How accurate is the NaI test for Pb-color change?

Greetings all!

Just finished the toughest organic chemistry class I have ever taken, and yet am having problems with a simple Gen Chem. question:

I live in Colorado Mountains in a 100 year old house which is great. What is not so great is the fact those 100 years ago, everyone painted with lead paint. About 8 years ago, we stripped the old lead paint off the house and attempted to collect all that we could, but of course, some of the flakes found there way into our soil. Now 8 years later, we have four egg layers (chickens for you non-farm types), and they are starting to pump out very good eggs. We take great pain to get our eggs as organic as possible, but I am worried about the possibility of lead pollution.