As nations meet this week to negotiate an agreement on plastics pollution, researchers warn that a lack of information will make it hard to enforce any agreement.

On a warm windy day in early April, Jace Tunnell steps out of his car at Morgan’s Point, a spit of land that juts out into the Houston Ship Channel in Texas. Tunnell, a marine biologist and reserve director at the University of Texas Marine Science Institute, sets his watch and gets to work, walking along the high-tide line and picking up every plastic pellet he can see.

The tiny pellets, known as nurdles, are the starting point in the creation of vast amounts of plastic products, and those, in turn, are part of a web of plastics that encircles the globe. Tunnell steps and bends, filling his palm, as he has done on beaches across the country. Each pellet is a data point about plastics. It’s joined by others collected as university students dip nets into the waters of the North Atlantic, satellite instruments measure light reflecting off plastic debris afloat on the ocean, and scientists drop GPS-tagged bottles into India’s Ganges River. ....