ROCHESTER, N.Y. — Catching his breath at a fitness club, Matt McHugh took a gulp of water from his trusty hard-plastic Nalgene bottle and pondered the idea of switching to an alternative made of glass, stainless steel or another kind of plastic.

Worries about a hormone-mimicking chemical used in the trendy sports accessory led a major Canadian retailer to remove Nalgene and other polycarbonate plastic containers from store shelves in early December.

"It's definitely a concern, but I'd like to learn more before I make any decisions about my water bottles," said McHugh, 26, a business manager for a reggae band. "For now, I'll probably keep using my Nalgene until it breaks. It's indestructible, I've heard."

Vancouver-based Mountain Equipment Co-op is waiting for Canadian health regulators to finish a preliminary review in May before it reconsiders restocking its 11 stores with the reusable, transparent bottles made with bisphenol A, or BPA, a compound created by a Russian chemist in 1891.

There is little dispute that the chemical can disrupt the hormonal system, but scientists differ markedly on whether very low doses found in food and beverage containers can be harmful. The U.S. Food and Drug Administration sides with the plastics industry that BPA-based products do not pose a health risk.

However, an expert panel of researchers reported at a U.S. government conference that the potential for BPA to affect human health is a concern, and more research is needed. The panel cited evidence that Americans have levels of BPA higher than those found to cause harm in lab animals.

Patagonia Inc., an outdoor-gear retailer based in Ventura, Calif., pulled polycarbonate water bottles from its 40 stores worldwide in December 2005, and a month later, organic foods chain Whole Foods Markets stopped selling polycarbonate baby bottles and children's drinking cups. Some environmental groups in the United States and Canada expect others will follow suit.

"Given there are comparably priced, greener alternatives, I'm quite convinced that within a couple of years we're going to see the end of this chemical in consumer products," said Rick Smith, executive director of Toronto-based Environmental Defense Canada.

The controversy turned an unwelcome spotlight on Nalge Nunc International, a division of Waltham, Mass.-based Thermo Fisher Scientific Inc. It employs about 900 people at a plant tucked behind a shopping plaza in the Rochester suburb of Penfield.

"Rarely has a chemical been the subject of such intense scientific testing and scrutiny, and still important agencies across the globe agree that there is no danger posed to humans from polycarbonate bottles," Tom Cummins, a Nalge Nunc research director, said in a statement.

The company declined to allow executives to be interviewed. Its consumer products arm, with estimated sales of $50 million to $65 million, accounts for a fraction of Thermo Fisher's $9.5 billion in annual revenues.

Nalge Nunc was founded in 1949 by Rochester chemist Emanuel Goldberg. The lab-equipment supplier evolved in the 1970s when rumors about its scientists taking hardy lab vessels on weekend outings led to a water-bottle consumer unit targeting Boy Scouts, hikers and campers.

In 2000, a new sports line of Nalgene-brand bottles offered in red, blue and yellow hues quickly became the rage in high schools and on college campuses.

Highly durable and lightweight, resistant to stains and odors, and able to withstand extremes of hot and cold, screw-cap Nalgene bottles are marketed as an environmentally responsible substitute for disposable water bottles. This holiday season, they were offered in new colors such as amber, moss green and vibrant violet.

In this city on Lake Ontario's southern shore, judgments about a long-admired local business invariably are leavened with sympathy.

"Nalgene is the hallmark water bottle for the backcountry," said businessman and skiing enthusiast Rob Norris, 58, as he shopped for a backpack at an Eastern Mountain Sports store.

"I don't have any reservations right now," he said. "To me, it's one of these overreaching things where there's some microscopic particles that could leach out of a piece of plastic. But who knows what's in the water we're drinking?"

But Ellen Guisto, 31, a stay-at-home mother of two, said a growing chorus of concern about the chemical makes her hesitate. "I'm not an alarmist by nature, but if I hear there's a chance that this may cause cancer, I don't think I would use it," she said.

With more than 6 million pounds produced in the United States each year, bisphenol A is found in dental sealants, the liners of food cans, CDs and DVDs, eyeglasses and hundreds of household goods.

Citing multiple studies in the United States, Europe and Japan, the chemicals industry maintains that polycarbonate bottles contain little BPA.

But critics point to an influx of animal studies linking low doses to a wide variety of ailments, from breast and prostate cancer, obesity and hyperactivity, to miscarriages and other reproductive failures.