When I lived in Wyoming, hunting season was a busy time. Complementing my usually uneventful daytime searches for deer or antelope were evenings often filled with pizza, beer and the butchering of a friend's kill. I remember sometimes picking bullet fragments from an elk or deer carcass. What I never imagined then, and what still surprises me today, is the extent to which those animals, seemingly a healthier and cheaper alternative to beef, may have been poisoning me.

Chronic lead poisoning is an evil disease. Exposure to this common metal can cause neurological, gastrointestinal and reproductive disorders, and possibly even criminal behavior.

In the past lead poisoning came from lead pipes and containers that leached into water and alcoholic beverages. More recently occupational or household hazards -- lead paint or leaded gasoline -- have been implicated.

Earlier this year scientists identified a new source of lead poisoning. Rifle bullets used for hunting big game are made primarily of lead and most modern bullets splatter when they hit their target. This splatter sends microscopic fragments much farther into an animal's body than previously recognized. Thus, hunters who use lead bullets expose themselves, their families and anyone else they feed to potential poisoning.

The story of how this threat to human health was discovered is circuitous. It starts with America's biggest bird, the California condor.

The magnificent condor is a scavenger that once soared throughout the American West. But by 1987 fewer than 30 existed in the wild, so the U.S. Fish and Wildlife Service captured the remaining birds to allow them to reproduce in captivity.

It turns out that lead poisoning was killing the California condors. They had been ingesting lead from fragmented bullets in unclaimed deer or in gut piles left by hunters. Birds are more sensitive to lead poisoning than people.

In May, a conference in Boise, Idaho, hosted by the Peregrine Fund and funded partially by the National Aviary in Pittsburgh evaluated the implications of lead poisoning for wildlife and for humans.

More than 12 million people hunt in North America. In Pennsylvania, nearly 1 million hunters harvest 300,000 to 500,000 deer each year. We therefore must ask if Pennsylvania's hunters are poisoning themselves and their families every time they eat venison. Scientists, state game departments and the U.S. Centers for Disease Control are investigating this question.

We know that hunters who use lead shot to kill waterfowl risk exposure to high lead levels. The data on lead exposure in hunter-killed deer are similarly provoking and come primarily from two sources.

Last year, the Peregrine Fund hired a hunter to shoot 30 white-tailed deer in northern Wyoming. Each deer was gutted and X-rayed. The carcass then went to a commercial game processor after which the meat again was X-rayed.

Researchers found lead fragments in each of the 30 deer studied, often far from the bullet's path. Likewise, X-rays showed that processed meat from 80 percent of those deer had metal fragments. About one-third of 232 processed meat packages contained visible lead fragments.

Officials in several midwestern states also are concerned about lead contamination in venison donated to food banks. In Minnesota, of approximately 1,200 donated meat packages, 27 percent of ground venison and 2 percent of steak cuts had detectable lead fragments. Concerned by these findings, the Minnesota Department of Natural Resources then studied the fragmentation of bullets in deer and sheep carcasses shot with different types of lead bullets.

The results were terrifying. On average, each carcass contained between 60 and 141 lead fragments; one had nearly 500. Most lead pieces were so small that people could not detect them without X-rays or chemical analysis. Fragments also were often far from bullet exit holes -- in some cases, up to 14 inches away. Lead levels unsafe for children were detected up to 18 inches away from exit holes.

As human populations increase, we have more consequential impacts on our planet. Birds often are a proverbial "canary in the coal mine" -- by succumbing first to environmental problems, they alert us to threats that humans face. Few wildlife biologists thought that the decline of the "ugly" California condor was a signal of danger to people. Nevertheless, the same problem that afflicts condors -- lead poisoning from fragmented ammunition -- also confronts those of us who eat game shot with lead bullets.

The level of risk to humans is still under investigation and the topic is controversial. We do know that consuming meat of deer shot with lead bullets puts birds at risk. Based on its research, the Minnesota DNR now recommends that hunters use non-lead bullets and that young children and pregnant women not eat venison killed with lead bullets. Likewise, the North Dakota deer-donation program now accepts only bow-killed deer.

I've heard people say that game can be killed by "acute" lead poisoning (by getting shot) or by "chronic" lead poisoning (through long-term exposure). It is therefore ironic that acute poisoning for a deer can result in chronic poisoning to a human.

As citizens, we have a responsibility to make informed decisions about risk. In this case, where there are clear consumer alternatives to lead ammunition (several types of top-quality copper and copper-zinc bullets are commercially available), my choice is clear. This year, when I buy my bullets, I'm looking for non-lead ammunition.

Likewise, Pennsylvania hunters should inform themselves about the pluses and minuses of lead ammunition and make the decision that best suits their families' health and well-being.