Science Spotlight: Costanza-Robinson Lab

Environmental chemistry is broad field that spans the study of chemical processes in the atmosphere, earth, water and biological world. Associate Professor of Chemistry, Biochemistry and Environmental Studies Molly Costanza-Robinson has found her niche in the study of contaminant fate and transport.

A contaminant is any sort of chemical substance that is not naturally found in an environment or is found in low concentrations naturally that can cause harm to the organisms living in that environment when the concentration increases. DDT, Agent Orange, carbon monoxide and lead are all contaminants, and are harmful once they reach a certain concentration in the environment.

Contaminant fate and transport is the study of how the contaminating substance moves through and interacts with the environment. Costanza-Robinson is primarily interested in organic (hydrogen- and carbon- containing) human-generated contamination in the environment. She studies the fate and transport of contaminants generated by industry, agriculture and transportation.

“Over the course of my career, some of my work has focused on chlorinated solvents," she said. "These are solvents that everybody in industry loves. They’re huge in the computing industry, for example, because they clean all the oils off of silicon wafers. Dry-cleaners use chlorinated solvents too, to remove stains from your clothes. But many of these solvents are carcinogenic, and they’re so heavily used in industry that they are one of the most ubiquitous groundwater contaminants in the United States. I did a lot of my earlier work in Tucson, Arizona, related to a field site where the city and others had dumped chlorinated solvents for years. TCE (trichloroethylene) had seeped out into drinking water supplies, and in some areas, the detection level in wells was pretty much 100%. The largely Hispanic and less affluent community became a cancer hotspot and more $100 million has been paid out in environmental justice settlements, not to mention the cost of cleanup."

Big picture: Costanza-Robinson is working to develop a filter that could easily remove such pollutants from a contaminated water supply. She’s working with two thesis students, Annie Mejaes ’13 and Malcolm Littlefield ’13, to characterize an engineered clay that could be used as such a filter.

Littlefield elaborated:  “[We’re] characterizing surfactant-modified clay, which is a material that we would like to use as a filtration medium to remove organic contaminants from aqueous systems. By running the contaminated water through this surfactant-modified clay, the contaminants should partition from the aqueous phase into this organic phase that is created at the clay surface. 'Like dissolves like' is a common phrase thrown around in chemistry. All absorption filters use the same fundamental mechanism. It’s like a fish tank, which simply draws water from the tank, runs it through an activated carbon filter to which any organic contaminants (like fish pee) will stick. This would do the same thing, but at much lower cost [than an activated carbon filter].”

In an aqueous environment (i.e. in water) the clay that Costanza-Robinson and her students are using forms layers similar to slices of bread. Normally, the pollutants (think of them as potential sandwich fillings – lettuce, tomato, pickles, peanut butter, etc.) can’t fit in between these clay layers nor would they terribly keen on doing so, even if there were space. This is because the clay has a charged surface, while the pollutants are non-polar, meaning they have no charge, not even a little bit. For the nonpolar organic contaminant to get into the clay would violate the principle of “like dissolves like.” This is a real problem, because the “interlayers” of the clay are where most of the surface area is – if this area isn’t attractive to the contaminants, the filter isn’t going to be very effective.

Ever made a salad dressing and mixed oil and water? The oil won’t dissolve in water because oil is made up of nonpolar organic molecules, while water is a polar molecule. The two different types of molecules simply do not interact. To continue with the sandwich analogy, the fillings will not go in between two slices of dry bread on its own. The surface of the bread needs to be altered to make the environment between the slices favorable for fillings.

The clay the Costanza-Robinson lab uses is a “surfactant-modified clay,” which means that the surface in between the clay layers has been modified so it is only partially charged or not charged at all – in other words, it is now more “like” the contaminants.  Surfactant-modified clay might be thought of as bread that has been buttered to create a better environment for the fillings to stick to.  Costanza-Robinson, Mejaes and Littlefield want to understand the chemistry governing how the amount and type of “butter” between the clay layers influences the amount of contaminant that can be stuffed inside.

Costanza-Robinson was excited about the work ahead.

“We’re not the first to study these modified clays," she said. "People have been doing this for decades, but the research has focused largely on “this works” or “this doesn’t." We are trying to figure out the mechanism of that explains what works and what doesn’t. My students are studying different surfactants with different alkyl chain lengths and saying: do you need some minimum chain length before things can fit in there? Is there an optimal amount of surfactant coating on the clay surface that maximizes contaminant absorption? So we are starting with some mechanisms that we understand, that some people have figured out in the literature, and then we’re going to play with a few more variables that haven’t been considered before. It’s a brand new project in my lab. We don’t have any data yet. We’re exploring. We’re refining our questions. It’s a fun stage of the project.”

 

Editorial Note: An earlier version of this article incorrectly stated that water is a charged molecule and misrepresented the analogy of buttered bread and the clay layers that the lab examines. The above text has been corrected to reflect water's true nature as a polar molecule and to more accurately utilize the "butter" analogy. The Campus regrets these errors.