By Sarah Heissenberger, Summer Intern in Dr. Richard DiGiulio’s lab
Hi! My name is Sarah and I was a summer intern in the 2018 Duke Superfund Research Program. I worked on Project 4, ‘Mechanisms and Consequences of Evolved Adaptation to Environmental Pollution’, in the Dr. Richard Di Giulio’s lab. For several years, I have been studying the effects of a ubiquitous class of compounds known as polycyclic aromatic hydrocarbons (PAHs), and I was excited to continue to explore this focus here at Duke.
First some background. PAHs are primarily produced via the incomplete combustion of fossil fuels (coal, oil, diesel, etc.) and also by burning trash, wood, and cigarettes. One of the top ways in which humans are exposed to PAHs is through the consumption of barbecued food (sorry to cast a damper on your summer cookout!). In essence, there are many ways in which humans and animals alike are exposed. PAHs aren’t just contaminants of industrial concern – they are a concern for people and animals across the globe. Women who use open cook stoves in enclosed spaces, largely in developing countries, inhale high levels of PAHs. Similarly, people living in urban areas with dense traffic (PAHs are present in vehicle exhaust) also face high levels of exposure.
PAHs have a tendency to accumulate in the environment, particularly those of high molecular weight, and take a long time to break down, meaning that they can stick around for a long time. More alarming still, they tend to accumulate in fatty biological tissues, as they are non-polar, lipophilic (fat-loving) molecules. They can disrupt cellular signaling and enzymatic pathways, and cause changes in gene expression, potentially leading to a variety of adverse developmental, behavioral, and physiological effects.
We utilized two fish models, the zebrafish (Danio rerio), a well-studied lab model, and the killifish (Fundulus heteroclitus), which is native to Virginia’s Elizabeth River and has evolved a remarkable resistance to incredibly high levels of PAHs found in parts of the river. The PAHs entered the river during a time when the region supported an extensive logging industry. Creosote, derived from PAH-rich coal tar, can be used to treat and preserve wood, and large amounts of this chemical were released into the river.
Fish demonstrate incredible sensitivity to environmental contaminants, yet there is hope in the evolved resistance of the killifish. However, in biological systems, just as in life, there are always trade-offs: traits that allow such resistance have costs. The Di Giulio lab is interested in what these costs may be, as well as how the killifish actually manage this toxic exposure.
Under the mentorship of Dr. Rafael Trevisan, I investigated exposure effects to the well-studied PAH benzo[a]pyrene (known simply as BaP) across multiple generations. However, my study was unique in that I studied the potential effects that maternal dietary exposure to BaP could have on the F3 progeny of exposed zebrafish. Basically, could exposure effects be observed for the great-grandchildren of the exposed zebrafish, even if none of the later generations (F1, F2, and F3) were exposed? My project exemplified the theme of Duke’s Superfund Center, in which early life exposure can have later life (and generational) consequences.
I come to North Carolina from New Hampshire, where I recently finished my B.S. in Biology. I basically grew up outside – climbing the evergreen trees with the squirrels, swimming the valley lakes with the bluegill and bass, wandering the evening fields with the whitetail deer. I believe human health is intimately connected with the environment. To take care of the land is to take care of ourselves and preserve the future for our children. But in an increasingly urbanized and globalized world, our relationship to nature is becoming more distant and more complex.
Toxicology has always impressed me with its incredibly diverse and integrated subject matter – ecology, public health, physiology, behavior, cellular biology, and genetics. This interdisciplinary approach will be critical part of improving public health and environmental health. I am particularly interested in how animals sense, interpret, and navigate their environment, and how they become physiologically and behaviorally adapted to meet environmental challenges.
What’s next for me after Duke? I am planning to enter a PhD program in the next couple of years. For now I am enjoying North Carolina’s colorful wildlife, lush landscapes, research-oriented spirit, and the supportive, brilliant community here at Duke.