Selected organochlorine pesticides and polychlorinated biphenyls in urban atmosphere of Pakistan: concentration, spatial variation and sources.

Robust knowledge on the occurrence and distribution of persistent organic pollutants (POPs) in the atmosphere of low-latitude regions is inevitable to forecast their transportation to pristine ecosystem and assess toxicological impacts upon local biota. Despite the earlier revelation of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in soils/sediments and water bodies in Pakistan, knowledge about atmospheric levels and sources of these POPs remains limited. For the first time, a network of XAD resin-based passive air samplers (PAS) was established across megacities of Pakistan, i.e., Karachi, the coastal city, and Lahore, lying in an agricultural region. Typical geographical locations of the two cities allowed assessing the influence of source regions on the occurrence and distribution patterns of selected POPs. Average concentrations (ng/PAS) in both cities ranged as endosulfan 39-101, DDTs 63-92, HCHs 33-65, heptachlor 10-26, and PCBs 48-61. High concentrations of endosulfan and lindane as observed throughout Lahore were certainly due to their ongoing applications in surrounding agricultural fields. Lower proportions of parental DDTs as compared to their metabolites were observed in both cities, suggesting inputs of DDTs from older or secondary sources. Owing to ultimate discharge of country's agricultural/industrial waste through river streams in to Arabian Sea, the coastal region of Karachi was found potential source of weathered POPs that could be dissipated at regional/global scales by maritime advections. The study contributes to the pool of information on fate and geographical distribution of POPs in subtropical developing countries.