If pre-history gave us the Stone Age, the Bronze Age, and the Iron Age, then today's civilization must surely be identified as the Plastic Age.

Plastic is ubiquitous in our modern society. Try spending one day without using anything made of plastic...you won't make it past 10:30 in the morning.

Now scientists say that a common ingredient in most plastics, called Bisphenol A, or BPA, mimics estrogen and causes reproductive harm in rats at levels below what most humans are exposed to every day.

In fact, BPA was first developed in the 1930s as a synthetic estrogen. For whatever reason, someone decided that it would make a great liner for canned food products and an additive for plastics manufacturing.

As a result, 95% of adult Americans have a measurable amount of BPA in our blood and urine.

A study performed by Randy L Jirtle at Duke University in North Carolina and reported in the June 2006 issue of Science News revealed that pregnant mice who were fed low doses of BPA in their food gave birth to offspring who showed genetic changes, such as a tendency toward obesity.

Another study, published in the July 2007 issue of Reproductive Technology, was performed by the National Institute of Environmental Health Sciences. The NIEHS team conducted a short-term examination of newborn female mice exposed to varying levels of BPA. When those mice were re-examined at mid-life, they had reproductive anomalies that were not found in the control group, such as ovarian cysts and uterine growths.

The amounts of BPA given to mice in the NIEHS study fell below levels found in most humans.

What does this mean for humans? The good news is that humans metabolize BPA at faster rates than rats do, so the chemical leaves the body fairly quickly. The bad news is that we are continually exposed to levels of BPA above those which correspond to reproductive harm in rodents.

Experts report observing estrogenic-like changes in wildlife that are similar to the effects seen in lab animals exposed to BPA, revealing possible evidence that the chemical has leached into ground water and plants consumed by animals in the wild.

Another concern is that no long-term studies have yet been performed. With an agent that causes gene abnormalities, longer studies are needed because gene changes take time to manifest and observe.

This fall the National Toxicology Program will release a report stating its findings about whether BPA should be considered a genotoxic substance.

In the meantime, there are several things that people can do to reduce their exposure to BPA:

• Avoid canned foods such as soups and tomato-based pastas, which had the highest levels of BPA, and canned infant formula, which had over 200 times the recommended safety levels of BPA.

• Baby bottles and sippy cups had high levels of BPA as well, so avoiding these might be a good idea. Pliable, "cloudy" plastics such as the Medela brand baby bottles don't contain BPA.

• Some plastic wraps contain BPA, so check the labels for "BPA-free" wraps.

• Consider using an alternative to plastic water bottles. Consider natural plastic alternatives. Biota (http://www.biotaspringwater.com/) makes a corn-based plastic for its natural spring water. The bottle dissolves in 70-80 days, and uses no petroleum products in its manufacturing process. Other companies are experimenting with compostable or biodegradable plastics made from corn, hemp, or potatoes.

Or think about stepping out of the Plastic Age, as much as is possible. Glass food or beverage containers can make as much sense as plastic, so consider the possibilities for expanding beyond the overwhelming use of plastics. It's better for you, and better for the planet.