Peter J. Hansen, a professor of reproductive biology at the University of Florida, describes himself generally as a skeptic of many studies linking chemical exposure to declining sperm quality. Much research on the effect of environmental hazards on humans is typically done by administering doses of hazards to research animals in much greater concentrations than is typically found in water supplies, he said.

But the Nottingham study, he noted, detected the chemicals in the dogs’ tissue and also in the dogs’ food. And researchers did so over decades, tracking a concurrent decline in reproductive markers.

“I think it was very rigorous,” he said. “It’s much more clear from their data that there was a decline over time, which agrees with the human data but doesn’t suffer from the same research problems.”