Sterile EO = Ethylene Oxide.

Ethylene Oxide (EO) is an environmental pollutant and is toxic to humans. Congress classified it as a "hazardous air pollutant," according to the United States Environmental Protection Agency. Multiple studies have shown that EO increases the risk of several types of cancer.
Lymphoma and leukemia are the cancers most frequently reported to be associated with occupational exposure to ethylene oxide. Stomach and breast cancers may also be associated with ethylene oxide exposure.

It is used to produce chemicals, including antifreeze and pesticides.

You can find more information on the dangers to human health on various government websites, including the OSHA.gov, EPA.gov, Cancer.gov, and the CDC websites, for example.