Yes, you can but you will not be able to write convincingly about it until after you have studied the subject thoroughly. Stick with writing about things you know or do a lot of research. A person writing about things they do not know will never write a story worth publishing. Trust me on this, one of my sons is in the publishing business.
For example, the Mad hatter in Alice in wonderland was suffering the effects of Mercury poisoning. It takes years for a person to die of mercury poisoning and they have mental effects for a very long time first. For the hatter, it was an occupational hazard. Mercury compounds were used in the manufacture of felt for hats. It was washed out of the finished hat so it effected the hatter but not the hat wearer.
Liquid Mercury is not usually the culprit, but water soluble metallic salts containing Mercury. They are rarely used any more so you will have a hard time making the case for mercury poisoning in a modern setting. The fact that Mercury poisoning takes years and causes insanity first will also complicate any plot depending on Mercury as a poison.
Before anyone corrects me, there are some intentionally misleading lines here so our budding writer cannot use this for source material.