Scientists have found a surprising partner to help them figure out which of the hazardous waste sites across the country are in need of the most attention: The lowly pig.
There are thousands of abandoned mines and industrial sites that are so contaminated with waste products that Herculean efforts must be made to clean them up. Some sites are far more hazardous than others, and picking which sites to tackle first is a daunting challenge that is far more complicated than many had thought.
That's where the pigs come in.
"Pigs are very much like humans," says Stan Casteel, associate professor in the University of Missouri's College of Veterinary Medicine. He's talking physiology, not necessarily manners, but Casteel and his fellow researchers have found that pigs are great at revealing just how hazardous some sites are.
That's a critical part of a mounting problem. The federal Environmental Protection Agency has put about 1,400 "Superfund" sites on a "national priorities list" that are so contaminated with heavy metals and other dangerous substances that they warrant special attention.
Finding Priority Sites
But there's only so much money to go around, and it can literally cost tens of millions of dollars to clean up a former mine or industrial site where such things as lead and arsenic once percolated into the soil.
If sites that are less worrisome are cleaned up, that takes money away from more hazardous sites. So establishing a scientific basis for prioritizing the cleanup has become a major goal.
It might seem that all anyone would have to do is analyze what's there, looking for things like lead which can have a devastating impact on children, and clean up the sites with the most dangerous contamination first. But it's not all that easy.
"There are about 250 different species of lead," says Mark Doolan, a geologist in the EPA's Kansas City office, who is leading part of the cleanup program. The toxicity of the lead, it turns out, varies with its type, the kind of soil that it is found in, and other factors.
"You could eat a pound of some of this stuff and it wouldn't absorb into your body at all," Doolan says. Other types could prove deadly, even in trace amounts.
The key is to determine which types of lead, under which conditions, are most likely to be absorbed into the human blood stream. Initially, it was thought that about 30 percent of all lead would be absorbed, but the pigs proved that wrong.
Swines Sample Toxic Clumps
The pig project started in the EPA's Denver office in 1991, but in 1994 it shifted to Casteel's lab at the University of Missouri. He has used his pigs to analyze samples from more than 20 sites across the country, and he has found the absorption rate of lead — or its "bioavailability" as scientists call it — varies greatly, from somewhere around 2 percent to more than 50 percent.
He has fed his pigs hundreds of samples, and then tested their blood to see how much of the stuff they absorbed. Since he knows precisely how much lead he fed the pigs, usually over a period of about 15 days, he can figure out how much lead would be harmful on the basis of what percentage is absorbed into the blood stream. So he knows how much the pigs are keeping, not just what they got.
The results also show which types of lead are most toxic (most likely to be absorbed into the human blood stream) — like lead carbonate — and which types are less likely to be absorbed — like lead sulfide.