Not too sure what the science of it is abc123 but I am sure if you get right down to it -- all food is contaminated.
I do believe in using organic food wherever possible and have organic food part of our day every day (although not exclusively) but if you think of the toxins in the ground water and the rain then all food is exposed to some extent anyways and it goes through to the roots.
Was it last year where they said that rain around the world had traces of contamination in it from the nuclear power plant disaster in Japan??

I guess the wash tries to clean the residue that could be on the surface like the wax and chemicals that may have settled on the skin ??