The check may be in the mail. That doesn’t mean everything else should be.

The U.S. Postal Service is reminding people that metallic mercury and devices containing metallic mercury are always prohibited from the mail.

Don’t think you will be mailing metallic mercury anytime soon? It’s found in more things than you realize.

According to USPS, metallic mercury can be found in antique items such as thermometers, barometers, blood pressure monitors and similar devices.

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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.

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