Mercury is very toxic, implement in conditions such as ALS. As boys we played with mercury and it does, if dropped, separates into miniscal droplets, it is also absorbed through the skin and as a vapour it is just as bad, the reason that many dentists are against removing amalgam fillings.
Nowadays we have a much better understanding of what effects such things as mercury, asbestos and lead as well as vapours from soldering, welding and burning have on the human body. Most are cumulative and the effects can become suddenly debilitating even leading to death.
So proper precautions, eye protection, masks and gloves with plenty of ventilation should be the norm nowadays. Believe me when I say that someone dying from ALS in a very short period of time from being very fit is not very pleasant.