Hence, mercury is a toxic substance. Hazard is the likelihood that adverse health effects will occur. Taking one's temperature with a mercury thermometer is not hazardous, because the chemical is well contained within the thermometer. However, mercury released from a broken thermometer can be a health hazard. For example, if mercury is released in a hot location such as a drying oven, it can evaporate and cause mercury poisoning.
Exposure is the factor that links toxicity and hazard.
A toxic chemical cannot cause adverse health effects if there is no exposure. And if there is no exposure, there is no hazard. Exposure through ingestion can occur in several situations. Accidentally pipetting toxic materials into the mouth can result in acid burns of sensitive mucous membranes. Using pipetting aids eliminates this risk.