Scientists have spent decades trying to untangle puzzling questions over falling sperm concentrations. A new analysis of 25 studies of pesticides shows a clear connection, researchers say.

A prolonged decline in male fertility in the form of sperm concentrations appears to be connected to the use of pesticides, according to a study published Wednesday.

Researchers compiled, rated and reviewed the results of 25 studies of certain pesticides and male fertility and found that men who had been exposed to certain classes of pesticides had significantly lower sperm concentrations. The study, published Wednesday in Environmental Health Perspectives, included data from more than 1,700 men and spanned several decades.

“No matter how we looked at the analysis and results, we saw a persistent association between increasing levels of insecticide and decreases in sperm concentration,” said study author Melissa Perry, who is an environmental epidemiologist and the dean of the College of Public Health at George Mason University. “I would hope this study would get the attention of regulators seeking to make decisions to keep the public safe from inadvertent, unplanned impacts of insecticides.”