Shari Rudavsky, shari.rudavsky@indystar.com

C'mon confess, you've done it. Peed in the pool.

It seems like such an innocent act; after all, you're surrounded by water and there are plenty of chemicals to keep it clean.

But peeing in the pool may not be so innocuous.

A Purdue University professor recently published a study showing that uric acid, a major component of urine that is also found in smaller concentrations in sweat, can produce toxic byproducts when it interacts with chlorine, the compound used to keep germs from spreading in the pool.

"The data is pretty clear about the chemicals that are generated and the risk that they present," said Ernest (Chip) R. Blatchley III, a professor in Purdue's school of Civil Engineering, who worked with colleagues from the China Agricultural University. "It's a manageable problem."

The byproducts — cyanogen chloride and trichloramine — are known to have detrimental effects on lung health. These chemicals appeared in both laboratory reactions and samples of indoor swimming pool water, said Blatchley, who had previously looked at the chemistry of drinking water.

Most of the time the concentrations of these chemicals in a swimming pool remains low, but there are times, such as when a pool is being used heavily, that the levels can rise.

"A large swimming event or crowded pool, that's the circumstance that concerns me the most," said Blatchley, who published the findings in a recent issue of the journal Environmental Science & Technology.

While not everyone will necessarily fall ill in such circumstances, some may develop acute illnesses or chronic problems, he said.

But Blatchley hopes the findings help persuade competitive swimmers and others to think twice before taking a whizz in the pool. Although many pools have signs posted dissuading the practice, many serious swimmers see no need to interrupt their workout with a bathroom break.

So, Blatchley wants to get out the message to take two simple steps to lower the levels uric acid and other chemicals found in sweat and urine in a pool — shower before you enter the pool and leave the pool if you need to urinate.

"It's really just a question of courtesy to everybody else who swims. ... I don't think the things that we're suggesting are a burden," he said.

Now Blatchley is studying what happens when chemicals found in pharmaceuticals and personal care products, such as skin lotions and shampoos, enter a pool and interact with chlorine.

But as summer approaches, there's no reason to despair. The scientists focused their study, funded by the National Swimming Pool Foundation and others, on indoor pools. It's not clear whether these findings apply to outdoor pools.

Nor is Blatchley ready to declare swimming, the nation's fourth most popular form of exercise according to the Centers for Disease Control and Prevention, a health hazard.

"Dangerous is a bit of an overstatement," he said. "There's a lot of people that go swimming and they don't get sick at all."

And if more swimmers exited the pool to relieve themselves, they might be able to make swimming that much healthier for the others.

Call Star reporter Shari Rudavsky at (317) 444-6354. Follow her on Twitter @srudavsky.