There were high levels of arsenic found in bottled water that was sold in a number of major grocery stores, raising health concerns as arsenic can cause cancer if consumed by humans.

Two bottled water brands sold at Whole Foods, Walmart and Target were found to have the toxin following a new batch of tests that was commissioned by the California nonprofit Center for Environmental Health (CEH). The companies in question are Starkey, which creates bottled water products and is owned by Whole Foods, as well as Peñafel, which is owned by Keurig Dr Pepper and sold at Target and Walmart.

The aforementioned unveiled a press release Tuesday noting that these products have arsenic amounts “above the level requiring a health warning under California’s consumer protection law.” The toxic can reportedly cause cancer and reproductive harm, per the release.

CEH’s CEO, Michael Green, noted that some may see bottled water as being a safer choice than tap water, but it could lead to serious health problems in this case. “Consumers are being needlessly exposed to arsenic without their knowledge or consent,” Green said. “They are ingesting an extremely toxic metal.”

Green added that the exact levels of arsenic were not disclosed by the organization because it is now suing both Whole Foods and Keurig Dr Pepper over the issue. Nevertheless, CEH said its findings corroborated Consumer Reports research regarding high levels of arsenic in the bottled water brands.

The April Consumer Reports tests on Starkey water found that the arsenic levels in three samples came in between 9.48 to 9.86 ppb, while a fourth was 10.1 ppb, slightly higher than the federal limit of 10 ppb.