Miles, using words like "biochemical differences" doesn't make your argument any stronger. The effects of serum lead are most certainly different in adults than children, that much is beyond dispute. If that was not true there wouldn't be different standards for children and women of child-bearing age. There are a multitude of substances that affect developing brains differently than adult brains, not only lead but THC and others.
And to make the blanket statement that "any intake is harmful" is just incorrect. Intake does not equal lead in the blood. Any detectable levels of lead in the blood of children and women of child-bearing age is what has been deemed harmful.
Why would someone willingly put a toxic substance into their body?
You need to bone up on your toxicology if you're going to provide opinions on the subject. Everyone willingly puts toxic substances into their body on a daily basis. The most extreme example is water, which is toxic in excessive amounts. It causes hyponatremia, which can be fatal. Alcohol is another good example. A glass of red wine is harmless but a half gallon of vodka can kill you. Other substances like selenium are nutrients in small doses (sold as over-the-counter supplements) and toxic in high doses. The list goes on. To get a deleterious effect you have to consider not only the substance, but the dose.
