Like with other heavy metals and such, the chemical salts and oxide forms are more readily absorbed into the body than the pure elemental form, but even the pure elemental forms get absorbed. All of the forms are dangerous and present risks; that risk is determined by two things: toxicity and exposure. The more toxic something is or the more exposure there is the higher the risk. One of the main questions to be answered by each person is what they accept as an acceptable level of risk. Personally, I prefer to minimize that risk by using bonded bullets for game, and may switch to copper or alloy in the future, especially when my kids might eat what I shoot. I am also careful with the game I process, and I do it myself.
Heavy metal exposure is cumulative; the body has no real way to eliminate the heavy metals. This means that with continued exposure the level of the heavy metals increases; stopping exposure stops the accumulation. In the wild, heavy metals bio-accumulate naturally through the environment, starting by being absorbed from soil into plants, then accumulating through herbivores, and accumulating at even higher rates in predators and scavengers. Eating lead pellets, either with food, or, in the case of raptors and other birds, with rocks eaten as gizzard stones, just increases the exposure that much. Lead pellets left in the soils become oxidized fairly quickly, with also increases the toxicity. I spent my time in grad school sitting next to a couple guys studying how heavy metals get concentrated in the environment, so we had quite a few discussions about this.
In the end, each person needs to make the decision for themselves. I would rather that the government supported the research to provide people with good information than legislate people's choices.
