Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Chemistry

Supervisor

Hedberg, Yolanda

2nd Supervisor

Birceanu, Oana

Abstract

Corrosion is a natural process affecting the longevity and integrity of metals. N-Heterocyclic carbenes (NHCs) are robust organic compounds that can form strong σ-bonds with metal atoms, allowing for the formation of monolayers on the metal surface. This property makes NHCs promising for coating metals. However, their long-term effects on the aquatic environment are not well understood. The present study investigated the ecotoxicity of 1,3-diisopropyl-1H-benzoimidazolium bicarbonate (iPrNHC NCO3-), a candidate for organic coating enhancements, on various species of aquatic organisms. The results showed that high concentrations of iPrNHC significantly increased mortality rates in zebrafish embryos, planarians, Daphnia, and snail embryos, with notable impacts on heart rate and hatching. In contrast, low concentrations had minimal effects. A 96-hour study on planaria brown flatworms also found that higher temperatures (25°C) and neutral pH (7.5) increase the toxicity of iPrNHC, emphasizing the role of temperature and pH in its harmful effects.

Summary for Lay Audience

Civil infrastructure, such as bridges and railways, plays an important role in everyday life and is vital for the functioning and development of cities. Corrosion, a natural process that happens over time due to various environmental factors and aging, involving chemical reactions, is a major factor in the deterioration of civil infrastructure. Scientists estimate that it costs Canada an average of CAD 63.26 billion annually in repairs and corrosion prevention. Corrosion prevention practices could save up to 15%-30% of the annual global cost of corrosion. Paints and coatings are widely used as protective barriers for metals to separate metals from environment, but they are not completely impermeable to environmental factors. The current thesis tested whether newly created coating additives, called carbenes, which are effective at stabilizing and protecting metal surfaces for longer, are toxic to aquatic organisms. Using zebrafish and snail embryos, water flees and flatworms as models, this work explored whether heart rate, hatch rate, and survival were affected by exposure to various concentrations of carbene. Since the aquatic environment is exposed to major stressors, such as temperature and water chemistry changes, this study also looked at whether temperature and water pH affect how flatworms respond to carbene exposure. High concentrations of carbene showed notable effects on survival in all species and reduced heart rate and hatch rate in zebrafish and snail embryos, while lower concentrations, which are expected to be found in aquatic environments, had little impact on all studied aquatic species. This work also showed that carbene toxicity is higher at higher temperatures, while lower pH seems to protect animals against toxicity. This is the first multispecies study to explore the impacts of carbenes on aquatic organisms and to determine if water chemistry impacts toxicity. Overall, this work showed that carbenes have minimal effects low concentrations, over a short exposure time. While carbenes do not appear to be toxic, studies looking at their long-term effects, following exposure during sensitive periods of development, and at changing water conditions (temperature, pH, alkalinity, etc) should be conducted to get a better understanding of their mode of action.

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Available for download on Thursday, September 10, 2026

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