How Plastic contributes to ocean acidification

Due to the acidification of the oceans, marine fauna is in serious danger

by Lorenzo Ciotti
How Plastic contributes to ocean acidification

Due to the acidification of the oceans, marine fauna is in serious danger. The lowering of the marine pH creates the phenomenon of coral bleaching; the calcium carbonate that makes up shells, molluscs, crustaceans and even coral, decreases in relation to the increase in acidity, thus losing the algae that live above the surface of the organism, leading it to death.

Although many organisms suffer from this increasing acidification, some photosynthetic organisms benefit from it. One case is represented by diatoms; that is microscopic algae belonging to phytoplankton. For these organisms, the increase in CO2 in water increases their ability to carry out their own photosynthesis processes.

These processes can be carried out if in the presence of certain environmental conditions. The study Abiotic plastic leaching contributes to ocean acidification, published on the The Science of the total environment, said: "Ocean acidification and plastic pollution are considered as potential planetary boundary threats for which crossing certain thresholds could be very harmful for the world's societies and ecosystems well-being.

Surface oceans have acidified around 0.1 units since the Industrial Revolution, and the amount of plastic reaching the ocean in 2018 was quantified to 13 million metric tonnes. Currently, both ocean threats are worsening with time.

Plastic leaching is known to alter the biogeochemistry of the ocean through the release of dissolved organic matter. However, its impact in the inorganic chemistry of the seawater is less studied. Here we show, from laboratory experiments, that abiotic plastic degradation induces a decrease in seawater pH, particularly if the plastic is already aged, as that found in the ocean.

The pH decrease is enhanced by solar radiat ion, and it is probably induced from a combination of the release of organic acids and the production of CO2. It is also related to the amount of leached dissolved organic carbon, with higher acidification as leaching increases.

In coastal areas, where plastic debris accumulates in large quantities, plastic leaching could lead to a seawater pH decrease up to 0.5 units. This is comparable to the projected decrease induced in surface oceans by the end of the twenty-first century for the most pessimistic anthropogenic emissions scenarios."