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."