Rebecca Hoehn and Conner Lester are the 2025 recipients of the Nicholas School of the Environment鈥檚 Dean鈥檚 Award for Outstanding Graduate Student Manuscript. Each year, faculty members nominate manuscripts for consideration by Stanback Dean Lori Bennear.

鈥淭hese published manuscripts showcase our doctoral students鈥 drive to challenge prevailing ideas. I also appreciate that these two papers demonstrate the breadth of Ph.D. research: One makes advances in the understanding of the basic sciences, and one advances applied research with direct policy impact,鈥 Bennear said.

Bennear will honor the winners at the Nicholas School鈥檚 Ph.D. graduate student ceremony this Friday, May 9, at 10 a.m. in Duke鈥檚 Love Auditorium, within the Levine Science Research Center. Learn more about Nicholas School recognition ceremonies.

Tracking Flame-Retardant Exposures

A picture of blue rear car seats
Photo from Shutterstock

Hoehn is a Ph.D. student in the lab of Heather Stapelton, within the Division of Environmental Natural Sciences. Her winning paper, 鈥,鈥 was published in Environmental Science & Technology last May.

Flame retardants are chemicals added to consumer products, such as electronics, construction materials and furnishings, to reduce flammability. However, various studies have found associations between flame retardant exposure and negative health effects.

For their study, Hoehn, Stapelton and colleagues sampled the air in 101 vehicles built in the last decade and identified flame retardants in all vehicles tested. They also found that warmer outdoor temperatures corresponded to higher detected levels of flame retardants, and that seat foam was a source of the chemicals.

The findings suggest that those who spend more time driving are at greater risk of exposure to flame retardants, and that the federal requirement to add these chemicals to vehicles should be reevaluated, according to the authors.

Exploring Wind-Blown Ripples

A satellite view of impact ripples inside craters on Mars
Impact ripples appear inside craters on Mars. Image by NASA/JPL-Caltech/University of Arizona

Lester, a graduate student in Brad Murray鈥檚 lab within the Division of Earth and Climate Sciences, will receive his Ph.D. this spring. His paper, 鈥,鈥 appeared in Nature Geoscience this past April.

Across beaches and deserts worldwide, wind drives the formation of distinctive ripple-like patterns in grains of sand. The observation of similar ripples on Mars the same size as their terrestrial counterparts 鈥 despite a thinner atmosphere 鈥 has raised questions about how these undulations form. 

A previous explanation suggested that grain movement through air dictated ripple size, but Lester, Murray and colleagues propose a different story. Using a numerical simulation, Lester and team determined that ripple size stems from interactions between wind-blown grains and the surfaces they land on.

Their work could shed light on geological and environmental conditions on other planets, according to the authors.