Story highlights Microplastics are pieces of plastic less than 5 millimeters long

Chemicals can latch onto them, and plastics can transport the chemicals to marine life

More research is needed to determine if microplastics are harmful to humans

If you use exfoliating soaps, you might not know those little beads may be made of plastic -- or think about what happens to them when they go down the drain.

But it's on the minds of marine science researchers, as well as a major company.

Unilever, the company that makes Dove soaps, Vaseline, Pond's skin cream and other personal care products, announced recently it's phasing out the use of "plastic micro beads as a 'scrub' material" in its personal care products.

By 2015, the phase out should be complete, Unilever said. The company said the "the issue of plastics particles in the ocean is an important issue."

Microplastics are plastic pieces less than 5 millimeters (0.2 inches) long, and they are a major type of marine debris.

They are used as scrubbers in hand cleansers and other domestic and industrial cleaning products, according to a 2009 review of the issue led by Richard Thompson, professor of marine science at the University of Plymouth in the United Kingdom. They also get into the environment through plastic pellets and powders being spilled in the manufacturing process for plastic products, in addition to the deterioration of larger pieces of plastic.

Research in microplastics suggests that very small particles, even tens of microns in diameter, can be retained in the tissues of marine invertebrates, Thompson said. A 2008 study from Thompson's group found that microplastic particles remained in mussels for 48 days.

"It remains to be seen whether they produce harmful effects in their own right," he said.

An issue of more immediate concern is the particles' ability to absorb contaminant chemicals in the water, he said.

Small plastic particles have a large surface area compared to their volume, offering ample opportunities for chemicals to latch onto their surfaces. The absorption of chemicals by these microplastic beads may be of concern to marine life, which could ingest them, Thompson said.

In an experiment that Thompson and colleagues conducted, they simulated the transfer of the pollutant phenanthrene to the gut of the lugworm through the ingestion of microplastics. The lugworm, used by fishermen for line angling, is at the bottom of the food chain, so lots of other species eat it, creating the potential to spread chemicals to larger and larger creatures.

The study suggests that when a worm lives in a sedimentary environment high in natural carbon, such as sand on a beach, small plastic particles could increase the transport of chemicals to the worm. But in muddy conditions, where there is less carbon in the environment, there is less chemical transfer.

This was a laboratory modeling experiment, however, and generally there are few studies on the subject, Thompson said.

"We still don't have a very clear handle on the quantities that organisms might be ingesting," Thompson said.

There is no evidence yet for harmful effects on humans, but there hasn't been much research in this area, Thompson said.

Thompson applauded Unilever's action to address the issue. He pointed out that the plastics will not degrade over time naturally, so more and more of them accumulate in the environment every year.

"I think the potential for broader harmful effects -- a wider range of organisms, potentially including us -- is only going to increase unless we do something about it," he said.

The next question is: What is going to be used as an alternative to the plastic micro beads?

A spokesman for Unilever said in an e-mail Tuesday, "We are currently in the process of researching suitable alternatives."