A new study has found that high concentrations of microplastics in sand could impact the temperature of the sand and interfere with incubating sea turtles.

Researchers from Florida State University used sand from beaches at the FSU Coastal and Marine Laboratory and mixed it with black and white microplastics. The microplastics made up between 5% to 30% of the total volume of the samples of sand mixtures.

To measure sand temperature, the team placed thermometers into each sample at the same depth that loggerhead sea turtles lay their eggs, about 40 centimeters below the surface of the sand and about 30 centimeters from the drum wall.

The researchers recorded temperatures from July 2018 to September 2018. In general, sand samples with more microplastics had higher temperatures. Samples with 30% of black microplastics showed the highest increases in temperature, with temperatures around 0.58 degrees Celsius higher than the control group’s temperatures.

The amount of microplastics in the samples had the greatest influence on temperature, while the color of the microplastics “had an ambiguous effect on sand temperature,” according to the study authors. They published their findings in Frontiers in Marine Science.

“Sea turtle sex, fitness and hatchling success is influenced by temperature,” lead author Mariana Fuentes, an associate professor at Florida State University’s Department of Earth, Ocean and Atmospheric Science, said in a statement. “Not much is known on how the presence of microplastic affects the thermal profile of sand. Understanding how changes to the environment could affect the temperature of nesting grounds is important for monitoring the future of these keystone species.”

The higher temperatures of sand mixed with higher concentrations of microplastics could be explained by the specific heat in polyethylene, which is higher than sand, according to the study. This could mean that sand samples with more microplastics are not losing heat overnight as quickly.

Although the high 30% concentration of microplastics used in the study has not been replicated in the environment just yet, the team is concerned that even smaller concentrations of microplastics could influence the temperature of sand enough to impact sea turtle hatchlings.

According to the Sea Turtle Conservancy, increasing temperatures could cause more sea turtle hatchlings to be female, which threatens the genetic diversity of the species. While climate change was already putting sea turtles’ food sources at risk and influencing hatchlings, this new study also spotlights concerns over growing amounts of microplastic pollution in the environment.

“Sea turtle eggs are sensitive to temperature, and microplastics are another factor adding to the heat they face,” Fuentes said. “This study gives us a baseline for future research on how they are affecting the nesting environment.”