Beach plastic is forever

Canadian resarcher Patricia Corcoran said she was studying the mineral components of Hawaiian beaches when she and a colleague noted large amounts of plastic debris on the shore, during a survey of Lydgate Beach on Kaua'i.

(Image: Plastic marine debris on a Kaua'i beach.)

“We wondered if the plastics on Lydgate Beach were derived from land-based or ocean-based sources. We also wondered how long the plastics would remain on the beach,” she said in an email to RaisingIslands. Corcoran is with the Department of Earth Sciences, University of Western Ontario, in London, Ontario, Canada.

She launched a study, using plastics from various Kaua'i beaches, treating the plastic particles in the same way she would have treated mineral sand particles. One finding: the stuff gets smaller and smaller, but it never goes away.

Her study, “Plastics and beaches: A degrading relationship,” with University of Western Ontario co-authors Mark Biesinger and Meriem Grifi, was published in the Marine Pollution Bulletin.

They found that while most of the plastic debris and particles on beaches is originally from the land, most used the ocean as the method of transport for getting onto beaches.

Also, there is more plastic on East Kaua'i beaches than on other shores. That may be a function of current patterns that drive marine debris onto shorelines from the east.

One technique for studying them was inspecting them using a Scanning Electron Microscope.

“I was able to recognize distinct textures related to chemical and mechanical weathering. Combining the textural images with compositional results determined from Fourier Transform Infrared Spectroscopy (FTIR), enabled us to recognize how both chemical and mechanical weathering contributed toward the degradation of plastic particles,” Corcoran said.

Some of the shapes were rounded, some angular, and some mere flakes. They showed evidence of both chemical and mechanical erosion, from exposure to ultraviolet radiation and from having been rubbed against sand grains during wind or wave action.

And the two kinds of degradation seem to support each other. Mechanical erosion from collisions with sand particles create fractures that are favorable spots for chemical weathering. And ultraviolet radiation increases brittleness, which makes mechanical breakdown easier.

“It...made me realize that beach environments are possibly the best natural settings in which plastics can be broken down, although they may remain in the environment in microscopic form indefinitely,” she said.

That's the bad news. The plastic gets smaller and smaller, until you don't see it, but it's always still there.

“We will be returning to Kauai in the coming year to conduct a more rigorous sampling approach of the plastic debris in order to determine which plastic types are most common (provides clues concerning sources), and which polymers degrade most rapidly under weathering conditions,” Corcoran said.


©2008 Jan TenBruggencate