Samuel Daughenbaugh, DePauw University
The Problem: We live in a plastic world. Plastics have saturated all aspects of our daily lives and, as a consequence, have also entered the natural world. About 8.3 billion metric tons have been produced in the past 60 years, playing a pivotal role in the advancement of modern society (Parker, 2018). Although they are used to create many things we enjoy and benefit from, there are serious consequences for the health of humans and the environment that are associated with their use.
We have found plastics in unexpected places, everywhere from human guts to the most remote locations on earth (Schwabl, 2018; Woodall, 2014). Plastics have a long list of negative effects on living organisms, but their impact in the ocean is of special concern. Pictures of turtles with straws up their noses, bottle caps spilling out of dead bird stomachs, and penguins strangled in plastic beverage rings are often posted on social media sites. Less widely known are the chemical additives that leach from plastics. Phthalates are one such group of additives that pose threats to the health of humans and marine life.
Phthalates have been valuable to the plastic industry because they promote flexibility and durability in many plastics (EPA, 2017). An astounding 470 million pounds of phthalates are used in the United States every year (EPA, 2017). This presents a significant problem because phthalates interfere with the production of important hormones that regulate growth and metabolism in humans and other animals (Boas et al., 2012).
This summer I am exploring the effects of three different phthalates– dimethyl phthalate (DMP), di-n-butyl phthalate (DBP), and di-2-ethylhexyl phthalate (DEHP)–on the larval development of marine invertebrates, using the purple-spined sea urchin (Arbacia punctulata) as a model. Sea urchin larvae float freely in the water column for an extended period of time and, therefore, are vulnerable to many marine pollutants.
Sea urchins are an important model because they are closely related to humans. Both humans and sea urchins use a signaling hormone called thyroxine, which is especially important for growth in early developmental stages (Heyland et al., 2006). Exposure to phthalates can disrupt the production of thyroxine. Additionally, larvae are very important to study because they form the base of food webs. Being at the bottom of the food chain means they feed animals at higher levels, many of which humans rely on for protein. Therefore, understanding how phthalates affect sea urchin growth and metabolism can lead to new insights into how these pollutants directly and indirectly impact human health.
I would like to thank my mentor, Dr. Robert Podolsky, for his continued support, guidance, and encouragement. This project is supported by the Fort Johnson REU Program, NSF DBI-1757899.
Boas, M., Feldt-Rasmussen, U., & Main, K. M. (2012). Thyroid effects of endocrine disrupting chemicals. Molecular and Cellular Endocrinology, 355(2), 240-248.
Environmental Protection Agency (Ed.). (2017). Phthalates. America’s Children and the Environment, 3, 1-19.
Heyland, A., Price, D. A., Bodnarova-Buganova, M., & Moroz, L. L. (2006). Thyroid hormone metabolism and peroxidase function in two non-chordate animals. Journal of Experimental Zoology Part B: Molecular and Developmental Evolution, 306B(6), 551-566.
Parker, L. (2018, December 18). A whopping 91% of plastic isn’t recycled. Retrieved from http://www.nationalgeographic.com
Schwabl, P. (2018, October). Assessment of Microplastic Concentrations in Human Stool. Conference on Nano and microplastics in technical and freshwater systems, Monte Verità, Ascona, Switzerland.
Woodall, L. C., Sanchez-Vidal, A., Canals, M., Paterson, G. L., Coppock, R., Sleight, V., . . . Thompson, R. C. (2014). The deep sea is a major sink for microplastic debris. Royal Society Open Science, 1(4), 140317-140317. doi:10.1098/rsos.140317