Annie Opseth

Determination of rate constants of imazethpyr photolysis in aqueous
solution and measurement of ions in the Seven Mile Creek Watershed

ACS Chemistry, Dr. Nienow
About My Research:

Imazethapyr is an herbicide used for weed control in rice, soybean and sunflower crops. Since it is a slightly toxic chemical, it is of interest to know how it reacts in different environments. A simulated environment can be set up in the lab to study the photodegradation of imazethapyr in water at different wavelengths using an instrument that mimics the UV light portion of sunlight. High-Performance Liquid Chromatography (HPLC) can be used to quantify the amount of imazethapyr remaining after it is exposed to the light source for a certain amount of time. By calculating the rate constants for imazethapyr’s degradation under different conditions we can get an idea of how it actually behaves in the environment. Another source of water contamination is farmland runoff; it can greatly increase the amount of ions in groundwater to a level that is considered unsafe. The source of the ions is the pesticides that farmers apply to their field during harvesting. Water samples can be taken at different sites along a water pathway to quantify the contaminants and determine how far they travel. Ion Chromatography (IC) can used to quantify the amount of different ions present in the water samples. We then know what ions are at the highest levels and need to be reduced for safer water quality. It can even be taken as far back as investigating which pesticides contain the most concentrated ions and looking for an alternative that farmers can use or proposing an alternative method for reducing farmland runoff.

This research was supported with a grant from the National Science Foundation.

In the student's own words :

"As research students, we have the chance to acquire knowledge about instruments, techniques and research in general that is not taught in the classroom. In addition to the scientific knowledge we gain, we learn about our responsibilities as scientists and the importance of being able to work efficiently and comfortably in groups. So far, my summer research experience has ensured me that I am choosing the career path that is a great fit for me."

Professional Abstract:

Imazethapyr is an herbicide, of the imidazolinone group, that is used to control weeds in rice, soybean and peanut crops. Imazethapyr absorbs light above 290 nm and for this reason, photolysis is likely to be a primary pathway for its degradation in water. Experiments were conducted in the laboratory to determine the direct photolysis rate constants of imazethapyr. The first-order rate constant (k) for the degradation of imazethapyr in pH 7 phosphate buffer under 254 nm lamps was determined to be 0.5680 min-1, while the rate constant for its degradation in pH 2 phosphate buffer was 0.0512 min-1.  Imazethapyr’s lowest pka value is 2.1, which when looking at these results, shows that imazethapyr’s degradation rate does vary with pH below its pka. The reaction quantum yield (Φ) of imazethapyr was found to be 0.057, using the PNAP/pyridine system as the actinometer. These results provide us with an idea of how imazethapyr acts in natural water environments.

More student thoughts:

"High Performance Liquid Chromatography (HPLC) is the primary instrument that I use in my summer research. Over the past weeks I have been able to draw on my previously learned knowledge of HPLC that I acquired in Quantitative Analysis this past fall. In this class I learned about mobile phases, stationary phases, retention time, and other RPLC parameters and how they can be adjusted to separate a specific compound. This knowledge has helped me work through various problems I have encountered when working with the RPLC and gives me a reference point to start from if I’m unsure of what step to take next."