When my Grandfather passed away about 4 years ago, we decided to move my Grandmother in with my parents and sell the grandparents' house.
Their basement was always filled with all sorts of cool stuff (my Grandfather owned and operated a dirt racetrack in the 40's and 50's, and owned an operated a gas station for about 45 years) and I was helping my parents go through it all. In the corner there was a large tin (bit bigger than a detergent bucket) that had once held lard. Inside the bin were two pairs of new, unworn WWII era combat boots and a vessel containing about two gallons of mercury.
We asked my grandmother if she had known about the mercury, and she said that my grandfather had bought it in the 40's as "dental grade mercury" and thought it would appreciate over time.
We did some research and found that most of the companies we called were going to charge us significant amounts of money to take it away... some investment
So instead we just dumped it into the stream running behind their house and called it a day.
Nah, I'm just kidding. We eventually found a company that would take it away for free.