Plastic bottles — for drinking water, baby bottles and other uses — are coming under increasing medical and scientific scrutiny, but the most current information suggests that more research is needed to definitively assess their health effects on humans.

Local Kaiser family-practice physician Landis Lum said consumers may want to change the way they use some plastic bottles in their lives, especially for children and pregnant women, who are more susceptible to germs in reused bottles and the potential for chemicals leaching from the plastic into the beverages.

He explained that there are different concerns associated with different types of plastics. Those symbols, letters and numbers that are now printed on bottles describe the kind of plastic used in the container, and allow them to xbe sorted by type for recycling since each melts at a different temperature. They don't explain how many times to re-use the bottle, he said.

The symbol is a triangle that contains numbers and often letters, and is found on the bottom of the bottle. The most common material used is PET — polyethylene terephthalate — a lightweight clear plastic found in various sizes of containers, from tiny half-pints to two-liter soda bottles. They are usually labeled with a number 1 in the triangle with PET or PETE underneath.

Lum said those bottles are designed for a single use, so he cautions against using them more than once. He said they can create health concerns two ways: They can seep chemicals into the beverage and can also harbor germs if used repeatedly without thorough cleaning.

The plastic manufacturers, who say reuse is OK, specifically say the bottles should be cleaned thoroughly with hot soapy water.

Lum said that would take care of the bacteria issue, but some studies indicate chemical leaching would still be a concern.

"Normal use is fine," Lum said, but repeated use shows some evidence that antimony — a catalyst used in the production of PET — seeps out and is possibly carcinogenic.

The bottles are designed to be used once, then recycled. "They might degrade with continued use," he said. The combination of the narrow neck and textured surfaces make them difficult to clean, even if consumers use hot soapy water or a solution that includes chlorine bleach.

Lum said pregnant women are more at risk, as are children because their neurologic systems are still developing.

And he also cautions against allowing the thin plastic bottles that contain PET to sit in hot places, which speeds up the rate at which the chemicals could seep into the beverage.

That's something many of us who live in a warm climate do regularly: leave water in a hot car or store it in hot places. However, Lum said, "you should not use it after it's been in a hot car or a hot garage."

Lum cited a February 2008 Arizona State University study that found sharply faster rates of release of antimony in bottles that had been heated.

Another recent concern has centered on clear, hard plastic polycarbonate bottles that have become popular over the past decade for water and baby bottles. Often, those are labeled with a number 7 in the triangle with the letters PC below.

The worry there is Bisphenol A, often known as BPA, which is a compound used in plastics that acts like the female hormone estrogen. The federal Food and Drug Administration has ruled these containers safe, Lum said, but others studies have made people more cautious about frequent use.

Just this month, FDA scientists said trace amounts of BPA are not a threat to infants or adults but said more research is needed to fully understand the chemical's effects on humans.

A written statement on the Internet said the "FDA is not recommending that anyone discontinue using products that contain BPA while we continue our risk assessment process. However, concerned consumers should know that several alternatives to polycarbonate baby bottles exist, including glass baby bottles."

Lum works for Kaiser Permanente and also contributes to a column titled "Prescriptions" in the Island Life section of The Advertiser. He encourages people to drink water when they are thirsty but not to excess.

"Drinking extra water has never been shown to be medically beneficial," he said.

And consumers might consider switching to other reusable bottles such as a more durable plastic, or metal containers such as stainless steel.

Lum recommends the more durable plastic — high-density polyethylene or HDPE (usually labeled with a 2 in the triangle with the letters underneath) — which tends to be white, or at least not transparent, and doesn't leach chemicals, he said. If you're at home or the office, he suggests using a glass or cup.

Lum thinks people are too quick to grab a disposable bottle of water without thinking. "It takes fuel to fly, ship & transport those heavy crates filled with bottled water," he said.

What about those big blue water-cooler bottles in many businesses? Lum said they have all been approved by the FDA, which requires bottled water producers to: