(Reuters) -Amazon.com urged a federal judge to dismiss a proposed class action over its alleged sale of rice tainted by arsenic and other "heavy metals," denying the accusation it fraudulently concealed contamination.

In a filing late on Friday in Seattle federal court, Amazon said the presence of heavy metals in rice was a "decades-old, well-known issue" that was easy to discover, and the plaintiffs did not claim there were more metals than regulators allowed.

Amazon also said Section 230 of the federal Communications Decency Act shields online platforms from liability over content from third parties, such as rice sellers.

Lawyers for the plaintiffs did not immediately respond on Tuesday to requests for comment.

The lawsuit on May 23 covered 18 types of rice sold through Amazon, including from brands such as Ben's Original and Amazon-owned Whole Foods' 365.

Plaintiffs Ashley Wright and Merriman Blum said they would not have bought or would have paid less for their Iberia basmati rice, one of the products, had they known it was contaminated or Amazon never tested it for heavy metals.

Exposure to heavy metals has been associated with nervous system problems, immune system suppression and kidney damage. It has also been associated with autism spectrum disorder and attention deficit hyperactivity disorder in young children.

The lawsuit followed a study by the nonprofit Healthy Babies, Bright Futures, which found arsenic in all 145 rice samples purchased nationwide, cadmium in all but one sample, and lead and mercury in more than one-third of tested samples.

The case is Wright et al v Amazon.com Inc, U.S. District Court, Western District of Washington, No. 25-00977.