Discarded or washed up in the ocean, plastic debris can build up on the surface of the water, forming floating islands of trash. Although it is difficult to detect, researchers believe that a significant amount of it also sinks. In a new study in ACS’ Environmental science and technologyOne team used computer modeling to study the distance that lightweight pieces of plastic travel when dropped into the Mediterranean Sea. Their results indicate that these particles can drift farther underwater than previously thought.
From old shopping bags to water bottles, plastic pollution is besieging the oceans. Not only is this debris unsightly, but animals can accidentally get stuck in it or eat it. And if left in the water, plastic waste can release organic pollutants. The problem is most apparent at the surface, where currents can collect this debris into what are called giant garbage patches. However, plastic waste also collects much deeper. Even materials that weigh less than water can sink as algae and other organisms feast on them, and through other processes. Pieces of this lightweight plastic, which typically measure 5 millimeters or less, have shifted at least half a mile below the surface. Researchers don’t know much about what happens when plastic sinks, but they generally assume that it falls directly from the surface. However, Alberto Baudina and his colleagues suspected that this lightweight plastic might not follow such a direct route.
To test this assumption, they used an advanced computer model developed to track plastic in the sea and combined already extensive data collected on plastic pollution floating in the Mediterranean. Then they simulated nearly 7.7 million pieces of plastic scattered across the sea and traced their virtual tracks to depths of about half a mile. Their findings indicated that the slower the pieces sank, the farther currents carried them from their points of origin, with the slowest movement averaging about 175 horizontal miles. While observations of the distribution of plastic underwater are limited, the team found that their simulations are consistent with those available in the Mediterranean Sea. Their simulations also suggested that currents may be pushing plastic towards coastal areas and that only about 20% of pollution near coasts originates from the nearest country. The longer journeys of these particles mean that this plastic has a greater potential to interact with and harm marine life, according to the researchers.