Plastic pollution is causing ocean to acidify, say researchers

Plastic pollution may already be causing harm to aquatic creatures, other wildlife, and humans, but researchers say its also contributing to the acidification of the ocean.

While not everyone is familiar with the acidification of the ocean, it’s a major problem facing oceans today, as increased acidity makes it difficult for calcifying organisms, like corals, to maintain their skeletons.

A study led by the Institut de Ciències del Mar (ICM-CSIC) based in Barcelona have discovered that sunlight plastic degradation contributes to this issue by releasing dissolved organic carbon compounds.

The sun’s ultraviolet rays degrades and ages plastic, fracturing it into small microplastics, some less than five milimetres wide.

Greater exposure to the sun also results in an increased release of chemical compounds into the sea from the plastic itself or additives, lowering the waters pH.

First author of the study and ICM-CSIC researcher, Cristina Romera-Castillo, said: ‘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.’

The study, which was published in Science of the Total Environment journal, also found that plastic degradation can result in carbon being emitted directly from the plastic or as a by-product of reactions in the organic compounds in the material.

This further decreases the water’s pH, contributing to the ocean’s acidification, and this  only gets worse the older the plastic gets.

Researchers exposed different types of plastic to a constant temperature and solar radiation before measuring water pH and the amount of carbon released by microplastics as they aged.

After six days of sunlight, aged plastics collected from beaches were found to release large amounts of organic carbon compounds and caused a significant decrease in water pH.

On the other hand, new polystyrene, low-density polyethylene (LDPE), from bags and packaging, and biodegradable plastic fragments didn’t cause a significant drop in pH.  

‘These results show that aged plastic affects acidification much more than new plastic, which is very worrying, since most of the plastic found in the sea, whatever type it is, is degraded,’ concluded Romera-Castillo.

Photo by Naja Bertolt Jensen