SYDNEY, Australia — ASK most people about the problem of waste plastics in the environment and they will talk about plastic bags caught in trees and the vast slicks of plastic trash found in remote areas of the Atlantic and Pacific. But the most menacing plastic waste problem is less visible and not so well publicized.

It’s the tiny fibers, less than one millimeter wide, that come from our clothes when we launder them. These fibers make their way into the world’s rivers and seas through the sewage and drainage systems of our cities. The pollution is worst near urban areas, but it is global and has increased by more than 450 percent since the 1960s.

These minute strands of plastic — virtually invisible to the human eye — are made from a variety of natural (animal and plant) and artificial polymers. You can’t see them when you walk along the seashore at low tide, but they’re there, by the ton.

In the samples my team and I recovered on shorelines from the poles to the Equator between 2004 and 2007, they were often over six times more abundant by number than larger plastic debris like bottles, bags and wrappers.