An estimated 150 millions of tonnes of plastic "disappears" from the global waste stream each year, much of it is believed to end up in the environment.
The findings appear in the Proceedings of the Royal Society B.
"The issue with plastic waste in the environment is that plastic has a non-hazardous ranking," explained co-author Mark Browne, from the University of California, Santa Barbara.
"It has the same ranking - at the moment - as food scraps or grass clippings. This is in contrast to electrical goods, which have a hard ranking attached to them.
He added: "As you don't really have a structure to deal with the plastics we use in packaging or products, they find their way into the environment."
Quoting the estimated 150 million tonnes of "lost" plastic, Dr Browne - a member of the research team at the National Center for Ecological Analysis and Synthesis (NCEAS) - said the unaccounted plastic was a concern.
"We cannot account for it in the waste stream," he told BBC News.
"There is a real issue there, both in terms of the quantity and in terms of impacts.