The amount of 'dangerous stuff' in a desktop pc is so minute it does not bear thinking about.
As far as CRTs go well there is lead in the glass but it's awfully damned small.
Dosage is everything.
Yes and the amount of energy a single light bulb uses is so minute that it does not really need to be thought about. But in fact it does.
Believe me, as a recycler I can tell you that INCREDIBLY small items tend to add up extremely fast. Say your city has 100,000 citizens, at about 3 people per household that's 33,333 homes. Most people have about 1 computer, others have 2 or more- I would say 9/10 people own a computer so the average would probably bring it to 11/10 to even 12/10. so lets say 35,000~38,000 computers in your town alone.
Now assume that the average computer lifespan is 4 to 5 years old. That means every 4 to 5 years there will be an additional 35,000~38,000 computers in your dump (assuming none of them ever make it to a recycling center of course)
Lets say that each computer contains 1/10 of an ounce of hazardous material. that comes out to 3,500~3,800 ounces of haz-mat or about 220~240 pounds of hazerdous material which would be about the size of two 5 gallon buckets...IN ONE SMALL CITY! Now imagine your township, then imagine your county, then your state, then the entire country...followed by the entire world.
In the end, there is no such thing as a "negligable amount" of ANYTHING since there are 6.5 billion people on this planet. If any one person uses 1/1000th of an amount of anything that will still come out to 6,500 units of
something.