A new law in Florida directs the state Department of Transportation to conduct demonstration projects using phosphogypsum – properties of which decay to a radioactive gas – as an aggregate in roadbuilding.
The controversial bill was signed June 29 by Gov. Ron DeSantis over objections by environmental groups that say the substance contains radioactive material that will harm groundwater and air quality. The U.S. Environmental Protection Agency has banned the use of phosphogypsum as an aggregate material in road construction and other uses since 1992. However, with radium-226 levels below a certain threshold, it can be used by farmers, according to the EPA.
The law is part of the state’s effort to recycle phosphogypsum, which is a byproduct left over from the production of phosphoric acid, an ingredient in fertilizer. Florida contains the world’s largest production of phosphate and has the most phosphogypsum stacks in the country. The stacks range from 5 to 800 acres and are 10 to 200 feet high. It is estimated 5.2 tons of phosphogypsum are created from making 1 ton of phosphoric acid.
Phosphogypsum contains uranium and thorium that decay to radium, and radium decays to radon. Radon, an odorless, colorless radioactive gas, emits from the stacks, the EPA says. It is also found in the natural decay of uranium and radium and is found in nearly all rocks and soils.
For use in agriculture, the EPA says, phosphogypsum cannot have a radium-226 concentration greater than 10 pCi/g.
Most of North Florida’s phosphogypsum stacks are below the EPA’s restricted level for agricultural use, according to the Florida Industrial and Phosphate Research Institute. However, phosphogypsum from Central Florida is above that level.
There is debate as to whether phosphogypsum is safe as a road aggregate.
