Persistent organic pollutants and mercury in the Himalaya

Abstract

Persistent organic pollutants and mercury are important contaminants due to their persistence in the environment and potential toxic effects on ecosystems and humans. Concerns related to these contaminants are particularly pertinent in Asia where the use of pesticides and mercury emissions have been increasing dramatically due to changing agricultural practices and rapidly expanding industrialization. Based on studies in European and North American mountain regions, evidence is increasing that alpine regions function as regional convergence zones for selected organic pollutants due to an effect called orographic cold trapping. It is hypothesized that such an effect may be particularly pronounced in the Himalaya because of dramatic elevational temperature and precipitation gradients relative to contaminant source regions in its immediate vicinity, and because of the regional monsoon system that has been shown to deliver particles and inorganic air pollutants to higher altitudes. A review of studies of persistent organic pollutants and mercury in the Himalayan ecosystem reveals that measurements of these contaminants are sparse and rarely adhere to strict quality control procedures, making it difficult to judge whether relatively high concentrations reported for these materials are indeed an indication of efficient transfer of toxic contaminants to Himalayan ecosystems. Knowledge gaps are identified and suggestions are made for research that would allow for the testing of the hypothesis that the Himalaya is an important cold trap for semi-volatile organic contaminants and mercury.

Mercury risk from fluorescent lamps in China: Current status and future perspective

“…It should be noted that significant interconversion between mercury species can occur in the atmosphere (e.g., oxidation of elemental mercury and reduction of oxidized mercury), which further complicates their transport and fate (Lin et al, 2006(Lin et al, , 2007. The distribution of elemental mercury is influenced by atmospheric circulations on the local, regional and global scales (Carpi, 1997;Lin and Pehkonen, 1999;Loewen et al, 2005;Schroeder and Munthe, 1998). Therefore, excessive mercury emissions from power plants can increase regional and even global mercury levels in the air.…”

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

“…Seasonal differences in direction of wind likely play a major role in atmospheric pollutant transport and deposition (Loewen et al, 2005). Since mean concentrations of LMW-PAHs in soils at each transect accounted for more than 80% of the total concentration of PAHs (Table 1), PAHs from the atmosphere were the main source of PAHs in soils.…”

“…Presence of more volatile PAH individuals in high altitude areas in China than in low altitude areas in Nepal was correlated with altitude. Based on the results of a study by Shunthirasingham et al (2013), the main source of soil PAHs in the mountains at high altitude was atmospheric deposition because the areas at altitudes above 3000 m in the Himalaya are largely unpopulated by people and are thought to be largely free of PAH pollution (Loewen et al, 2005). When PAH depositions result from long-distance atmospheric transport, soil concentrations of PAHs increased with increasing altitude (Daly et al, 2007).…”

“…The altitudinal dependence of the concentrations of the more volatile compounds is also called the "cold trap effect" (Wania and Mackay, 1993;Wang et al, 2006). Greater precipitation in the NSHC, often in the form of snow, which is thought to be a very efficient scavenger of more volatile PAHs (Loewen et al, 2005;Guzzella et al, 2011), could provide a significant mechanism for the deposition of PAHs in soils in high altitude areas. One reason for the weak correlation between the concentrations of LMW-PAHs in the soils of Nepal and altitude is the fact that Nepal is more strongly influenced by the Indian monsoon and has a greater spatial variation of altitude and precipitation than the TPC.…”

“…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). Therefore, it is important not only to know the spatial distribution of the concentrations, pathways (sources), and potential health effects of PAHs in the soils on both sides of the Himalayas between China and Nepal but also to understand the cross-border migration and spatial variability of atmospheric deposition of PAHs between South Asia and the most pristine and remote areas of the TPC.…”