Articles | Volume 18, issue 2
Research article
01 Feb 2018
Research article |  | 01 Feb 2018

Atmospheric organochlorine pesticides and polychlorinated biphenyls in urban areas of Nepal: spatial variation, sources, temporal trends, and long-range transport potential

Balram Pokhrel, Ping Gong, Xiaoping Wang, Sanjay Nath Khanal, Jiao Ren, Chuanfei Wang, Shaopeng Gao, and Tandong Yao

Abstract. The study of persistent organic pollutants (POPs) in low-latitude tropical and subtropical urban cities is necessary to assess their local and global impacts on ecosystems and human health. Despite studies on levels of POPs in water, soils, and sediments, analysis of the distribution patterns, seasonality, and sources of POPs in urban regions of Nepal remain limited. Polyurethane foam (PUF)-based passive air samplers were deployed in three major cities in Nepal: Kathmandu (the capital city), Pokhara, and Hetauda (agricultural cities). Dichlorodiphenyltrichloroethane (DDT) and hexachlorocyclohexane (HCH) were the dominant organochlorine pesticides in the atmosphere at all sites. The average concentrations of POPs were   DDTs, 8.7–1.0  ×  103 pg m−3;   HCHs, 5.3–3.3  ×  103 pg m−3; HCB, 5.8–3.4  ×  102 pg m−3;   endosulfan, BDL–51 pg m−3; and  6PCBs, 1.4–47 pg m−3. Isomer and metabolite ratio analyses suggested that the concentrations present were from both new and historical applications of the POPs. Vegetable production sites and their market places appeared to be the major DDT and HCH source areas. Higher atmospheric concentrations of DDT and HCH occurred during the pre-monsoon and monsoon seasons, and winter, respectively, closely associated with their local application for soil preparation and vegetable spraying. The estimated travel distances of the POPs (HCB, α-HCH, γ-HCH, and p, p′-DDT) under the Nepalese tropical climate were all above 1000 km, suggesting that high precipitation levels in the tropical climate were not enough to scavenge the POPs and that Nepal could be an important source region for POPs. Due to their close proximity and cold trapping (driven by low temperatures), the high Himalayas and the Tibetan Plateau are likely the key receptors of POPs emitted in Nepal. These results add to the information available on POPs from tropical developing countries.

Short summary
As Nepal is a tropical country close to the Himalayas, it is essential to investigate concentration levels and long-range transport potential of persistent organic pollutants (POPs) in its cities to assess whether these pollutants can contaminate the high Himalaya. We found high concentration and long travel distance (> 1000 km) of dichlorodiphenyltrichloroethane and hexachlorocyclohexane in the atmosphere of Nepalese cities, suggesting Nepal can be an important regional source region for POPs.
Final-revised paper