Ryan Espy

Photolysis rates of imazethapyr

ACS Chemistry, Dr. Nienow

Update:

Ryan Espy graduated from Gustavus in 2009, and is currently a graduate student in Chemistry at Purdue University.

About My Research:

Imazethapyr is a relatively new agricultural chemical used to prevent weeds in soybeans, beans, and alfalfa. Chemicals from crops naturally run off into river water, which later becomes our drinking water. Since imazethapyr has been detected in over 50% of Midwestern U.S. water samples, we are interested in determining its chemical properties and what other compounds it breaks down into in a natural environment or in water refinery plants. Imazethapyr itself is only slightly toxic, but with light and heat it breaks down into other unknown compounds. We have been doing tests by adding known amounts of imazethapyr to purified water as well as water from the Minnesota, Mississippi, and St. Croix rivers. Since there are many different factors that could be causing this compound to degrade, we are trying to reproduce environmental factors one piece at a time to determine which have the largest effects. Eventually we hope to determine what compounds imazethapyr breaks down into and whether or not they are harmful for the environment.

In the student's own words :

"I really enjoy being able to do chemistry that I haven chosen to do and then being allowed to take the project in a direction which interests me the most. Because of this reason, the experience is completely unlike that of labs for class, and the results are usually more gratifying."

Professional Abstract:

Imazethapyr is a relatively new agrochemical used to prevent weeds in soybeans, beans, and alfalfa. Since imazethapyr has been detected in over 50% of Midwestern U.S. water samples, we are interested in determining its pathways of photolytic abiotic degradation. We have observed photolysis of imazethapyr in deionized water (direct) and Minnesota River water (indirect). Imazethapyr degraded in both laboratory and natural UV-light sources. Under 254 nm light, direct photolysis has a rate constant of k = 0.451 min-1. Additional experiments with natural organic matter (NOM) in deionized water show that low NOM concentrations increase the rate constant (k = 0.526 min-1 for 1.6ppm NOM), whereas high NOM concentrations decrease the rate constant (k = 0.333 min-1 for 9.6ppm NOM). Thus, the slow, indirect photolysis rate constants are attributed to light filtering caused by NOM in the river water. On the other hand, river water with lower NOM concentrations may cause imazethapyr to degrade faster due to singlet oxygen and/or hydroxide radicals. Currently, we are working to elucidate the photolytic degradation pathways, by-products, and are also examining the hydrolysis of imazethapyr.

More student thoughts:

"Although Gustavus features very personalized attention to students from professors during the school year, the one-on-one time during research is even better. It really makes us feel more like colleagues rather than students."