Thana Dharmarajah of The Guelph Mercury reports that scrubbing lettuce won’t get rid of the pathogens hiding in the edges of the leaves or the pores of the vegetable, according to a University of Guelph food microbiologist.
Leafy vegetables such as spinach and cabbage, which tend to be eaten raw, have a higher risk of contamination, said Keith Warriner.
The vegetables can be exposed to contamination in the field through irrigation if the water source is contaminated with sewage, he said.

Bacteria can also be passed onto the lettuce when it’s being harvested for bagged salads and kept in containers of water, which could be contaminated, Warriner said.
Simple washing of the vegetables can only remove 90 per cent of the pathogens, such as salmonella and E. coli, even when done with different sanitizers such as bleach, he said.
Warriner has found a more effective of cleaning the vegetables, which involves the use of hydrogen peroxide and exposure to ultraviolet light.
The same method has been used in the carton packaging industry.
For example, cartons of milk and orange juice are sprayed with hydrogen peroxide and exposed to ultraviolet light before the contents are poured inside.
The process produces ions which kill the bacteria that hide inside the crevices of the cartons.
The UV light converts the hydrogen peroxide into antimicrobial free radicals that penetrate into the packaging material to kill the bacteria, Warriner said.
The food scientist, along with graduate student Christina Hajdok, tested the method on produce by contaminating tomatoes, cauliflower, iceberg lettuce, romaine lettuce, Spanish onions and broccoli with salmonella.
After cleaning the vegetables using the hydrogen peroxide and ultraviolet light method, Warriner and Hajdok found they were able to remove 99.9 per cent of the salmonella.
Warriner said the free radicals are short-lived and do their job within seconds and are converted to water as the byproduct.
“(Consumers) will have a greater ease of mind that the produce they buy will have less contamination than when it is washed,” Hajdok said.
Warriner said in October 2005, 23 people in the United States became sick from eating lettuce contaminated with E. coli 0157:H7.
Next to meat, fresh produce is the most common cause of food-borne illnesses, he said.
The researchers say they plan to continue testing the method on other items such as strawberries and raspberries.
This method of cleaning produce makes food safer to eat and also extends the shelf life of products because vegetables are often spoiled by bacteria, he said.