Sanjay Mohanty and Eric Hoek in UCLA Newsroom: Biosolids used as fertilizer could contain more plastic than previously thought

A study by UCLA scientists raises a concern about the makeup of some of the fertilizers being used on crops, gardens, and landscaping. A portion of the fertilizer used in the U.S. and around the world comes from a source you might not expect: wastewater treatment plants. The UCLA research suggests that fertilizer could contain far more plastic particles — as much as 25 times more — than was previously suspected. 

“You can detect when microplastics come in to treatment plants, but the moment they’ve gone through the treatment, we can’t detect most of them anymore,” said Sanjay Mohanty, a UCLA professor of civil and environmental engineering and the study’s corresponding author. “Since most plastic materials are not readily biodegradable, our concern is the biosolids produced by treatment plants contain a lot of pollutants that could stick to the microplastics.”

“This is an important discovery because it points out what we don’t know about microplastics in wastewater biosolids and the possible associated risks of using biosolids to grow our food,” said Eric Hoek, a co-author of the paper, UCLA professor of civil and environmental engineering and faculty director of the UCLA Sustainable LA Grand Challenge.