Pool patrons may risk exposure to a chlorine-byproduct linked with cancer and birth defects, according to new research. A study published in Environmental Science & Technology indicates that swimmers registered detectable levels of haloacetic acids in their urine within 30 minutes of a swim. The study included almost 50 volunteers.

The Environmental Protection Agency limits HAA levels in drinking water but “well-managed pools should have concentrations that are less than what is found in drinking water,” says Mary Ostrowski, director of chlorine issues for the American Chemistry Council in Washington, D.C. “In a properly maintained pool, any risk is likely to be very small.”