CHICAGO >> Chinese factory workers exposed to high levels of the plastics chemical BPA had low sperm counts, according to the first human study to tie it to poor semen quality.

The study is the latest to raise health questions about bisphenol-A and comes two weeks after Canada published a final order adding the chemical to its list of toxic substances.

Whether the relatively low sperm counts and other signs of poor semen quality translate to reduced fertility is not known. Study author Dr. De-Kun Li, a scientist at the Kaiser Permanente Division of Research in Oakland, Calif., noted that even men with extremely low sperm counts can father children.

But Li said finding that BPA may affect sperm is troubling because it echoes studies in animals and follows his previous research in the same men that linked BPA exposure with sexual problems.

If BPA exposure can reduce sperm levels, “that can’t be good” and means more study is needed to check for other harmful effects, Li said.

The study was published online Thursday in the journal Fertility and Sterility. The National Institute of Occupational Safety and Health funded the research.

Andrea Gore, a pharmacology and toxicology professor at the University of Texas who was not involved in the research, called it an important but preliminary study.

The results “are at least suggestive of the possibility that BPA may be one of the compounds that are causing some of these changes” in sperm, she said. But Gore said stronger evidence is needed to prove that BPA is indeed the culprit.

BPA is used to make resins and strengthen plastics and is found in many consumer products: hard plastic bottles, metal food container linings, dental sealants and eyeglasses. Most Americans’ urine contains measurable levels of BPA.

Studies in animals have linked the chemical with reproductive problems and cancer. That’s led to millions of dollars in new research in people.

Steven Hentges of the American Chemistry Council, an industry group, said the study in China “is of limited relevance” to U.S. consumers, who typically are exposed to very low BPA levels that pose no health threat.

The study involved 130 Chinese factory employees who worked directly with materials containing BPA and 88 workers who didn’t handle it and whose exposure was similar to that of typical American men.

Low sperm counts were found in workers who had detectable levels of bisphenol-A in their urine. Poor sperm quality was two to four times more prevalent among these men than among workers whose urine showed no sign of BPA. The lowest sperm counts were in men with the highest levels of BPA.

BPA in urine was linked with lower-quality semen even in men who didn’t work with the chemical, although their average BPA levels were much lower than in the other group. Li said the average level in this group was similar to that detected in U.S. men.

The U.S. Food and Drug Administration has been evaluating the chemical’s safety but declined to say if it is considering following Canada’s lead in declaring the chemical toxic.

In an e-mailed statement, the FDA said it is working with the National Institutes of Health and others “to advance scientific understanding of BPA and inform our decisions.”