Natural occurring chemicals that are potentially toxic to people are

Radon gas and crude oil seeps. Radon is a radioactive noble gas. It is cancer causing. It cannot be seen, smelled or tasted but it can potentially be a hazard in your own home. 
Temporary exposure to crude oil or crude oil fumes may cause irritation to nose, lungs and throat, headache, loss of coordination, nausea, dizziness and the like. Chronic exposure may cause convulsion, irregular heartbeats and even coma. 

Olá. porque a reação na temperatura é muito rapida a do copo : )