Metallic mercury, also known as elemental mercury, is a shiny, silver-white metal that’s historically referred to as quicksilver. It’s liquid at room temperature and, when dropped, it breaks into smaller droplets that can go through small cracks or become strongly attached to certain materials.
According to the Environmental Protection Agency, at room temperature, exposed elemental mercury can evaporate to become an invisible, odorless toxic vapor. If heated, it is a colorless, odorless gas.
Exposure can cause tremors, emotional changes, insomnia, neuromuscular changes, headaches, kidney damage, respiratory failure and, with high exposure, death.
Mailing metallic mercury, or other prohibited items, can land someone in some seriously hot water.
If a person knowingly mails items or materials that are dangerous, they can ace a civil penalty of at least $250 but not more than $100,000 per violation, along with the cost of any cleanup, as well as a potential for criminal penalties. When in doubt, check with your local post office to get info on U.S. laws and USPS Postal Service hazmat guidelines.