a few drops of bleach in several gallons of H20…
"To address the lettuce and E.coli problem, Frank studied how and where E. coli cells survive on lettuce leaves.
“Lettuce breathes through stomata or holes on the leaves,” he said. “The E. coli cells attach to the surface around and inside these holes.”
E. coli Likes Cut Edges and Bruises
He also found E. coli cells favor the cut edges of lettuce. “The edges of cut lettuce pieces had tremendous numbers of attached E. coli cells,” he said. “The bruised areas did, too.”
In the lab, washing the lettuce with a bleach solution was found effective for removing the E. coli cells on the lettuce surface.
“The solution removes or kills the cells on the surface of the lettuce, but those inside the holes still survive,” Frank said.
UGA food scientists are working with the food industry to apply this chlorine method. But Frank warns consumers not to try it at home.
“Chlorine bleach is much too strong to be used at home for rinsing vegetables,” he said. “Consumers shouldn’t use chlorine to rinse vegetables at home.”
http://www.ugacfs.org/hottopics/lettuce.html
hydroponic lettuce farms use a 10% bleach solution in growing the product…
Dole uses 50ppm in their 2nd wash of processed lettuce…