“This is a big deal,” said President Barack Obama as he signed into law the bill that updates — for the first time in 40 years — the nation’s main chemical safety legislation. Called the Frank R. Lautenberg Chemical Safety for the 21st Century Act to honor the late senator for whom this was a special cause, the law revises the Toxic Substances Control Act that gives the U.S. Environmental Protection Agency authority to regulate chemicals used commercially in the United States.

As Obama noted at the June 22 signing ceremony, TSCA was supposed to ensure that chemicals used in the U.S. were safe for human health and the environment. But, said the president, “Even with the best of intentions, the law didn’t quite work the way it should have in practice.”

In fact, TSCA allowed the approximately 62,000 chemicals already on the market when it was passed in 1976 to continue being used without safety testing. It also placed enormously high hurdles for the EPA to clear before demonstrating a chemical was hazardous enough to ban. Even asbestos has failed to meet those requirements. It was widely agreed, by industry and environmental advocates alike that TSCA was badly in need of revision.

As the Lautenberg Act’s lead sponsor Senator Tom Udall told Ensia by email, “Most Americans believe that if they can buy a product at the grocery store or the hardware store, the government has tested it and determined that it’s safe. But that hasn’t been true. There has been no cop on the beat testing chemicals to make sure they’re safe — even the ones in your home.”

But exactly what the revisions should look like was a matter of considerable debate, and the new legislation was years in the making. Overall, the revised TSCA gives the EPA far more authority to act on hazardous chemicals. And while questions and reservations about the bill remain on all sides, it’s largely been greeted with hope that the new law will enable the EPA to do a better job of evaluating and acting effectively on chemical safety.

EPA is already putting the new legislation into practice. But as Environmental Defense Fund lead senior scientist Richard Denison said, “It’s not going to be an overnight process. The original law dug a very deep hole that we have to climb out of.”

As that process gets underway, here’s what anyone concerned about the safety of chemicals we all encounter daily, should know about what the new TSCA will — and won’t — do:

1. What does TSCA regulate?

TSCA regulates chemicals used commercially in the United States. That said, TSCA does not regulate pesticides, chemicals used in cosmetics and personal care products, food, food packaging, or pharmaceuticals. Some chemicals, however, have multiple uses and so may be regulated concurrently by TSCA and other federal laws. For example, TSCA regulates the plastics ingredient bisphenol A when it’s used as a receipt paper coating, but the Federal Food, Drug and Cosmetic Act regulates BPA when it’s used in food packaging.

2. Will the new law make it easier for the EPA to restrict or ban use of highly toxic chemicals?

Unlike the old law, the new TSCA requires EPA to review the safety of all chemicals used commercially in the U.S. “The EPA is actually required to look at existing chemicals,” says Wendy Cleland-Hamnett, director of the EPA’s Office of Pollution Prevention and Toxics. “Under the old TSCA there was no mandate that the EPA look at existing chemicals. That’s huge.”

The new TSCA “gives EPA sweeping new authority to prioritize and evaluate existing chemicals so it will be easier for EPA to regulate these substances, if found to pose unreasonable risks,” says chemical regulation expert Lynn Bergeson, managing partner at the law firm Bergeson & Campbell.

Now new chemicals must be found safe before they can be sold.The EPA must also review all new chemicals and decide if they present “an unreasonable risk” to human health and the environment. If such risks are found, the EPA may restrict or ban a chemical. Under the old TSCA, chemical manufacturers had to submit certain information to the EPA before new chemicals could go on the market — but unless the EPA raised objections within 90 days, the chemicals could be sold without further scrutiny. According to the EPA, the agency has taken action on only about 10 percent of the nearly 40,000 new chemicals submitted to the agency between 1979 and September 30, 2015. EDF’s Denison says this 10 percent may be an overestimate.

Now new chemicals must be found safe before they can be sold, says Environmental Working Group legislative attorney Melanie Benesh.

What the EPA does under the Lautenberg Act will, however, also depend on available funding. The law requires the chemical industry to help pay for the program, but the EPA also depends on federal budgets as determined by Congress. Udall says he “will be fighting to make sure the EPA has the resources it needs to do its job.”

3. Will the new law let EPA restrict or ban use of highly toxic chemicals more quickly?

Yes — in theory. The new law requires the EPA to prioritize chemicals for evaluation. It also sets enforceable deadlines for the EPA’s chemical reviews.

By mid-December 2016 (within the bill’s first 180 days) the EPA must have begun to review at least 10 chemicals. These will come from a list of existing chemicals the agency had already decided to evaluate. Within the first three-and-a-half years, the EPA must have 20 ongoing chemical evaluations. Reviews are supposed to be completed within three years, but that deadline can be extended six months. The EPA is supposed to issue any regulations within two years after that. The EPA can extend either of these deadlines but extensions for one chemical can’t add up to more than two years.

Given the enormous backlog, progress through the untested chemicals will still be slow — to say the least. In fact doing the math on 62,000 chemicals shows it could take the EPA centuries to work through every substance. But given that the old TSCA had no chemical review deadlines, the Lautenberg Act aims to improve substantially on the decades-long reviews of single chemicals that occurred under its predecessor.

4. What chemical hazards is the new TSCA designed to protect us from?

The first chemicals the EPA will evaluate must come from a list the agency has already decided merit review — chemicals that pose concerns for children’s health, are carcinogenic, environmentally persistent, toxic and build up in fat or other living tissue, or are widely found in biomonitoring programs.

When choosing chemicals to review, the EPA must give priority to those with large exposure potential, those that are environmentally persistent and bioaccumulate, and those that are stored near important drinking water sources.After that, when choosing chemicals to review, the EPA must give priority to those with large exposure potential, those that are environmentally persistent and bioaccumulate, and those that are stored near important drinking water sources. The new law also tells the EPA to address chemicals that are likely to pose health and safety threats to those considered most vulnerable — including infants, children, pregnant women, workers and the elderly.

Additional criteria for chemical prioritization are due from the EPA by June 2017.

5. What chemical hazards will the new TSCA leave untouched, if any?

The new law authorizes the EPA to review all existing and new chemicals, to identify those that pose unreasonable risks, and to regulate or eliminate those risks. The goal is to leave no unreasonable risk untouched. The details of EPA’s risk evaluations, however, have still to be worked out in a rule that must be completed by June 2017. These — along with the additional chemical prioritization criteria — will play a big role in determining exactly how effective the Lautenberg Act will be at reducing exposure to hazardous chemicals.

6. Will the new law do a better job of preventing disastrous chemical spills?

While TSCA is not intended to address or prevent chemical spills, the new law’s requirements should eventually help reduce the impact of spills or other accidents. Among these is the requirement that chemical companies disclose their products’ contents in emergencies rather than claim such information as trade secrets.

7. Will the new law keep hazardous materials out of furniture, clothing and personal care products?

Because some chemicals used in these products (which aren’t covered by TSCA) have additional uses that fall under TSCA’s purview, the upgraded review process could potentially avert hazardous chemicals’ use in a wide range of consumer products.

8. Is the new TSCA likely to proactively change chemical companies’ practices?

Because the new TSCA requires all chemicals to be evaluated, it’s expected to influence which chemicals are chosen as product ingredients, how chemicals are used in manufacturing and how chemicals are manufactured as companies try to avoid using chemicals likely to be restricted or banned. This may also create an incentive for new, safer chemicals and finished products.

9. What are its implications with respect to environmental justice?

The new TSCA requires the EPA to consider impacts of chemical exposures on those most “susceptible” to these effects, “such as infants, children, pregnant women, workers, or the elderly.’’ How the EPA defines “susceptible” and “vulnerable” and how it considers impacts to these groups is yet to be determined. But already, public interest groups have asked the EPA to consider social and economic factors.

10. What aspects have yet to be settled, and what can citizens do to influence them?

Instead of hammering out chemical prioritization criteria and the details of how the EPA will evaluate chemical risks before the Lautenberg Act was passed, lawmakers decided to leave those torules that will become part of the overall law. The rule-making process involves official public comment periods, so the EPA will be considering those as it writes these rules, along with a rule about potential chemical industry fees that will go toward covering some of the law’s costs. Initial public comment periods for these rules are already closed. The law also includes public comment periods before the EPA finalizes these rules, as well as for ongoing chemical selections and evaluations.

And, points out Kathy Curtis, Clean and Healthy New York executive director, the new law leaves ample room for continued action on the part of state legislatures and citizens. This includes action on chemical uses TSCA doesn’t regulate and new bills on chemical use reporting — both of which have been instrumental in influencing which chemicals get used in consumer products.

As many have cautioned, substantive changes will take time. But according to the EPA’s Cleland-Hamnett, the new law opens the potential for “a huge increase in human health and environmental protection.” But this won’t happen without public engagement on the part of those with a stake in the outcome — essentially, all of us.