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One senior pilot told the BBC that dual engine failure could also result from fuel contamination or clogging.

The water company provides the sludge for free and Mr Oliver says he's careful how much he uses and trusts the company to make sure it doesn't have chemical contamination.

“The other thing we have to remember,” he said, “is the possibility of contamination on the food preparation surfaces and utensils.”

In general, intestinal parasite infections are far more common in developing countries, where deworming practices are sometimes performed on populations that are exposed to high levels of contamination that put them at risk.

Residues from burnt waste can also pollute surface and groundwater, leading to long-term land contamination.