Investigations of environmental transformation products
Creators: name: Knutson, Christopher Joseph
Publisher: name: University of Iowa
Year: 2023
Subjects: Environmental
HPLC
NMR
Products
Transformation
public abstract

description: As the complexity of our society continues to advance, so do the number of chemical contaminants entering our environment. These contaminants are subjected to a wide range of transformation processes, both natural and engineered. As a result, reconnaissance encompassing only initial contaminants may not provide accurate risk assessment.
description: The aim of this work has been to explore the environmental fate of selected, widely used, steroids and fungicides upon exposure to water treatment protocols. Specifically, we considered potential chemically relevant processes these contaminants might encounter while migrating through natural and engineered water systems as described in chapter 1 in order to test the hypothesis that transformation products will emerge. Some of the contaminants tested were indeed found to form transformation products under simulated water treatment conditions. The results of these experiments can be used to guide occurrence studies for these newly identified transformation products. They also enable collection of product samples that can be tested for biological effects. Ultimately, the goal was to expand our understanding of how selected environmental contaminants transform during migration through the water system while also increasing our knowledge of transformation products currently being overlooked by existing water analysis protocols and chemical reconnaissance.
description: Chapter 2 discusses the formation and structure of an unusual new bioactive photo-induced rearrangement product of the steroid dienogest. Crystallization of the purified product, dienogestenol, and X-ray crystallographic analysis enabled confirmation of it’s somewhat surprising structure and allowed assignment of its absolute configuration. Dienogestenol was shown to have bioactivity similar to that of the parent compound, albeit with less potency. The existence of dienogestenol, and its bioactivity, was previously unknown, which demonstrates the importance of thoroughly investigating how environmental contaminants transform in our environment as they migrate into our water systems. Also in Chapter 2, numerous attempts are described to oxidize another commonly used steroid, 17β-trenbolone, and purify the product (trendione) in order to explore potentially similar reactions of another important steroid. However, these attempts were unsuccessful.
description: In Chapter 3, the viability of using computational chemistry to predict the products of selected pharmaceutical steroids upon exposure to chlorination conditions used in water treatment was tested in parallel with experimental studies. In nearly all cases examined, the chlorination product of a given steroid could be predicted with reasonable accuracy as verified by benchtop chemistry in the lab. In the only instance where the computational prediction was not consistent with the laboratory results, a rationale for the discrepancy is presented which may help to better define a framework wherein researchers can use computational chemistry to predict the transformation products of environmental contaminants. The findings also established that when modeling transformation products by using a class of molecular substructures, consideration of substituent groups elsewhere in the overall structure must be incorporated, otherwise the accuracy of computational predictions may be compromised.
description: Chapter 4 extends this exploration of environmental contaminant transformation products to consider the chlorination products of strobilurin antifungal agents. The use of this class of antifungal agents is rapidly increasing, yet little is known about their fate in water treatment systems. This chapter addresses the effects of chemical softening (elevated pH), chemical disinfection (reaction with chlorine), and flocculation on a selected set of strobilurin fungicides. Trifloxystrobin and kresoxim-methyl both proved to be susceptible to base hydrolysis at elevated pH, and azoxystrobin, kresoxim-methyl, and dimoxystrobin were all susceptible to chlorination. These findings established that strobilurin fungicides are not necessarily completely decomposed in the environment, rather, they are sometimes transformed into structurally similar compounds with as-yet unknown bioactivity.
description: Chapter 5 describes limited studies of secondary fungal metabolites that were identified prior to the directional change of this thesis work to environmental transformation studies. Fungi have long been an important source of useful bioactive natural products beyond the strobilurins, with well-known examples such as penicillins, pravastatin, and cyclosporin.1 This work mainly involved dereplication of secondary fungal metabolites during exploration of selected fungal fermentation extracts for novel molecules with bioactivity. Only a few metabolites were encountered and identified prior to shifting focus to environmental work, but these initial studies provided experience with chromatography and spectroscopy that proved to be useful in the studies described in earlier chapters of this thesis.
description: Collectively, this work confirmed the hypothesis that contaminant transformation products would emerge as the result of both natural and engineered environmental processes. This work recognizes that the traditional approach of evaluating potential products of each individual contaminant of interest is by simulating relevant environmental processes in the laboratory is time-and resource-intensive and is currently unable to keep pace with the rate of new contaminants being introduced to the environment. However, it does lay groundwork for using computational chemistry to predict new environmental transformation products with support being provided by selected, representative laboratory experiments.