Scientists are dueling over whether waste from human excrement should be disposed of on farm land, a common practice in parts of Southwestern Ontario

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A method commonly used in the London region to handle the pound of poop that people produce daily has prompted a heated public battle between scientists.

On one side of the excrement fight is a group raising the alarm against the disposal of sewage sludge on farm land, arguing the practice poses unacceptable health risks and should be halted.

“Governments are playing Russian roulette with sewage sludge. Over time, there is a high probability this game will be lost at the public’s expense,” the scientists wrote in an open letter published in newspapers his year.

The scientists signing the letter were Sierra Rayne, an independent scientist; John Werring, a senior science and policy advisor for the David Suzuki Foundation; Richard Honour, executive director for The Precautionary Group; and Steven Vincent, professor of neuroscience at the University of British Columbia.

That letter has drawn a strongly worded statement issued recently by another group of scientists who accuse the first group of fear-mongLoyoering, misrepresentation and unfairly demonizing the practice of applying so-called biosolids to agricultural land.

“When biosolids are applied carefully and judiciously to agricultural soils, this material adds nutrients to the soil that benefit crop production and reduce the need for chemical fertilizers,” the scientists said in their statement.

Signing the statement were Paul Sibley, a professor in the University of Guelph’s department of environmental biology; Lynda McCarthy, a professor at Ryerson University’s department of chemistry and biology; Chris Metcalfe, director of the Institute for Watershed Science at Trent University; and J.E. Loyo, a lecturer at Rice University in Houston.

While the two groups of scientists strongly disagree over whether biosolids should be applied to farm land, they agree biosolids are a major disposal issue for society.

With each person producing about half a kilogram of excrement a day, about six billion kilograms are produced each year by Canadians alone.

Biosolids are the sludge that remains after excrement has been treated by municipal sewage treatment plants. It’s estimated that between 35 to 45 per cent of biosolids produced in Ontario are spread on farm land.

Municipalities that use the land-application disposal method in the London region include Oxford County, Sarnia and Chatham-Kent.

St. Thomas has approved a plan to to move away from disposing biosolids in a landfill to spreading on agriculture land.

London incinerates its biosolids and disposes of the ash in a landfill.

In calling for a moratorium on land application, the scientists point to heavy metals, flame retardants and pharmaceuticals in biosolids.

“If you apply the sludge to the land, we have transferred our toxic effluent onto the landscape,” the group argued in its open letter.

They called for municipalities to stockpile or landfill biosolids until a more responsible means of dealing with the problem is implemented.

Sibley, of the University of Guelph, counters that presence of contaminants does note equal a health risk.

“Exposure can occur, but it is very unlikely, and when it does occur it is at levels that are very far below any kind of threshold that is likely to induce an effect.

“We feel the evidence does support this is a safe practice. There is always a degree of uncertainty but by and large it is a safe practice,” Sibley said in an interview.

Disposing of sewage sludge in specially designed landfills, as recommended by the scientists calling for a moratorium, is not practical, Sibley said.

It would cost millions of dollars to build the landfills, money cash-strapped municipalities don’t have, he said.

Sibley has calculated it would require the equivalent of 2,700 Olympic-sized swimming pools to accommodate the annual biosolid production of Ontario residents.

“Every year you would have to add another 2,700 Olympic-sized swimming pools to accommodate all of that,” he said.