MULBERRY – They tower over the Central Florida landscape, looking like flat-topped mesas imported from the desert Southwest.

And every year, the giant piles, or stacks, of phosphogypsum get a little bigger – 30 million tons bigger.

That’s not good news to some people, who say the byproducts of phosphate mining pollute the air and groundwater with chemicals and minerals including uranium, fluoride, sulfur and arsenic.

There have been many proposals to gradually reduce these “gypstacks,” including the gypsum for road beds and as a soil conditioner. But one ingredient in the phosphogypsum has blocked those efforts: radium, which deteriorates into deadly radon gas. And the federal Environmental Protection Agency doesn’t take a shine to radon gas, which can cause cancer if inhaled continuously. It has banned use of phosphogypsum except for experiments.

On Thursday, a conference on uses of phosphogypsum is planned in Tallahassee, with a message aimed straight at Washington: Relax the rules on using gypsum and the mountains will gradually disappear.

The Phosphogypsum Fact-Finding Forum will be from 8:30 a.m. to 5 p.m. Thursday at the August B. Turnbull III Florida State Conference Center. It is at 555 W. Pensacola St., four blocks west of the state Capitol.

It is sponsored by the Florida Institute of Phosphate Research, the state-funded research organization based in Bartow.

“The only way we can reach EPA is politically,” said Richard F. McFarlin, executive director of the institute. “What we really need to do is get the state to take a position on that.”

EPA officials will not attend because of several ongoing lawsuits over phosphogypsum. The agency has banned its use because of radioactive emissions. EPA’s limit for use is 10 picocuries of radium per gram, well below the levels usually found in the mounds.

EPA has opposed using gypsum in road beds and construction projects because radon gas could pose a danger in the future if homes are built over those areas.

The regulations won’t be relaxed anytime soon, said EPA spokesman Dave Ryan. But the agency hopes to propose rules by January that will allow more use for experimental purposes.

There’s a catch: the gypsum will have be returned to its original source when the experiments are done.

The main question seems to be if the health dangers should remain concentrated in gypstacks or dispersed in small doses.

McFarlin said several studies have shown there would be minimal risks involved from spreading phosphogypsum on grazing pasture, road beds or earthen covers for landfills.

But some environmental advocates claim the institute is merely doing the bidding of phosphate companies and the National Fertilizer Institute, which is pushing EPA to relax the rules.

“If the stacks are covered properly, radon levels are low within a very few feet,” said Gloria Rains, chairwoman of ManaSota-88, an environmental advocacy group. “It is absolutely absurd to expose people to this material rather than contain it on site.”

There are 27 gypsum mountains in Florida, with most concentrated in the Bone Valley region of southern Polk, eastern Hillsborough and Hardee counties. Ten are still active and continue to receive the byproducts of phosphate mining and processing. Estimates peg the amount of gypsum in the stacks at 700 million tons.

By 2001, all new gypstacks must be lined at the bottom to prevent toxins from leaching into groundwater. Existing stacks will be closed unless the mines can prove they are not affecting the water table.

That’s too late to do anything about the millions of pounds of phosphoric acid that was sent straight into the aquifer when a sinkhole developed under a stack at IMC-Agrico’s New Wales plant in eastern Polk last year. Pumping is keeping the tainted water from flowing westward toward more populated areas.