Only after the last tree has been cut down.  Only after the last river has been poisoned.  Only after the last fish has been caught.  Only then will you find that money cannot be eaten.

In North Carolina, a woman who lives near a large hog operation wakes up in the night and finds the odor so intense she can barely breathe.

In Utah, people who live near a 600,000-hog operation complain of minor respiratory ailments ranging from shallow breathing to sleep disturbances and coughing.

In Prince Edward Island, an asthma sufferer working in a field near a large hog operation keels over. He blames it on the quality of the air, although the cause is not scientifically documented.

Welcome to the smelly realities of large-scale hog farming. It's an industry that has undergone explosive growth in the last 15 years in key agricultural states such as North Carolina and Iowa, and Canadian provinces such as Manitoba, Saskatchewan, Alberta, Ontario and Prince Edward Island.

It's also an industry that has many public health officials, environmentalists and communities more than a little concerned about the health impacts of hog-tainted air.

"In the preliminary health research studies that have been done, the number one issue... is that people who live next to such operations are reporting increased respiratory problems," says Dr. Melva Fager Okun, deputy director of the Environmental Resource Program at the School of Public Health, University of North Carolina, Chapel Hill, N.C..

"I think this is a concern for all people, but especially people with pre-existing respiratory problems. It adds stress to their situation."

Her concerns are shared by Dr. David Wong, a pediatrician in Summerside, Prince Edward Island. "People living close to hog farms can have problems with their respiratory system," he says. "Hog farms are notorious for the odor. Hogs eat a lot, and pass a lot of excreta, with high ammonia content. It can be highly irritating to the airways of people, especially those who have sensitive airways."

People whose asthma is not under good control, he says, "will have more problems than others."

Dr. Okun, whose doctorate is in public health, has spent the last 10 years working on this issue, attending hundreds of community meetings, studying federal, state and local policies and talking both with industry and affected communities.

She notes that although intensive research has been done on the health impacts of hog farms on farm workers, "we have been lax in studying many of the community public health effects." Part of Dr. Okun's work has been supported by the North Carolina Association of Local Health Directors, which became concerned at the environmental impacts of large swine operations that moved into the state in recent years.

Canada is faring little better when it comes to such research. Lee Whittington, manager of information services at the Prairie Swine Centre in Saskatoon, Saskatchewan, concurs that little "out of the barn" study has been done on the health impact of such operations on neighbors.

Part of the problem, says Dr. Okun, is that communities and legislators are still playing catch-up with the growth in large-scale swine operations. In North Carolina, for example, there are more than 3,500 large hog operations and about 10 million swine.

"This is really new," says Okun. "Maybe you didn't need so much attention when you had 500 hogs (in one location). But all of a sudden you've got 5,000, 10,000, maybe 20,000 hogs in the same location. The impacts are different."

So just what do we know about the impact on lung health?

The first preliminary study on the issue was done in 1997 in Iowa, the top hog-producing state in the U.S. The research found that people in affected communities and farm areas experienced the same problems reported by farm workers, only on a less severe scale. The main symptoms included increased sputum, cough, shortness of breath and chest tightness.

A second study, by researchers at the University of North Carolina, Chapel Hill, looked at the impact of living next to 6,000-head hog operations and compared the reported health problems to those experienced by people living next to a cattle operation. These two groups were then compared to people living in rural areas, but not situated near livestock areas. "Again, the people living next to the hog operations all reported increased problems, especially in the respiratory area."

Another study at Duke University examined the mental health impact of living near such areas. Neighbours living in the odor-affected areas reported increased tension, depression, anger, fatigue and confusion.

All these studies were done by well-respected, university-based researchers. Dr. Okun stresses that she considers these studies preliminary, and notes that the results have been criticized because they reported residents' responses rather than counting the number of visits to doctor's offices.

The major challenge now is to conduct a more rigorous study, she says.

"I think the information is there. There just hasn't been sufficient funds or opportunity to pull all of this together."

States and provinces vary in the regulations they impose to protect air from agricultural air pollutants. Dr. Okun has numerous recommendations for making them more effective.

In most cases, little if anything is done to control emissions from hog waste lagoons, according to material provided by the Prairie Swine Centre. Solid covers such as steel or concrete would cost as much as $50,000 (Cdn) for a lagoon serving 200 hogs.

The centre, along with many other agricultural research centres, is working on projects to reduce lagoon odor. One solution that appears promising is a low-cost "balloon-type" tarp that has reduced emission of odorous gases from lagoons by more than 95%.

Dr. Okun believes that some progress has already been made to improve the waste management practices on hog operations. Liners are now required in the waste lagoons.

"The future is very exciting," she says. "Alternative technologies are being tested and the state has made a commitment to phase out all hog waste lagoons in the next five to 10 years."

Where does that leave the thousands of people throughout North America who live near large hog operations and are susceptible to lung problems?

That's a tough question, says Dr. Wong. "Those with asthma should have optimal control of the disease by using preventive medication."

If financially feasible, he suggests that moving away from these farms "can be one solution."