Updated June 30, 2023 at 1:24 PM ET

Florida is another step closer to paving its roads with phosphogypsum — a radioactive waste material from the fertilizer industry — after Gov. Ron DeSantis signed a controversial bill into law Thursday.

Conservation groups had urged DeSantis to veto the bill, saying phosphogypsum would hurt water quality and put road construction crews at a higher risk of cancer.

"By signing off on this reckless handout to the fertilizer industry, Gov. DeSantis is paving the way to a toxic legacy generations of Floridians will have to grapple with," said Elise Bennett, Florida and Caribbean director at the Center for Biological Diversity, in a statement sent to NPR.

The Environmental Protection Agency also has a say: The agency regulates phosphogypsum, and any plan to use it in roads would require a review.

"Any request for a specific use of phosphogypsum in roads will need to be submitted to EPA, as EPA's approval is legally required before the material can be used in road construction," the EPA told NPR on Friday.

Here's what to know about phosphogypsum and the new law.

What does the law do?

The new law looks to clear the way for phosphogypsum to be used as a pavement aggregate alongside crushed stone, gravel, sand and other materials. In recent years industrial byproducts and reclaimed materials also have been used as aggregates, according to the Federal Highway Administration.

HB 1191 compels the Florida Transportation Department to conduct "demonstration projects using phosphogypsum in road construction aggregate material to determine its feasibility as a paving material," as it studies using phosphogypsum in roads.

Florida's transportation agency now has less than a year to complete a study and make a recommendation; the bill sets a deadline of April 1, 2024.

Bennett criticized the plan, saying that under the new law, radioactive waste would be dumped in roadways "under the guise of a so-called feasibility study that won't address serious health and safety concerns."

DeSantis signed the bill into law several days after formally receiving it. The Republican-dominated Florida Legislature had approved the measure by a wide margin.

What is phosphogypsum and why is there so much of it?

In fertilizer, phosphorus is important for plants to grow strong roots and for crops to be productive. To make phosphoric acid for fertilizer and a few other uses, phosphate rock is dissolved in sulfuric acid. Phosphogypsum is what's left over.

The commonly used production process, which dates to the 1840s, is not very efficient. For every ton of phosphoric acid produced, more than 5 tons of phosphogypsum waste is generated.

Florida has been an important source since the 1800s; currently, the EPA notes, "Florida alone accounts for approximately 80 percent of the current capacity, making it the world's largest phosphate producing area."

Florida's prominent role means the state also has massive waste sites called phosphogypsum stacks, or "gypstacks." Such stacks can be very large — spanning up to 800 acres and about 200 feet in height. They've been linked to serious water pollution over the years, due to sinkholes and other breaches.

Is phosphogypsum dangerous?

"Phosphogypsum contains appreciable quantities of uranium and its decay products, such as radium-226," according to the EPA, which also notes that because the fertilizer production process concentrates waste material, "phosphogypsum is more radioactive than the original phosphate rock."

"The radium is of particular concern because it decays to form radon, a cancer-causing, radioactive gas," the EPA adds.

An analysis commissioned by the Fertilizer Institute, a group that represents the fertilizer industry, disagrees, saying that using phosphogypsum in road construction won't produce radioactive doses that are above the EPA's acceptable risks. Such work, it stated, "can be done safely and results in doses that are a small fraction of those arising from natural background radiation."

Last November, researchers in China who reviewed numerous existing studies on recycling phosphogypsum said they were optimistic about its potential use in road construction materials. But they also concluded that more studies were needed, noting that "few studies have focused on its durability or analyzed its long-term effects on soil and water resources."

Conservation and environmental groups banded together to fight the Florida bill, saying it caters to the fertilizer industry — which, they said, previously has shown it can't adequately manage the more than 1 billion tons of waste currently stored in the state.

In a letter to DeSantis, the Center for Biological Diversity and more than 30 other groups stated that "Florida should not be a test subject in the industry's reckless experiment."

Is Florida's plan legal?

The EPA says "phosphogypsum remains prohibited from use in road construction," as it has been almost continuously for more than 30 years.

Under former President Donald Trump, the EPA briefly rescinded that policy starting in October 2020. But it reinstated the rule in June 2021.

The Florida legislation doesn't address the federal prohibition outright. Its supporting documents note that the EPA allows some uses for research purposes — and the law also asserts that phosphogypsum is not technically a "solid waste."

When Florida's lawmakers approved the bill in early May, the EPA told NPR,
"The legislation passed in Florida would not affect the requirement ... that U.S. EPA review proposed alternative uses of phosphogypsum on an individual, case-by-case basis."

The agency said Florida would have to apply for approval of its plan, citing the code of federal regulations. As with any other proposed project, the EPA would then open a public comment period, release its own technical analysis and seek input about the proposal.

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