Columbia subject headings:
Conservation of natural resources--Economic aspects--United States.
Environmental protection--Economic aspects--United States.
Recycling (Waste, etc.)--Economic aspects--United States.
Harvard subject headings:
Conservation of natural resources--Economic aspects--United States.
Environmental protection--Economic aspects--United States
Recycling (Waste, etc.)--Economic aspects--United States.
Princeton subject headings:
Conservation of natural resources--Economic aspects--United States.
Environmental protection--Economic aspects--United States.
Recycling (Waste, etc.)--Economic aspects--United States.