Fifty years ago, environmentalists worried mostly about contaminants like oil and certain toxic pesticides, the DDT billowing from crop dusters and municipal trucks, for instance. But as agricultural technology has changed, the types of contaminants in our waters and soils have changed as well. Antibiotics, hormones, and new herbicides have become more widespread, and we don’t fully know the consequences—for agriculture, the ecosystem, or public health.
That’s part of what Ludmilla Aristilde, Biological and Environmental Engineering, seeks to understand. “We know that in the environment, contaminants don’t exist by themselves, they exist with natural compounds and particles,” she says. “We want to understand how natural processes can transform contaminants, as well as how contaminants are trapped in the environment, how they degrade or persist.”
Underlying this investigation is the need for a molecular understanding of both chemical and biological dynamics within the complex matrix of soil and water environments, how organic materials, microbes, metals, and minerals all interact. By discovering these mechanisms, Aristilde’s research group is making strides towards understanding natural processes that maintain environmental health in the face of new and profuse contaminants and the inevitable impact of climate change.
Environmental Behavior of Pharmaceuticals and Herbicides
Antibiotics do important work to keep us healthy and to keep animals healthy—but only about 40 percent of consumed antibiotics is actually metabolized. Up to 60 percent passes through and is often transferred to manure on fields. While it has been observed that these antibiotics become trapped in soils, especially when there are high concentrations of metals and minerals, the mechanism wasn’t known for how the metals contributed to this trapping.
In a recent study, Aristilde and her group found that, contrary to prevailing hypotheses which attributed the trapping to electrostatic interactions, the metals in fact change the structure and configuration of minerals in the soil, and this shifting creates nanopores where the antibiotics become encased. Understanding this mechanism sets the stage for better detection and extraction of these antibiotics down the line.
The study is also important because it reinforces a truth that Aristilde is finding over and over again: that structure, in addition to chemical properties, is a key piece of the picture. “It’s not all about the chemical interactions,” Aristilde says. “There’s another layer of complexity—the role of structures, the contaminant structure and the binding conformation in concert with interaction chemistry. There’s always one more layer of complexity in environmental research.”
“There’s always one more layer of complexity in environmental research,” Aristilde says.
Another inquiry underway in Aristilde’s lab is looking at how different classes of antibiotics and herbicides affect natural biological processes. As a graduate student at University of California, Berkeley, Aristilde found that a specific class of antibiotics can mimic the actions of molecules that are native to cells and can disrupt cellular functions like photosynthesis. “Contaminants mimicking the action of natural molecules in our cells was not a surprise, but finding that this specific antibiotic interferes with photosynthetic enzymes was new,” Aristilde says. “It came to mind that there are potential dangers beyond the well-defined targets of antibiotics and herbicides. There are non-targeted organisms that can also be vulnerable.”
Breakdown of Organic Matter and Contaminants
“As the climate warms, all of this organic material that’s stored in soils can be made available for respiration, which has carbon dioxide as its byproduct,” says Aristilde. “Knowing how the organic material is degraded—the cellular controls on the metabolism—is essential to predicting the microbial contribution to how much carbon dioxide is released from organic matter breakdown.”
Enzymes produced by microbes and secreted outside of their cells are required to break down complex organic materials into simpler compounds that microbes can use for food. Research efforts in the Aristilde group are investigating how the activity of these enzymes is controlled by the chemistry of the environment where they are secreted. The same enzymes are also used to engineer transformation of organic waste during biofuel production.
In a recent publication, Journal of Structural Biology, Aristilde presents a computational chemistry approach that figures out a link between enzyme structure and the sensitivity of enzyme activity to their chemical environment.
Aristilde is also interested in what is going on inside microbes, the cellular metabolism. Many contaminants and types of natural organic matter can be classified as aromatic—containing a ring structure. Examples include many herbicides, plastics, and oil contaminants but also lignin, which forms the structural material in many plants. Aristilde’s lab is interested in how soil microbes use these aromatic components—because the way the different components of organic matter are broken down and metabolized has important implications for progress in the biofuel industry and remediation technology.
Along these lines, Aristilde’s group is also looking at aromatic contaminants and how and why microbes choose between contaminants and natural substrates, as well as how soil microbes have diversified their metabolism to make use of different substrates. These inquiries could help engineer new and improved approaches for bioremediation and the generation of biofuels.
A Product of Her Environment
Aristilde looks at how molecules and microbes are interacting beyond what the eye can see, but she also keeps the big picture always in mind. “I work at the interface of environmental chemistry and environmental health,” she says. “For me, the public health implications are huge.”
Aristilde grew up in Haiti and experienced how poor water sanitation can endanger a population. Her father was an educator and also a farmer, raising chickens and pigs and growing sugar cane, sweet potatoes, spinach, and corn in rotation. “The combination of those two things—the environmental contaminants and soil health, and what makes soil the most amenable to crops—those things were common threads in my upbringing,” she says. “My parents were also both teachers, so education has also been a big part of my life.”
Aristilde immigrated to the United States when she was a teenager and fell in love with chemistry while finishing high school in Brooklyn. “I had a wonderful chemistry teacher from Jamaica, and I just absolutely loved chemistry and was fascinated by its everyday role in our lives,” she says. “Being exposed to those things as a young girl, they stayed with me.”
Aristilde enrolled as an undergraduate at Cornell, and her professional tract was solidified during an internship in India. “I was talking to the villagers there, and their stories reflected the things that I had been exposed to in Haiti. We were talking about groundwater contamination, a consequence of using wastewater directly to irrigate their agricultural land because they didn’t have the infrastructure for wastewater treatment,” she says. “That experience sealed it for me. I knew I wanted to study environmental chemistry to help deal with what’s going on in the environment, I wanted to know how things behave and the implications for ecosystem health and public health.” After graduating from Cornell, Aristilde went to University of California, Berkeley where she obtained an MS degree in environmental engineering and a PhD in molecular toxicology.
Now as a Cornell faculty, Aristilde seeks to uncover mechanisms in environmental processes and how that information can be used at the forefront. “I talk to people and say, let’s see how we can optimize these processes,” Aristilde says. “I like the idea of utilizing what the environment already does. We can take advantage of the natural ways the environment deals with and manages organic matter or contaminants to come up with better and more sustainable engineered solutions.”