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Millions of mice, rats, fish, birds and other animals are killed in the name of science every year in the United States. A new bipartisan bill that passed the U.S. Senate on June 7 and now awaits a presidential signature to become law aims to curb this practice in favor of more animal-friendly—and often quicker and cheaper—forms of chemical testing.

Both animal rights groups and the toxicologists who test chemical safety, sometimes on animals, support the update, which is part of a broad-sweeping reform to the Toxic Substances Control Act (TSCA)—a 40-year-old law that governs chemicals and regulates their safety.

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The bill provides the Environmental Protection Agency (EPA) with more authority to require review of untested chemicals, and encourages the use of modern alternatives to traditional animal testing.

Out of the 83,000 chemicals in use in the United States, most have not been tested for toxicity to humans.

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This is in part due to the way the current TSCA restricts the EPA’s authority, and also because the approach is decades-old, ignores modern technology, and relies heavily on testing chemicals on animals.

Animal testing, in addition to being ethically controversial for many Americans, is also expensive and time consuming.

“To find out whether a substance produces cancer or not on animals costs at least $1 million—that’s why we have so few substances tested at all,” said Thomas Hartung, a toxicologist and director of Johns Hopkins Center for Alternatives to Animal Testing (CAAT) in Baltimore, MD.

Because of these factors, the decision to avoid animal testing will help protect human health as well as animals.

“It’s not only about not using animals for ethical reasons, it’s about costs and how long it takes—four-five years for cancer testing,” Hartung said.

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The TSCA reform bill would modernize the scientific approach to testing chemical substances by using data to screen the chemicals deemed most likely dangerous to human health.

“It’s a tiered approach to testing, and it would specify how to set priorities for chemicals that need to be tested,” William Farland, an expert on toxicology at Colorado State University and chair of the Society of Toxicology’s TSCA Task Force, said. Farland and the task force worked for years with congressional members and their staff to ensure the science of toxicology was included in discussions around the TSCA reform bill.

As part of the bill, the EPA would create a database of validated alternatives to animal testing that would be updated as the science evolved. Also, the EPA would be expected to fund research and development of new alternatives to animal testing.

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While some of this was already being done by the EPA and toxicologists informally, the new law would take it further faster, experts agreed.

“Writing this into law is one way to encourage the EPA to do and fund research that will increase alternative tests that are available,” Farland said.

“It’ll encourage others to develop those types of tests, and will stimulate the idea that we’ll be able to get some of the answers we need without using whole animal tests,” Farland added.

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As toxicologists, Farland said, “it’s in our interest to make sure the bill is written in a way that encourages the best science and gives the EPA the kinds of tools that can help it stay up to date.”

Researchers are increasingly developing viable alternatives, Hartung said.

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“There is big data coming to toxicology,” Hartung said, adding that computational approaches are already being widely used by European regulators.

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“It’s a very progressive approach by which a lot of information is used to characterize a chemical and find out (how it behaves),” Hartung said. “This approach will help characterize more chemicals to prioritize the few for which more extensive testing is necessary.”

For example, the most recent chemical legislation in Europe brought together data on some 15,000 chemicals. For one, this analysis helped show that a computational approach using that data predicts skin irritation as well as animal tests do.

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Another alternative to animal testing is to grow your own human organs. CAAT announced in February that it had grown mini-brains, and Hartung said others had developed mini-livers and other organs.

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Growing mini-organs has never been easier thanks to the discovery that skin cells could be transformed into embryonic stem cells—avoiding the controversy of getting stem cells from embryos, Hartung said.

“These stem cell models really opened up fantastic models for many organs, and it’s only started being integrated into testing but we expect over the next few years that a lot of these methods will lend themselves to be used in (chemical substances) testing,” Hartung said.

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“I’ve really been astonished at how fast some of these developments have taken place,” Hartung said.

While human mini-organs may seem better for testing than animals of another species, testing on isolated organs still doesn’t work as well a whole biological system.

“We have to have a way to test chemicals in biological systems,” said Farland. “We don’t want to wait until we see something happen in humans so we need to use surrogates for those tests, and typically those have been on animals.”

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In addition to being used for chemical safety tests, animals—most often mice or rats—are still used to test pharmaceuticals, cosmetics, and medical procedures.

In some cases, there’s no existing alternative to seeing a chemical’s effect on a biological system “with the ability to transport that chemical, metabolize, or change that chemical into something else, and seeing the different susceptibilities of different organs—an animal becomes integral for all of that information,” Farland said.

Hartung agreed with that, saying that alternative methods do exist, “but there’s clearly some aspects of safety assessment where there’s no reasonable alternative method.”

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But animal rights advocates countered that animal testing wasn’t always predictive of a chemical’s effect on human health.

“The predictivity of animal tests, even between like species, is only around 50%,” said Sara Amundson, executive director of the Humane Society Legislative Fund. “There’s no possible way of actually assessing 80,000 plus chemicals for human and environmental consequences without utilizing 21st-century science."

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Amundson said the the TSCA update is "not meant to replace all animal testing tomorrow, but it is certainly the precursor to ensuring that good 21st century science that happens to minimize the use of animals is considered.”