The waste was left there by an American battery recycling plant called Metales y Derivados that was shut down in the mid-90s. Its owner fled to San Diego without cleaning it up. It took a coalition of environmental activists and neighbors ten years to get the government to clean the site. Today, it is exhibit A for environmentalists who oppose the North American Free Trade Agreement, which opened the door for rapid cross-border industrialization with only limited provisions for environmental protection.
NAFTA didn’t establish any multinational environmental regulations when it was signed 20 years ago. It created no tri-national environmental police. It implemented no fines for polluters.