Plastics Increase Acidity of the World’s Oceans, Study Finds

The trillions of pieces of plastic that end up in Earth’s oceans each year are wreaking havoc on the hundreds of thousands of marine organisms who live there. Mammals like whales and smaller organisms like fish ingest plastic particles, which contain toxins that stay in the animals’ bodies and are passed along to the organisms that feed on them, while dolphins, turtles and other marine life become entangled in discarded fishing nets.

Now, new research has shown that, not only does plastic harm marine animals, it also contributes to ocean acidification.

Ocean acidification occurs when the pH levels of the planet’s oceans decrease due to their uptake of human-produced carbon dioxide from the atmosphere. Higher levels of acidity in the ocean makes it hard for organisms that use calcification — like corals, oysters, urchins and planktons — to build their skeletons. When these organisms falter, it can affect other marine species that rely on them for habitat and food.

A new study led by scientists from Barcelona’s Institut de Ciències del Mar (ICM-CSIC) has found that the interaction of plastic with sunlight causes a mixture of chemicals to be released into the ocean, reported Mongabay. The organic acids that are leached into the ocean lower the seawater’s pH and cause a rise in acidity. Plastic deteriorating in the sun can also result in a release of carbon dioxide, causing pH levels to fall even further.

“The main factor producing the acidification is the greenhouse gas emissions that are dissolved in the ocean,” postdoctoral researcher at ICM-CSIC Cristina Romera-Castillo, who was lead author of the study, told Mongabay. “But I think it’s interesting to know that plastic is also contributing to the acidification.”

The study, “Abiotic plastic leaching contributes to ocean acidification,” was published in the journal Science of The Total Environment.

About 30 percent of the carbon emissions produced by humans are absorbed by the world’s oceans, which has caused a decrease in pH levels, Mongabay reported, with the corresponding rise in acidity. Ocean acidification doesn’t happen equally across the world, however. The pH of surface waters has gone down an average of about 0.1 pH units, which has caused many changes that will be exacerbated if greenhouse gas emissions continue to increase.

“Thanks to this study we have been able to prove that in highly plastic-polluted ocean surface areas, plastic degradation will lead to a drop of up to 0.5 pH units, which is comparable to the pH drop estimated in the worst anthropogenic emissions scenarios for the end of the 21st century,” Romera-Castillo said, as reported by Earth.com.

The research team used new plastics and aged plastics gathered from beaches in the Canary Islands for their study, Mongabay reported. The plastic fragments were placed inside glass bottles full of seawater and exposed to levels of ultraviolet light comparable to those of the sun. 

The scientists found that old, decaying plastic released higher levels of broken down organic carbon into the ocean. After just six days of sunlight exposure, a significant amount of organic carbon was released by older plastics, leading to a marked decrease in pH, reported Earth.com. However, new low-intensity polyethylene (LDPE), polystyrene and plastic fragments that were biodegradable did not cause pH to fall considerably.  

“I think it’s important that people know about this phenomenon,” marine biologist and ocean acidification expert at the University of Plymouth Jason Hall-Spencer, who was not involved in the study, told Mongabay, “because what we’re often told is that plastics, once they get into the ocean, will last for millions of years, won’t break down or be there effectively forever.”

How much plastic contributes to ocean acidification is another question. Hall-Spencer said that the effects of plastic acidification could be lessened by the mixing of the water by the ocean’s currents and waves. Carbon dioxide-consuming organisms encrusted on the plastics could also mitigate the amount of acidification the plastics contributed, Hall-Spencer said, adding that much of the ocean plastic falls to the seafloor, away from sunlight.

Plymouth Marine Laboratory marine ecologist and co-chair of the Global Ocean Acidification Observing Network Stephen Widdicombe, who was also not involved in the study, pointed out that the findings of the study are important because they demonstrate that plastic could further coastline ocean acidification, though additional research would be necessary to determine if the same results would occur in a broader, natural setting.