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

Abstract

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 × 10 3 pg m −3 ; HCHs, 5.3-3.3 × 10 3 pg m −3 ; HCB, 5.8-3.4 × 10 2 pg m −3 ; endosulfan, BDL-51 pg m −3 ; and 6 PCBs, 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.

Trans-Himalayan Transport of Organochlorine Compounds: Three-Year Observations and Model-Based Flux Estimation

“…Concentrations of POPs in the source region are broadly similar to levels previously reported for Kathmandu, Hetauda, and Lahore (Table ). The similarity suggested that data obtained by XAD-PAS are overall comparable to values derived from PUF-samplers (Table ).…”

“…Serious pollution with POPs has previously been observed in South Asian countries. For example, extremely high concentrations of DDT and HCHs were found in Kathmandu and Hetauda . Due to the close proximity between Nepal and the Himalayas, it is interesting to know the extent to which high elevations within the Himalayas have become contaminated.…”

“…Compared with other mountain ranges, the Himalayas are more severely influenced by air pollution. Remarkably high atmospheric concentrations of black carbon (BC), persistent organic pollutants (e.g., HCHs), and polycyclic aromatic hydrocarbons (PAHs) are found in India − and other south Asian countries, such as Nepal and Pakistan . Generally, mountain terrain modifies large-scale winds and uplifts air masses and the associated pollutants to upper tropospheric layers .…”

Changes in Urban Gas-Phase Persistent Organic Pollutants During the COVID-19 Lockdown in Barcelona

“…The concentrations of total PCBs in B1 and B2, 58 and 23 pg m −3 , respectively (sum of congeners reported in Table 2) (Pozo et al, 2011), China: 600-7,600 pg m −3 (Cui et al, 2017), and Bangladesh: 7-1,800 pg m −3 (Nost et al, 2015). They were similar to those reported in Nepal: 1.2-47 pg m −3 (Pokhrel et al, 2018).…”

“…The concentrations of HCB found in the B1 and B2 periods in Barcelona, 25.5 and 5.4 pg m −3 , respectively (Table 2), were generally lower than those found in other urban areas from India: average values of 120-260 pg m −3 (Chakraborty et al, 2010), Bangladesh: 70-685 pg m −3 (Nost et al, 2015), Bosnia Herzegovina: 34 pg m −3 (Lammel et al, 2011), Nepal: 6.3-1,500 pg m −3 (Pokhrel et al, 2018), or China: 261 pg m −3 (Zhang et al, 2010). The concentrations of PeCB, 8.5 and 0.8 pg m −3 in B1 and B2, respectively, were similar to those described in Bosnia Herzegovina, 9.9 pg m −3 (Lammel et al, 2011).…”