A public interest group said this week that it had found toxic substances in a number of school supplies, including asbestos in a Playskool crayon and another carcinogen, benzene, in a dry-erase marker.

The findings were detailed in a report published Tuesday by the group, the U.S. Public Interest Research Group Education Fund, which had an independent laboratory test 27 back-to-school products.

“We wish that we didn’t have to do a study like this, but the reality is that corporations — from manufacturers, distributors and retailers — aren’t doing this for us,” said Dev Gowda, an author of the report who also directs the group’s campaign to persuade manufacturers to drop toxic substances from personal care products.

The group tested crayons, markers, binders, water bottles, lunchboxes, notebooks, rulers and glue. The products were purchased nationwide at a variety of businesses.

The group, which has been surveying toys for more than three decades, recommended that the companies that make or offer the products stop selling them and start notifying consumers about the chemicals they appear to contain.

It also called on policymakers to continue to support the Consumer Product Safety Commission, a federal agency, and urged the commission itself to test more school supplies for dangerous chemicals.

Of the crayons tested, one, a green Playskool crayon, tested positive for trace amounts of tremolite, a form of asbestos. The crayon was part of a set of 36 manufactured by Leap Year Publishing.

Julie Duffy, a spokeswoman for Hasbro, which owns the Playskool brand, said that it would be conducting a thorough investigation. John Sorenson, a spokesman for Leap Year Publishing, said that all of its products, including the green crayon mentioned in the report, “are thoroughly tested by independent labs” to meet or exceed federal standards.

“We are currently reverifying that they are safe and free of any asbestos, as well as requesting a review of PIRG’s testing methods,” he said.

Crayons sold under five other brands — Crayola, Up & Up, Cra-Z-Art, Disney Junior Mickey and the Roadster Racers, and RoseArt — tested negative for asbestos.

One dry-erase marker tested positive for benzene, a known carcinogen. It was produced by The Board Dudes, a brand owned by Mattel.

In a statement, Mattel said it took such reports seriously, “aggressively” tests its products and was reviewing the claims. The markers, the statement added, “contain substance levels that fall within the permissible limits.”

Washable markers, from Crayola and Jot, tested negative.