The US east coast city of Philadelphia has earned the unfortunate nickname of "Filthadelphia". It used to send most of its recyclable waste to China. But when Beijing abruptly changed its policy in autumn last year and refused to take "contaminated" recycling, many US cities found themselves facing a crisis. Philadelphia resorted to burning half of its recycling in an incinerator, a process that gives off toxic fumes. Our correspondents report.
A programme prepared by Patrick Lovett and Rebecca Martin.
