Organochlorine Pesticides (OCPs) And Polycyclic Aromatic Hydrocarbons (PAHs) In Topsoil Cross The Central Tibetan Plateau (CTP): Distribution And Influence Factors

Forty-four soil samples were collected across the Central Tibetan Plateau (TP). Baseon the analyses of the concentration, composition, distribution and influence factorsof organochlorine pesticides (OCPs) and polycyclic aromatic hydrocarbons (PAHs),we use multivariate statistical analysis to determine the relationship between influencefactors and the OCPs concentrations to delineate the primary and secondaryrelationships between these factors. In addition to this, we identify the main origins byusing the ratio of PAHs and discuss the transport mechanism by using the correlationanalysis. The following conclusions are obtained.1. The detection rate for most of OCPs in soil samples was very low. The compositionof the compounds of α-HCH, δ-HCH, HCB,2,4’-DDT and4,4’-DDD is in the order ofγ-HCH>4,4’-DDD>4,4’-DDE>α-HCH>HCB>δ-HCH>2,4’-DDT. The totalconcentration of OCPs range from50.0ng/kg to47600.0ng/kg. Compared to OCPs,the detection rate is a little higher for PAHs, and the total concentration is range from10.0ng/kg to78380.0ng/kg. The composition of the soil PAHs is dominated with(2+3)-ring PAHs and followed by4ring PAHs and (5+6) ring PAHs across NgariPrefecture and Bangor area, while dominated with4-ring and follow by (2+3) ringand (5+6) ring across Shigatse area.2. Opposite distribution of∑OCPs and∑PAHs is found across study region, that of∑OCPs is increase with the distant from city to sampling sites, while∑PAHs isdecrease with the distant from city to sampling sites.3. The scatter diagram shows that the soil concentrations of OCPs are associated withthe altitude of sampling site, soil clay minerals, fine particle fractions, and the soilorganic carbon (SOC) has weakly influence on OCPs.4. For the influence factor, altitude of sampling site play a role of cold trapping drivenby temperature and clay mineral (fine particle fractions) plays a primary role insorption of POPs, while SOC plays negligible role in the accumulation of OCPs.5. The HCHs mainly come from application of lindane. DDTs is a mixture ofhistorical residues and new input of dicofol. For PAHs, low-temperature combustion, biomass combustion and petroleum emission is the primary source in Ngari Prefectureand low-temperature combustion and biomass combustion is the major source inBangor area. On the contrary, PAHs is a mixture source of high-temperaturecombustion, petroleum combustion, petroleum residues and vehicle emission.6. The phenomenon that strong positive correlation between (2+3) ring PAHs anddistant and negative correlation correlation between4-ring/(5+6) ring PAHs showedthat (2+3) ring PAHs with lower molecular weight and higher vapor pressure, areeasier to volatilize to air and transport to long distant region. On the contrary,4-ring/(5+6) ring PAHs, which have higher molecular weight and lower vapor pressure,are easier to adsorb in the particulate matter and subjected to weak volatilization.