Columbia subject headings:
Environmental policy--Canada.
Environmental policy--United States.
Hazardous substances--Law and legislation--Canada.
Hazardous substances--Law and legislation--United States.
Harvard subject headings:
Hazardous substances--Law and legislation--Canada.
Hazardous substances--Law and legislation--United States.
Princeton subject headings:
Environmental policy--Canada.
Environmental policy--United States.
Hazardous substances--Law and legislation--Canada.
Hazardous substances--Law and legislation--United States.