While the article I saw didn't address specifically how much Hg was in each bulb, they indicated that there was enough to take precautions in cleaning it up.
I was curious about your question too and on a brief search found an article regarding Wal-Mart asking its CFL bulb suppliers to reduce/remove the mercury in their bulbs in their future.
Walmart noted that "A CFL bulb can save up to $30 in electric costs over its lifetime, prevent more than 110 pounds of coal from being burned, and reduce greenhouse gas emissions by 450 pounds" I'm not sure if this is accurate or who did this study but hey, we all know CFl bulbs > incandescants.
They also provided this, which felt like either research they conducted or was brought to them by consumers:
"Wal-Mart said it estimates a third less mercury will be used in the production process of the bulbs it buys, effectively removing an average of 360 pounds of mercury per 100 million CFLs sold in its stores."
If that is accurate then currently per 100 million bulbs there are 1080 lbs of mercury. To break it down it becomes .0000108 lbs per bulb. Putting it into a meaningful unit, thats roughly 0.004 grams. Which could be enough to cause people harm.
The biggest fear is that this much mercury could head to the dumps and seep into the ground and further into our eco-system. However, I'm not a chemist but I wonder where was this mercury before we put it into products, and was it harming anything where it was? And is there anything we can do to reuse it or return it?
The best chance to reuse it is to send it off to hazardous waste where they can sort, properly dispose of, or possibly recycle something like mercury.
I do believe that if you bring your old bulbs to home depot they will be able to dispose of it. Just as you should dispose of motor oil and other things that shouldn't just go into the trash. With many contractors buying through home depot I'm sure there are all kinds of waste materials that need to be thrown away properly so I'm glad Home Depot lets you.
