WASHINGTON -- Congress this week is poised to pass legislation overhauling chemical safety for the first time in 40 years -- with strong bipartisan support, no less.

It would be the first major new environmental law in two decades. One might expect the feat would be a happy moment for those who have advocated change for years.

Except, they aren't all exactly happy.

The environmental and public health community is fairly tepid about the final version of the measure, a negotiated text released last week that combines elements of previously passed Senate and House bills. Some groups have endorsed it. Others are opposed. Many simply point out the bill's strengths and flaws, without taking a position for or against its passage. The consensus is that the bill is good, but not good enough, and probably the best Congress could do.

The bill, called the Frank R. Lautenberg Chemical Safety for the 21st Century Act, would reform the Toxic Substances Control Act, a 1976 law guiding the regulation of thousands of chemicals used in goods in the U.S. The current law is widely maligned as ineffective and out of date, incapable of assessing the safety of all the chemicals in consumer goods today.

"There is a widespread acknowledgement and understanding that nobody is well-served by the current law," said Rep. John Shimkus (R-Ill.) on the House floor Tuesday, as members voted 403 to 12 to pass the bill. Shimkus was a lead sponsor in the House.

A spokesman for Senate Majority Leader Mitch McConnell (R-Ky.) said the Senate would likely vote on the bill this week. It is expected to pass there, and the White House has said President Barack Obama will sign it.

The law would give the Environmental Protection Agency new authority to evaluate the safety of a chemical before it enters the marketplace (which may seem intuitive, but it's not the case under current law). It would also allow EPA to start evaluating the safety of chemicals already known to be risks -- including chemicals found to persist in the human body and in the environment. It also limits companies' ability to claim information about what's in their products as confidential business information -- which means regulators, health providers and the general public will have more access to information.

The law would be especially beneficial for regulating new chemicals -- which are introduced at a rate of roughly 700 a year, according to Richard Denison, lead senior scientist at the Environmental Defense Fund. "They will be required to make a safety finding to get on market, which gets away from the passive system we have now," Denison said. "EPA no longer has to prove evidence of risk before it can require testing."

Public health and environmental advocates are less enthusiastic about other parts of the bill. They have concerns whether EPA funding is adequate for all this new work, and whether the bill's timeline for reviewing chemicals is fast enough.

The bill would prevent states from regulating a chemical while EPA is assessing whether it should be controlled at the federal level, but it would allow existing state laws to stand. There's also language in the legislation that says EPA must consider the "cost-effectiveness" of any proposed rule -- a requirement vague enough to concern advocates.

"We don't know what it means for a regulation to be 'cost-effective,'" said Melanie Benesh, legislative attorney at the Environmental Working Group. "There's a concern that it's another way of saying its going to be the least-burdensome on industry, which makes it hard for EPA to make good regulations."

The Environmental Working Group said the final bill falls short of what's needed to really reform chemical regulation, and is too friendly to the chemical industry. Groups like the Breast Cancer Fund outright oppose it.

Andy Igrejas, director of Safer Chemicals, Healthy Families, a coalition of 450 health and environmental groups, falls somewhere in the middle. Some members of the coalition are against the bill, while others decline to endorse it.

"It's definitely a mixed bag," said Igrejas. "The idea that they had to have elements that go backward and that's their price for allowing limited reform -- I think that's what sticks in the craw of people who work on these issues."

Denison and the Environmental Defense Fund support the bill, along with groups like the March of Dimes and the Physicians Committee for Responsible Medicine. "None of [the bill's components] are perfect. All have elements of compromise," Denison said. "But they are, I think, unequivocally improvements over the status quo."

The bill was a collaboration between Republican Sen. David Vitter (La.) and Democratic Sen. Tom Udall (N.M.), who took up a years-long effort from the late Sen. Frank Lautenberg (D-N.J.) to reform the law.

"This landmark reform is a major improvement over current law," Udall said in announcing the negotiated House-Senate version. "It will overhaul a law that has been broken from the beginning and do what TSCA should have done in the first place -- ensure there is a cop on the beat keeping us safe."

The bill's likely passage is a rare departure from partisan deadlock in Congress. There are several reasons for its apparent success. For one, more consumers are demanding products free of suspect chemicals -- leading big box retailers like WalMart and Target to stop selling goods that contain them. And states like California, for example, have passed much stricter laws on things like carcinogenic flame retardants and bisphenol-A, a likely endocrine disruptor, which have in turn compelled more retailers to bar potentially harmful chemicals.

Meanwhile, Europe has passed tough chemical regulations, so companies that sell products there are already complying with stricter standards. The industries that produce these chemicals and products are seeing the value of a more straightforward federal system in the U.S., as do their allies in Congress.

The bill has support from major industry groups -- including the U.S. Chamber of Commerce, the National Association of Manufacturers, and the American Chemistry Council, whose CEO Cal Dooley called it "a major win for America’s economy and American consumers."

Environmental Working Group's Benesh said it remains to be seen whether the bill will live up to promises of meaningfully changing the chemical safety system.

"I think we will know how effective this new law is after the first lawsuits are filed and have been settled," Benesh said. "Then we will know how much power EPA has, and how fully they will be able to exercise it."