The degradation of plastic in the ocean contributes to its acidification

A new study led by Institute of Marine Sciences (ICM-CSIC) of Barcelona revealed that the degradation of plastic due to the effect of sunlight contributes to the acidification of seawater. This is due to the release of dissolved organic carbon compounds from both the plastic itself and its additives, and the CO production_two.

“Thanks to this study, we were able to verify that in areas of the ocean surface highly contaminated by plastic, its degradation will lead to a drop of up to 0.5 pH units, which is comparable to the pH drop estimated in the worst case scenarios. anthropogenic emissions until the end of the 21st century”, he says. Cristina Romera-Castilloresearcher at the ICM-CSIC and first author of the study, which was published this week in the journal Total Environmental Science.

Acidification and plastic pollution are two of the biggest problems facing the ocean today. In this sense, since the industrial revolution, the increase in the acidity of the seas and oceans has caused some calcifying organisms, as is the case with corals, make it difficult to maintain their skeletons. On the other hand, it is known that each year about 13 million tons of plastic end up in the sea, and an estimated 250,000 more tons are found floating in the ocean.

The acidification process

The ultraviolet light of the sun is the main factor of plastic degradation and aging. This degradation gives rise to fractures that cause the plastic to break into smaller pieces, some smaller than 5 millimeters, better known as microplastics.

be exposed to sunlight and erosion, the plastic is “aged”, and its degree of degradation depends on how long it has been exposed to these conditions. This exposure leads to a greater release of chemical compounds into the water and causes a drop in its pH.

The chemical compounds that plastic releases into seawater during its degradation can be components of the plastic itself or additives that are added to give it color or strength. Some of these compounds are organic acids, which explains why they contribute to the pH drop.

However, during plastic degradation, CO is also produced._two, which can be emitted directly by it, or be the product of the reactions that sunlight triggers in the organic compounds released by the plastic. In turn, this CO_two released participates in a series of reactions that also cause a drop in the pH of the water.

Differences between new and old plastic

For the elaboration of the work, the research team exposed different types of plastics (new and old) to a constant temperature and solar radiation. He then analyzed the pH of the water and the amount of organic carbon that released microplastics as a result of its degradation.

With only six days of exposure to sunlight, a mixture of aged plastics collected on the beaches released a large amount of dissolved organic compounds and a significant decrease in the pH of the water was observed. In experiments with the new plastic, however, polystyrene, low-density polyethylene (LDPE) — from which bags and other containers are made — and biodegradable plastic were used. Of these, only the polystyrene (expanded polystyrene) produced a substantial drop in pH, since no significant differences were observed with the others.

“These results highlight that aged plastic affects much more than new plastic. acidificationwhich is very worrying, since most of the plastic found in the sea, of whatever type, is degraded”, concludes Romera-Castillo.