Pesticides and sludge/chemical fertilizers are no good, but worrying about bacteria is very un-paleo. Do you think paleolithic people worried about getting all the dirt off their food? Probably not. There is good evidence that dirt is good for you, there is even a study showing soil bacteria fight depression.

I would look to buy produce grown organically using properly composted manure fertilizer.

If you google Dom and kefir you will arrive at an amazing site with a lot of information on how to make your own stuff. One of the things he touts is good old fashioned lye made from hardwood ashes and water. Apparently a solution of DILUTED lye will sterilize things and a weaker solution can be used as a vegetable wash that will elimate surface pesticides. Systemic ones are another thing entirely and best avoided by using organic produce.

My kids used to raid the veggie garden and more than one carrot was just wiped on their jeans before being devoured. That was safe because the garden soil just had organic compost added to it and no pesticides were used.

To remove little green worms from leafy veggies I just put a touch of salt in a basin of water to wash the greens and the little buggers would float up to the surface. Anyway, they were just more protein. ;-)

I have a problem telling you how to make sure all pesticide residues could be removed from cauliflower, but aren't you buying organic? As for yams, wash them before cooking and then slip the peel off after it is cooked.