or chemical processes. To prepare abiotic controls, microcosms were wet autoclaved at 120˚C for one hour to sterilize the soil, followed by a 24-hour re-acclimation period. A total of three sequential autoclaving and re-acclimation periods were carried out to ensure suppression of biological activity within those soil microcosms. Although the target pharmaceuticals are co-administered as treatment for COVID, soil microcosms were amended with single pharmaceutical solutions to gain insight on individual compound behavior rather than interactions between the compounds that could have influenced their respective behavior. Microcosms were amended with pharmaceutical solutions via glass syringe to ensure consistency of amendment between microcosms. Total concentrations were 101 µg/kg soil and 97 µg/kg soil for ritonavir and nirmatrelvir, respectively. Following pharmaceutical amendment, soil microcosms were stored upright in the dark until the time of sacrifice. Microcosms were aerated weekly and moisture content was adjusted as needed. Results from this study gave insight to the potential for persistence (i.e., half-lives) of ritonavir and nirmatrelvir in aerobic soil. Over the duration of the study, no half-lives were observed for abiotic soil microcosms regardless of soil series or compound, but some loss was exhibited for both compounds after a lag period. This was likely due to resurgence of biological activity, after which loss occurred, signaling chemical processes were occurring slower than biological processes. Observed biotic half-lives for ritonavir were approximately 121 days, 62 days, and 40 days in MOR, PSF2, and PSF3 soil, respectively. Observed biotic half-lives for nirmatrelvir were approximately 80 days, 18 days, and 17 days in MOR, PSF2, and PSF3 soil, respectively. Differences in loss between the agricultural soils and forested soil was likely due in part to differences in management for the agricultural soils and lack thereof for the forested soil, which impacted the abundance and diversity of microorganisms present within the soil. Additionally, data from this study suggested that soil pH influenced ionization of each compound. Generally, nirmatrelvir had a larger percentage ionized than ritonavir at the pH values of the soils used in this study (i.e., pH range of 5-7). The ionization of each compound influenced the interactions between the compounds and the soil and the decay rates for the compounds within each soil. Results of this study provide insight to the potential for environmental persistence of the two compounds nirmatrelvir and ritonavir that make up the COVID-19 therapeutic, PAXLOVID. Additionally, results from this study may aid in decision making for land reclamation efforts that utilize wastewater treatment plant (WWTP) residuals, where contamination of the land could have long term effects.