Wednesday, November 26, 2008

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


Eric said...

If they don't go away, then all that plastic will eventually be degraded into microscopic bits and incorporated into marine sediments and beach sands. As you pointed out last year in an earlier article, plastic absorbs organic pollutants, in contrast to mineral-based or coral-based sediments and sands which geenrally do not. So in the long run, we may see increases in the absorptive capacity - and consequently the potential toxicity - of marine sediments and beach sands exposed to organic pollutants.

Anonymous said...

1st - Eric - it only absorbs AFTER and assuming it isn't swallowed by some unhappy creature first

2nd - as a morning walker I carry a bag with me & pickup plastic, metal, etc as I go along my route, then discard it properly; if all walkers-for-exercise picked up plastic it would make a dent in what goes into the ocean. And you get to bend over, increasing the muscles worked in your 'walk'!

Anonymous said...

I've just returned from Sand Island, Midway Atoll, Papahanaumokuakea....In one small sample of beach sand (a small fraction of a film cannister from Rusty Bucket Point on the North Shore) I counted 172 plastic fragments visible under a 10x hand lens. On returning home to Marrowstone Island, Washington State, I took a sample from my home beach. In one film cannister of sand, I saw one small piece of "micr0-plastic". The sand at Midway is totally mixed with small plastic. My fear is the PCB and other toxic absorption which can enter many food webs as plastics go micro all over the world. It is clear that it is everywhere on the planet. We need to go to the sources to find alternatives.

Ron Hirschi
Marrowstone, Washington State