By Alyssa Friedman and Viktoria Leopold
Cover image credit: https://medicalxpress.com/news/2018-11-zebrafish-larvae-appetite-suppressants.html
In recent years, concern about environmental contaminants has grown mainstream, spurring research into the potential impact of certain chemicals on embryonic development, or how an organism spends the early stages of its life. Endocrine-disrupting chemicals (EDCs) are particularly alarming because of how they mimic or interfere with the body’s hormones, causing a range of developmental and reproductive problems. During a seminar talk by Dr. Larissa Williams from Bates College, she discussed the state of current research on this topic.
Research Overview
Professor Williams became interested in EDCs after her time in the Duke Marine Lab. There, she studied how tributyltin—a toxic chemical put on the bottom of boats to halt barnacle growth—harms snails and other marine creatures. Williams graduated from Smith College in 2005 and received her PhD in Environmental Toxicology at North Carolina State University in 2010. She completed a post-doc at Woods Hole and is now a biology professor at Bates College, where she studies developmental toxicology in zebrafish and how specific proteins respond to oxidative stress agents. Zebrafish are a powerful model organism, Williams explained, because they share 80% of the human genome and have a short life cycle.
Impact of TPhP Exposure
One of Williams’ projects focuses on the impact of the chemical TPhP on cardiac development in zebrafish. TPhP stands for triphenyl phosphate, which is a plastic additive used for wiring, vinyl polymers, among other common products. It is also used as an alternative to carcinogenic plastic additives. Although TPhP is easily biodegradable, its continuous release causes sustained exposure for aquatic organisms. TPhP has been detected in wastewater, landfill, soil, fish, and ambient air. Furthermore, Williams notes that the effects of TPhP may be dose-dependent and even harmful in small concentrations.
To examine the impact of chronic exposure to low concentrations of TPhP, Williams re-dosed zebrafish with the chemical each day. She and her team then compared phenotypes and analyzed gene expression. Williams found that even at micromolar concentrations, the presence of TPhP resulted in an increase in severe heart abnormalities and a decrease in body length for the animals tested. This implies that chronic exposure to even small amounts of TPhP has a negative impact on organism development, raising concerns about potential harmful effects of TPhP exposure in humans as well.
Bisphenol Toxicity
In addition to TPhP, bisphenol compounds, like BPA, BPF, and BPS, are widespread environmental contaminants that act as endocrine disruptors. While BPA has received significant attention due to its prevalence in plastics, BPS and BPF are becoming increasingly common as replacements, despite their similar toxicological profiles. These chemicals are found in everything from plastic bottles and food packaging to paper receipts and wastewater. Thus, Williams and her team decided to study the impact of BPS on zebrafish and sponges, which are both species that live in areas heavily exposed to these contaminants, such as certain streams, rivers and lakes.
The results showed that exposure to high levels of bisphenols led to hatching issues, blood pooling, and reduced blood flow—all signs of developmental toxicity. The zebrafish showed a decrease in body length, while the sponge populations also showed a size reduction. Additionally, an increase in chemical markers linked to oxidative stress suggests that BPS creates an imbalance of cell-damaging free radical particles in these organisms. The study demonstrated that despite the approximately 700 million years of evolutionary divergence between these species, BPS caused similar developmental toxicities, which demonstrates the sweeping impacts of endocrine disruption across different species.
Reflections and Conclusions
One of the most important takeaways from Williams’ research approach was her emphasis on collaboration. In her talk, Professor Williams highlighted a moment in her data collection process where she felt stuck and did not know how to interpret the results—an inevitable part of research. She highlighted the importance of collaborating with other scientists and asking questions to learn new perspectives, which helped her project succeed.
So far, Williams has only been working with embryonic zebrafish. In the future, she hopes to study reproductive problems and other issues in adult zebrafish. Williams and her team are also interested in transgenerational experiments, in which they will observe offspring of zebrafish exposed to TPhP and other chemicals.
Ultimately, Professor Williams’ research has shown that even small concentrations of endocrine-disrupting chemicals can impact zebrafish. The presence of bisphenols indicates developmental toxicity, potentially in other species, including humans. Although the presence of plastics and chemicals in our daily lives is unavoidable, she suggests limiting personal exposure by using a reusable metal water bottle and being mindful of plastic use.