More than 200 scientists from 38 countries spoke with one voice today, calling for curbs on the global production and use of a class of chemicals found in hundreds of grease- and water-resistant industrial and consumer products. To avoid long-term harm to the environment and human health, nations should act now to limit use of the toxic compounds, which can persist for long periods in the environment, the scientists conclude in a statement appearing in Environmental Health Perspectives. Industry groups, however, say currently used versions of the chemicals are safe.

The synthetic chemicals, called polyfluorinated and perfluorinated substances (PFASs), have unusually strong fluorine-carbon bonds that can resist heat and help materials repel water, oil, and stains. These special properties make fluorinated chemicals a key ingredient in a wide range of products, including nonstick cookware, cosmetics, microwave popcorn bags, waterproof outdoor gear, carpets, and firefighting foams. Because PFASs are nearly indestructible, they can persist in the environment for decades or more and are prone to accumulate in the tissues of wildlife and humans.

Researchers have found that two of the most-studied fluorochemicals, perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA), can damage the liver and disrupt reproduction and development in wildlife and lab animals. Emerging epidemiological evidence suggests the compounds—which have been detected in nearly every person who has participated in national studies—can cause similar problems in humans.

Increasing concern about PFOS, PFOA, and other fluorinated chemicals has prompted industry to voluntarily phase out some of the chemicals, and for some governments to impose regulations, causing a major drop in the use of once-common compounds. But many companies have replaced “long-chain” PFASs (named for the length of their carbon backbone), which include PFOS and PFOA, with “short-chain” alternatives.

Industry representatives say data show that the replacements are safe. “There is substantial scientific data supporting the conclusion that short-chain PFASs are expected to pose no significant risk while delivering important societal benefits,” says Jessica Bowman, executive director of the FluoroCouncil, the fluorochemical manufacturers’ trade group in Washington, D.C.

The 208 scientists signing today’s statement—known as the Madrid Statement—have a different view. Although the short-chain alternatives are less likely to accumulate in animals and humans—bioaccumulation potential tends to increase with the length of the carbon chain—they still concentrate in plants. And “if you eat plants highly contaminated with short-chain PFASs on a regular basis, you will have a high irreversible exposure,” says Ian Cousins, an environmental scientist at Stockholm University, who is one of 14 lead authors of the consensus statement.

But it is the longevity of the short-chain compounds that concerns Cousins most. If the compounds get into water supplies, for instance, “short-chain PFASs will remain in the drinking water for decades to centuries,” he says. “People drinking the water will be highly exposed and cannot easily reduce their exposure.” Fluorinated chemicals “never go away” and break down only over “geologic time,” adds chemist Arlene Blum, director of the Green Science Policy Institute in Berkeley, California, and a lead author of the statement. To avoid future problems, nations need to act now to limit the chemicals to “essential uses” and invest in developing nonfluorinated alternatives, the researchers argue.

Denmark is the only country that now regulates short-chain PFASs, but only in limits imposed on materials that come into contact with food. And efforts to study the global effects of different PFASs have been difficult, researchers note, because companies have been reluctant to release proprietary details regarding the amounts, uses, and properties of their chemicals. The Madrid Statement urges governments and manufacturers to make all data on alternatives that are not publicly available accessible, rather than forcing publicly funded researchers to spend years and significant sums investigating the properties and effects of these commercial products.

The scientists’ call for safer alternatives is critical, says Bruce Lanphear, an environmental health expert at Simon Fraser University, Burnaby, in Canada, who has not signed the statement. “Too often,” he says, “established toxicants are replaced with chemicals of unknown toxicity that are subsequently found to be toxic.” But he’s not sure the world’s chemical regulators are ready to respond effectively. “In the absence of an effective chemical regulatory system, we would need dozens if not hundreds of these statements, each targeting a distinct or suspected toxicant,” he says.

There has been some movement. In March, the scientific advisory panel for California’s Environmental Contaminant Biomonitoring Program unanimously agreed to start monitoring all classes of PFASs after learning that short-chain PFASs in food packaging were detected in human blood. The California move is noteworthy, observers say, because the state is one of the world’s largest markets for consumer products. Internationally, the United Nations’ Stockholm Convention, a chemical regulation agreement that the United States has not ratified, has already imposed strict global limits on PFOS and may soon endorse complete elimination of the chemical.

Industry groups are watching these developments closely, but say developing effective alternatives may be difficult. For example, although researchers have developed nonfluorinated alternatives to some long-chain PFASs, Bowman notes they have proved unsuitable for many applications because they don’t meet performance requirements.

Liza Gross is a freelance science journalist in Kensington, California, who writes frequently on the intersection between science and society.