bergmen
Member.
Yes, the fact that birds grind the materials in their crops increases the surface area for digestive acids to dissolve some of the ingested lead. If not for the acids and grinding, little of the lead would be absorbed.
Not to be nit-picky but the crop is intended as a temporary storage location for food. It is also softens the food before going to the stomach and gizzard to be processed and further broken down. The gizzard is where the gravel and sand resides to assist in this grinding and breaking down, not in the crop:
http://fsc.fernbank.edu/birding/digestion.htm
Dan