smelter in 1922, followed by the lead smelter in 1928 and the zinc refinery in 1952. Annual capacities were 70,000 tonnes of copper, 122,000 tonnes of lead, and 45,000 tonnes of zinc, although the need to keep below emission limits and temperature inversions that trap gases over the city, smelter, and surrounding area have tended to keep production below these levels. Several local mines produce 'dirty concentrates' that contain metallic impurities that cannot be separated by the flotation process. Over the years, the La Oroya metallurgists have devised methods to separate and recover these metals as byproducts, and the three main smelters have become heavily integrated for this purpose. La Oroya is one of the few smelting operations in the world with this capability. As a result, La Oroya produces gold and silver (mainly from refinery residues), antimony, arsenic trioxide, bismuth, cadmium, indium, selenium, tellurium, sulfuric acid and oleum. This technology has helped the operation to reduce the emission of some noxious and toxic metals; however, the integrated nature of the plant has hindered the modification of individual parts of the plant. With the acquisition of La Oroya, Doe Run inherited a complicated and partially semi-obsolescent smelter complex. The operation had suffered from disrepair, previous owners had invested little in modernization or clean operations. As a result of years of pollution, the hills immediately around the smelter became completely denuded, the river became more toxic, and the health of area inhabitants suffered. Residents have been found to have alarmingly high concentrations of lead in their blood and their drinking water, and many have bronchial troubles. A 1999 study (conducted two years after Doe Run's acquisition) showed high levels of air pollution, with 85 times more arsenic, 41 times more cadmium, and 13 times more lead than amounts generally considered safe. Pollution When Doe Run bought La Oroya, it took over Centromin's PAMA, (Programa de Adecuación y Manejo Ambiental or Environmental Remediation and Management Program), an environmental contract requiring environmental remediation measures. The measures required new sulfuric acid plants, elimination of fugitive gases from the coke plant, use of oxygenated gases in the anodic residue plant, a water treatment plant for the copper refinery, a recirculation system for cooling waters at the smelter, management and disposal of acidic solutions at the silver refinery, an industrial wastewater treatment plant for the smelter and refinery, a containment dam for the lead mud near