Atmospheric transport and accumulation of organochlorine compounds on the southern slopes of the Himalayas, Nepal.

Studies have been devoted to the transport and accumulation of persistent organic pollutants (POPs) in mountain environments. The Himalayas have the widest altitude gradient of any mountain range, but few studies examining the environmental behavior of POPs have been performed in the Himalayas. In this study, air, soil, and leaf samples were collected along a transect on the southern slope of the Himalayas, Nepal (altitude: 135-5100 m). Local emission occurred in the lowlands, and POPs were transported by uplift along the slope. During the atmospheric transport, the HCB proportion increased from the lowlands (20%) to high elevation (>50%), whereas the proportions of DDTs decreased. The largest residue of soil POPs appeared at an altitude of approximately 2500 m, and may be related to absorption by vegetation and precipitation. The net deposition tendencies at the air-soil surface indicated that the Himalayas may be a 'sink' for DDTs and PCBs.

Mercury distribution in the foliage and soil profiles of the Tibetan forest: processes and implications for regional cycling.

Remote forests are considered a pool of Mercury (Hg) in the global Hg cycle. However, notably few studies have investigated the fate of Hg in the Tibetan forest. In this study, fifty-two foliage samples and seven litter/soil profiles were collected throughout the Tibetan forest. The concentrations of total Hg (THg) in foliage were positively correlated with longitude and negatively correlated with altitude, indicating that the emission of Hg is expected to decrease with increasing distance from emission sources to the Tibetan forest. The deposition flux of THg in the Tibetan forest (with an air-to-forest ground flux of 9.2 µg/m(2)/year) is ∼2 times the flux in clearings, which is suggestive of enhanced Hg deposition by the forest. The depositional Hg is eventually stored in the forest soil, and the soil acts as a net 'sink' for Hg.

Persistent organic pollutants in the Tibetan surface soil: spatial distribution, air-soil exchange and implications for global cycling.

There are limited data on persistent organic pollutants (POPs) in the soils of the Tibetan Plateau. This paper presents data from a survey of organochlorine pesticides (OCPs), polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in 40 background surface (0-5 cm) soils of the Tibetan Plateau. Soil concentrations (pg/g, dw) ranged as follows: DDTs, 13-7700; HCHs, 64-847; HCB, 24-564; sum of 15 PCBs, 75-1021; and sum of 9 PBDEs, below detection limit -27. Soil DDT, HCB, PCB and PBDE concentrations were strongly influenced by soil organic carbon content. HCH concentrations were clearly associated with the proximity to source regions in south Asia. The air-soil equilibrium status of POPs suggested the Tibetan soils may be partial "secondary sources" of HCB, low molecular weight PCBs and HCHs and will likely continue to be "sinks" for the less volatile DDE and DDT.

Passive air sampling of organochlorine pesticides, polychlorinated biphenyls, and polybrominated diphenyl ethers across the tibetan plateau.

So far there are limited data on persistent organic pollutants (POPs) in the atmosphere of the Tibetan Plateau. XAD 2-resin based passive air samplers were therefore deployed for 1 year (between July 2007-June 2008) at 16 locations across the Tibetan Plateau. Based on previously reported sampling rates (R) derived in the north and south America, and their correlations with atmospheric temperature and pressure, R values in the present study were in the range of 2.2-3.3 m(3) d(-1) (average = 2.7 +/- 0.3). Derived air concentrations (pg/m(3)) ranged as follows: DDTs, 5-75; HCHs, 0.1-36; alpha-endosulfan, 0.1-10; HCB, 2.8-80; sum of 15 PCBs, 1.8-8.2; and sum of 9 PBDEs, 0.1-8.3. The highest DDTs occurred at Qamdo, where the sampling site is near to farm land, indicating the spatial distribution of DDTs across the plateau may be influenced by scattered local usage of DDT. Higher levels of HCHs were observed at sites with high elevation (>4000 m) and close to the China-India border, indicating possible long-range atmospheric transport. The highest levels of HCB, PCBs, and PBDEs were found at a site impacted by forest fire during the sampling campaign.

Deposition and postdeposition mechanisms as possible drivers of microbial population variability in glacier ice.

Glaciers accumulate airborne microorganisms year by year and thus are good archives of microbial communities and their relationship to climatic and environmental changes. Hypotheses have focused on two possible drivers of microbial community composition in glacier systems. One is aeolian deposition, in which the microbial load by aerosol, dust, and precipitation events directly determines the amount and composition of microbial species in glacier ice. The other is postdepositional selection, in which the metabolic activity in surface snow causes microbial community shifts in glacier ice. An additional possibility is that both processes occur simultaneously. Aeolian deposition initially establishes a microbial community in the ice, whereas postdeposition selection strengthens the deposition patterns of microorganisms with the development of tolerant species in surface snow, resulting in varying structures of microbial communities with depth. In this minireview, we examine these postulations through an analysis of physical-chemical and biological parameters from the Malan and Vostok ice cores, and the Kuytun 51 Glacial surface and deep snow. We discuss these and other recent results in the context of the hypothesized mechanisms driving microbial community succession in glaciers. We explore our current gaps in knowledge and point out future directions for research on microorganisms in glacial ecosystems.

[Ionic chemistry in snowpits from Yamzhog Yumco Basion].

During August and September, 2006, a total of 50 samples had been collected from three different snowpits at the Yamzhog Yumco Basion in the south of the Tibetan Plateau. All samples were analyzed for major cations (Na+, NH4+, K+, Ca2+ and Mg2+), anions (Cl-, SO4(2-) and NO3-) and stable oxygen isotope ratio. The results of analyses show that the three snowpits represent accordant chemical characteristics, with NO3- (16.1-187.2 microg x L(-1), averaging at 93.7 microg x L(-1)) and Ca2+ (19.0-236.7 microg x L(-1), averaging at 81.0 microg x L(-1)) being the highest concentration of anions and cations respectively. Compared with data from other representative sites, major ion concentrations in the Yamzhog Yumco Basion accord with those in the south of the plateau, but they differ much from those in the north of th eplateau. Remarkable variabilities of major ion concentrations from monsoon period to non-monsoon period are demonstrated. Ion concentrations of NO3-, NH4+ increase 30%-40% in monsoon period due to the influences of vegetation, live-stock, anthropogenic activity and thunderstorm, whilst the concentrations of crustal source ions, such as Ca2+, Mg2+ reduce 80% due to decrease of dust and strong wind from the north of the plateau and crustal aerosols being washed out of the atmosphere by heavy precipitation during the monsoon period. Variation of ion concentrations are also impacted by elevation and post-deposition process, with Ca2+, Mg2+ increasing with a decrease in elevation and SO4(2-), NO3- decrease with an increase in elevation and the influence of post-deposition.

[Progress about the research of atmospheric persistent organic pollutants in remote areas].

Recently, atmospheric distribution, transport, and reaction of persistent organic pollutants (POPs) in remote areas are getting more attention. Based on the passive air sampler, the networks are established for studying the temporal and spatial distribution of atmospheric POPs in remote areas. The results suggest that the atmospheric concentrations of POPs display a peak value in the 1980s. As the use of POPs has been forbidden after 1980s, concentrations of POPs in air are generally reduced. Concentration of POPs in atmosphere is influenced by temperature and seasonal usage. High concentration of organochlorine pesticides is observed in summer and the comparatively low level is detected in winter. For PAHs, the trend is contrary. High volatility and long-range transport of POPs lead to the global distribution of POPs and accumulation of POPs in remote areas. High mountain is the "acceptor" of atmospheric POPs and cold condensation plays the main role in capturing POPs in high elevation areas. Distribution, transport, exchange direction and exchange flux of POPs among air/water, air/soil, air/snow and air/vegetation interfaces are mainly controlled by temperature, precipitation and characteristics of POPs. Models were developed on the basis of the effect of these factors. Taken together the transport model and source analysis of POPs, transport mechanism of POPs seems to be clearer. This paper reviewed the progress about the above-mentioned scientific topics and discussed the deficiencies of current researches. Furthermore, it pointed out the further work needed for the study of atmospheric POPs in remote areas.

The recent deposition of persistent organic pollutants and mercury to the Dasuopu glacier, Mt. Xixiabangma, central Himalayas.

High mountains may serve as condensers for persistent organic pollutants (POPs) and the ice/snow core can provide long-term records of atmospheric deposition of pollutants. In this study, organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) in firn core from Dasuopu Glacier were analyzed and the seasonal variation and deposition flux of these pollutants were investigated. PCB 28 was always detected in samples from different firn core layers and concentrations of PCB 28 were in the range of 0.09-0.3 ng/l. Hexachlorobenzene (HCB) and total DDTs (p-p'-DDD and p-p'-DDT) were not always detected and were only present in some samples. No p-p'-DDE and hexachlorocyclohexane (HCH) were detected above the level of determination limits. Concentrations of HCB ranged from 0.04 to 0.07 ng/l, and total DDTs were in the range of 0.15-0.3 ng/l. Total glacier PAHs was below 26 ng/l. The levels of OCPs and PAHs in Dasuopu glacier were roughly similar to values from the European mountain areas but lower than those from Lys glacier (Italy) and glacier from Rocky Mountain. Hg concentration (2-35 ng/l) in firn core samples was higher than that of remote region of Arctic. PCB 28 didn't show obvious variation in different seasons, however for major PAH compounds higher values were observed in summer than in winter. With regard to Hg, it displayed winter maximum. Deposition flux of OCPs, PAHs and mercury showed similar results with maximum flux occurring in the 2000s. After 2000/2001, deposition flux decreased and reflected the possible decrease of emissions of these atmospheric pollutants in the adjacent region.

Gradient distribution of persistent organic contaminants along northern slope of central-Himalayas, China.

High mountains may serve as condenser for persistent organic pollutants (POPs) and the vegetation in remote areas has been used as a means to characterized atmospheric concentrations of air pollutants. In this study, organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs) in Himalayan spruce needle samples from Zhangmu-Nyalam region (central-Himalayas) were analyzed and the altitudinal gradient of these pollutants was investigated. Total HCHs and DDTs concentration in needles were in the range of 1.3-2.9 ng g(-1) dry weight and 1.7-11 ng g(-1) dry weight, which were lower than concentrations reported in spruce needles from Alps, however higher than concentrations in conifer needles from mountain areas of Alberta. Total Himalayan spruce needle PAHs was below 600 ng g(-1) and fluorene, phenanthrene and acenaphthene were abundant individual compounds measured. The ratios of alpha-HCH/gamma-HCH in pine needles were similar with the usual values for technical HCH, implying technical HCHs might be used in this region. The high ratios of o-p'-DDT/p-p'-DDT and no p-p'-DDE measured in this study led to the suspicion that a new source of o-p'-DDT and/or p-p'-DDT existed in this region. In addition, higher ratios of low molecular weight-/high molecular weight-PAHs in this region indicated that petroleum combustion, vehicle emission and low-temperature combustion might be the major contributions of PAH source. To examine the POPs distillation, the analyte concentrations were correlated with altitude. The more volatile OCPs, alpha-HCH, gamma-HCH, aldrin and alpha-endosulfan positively correlated with altitude, however, less volatile OCPs (DDT and DDD) inversely related with elevation. Almost all PAHs detected in this area showed positive correlations with altitude. It is worthy to note that heavy PAHs (Benzo[k] fluoranthene and Benzo[a]anthracene) displayed positive correlation, which implied the sources of PAHs were near the sampling sites. The distillation of POPs was strongly affected by the proximity between sampling sites and contaminant sources. If the contaminant sources are close to the mountains, it may be the dominant factor that controls the concentration gradient.