When soil is tilled and then rained on, the smaller, lighter particles like silts and clays often wash away or go downward, leaving larger, heavier particles like sands and pebbles at or near the surface. Strong winds will also blow away the light particles. Wouldn't lead pellets also tend to be left on the surface?
I think its a different story in wetlands where the pellets would work their way downward through the soft, usually undisturbed, bottom sediments. As an old waterfowler, I would like to believe the switch to non-toxics has lessened lead poisoning in ducks, especially those that root around in bottom sediments to feed. Ditto with swans that now are so abundant we have a season on them (we are roasting mine on Thursday).
As questionable as some of the lead poisoning studies may be, there have been so many of them now involving so many species, as well as those dealing with human ingestion of wild game, that I am ready to throw in the towel and go unleaded.
It might even help tone down the gun-grabbers and anti-hunters by taking away one of their old, highly exaggerated talking points.
