Radioactive Mussels Discovered In Round Lake Near Tampa

September 21, 2000

TAMPA, Fla. — Freshwater mussels in at least one west Central Florida lake — and perhaps several others — may contain elevated amounts of radioactive radium, apparently the result of maintaining the lake’s levels with water from the Floridan Aquifer, according to a University of Florida lake specialist and a state water official.

Although humans rarely eat the lake mussels, the radium levels are considered high enough to pose a health risk and prompt a warning against eating the mollusks. In addition, the radium could make its way up the food chain, starting with animals that do dine on the mollusks, said Mark Brenner, an assistant professor of fisheries and aquatic sciences with UF’s Institute of Food and Agricultural Sciences.

“In addition to possible human consumption, other animals such as raccoons and otters may feed on these freshwater mussels,” Brenner said.

Brenner found that mussels are capable of storing radium in their tissues in large quantities. For example, a gram of tissue from mussels in Round Lake near Tampa contained nearly 100,000 times the radium contained in a gram of lake water. Researchers currently are testing mussels from six augmented lakes with plans to test more of the 50 lakes and wetlands in the Southwest Florida Water Management District’s 16-county region that have their water levels maintained using this method.

“It was a real shock to find extremely high radium levels in the tissues of mussels,” said Brenner, who also directs the UF’s Land Use and Environmental Change Institute. “A risk assessment completed as part of this project concluded that long-term consumption of mussels with high levels of radium could result in an increased cancer risk in humans.”

Doug Leeper, an environmental scientist with the district, came to the same conclusion.

“The Southwest Florida Water Management District has conducted preliminary assessments of health risks associated with radium levels we’ve observed and so far the recommendation would be that people not consume freshwater mussels on a regular basis,” Leeper said.

Radium occurs naturally in the limestone surrounding the aquifer and slowly dissolves into the water. Brenner said researchers will be looking at radium levels in all aspects of the lake environment.

“We’ve looked at some fish in Round Lake, and there was really no detectable radium in the flesh,” Brenner said. “Radium levels in both the water in the lake and the well water coming into the lake are below the maximum amounts allowed under federal standards for safe drinking water, so the lake water is safe to swim in and drink.”

The practice of replenishing lakes with aquifer water dates back to the 1960s, when a growing Hillsborough County started drawing more water from the aquifer to meet the needs of both residents and agricultural interests.

“As the aquifer water was withdrawn, the water level in the lakes began to drop rather precipitously,” Brenner said. “People who lived around the lakes were rather upset because they had purchased lakeside property and then found themselves far from the lake shore.”

The solution homeowners and water managers came up with at the time was to dig wells and replenish lake water from the deep aquifer. While officials at the time suspected the practice would result in changes in the lakes, Brenner said the introduction of radioactive radium wasn’t anticipated.

“Normally, these lakes would be filled with rainwater and shallow aquifer water and probably would not contain very high levels of radium,” Brenner said. “The underlying problem appears to be that these lakes are being supplemented with deep aquifer groundwater that naturally contains dissolved radium.”

Brenner said he had no direct evidence that humans are eating mussels from lakes in west Central Florida, but he said he suspects they are.

“I get phone calls from people asking if its OK to eat these freshwater mussels,” Brenner said. “This suggests to me that if people ask, it’s crossing their minds. And I assume that there are people who don’t ask, they just eat the mussels.”