Doe Run Peru, a subsidiary of U.S.-based Renco Group and the subject of an ongoing battle between that firm and the government of Peru, has a bumpy history in La Oroya since it acquired smelting operations from the government of Peru there in 1997. The firm directly provided 3,500 jobs in Peru, gained the support of many workers and local people, and claims to be a more responsible environmental caretaker than its state-owned predecessor.

Yet emissions of lead, sulfur dioxide, and other chemicals were far above the Peruvian air standard while the smelter was operating. In 2005 ...