2.1. Sample collection
Three SeCu and two SeAl plants, all located far from other possible pollution sources, were selected for the study, the aim of which was to assess the potential influence of UP-POPs emissions from secondary non-ferrous metal processing plants on the surrounding environments. Basic information about the five plants is given in Table 1. Ambient air samples were collected from three sampling sites near each plant. Two air samples were collected downwind of each plant (about 300 and 500 m from the stack, called A and B, respectively), and one sample was collected upwind of each plant (about 1000 m from the stack, called C), to act as a control sample. The air samples were collected using polyurethane foam (PUF) disk passive air samplers (PASs). The samplers were left at the sampling sites for about two months, between April and October 2011 (Table 1). Before use, the PUF disks (14 cm diameter and 1.35 cm thick) were cleaned by washing them with water and then Soxhlet extracting them with acetone for 12 h. When the air sampling period was complete, each sample was tightly wrapped in aluminum foil and packed in a sealed