Chemicals that must be reported if released into the environment are considered to be hazardous substances by regulatory agencies such as the Environmental Protection Agency (EPA) in the United States. These agencies have guidelines and regulations in place to identify, classify, and require reporting of hazardous substances to protect human health and the environment. The specific criteria and reporting requirements may vary by country, but the aim is to ensure the safe handling, transportation, and disposal of substances that can pose risks to the environment and public health.