Scientist Uses Pigs To Test Toxic Sites

ByLee Dye

March 8 -- 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.

The pigs' diet includes a clump of food that looks a little like cookie dough, Casteel says, with a small sample from the site embedded inside. It doesn't hurt the pigs, because they don't get enough lead to be toxic, he says.

The primary concern over lead is its impact on children. Lead is similar to calcium, and young children need a lot of calcium for their growing skeletons. The lead literally mimics the role of calcium, so if children ingest lead, more of it will end up in their bones. That can lead to brittle bones, growth deformities, and most unfortunately, irreversible brain damage.

The concern over children is the reason Casteel uses immature pigs in his research. Like children, they have a preference for lead.

The pigs have also confirmed something that many scientists suspected. The soil that contains the lead at a hazardous site can be amended to lower the absorption rate.

An old lead smelter in Jasper County, Mo., left the land so contaminated that the EPA is faced with cleaning up 2,700 different properties, Doolan says. Scientists there, under a program sponsored by the Missouri Department of Natural Resources, applied phosphorus to the land, theorizing that it could reduce the "bioavailability," or the absorption rate, of the lead.

Sorting Good Lead From Bad

Samples from the site were then fed to Casteel's pigs with encouraging results. The pigs absorbed less than half as much lead as they had before the application of phosphorus, a common ingredient in most lawn and garden fertilizers.

What that means, Doolan says, is the soil can be treated in place instead of dug up and hauled away, reducing the cleanup cost by around 75 percent.

That means more money can be allotted to areas that resist on-site treatment.It also means there's something the rest of us can do if we suspect our area may have contaminated soils. Casteel says the most important thing is to insure that children do not come in direct contact with the soil.

He recommends planting a lawn and treating it with fertilizer that has heavy phosphorus content.

Many areas, of course, are so contaminated that there's no other way than to spend hundreds of millions of dollars to get rid of the problem. But thanks to Casteel's pigs, at least we're better equipped now to figure out which areas need the most attention.

Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.

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