Ocean Pollution

Are Florida's dolphins at risk from plastics in rain?

Previous studies have found profound levels of plastics within dolphins' stomach contents, breath, and even their urine. Now researchers from the College of Charleston want to know just how severe the pollution crisis is by investigating rainfall and red tides.

04/02/2025
Words by Rob Hutchins
Photography by Lewis Burnett
Additional photography by Sarasota Dolphin Research Programme

Growing concern among the scientific community over the impact of chemical contaminants derived from plastics upon marine life has prompted researchers in Florida to launch a bold new investigation into the concentration of plastic particles found within the local dolphin population following periods of excess rainfall and red tides.

Since 2016, the College of Charleston and its partners at the Sarasota Dolphin Research Programme (SDRP) have been studying plastics pollution exposure in Sarasota Bay’s bottlenose dolphins.

Among their most startling findings, these studies have previously uncovered profound levels of plastics within dolphin stomach contents and breath, while the chemicals used to make these plastics – known as phthalates – have been found in dolphin urine.

With the aim of delving further and uncovering the extent of the issue, a new study is now looking into how climate-influenced events like major storms, rainfall, and red tides – periods of discolouration of the seawater caused by a bloom of toxic red algae (dinoflagellates) – impact phthalate exposure and the health of Sarasota Bay dolphins.

Phthalates are the chemical compounds used to make plastics both flexible and durable and are used as both solvents and stabilisers in the plastic production process. Owing to their ubiquity and widespread occurrence in our everyday lives, they have, in recent years, earned themselves the nickname the ‘everywhere chemical’. 

These chemicals are easily released as plastics deteriorate and are found in everything from PVC pipes, to food packaging and even cosmetics and perfumes. Exposure is so common that more than 95% of humans have detectable levels in their urine.

The issue with phthalates is no longer confined to humans, either. So far ‘everywhere’ are these chemicals that recent research revealed that around 75% of Sarasota Bay dolphins now have detectable levels of the chemicals in their bodies, higher even than the concentrations found in humans.

This exposure is of particular concern for dolphins because phthalates – which are known endocrine disruptors – impact directly upon mammalian hormone systems. Hormonal changes can cause problems with growth, fertility, and reproduction – all of which could have population-level impacts on dolphins.

Human studies, meanwhile, have shown that phthalates can even lead to heart problems and neurological disorders.

By analysing urine samples collected over three decades, researchers from the College of Charleston and the SDRP now aim to identify environmental influences on phthalate exposure and links to dolphin endocrine disruption, reproductive issues, growth abnormalities, and cardiovascular health. 

This study will, therefore, provide valuable insights into how environmental changes can impact dolphin exposure to these chemicals of growing concern.

“In previous studies, we found that there were unexplained differences in phthalate concentrations in Sarasota Bay dolphins, depending on when urine samples were collected and what part of the bay the dolphins frequented,” said Leslie Hart, associate professor at the College of Charleston and the project’s lead researcher. “Through this study, we’re trying to tease out the factors that could account for some of the differences.”

There have been previous studies to indicate that phthalate contamination can increase when rainfall causes excess runoff and flooding. These findings have emerged, in recent years, from other parts of the world where phthalates concentration has become of increasing concern. For the Florida study, researchers will be comparing tropical storm and rainfall records for the Sarasota Bay area to the phthalate levels in the bay’s dolphins, using archived urine samples from more than 200 animals.

And, because previous studies from the SDRP have shown that dolphins are quite often forced to eat different prey items when fish populations decline during a red tide event – an occurrence which could also impact phthalate levels – the team will compare the urine samples with archived cell counts of the dinoflagellate that causes such red tide blooms.

“Long-term forecasts predict increasingly warmer ocean temperatures, which provide fuel for tropical storms and hurricanes that can bring flooding and excess runoff from land,” said Hart. “As these waters drain into our local bays, they carry nutrients and chemicals, including phthalates and plastics, from the land, increasing the risk of contaminant exposure for local dolphin populations.

“Additionally, red tide blooms – driven by nutrient inputs – often lead to fish die-offs, potentially increasing trophic-associated exposure to phthalates and plastics.”

Funded by Sea Grant and made possible thanks to the data gathered about the long-term resident dolphins of Sarasota Bay over more than 55 years through the Sarasota Dolphin Research Programme, the study will aim to arm local wildlife managers and conservationists with the knowledge needed to mitigate the worst risks.

“As phthalates have become ubiquitous in our environment, there’s a growing concern over what the impacts could be,” said Randy Wells, director of the Sarasota Dolphin Research Programme and vice president of marine mammal conservation at Brookfield Zoo Chicago. 

“If humans are causing disturbances to things like dolphin reproduction because of plastics and chemicals from plastics, wildlife managers need to know so they can work to mitigate the risks. Over more than five decades, Sarasota Bay has served as a natural laboratory where we can answer critically important questions like this.”

Click here for more from the Oceanographic Newsroom.

Words by Rob Hutchins
Photography by Lewis Burnett
Additional photography by Sarasota Dolphin Research Programme

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