Faeces on food crops - safer than you'd think

Spreading human sewage on fields growing food crops doesn't sound appealing, but it's a great fertiliser. What's more, the practice may be safer than generally thought.

The dangerous O157 strain of the common Escherichia coli bacteria found in human excrement dies out faster than expected when sewage sludge is applied to soils, say scientists at Imperial College London.

Until 1998, over a quarter of the UK's sewage sludge - the main solid waste produced by wastewater treatment - was dumped at sea. Just under half was spread onto farmland, and less than a tenth incinerated or placed in landfill. Then the European Union banned sea disposal, leading to a doubling in the amount of sewage sludge in the UK burnt or placed in landfill.

Now Michael Rogers and his colleagues have shown that levels of E. coli O157, which produces a toxin that causes potentially fatal kidney damage, soon plummet when applied to fields in sludge. "Within 70 days, they went down to as little as 10 bacteria per gram, from 100,000 per gram initially," says Rogers, who presented his findings this week in York at the annual meeting of the UK Society for General Microbiology.

That should give farmers greater confidence that they can use sewage sludge to improve soil quality while remaining within guidelines that limit levels of dangerous bacteria in their fields.

Source NewScientist.com