Which organization in the united states studies and assesses the environment to protect it and the people affected by any negative change in the environment?

it is the United States Environmental Protection Agency/EPA

Explanation:

Environmental Protection Agency acts as an autonomous federal agency, which was created in 1970. Agency establishes and implements laws and standards which helps in protecting the environment and controlling pollution.

The EPA has established to protect and preserve the natural environment. Agency tries to improve the health of humans by examining the effects and placing limitations on the use of pollutants. The EPA coordinates the production, processing, disposition, use of chemicals and other pollutant