Picture a hog, one hog.

Now imagine all the manure it produces in one year, about two tonnes.

Multiply that one hog and its manure by 1.8 million -- the number of all the hogs in Southwestern Ontario.

Then add in all the cattle, chickens, turkeys and sheep that live in the area's farm belt -- 20 million or so more creatures, with varying levels of waste left behind each year.

The best estimate, maybe 15 million tonnes of manure a year.

One more exercise -- also not pleasant, but your health may depend on it. Think of what all that manure -- much of it spread as fertilizer on farm fields, where it can wash into waterways -- contains or can form in the environment:

- Nitrates, which can contaminate drinking water and restrict the oxygen in the bloodstream in infants.

In infants under six months, it can cause methemoglobinemia, or blue baby syndrome.

Nitrate is a problem in our area. Due in part to manure spills and farm runoff of fertilizer, nitrate concentrations in the Ausable River frequently rise above acceptable levels for wildlife. According to a 2004 report, those levels appear to be rising across the river basin.

- Airborne chemicals, such as hydrogen sulphide and ammonia.

- Parasites such as BC parvum and giardia, that can enter the drinking water supply and can't be destroyed by chlorine.

Such parasites cause severe diarrhea, nausea, fever, vomiting and fatigue in humans, and serious long-term risks to the elderly, the very young and those with damaged immune systems.

If manure really does flow downhill, humans are the sitting ducks at the bottom.

And the scariest thing flowing our way may be the so-called superbugs, antibiotic- resistant bacteria that can give disease the upper hand on humans and spark devastating epidemics.

"There are three things that keep us alive," says Dr. Gregor Reid, a professor of microbiology, immunology and surgery at the University of Western Ontario.

"Air, food and bacteria."

Everyone focuses on global warming as the looming environmental disaster, he notes.

There's an internal disaster just as deadly looming inside our bodies, Reid says.

"That has been missed in the environmental story."

Don't get Reid wrong. He's a fan of bacteria, so much so he says things like, "We have to understand things from the bacteria's point of view."

Bacteria has a bad reputation, but without the 1,500 kinds working in our body, we couldn't survive.

Bacteria reacts to antibiotics the same way a person reacts when someone points a gun at them, Reid says.

Some bacteria freeze, some hide and some fight back.

"We are forcing the harmful bacteria into a corner. They obviously fight back."

The bacteria that fight back, that become resistant to antibiotics, create a host of problems.

On many farms, livestock are given large amounts of antibiotics, mainly to encourage growth.

Bacteria within the livestock develop a resistance to the antibiotics.

Those antibiotic-resistant bacteria may be transmitted to humans in any number of ways, directly through food or through manure.

The manure can get into surface water. That surface water can flow into drinking water systems or be used to irrigate vegetable crops. The crops may even get it directly from manure. And then livestock eat crops that contain the bacteria.

Just as livestock operations have intensified, so has use of antibiotics for growth.

In the 1950s, the recommended levels of antibiotics in animal feed was set at five to 10 parts per million.

That has increased up to 20 times, says Dr. George Khachatourians of the University of Saskatchewan

Worse, studies have also shown many feeds -- 25 per cent in one U.S. study -- had more than the recommended level of antibiotics.

The larger the farm, the more likely it is antibiotics are used.

How much?

More than 40 per cent of the antibiotics made in the U.S. are given to animals, according to a 1998 paper.

The list of antibiotics given to livestock includes bacitracin, chlortetracycline, ery-thromycin, tylosin, neomycin, thromycin, lincomycin, neomycin, oxytetracycline, penicillin, streptomycin,tylosin and virginiamycin.

Khachatourians, in a 1998 study, detailed several examples of antibiotic-resistant bacteria found in poultry, hogs and cattle, and in some cases, in humans who ate those items:

- For example, a 1985 outbreak of salmonella affecting about 1,000 people in California was traced to meat contaminated with a drug-resistant strain of the disease.

- In Britain and Germany, strains of resistant E. coli was found in pigs and in pig farmers and their families.

- Outbreaks of E. coli O157:H7, a rare variety of the bacteria that produces potent toxin, from eating potatoes and drinking apple cider were traced to contact between the produce and manure, he wrote.

Other studies have shown that farm families on hog operations have higher incidences of antibiotic-resistant E. coli than urban dwellers.

Ever since the deaths in 2000 of seven people from E. coli-laced water in Walkerton, Ontario farmers have had to follow tighter guidelines on spreading manure, says Sam Bradshaw, environmental specialist with Ontario Pork.

By avoiding spraying manure on saturated soils or in heavy rains, farmers can avoid manure runoff, he notes.

As for antibiotics, hog farmers at least don't need to use them for growth, Bradshaw says.

"We will use antibiotics on pigs when they are sick just until they are better."

That's the difficulty in researching the risks of manure. Different practices determine what goes into livestock and what comes out, and different soils, weather conditions and other factors determine how manure reacts with the environment.

The research is hardly exhaustive enough to prove beyond a doubt that "if I eat this piece of steak I will get this antibiotic-resistant bacteria," Khachatourians says.

Yet, there is enough proof out there to be concerned, he says.

"We have to keep this issue alive. The real issue is are we passionate about who is right or wrong, or passionate about what this is costing us?"