Polycyclic aromatic hydrocarbons and polychlorinated biphenyls in urban soils from Kathmandu, Nepal

Abstract

Kathmandu, the capital of Nepal, faces increasing environmental problems such as heavy air pollution and lack of proper waste management. The aim of this study was to examine if the soils are also affected by pollution, with the focus on polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). The sum of 20 PAHs in surface soils ranged between 184 and 10279 lg kg À1 . The most abundant PAHs were perylene (14.6%), benzo(b+j+k)flouranthene (10.7%), naphthalene (10.7%) and phenanthrene (9.8%), with perylene concentrations varying strongly. The significantly more positive d 13 C values of perylene in samples with elevated concentrations indicate biological production, possibly by anaerobic degradation of perylene quinones. PAH ratios also indicate the influence of petrogenic PAH sources, especially at petrol stations and some street samples. The sum of 12 PCBs ranged from 356 to 44710 ng kg À1 . The most abundant were congeners 52 (19.4%), 101 (14.3%), 118 (13.4%) and 138 (11.7%). The low PCB concentrations and pattern were interpreted as a diffuse background contamination being the main PCB source in the urban soils. Indications for recent contamination were found in river sediments from the inner city, as well as in industrial and street samples. Classified by land use, the samples taken from the gutter contained the highest PAH and PCB concentrations as a result of accumulation. The lowest values were found in surface soils from Swayambunath (a park) and a garden area. A gradual decrease in concentration with depth was present for both compound classes in the profiles sampled at Swayambunath. No trend was visible in the garden profiles as a result of soil disturbance of the soil by agricultural treatment. Enhanced microbial degradation and volatilization in the warm/humid monsoon climate is probably the main cause for low pollutant concentrations. Increased photodegradation and the short accumulation period might be other important factors. Concerning its state of soil pollution, Kathmandu fits rather well into a global distribution pattern of persistent organic pollutants, with high concentrations in temperate (higher latitude) regions and very low ones in the tropics (lower latitude regions) due to global distillation.

Distribution and risks of polycyclic aromatic hydrocarbons in suburban and rural soils of Beijing with various land uses

“…Most of the polycyclic aromatic hydrocarbons (PAHs) in the environment originated from incomplete combustion processes such as fossil fuel combustion, biomass burning, volcanoes, and wildfires (Aichner et al 2007;Liu et al 2014). PAHs are also resulted from petroleum products or oil spills as secondary sources.…”

“…PAHs are lipophilic chemicals that are prone to adsorb onto soil particles. Consequently, soil serves as a PAH source and sink in urban areas, accumulating PAHs from processes such as atmospheric deposition and water irrigation (Aichner et al 2007;Bu et al 2009). The characteristics of PAHs in urban soils have been helpful in understanding the long-term history of pollution and their connection with urbanization and industrialization Peng et al 2015).…”

Identification of sources of polycyclic aromatic hydrocarbons based on concentrations in soils from two sides of the Himalayas between China and Nepal

“…In recent years, the LRAT of PAHs has been studied in remote mountainous regions (Elliott et al, 2012;Aichner et al, 2007). The main source of PAHs in the mountains is deposition from the atmosphere (Wang et al, 2007).…”

“…Studies of the Himalayas have indicated that PAHs emitted in Nepal and India may be transported by the Southern Asian monsoon along valleys from the Indian Subcontinent to the Himalayas (Kang et al, 2009). It has been reported that concentrations of PAHs in soils of Nepal (184e10,279 ng/g, dry weight (dw)) (Aichner et al, 2007) were greater than those reported in northern slope of the CentralHimalayas on the TPC (5.5e62.2 ng/g, dw) . The concentration of PAHs in soils might pose risks to the ecosystem of the Himalayas, which is also an important source of freshwater for as much as one sixth of the world's population (including China, India and Nepal) (Loewen et al, 2005).…”

Source Apportionment and distribution of Polycyclic Aromatic Hydrocarbons in Imo River Sediments near Afam Power Station, S.E. Nigeria: Molecular index and Multi-Variate Approaches

“…To the best of our knowledge, this is the first time multivariate statistical tool is used for purposes of source apportionment within the subsaharan tropical coastal environment. Fluxes of PAHs have been increasing within the past decades with their attendant health risk (Van Metre et al, 2000;Schneider et al, 2001;Lima et al, 2003;Walker et al, 2005;Aichner et al, 2007;Scholz-Bottcher et al, 2009), necessitating the identification of the sources of these compounds in the present study. As PAHs released in the study area may be globally distributed, knowledge of PAH sources in this tropical environment is a prerequisite for understanding the global PAH dynamics.…”