Toxicology is the study of the interaction between chemicals and biological systems. Toxic chemicals have the ability to cause adverse effects in living organisms. During hazardous waste operations which involve chemicals known or suspected to have some degree of toxicity, it is important to identify the chemicals involved and the toxicity hazards they present, and to determine their acceptable occupational exposure levels. This course is the third in a series of modules designed to meet the annual 8-hour refresher requirements for HAZWOPER general site workers. Learners who successfully complete this course should be able to identify routes of entry and the factors influencing chemical toxicity. Learners should also be able to recognize the types of toxicity hazards, exposure limits and guidelines, and the requirements for medical surveillance.