Senate Democrats are calling on retailers to stop selling bath products that contain small plastic beads.

Sens. Chris Murphy (Conn.), Kirsten Gillibrand (N.Y.) and Richard Blumenthal (Conn.) sent a letter to the Retail Industry Leaders Association and the National Retail Federation on Friday asking the groups to urge their members to stop selling products that contain polyethylene and polypropylene plastic microbeads.

The letters are in response to a recent Southern Connecticut State University study, which found evidence of microbeads in the Long Island sound. These microbeads — often used in soaps and shower gels to exfoliate the skin — build up as plastic pollution and get mistaken for food by fish, threatening aquatic life.

“Due to their tiny size, microbeads often cannot be successfully removed from wastewater streams by municipal sewage plants,” the senators said in their letter. “Just one personal care product can contain hundreds of thousands of these beads, which typically do not biodegrade, as they require high heat processing to break down.”

The beads have also been building up in the nation’s Great Lakes. In May, Sens. Debbie Stabenow (D-Mich.) and Gary Peters (D-Mich.) introduced the Microbead-Free Waters Act of 2015 in a bid to phase out the manufacturing and sale of microbeads found in household products altogether.