K Sutherland, of Queenstown, asks :-

When staying in SE Asia I noticed vegetables etc growing in contaminated water. Were they safe to eat? (Watermelon is mostly water.)

Aswathi Soni and Phil Bremer, food scientists at the University of Otago; responded.

Vegetables grown in contaminated sites should definitely not be considered to be safe to eat. If the contaminated water comes from industrial runoff, it could contain chemicals (pesticides, insecticides, oil, grease, antifreeze, and other toxic chemicals from vehicles), or heavy metals (such as lead, cadmium, arsenic, and zinc). These contaminants can accumulate in plants during their growth and cause acute (vomiting or diarrhoea) or chronic (increased risk of cancer, or kidney or liver dysfunction) disease when eaten. It might not be possible to reduce the risk posed by these compounds by washing or processing of the vegetables.

In countries where sewage systems are not very efficient or if the water supply is open to animals, water can also contain faecal material and associated disease-causing bacteria such as Escherichia coli, Salmonella or viruses. These can cause either short-term (norovirus) or long-term (hepatitis A) illness. Bacteria and viruses from contaminated growing water can be present on the outside of vegetables and they can be internalized by the plants either during their growth or during harvesting. Microbial contamination on the outside of vegetables can be reduced by washing steps but micro-organisms within the vegetables are almost impossible to remove and the product can only be made microbial safe by cooking or some other processing method.

Eating raw vegetables such as spinach and cabbage has been known to cause the majority of the illnesses, due to being contaminated by faecal matter. In an outbreak in the US, Salmonella was found to be the causative agent of severe food poisoning associated with the consumption of watermelon. In another case, eating salad with raw broccoli contaminated with E.coli led to food poisoning. All these and many other events indicate that eating vegetables or fruits that could be contaminated would lead to severe illnesses.

Hence, good quality water is essential for the safe growing and processing of fruits and vegetables.

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