Linking PAHs concentration, risk to PAHs source shift in soil and water in epikarst spring systems, Southwest China.

A systematic assessment of the variations in the ecological risk of PAHs and the key emission sources controlling the variations is of great importance to human health and aquatic organisms. PAH concentrations, composition, source, and ecological risk in soils and water in two different periods (2010-2011 and 2019) of three typical epikarst springs in Southwest China were investigated. Results showed that PAH concentrations in soil and water have an overall downward trend (a reduction of 57 % and 93 %, respectively) in the past 10 years, which is consistent with the downward trend in the relative contribution rate of raw coal production (a 66 % reduction). In terms of composition, the proportion of low-ring PAHs decreased, medium-ring and high-ring PAHs increased in the soil profile. The proportion of low-ring PAHs did not change obviously, the proportion of medium-ring PAHs increased, and the proportion of high-ring PAHs decreased in epikarst springs. The source of PAHs changed remarkably over time, the relative contribution of coal combustion to PAHs decreased from 38 % to 20 %, and the vehicle contribution of PAHs increased from 31 % to 44 % in soils. The relative contribution rate of unburned oil and coke oven and biomass combustion change is less. Furthermore, the ecological risk of PAHs in the soils was reduced from moderate risk 2 to moderate risk 1, the risk in epikarst spring was reduced from high risk to moderate risk 2 after 10 years. This study demonstrates that substituting petroleum and coal with green energies can reduce PAH concentrations and risk.

Matrix Stiffness Potentiates Stemness of Liver Cancer Stem Cells Possibly via the Yes-Associated Protein Signal.

A hepatocellular carcinoma tissue has mechanical heterogeneity, where the stiffness gradually increases from the core to the invasion front. Furthermore, there is evidence that stem cells from liver cancer (LCSCs) preferentially enrich the invasion front, exhibiting the stiffest modulus in the tumor. LCSCs have the features of stem/progenitor cells and play a vital part in liver cancer development. However, whether matrix stiffness affects LCSC stemness remains unclear. Here, we established a three-dimensional hydrogel for culturing LCSCs to simulate the stiffness of the core and the invasion front of a liver cancer tissue. The results showed that a stiffer matrix (72.2 ± 0.90 kPa) significantly potentiated LCSC stemness as compared with a soft matrix (7.7 ± 0.41 kPa). Moreover, Yes-associated protein signaling might mediate this promotion. Together, our findings illustrate the relationship between matrix stiffness and LCSC stemness, which may aid the production of novel treatment approaches against liver cancer.

Microbial community structure characteristics among different karst aquifer systems, and its potential role in modifying hydraulic properties of karst aquifers.

Little is known about how microbial activity affects the hydraulic properties of karst aquifers. To explore the potential impacts of microbial activity on the hydraulic properties of karst aquifers, microbiological analysis, heat tracer, isotope (dissolved inorganic carbon isotope, δ13CDIC) and aqueous geochemical analyses were conducted at six monitoring wells in Northern Guangdong Province, China. Greater hydraulic conductivity corresponded to a low temperature gradient to an extent; the temperature gradient in karst groundwater aquifers can reflect the degree of dissolution. Higher HCO3 - concentrations coupled with lower d-excess and pH values at B2 and B6 reflect potential microbial activity (e.g., Sulfuricurvum kujiense) causing carbonate dissolution. Microbial activity or the input of anthropogenic acids, as evidenced by significantly more positive δ13CDIC values, potentially affect carbonate dissolution in deep karst aquifers, which eventually alters hydraulic properties of karst aquifer. However, more direct evidence is needed to quantify the effects of microbial activity on carbonate dissolution in karst aquifers.

Instability of optical phase synchronization between chaotic semiconductor lasers.

The instability of optical phase chaos synchronization between semiconductor lasers under master-slave open-loop configuration is investigated. The phase difference between the master and slave lasers is obtained and analyzed in experiment by heterodyne detection and Hilbert transform, and in simulation by solving the rate equations. The results show that the phase difference only maintains in a short duration time and then jumps to another value. A statistical analysis shows that both duration time and jumping values are random, proving that the phase chaos synchronization is unstable. A theoretical analysis shows that the instability of phase synchronization is caused by the jumping of the external cavity mode in the master laser.

Curcumin Reduces Neuroinflammation and Improves the Impairments of Anesthetics on Learning and Memory by Regulating the Expression of miR-181a-5p.

OBJECTIVE: The purpose of this study was to explore the role of curcumin (Cur) in isoflurane (ISO)-induced learning and memory dysfunction in Sprague-Dawley rats and further elucidate the mechanism of the protective effect produced by Cur. METHODS: Rat models of cognitive impairment were established by inhaling 3% ISO. The Morris water maze test was used to assess the cognitive function of rats. ELISA and qRT-PCR were used to analyze the protein levels of pro-inflammatory cytokines and expression levels of miR-181a-5p, respectively. RESULTS: Cur significantly improved the ISO-induced cognitive dysfunction in rats and alleviated the ISO-induced neuroinflammation. miR-181a-5p was overexpressed in ISO-induced rats, while Cur treatment significantly reduced the expression of miR-181a-5p. Overexpression of miR-181a-5p promoted the cognitive impairment and the release of inflammatory cytokines and reversed the neuroprotective effect of Cur. CONCLUSION: Cur has a protective effect on ISO-induced cognitive dysfunction, which may be achieved by regulating the expression of miR-181a-5p.

The distribution of liver cancer stem cells correlates with the mechanical heterogeneity of liver cancer tissue.

The survival of cancer stem cells is usually limited to a specific tumor microenvironment, and this microenvironment plays a vital role in the development of tumors. The mechanical properties of the microenvironment differ in different regions of solid tumors. However, in solid tumors, whether the distribution of cancer stem cells relates to the mechanical microenvironment of different regions is still unclear. In this study, we undertook a biophysical and biochemical assessment of the changes in the mechanical properties of liver tissue during the progression of liver cancer and explored the distribution of liver cancer stem cells in liver cancer tissues. Our analysis confirmed previous observations that the stiffness of liver tissue gradually increased with the progress of fibrosis. In liver cancer tissues, we found obvious mechanical heterogeneity: the core of the tumor was soft, the invasive front tissue was the hardest, and the para-cancer tissue was in an intermediate state. Interestingly, the greatest number of liver cancer stem cells was found in the invasive front part of the tumor. We finally established that stroma stiffness correlated with the number of liver cancer stem cells. These findings indicate that the distribution of liver cancer stem cells correlates with the mechanical heterogeneity of liver cancer tissue. This result provides a theoretical basis for the development of targeted therapies against the mechanical microenvironment of liver cancer stem cells.

[Residual Characteristics and Health Assessment Analysis of OCPs and PCBs in Karst Groundwater].

Residual levels of organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) in karst groundwater in Nanshan Laolongdong were measured using a gas chromatograph equipped with a micro-63Ni electron capture detector to determine the residual characteristics including concentration, distribution, and source of OCPs and PCBs. Results revealed that the total concentration range of OCPs was 34.8-623.2 ng·L-1, and the mean value was 215.6 ng·L-1, among which the total concentration ranges of HCHs, DDTs, and other OCPs were 8.2-23.6, 4.5-363.7, and 22.2-235.9 ng·L-1, respectively, and the mean values were 15.9, 104.5, and 95.3 ng·L-1; the total concentration range of PCBs was 6.0-40.7 ng·L-1, and the mean value was 16.8 ng·L-1. Overall, the pollution of OCPs and PCBs was above average; the results of multiple comparisons revealed that statistically significant differences occurred in the concentration of some OCPs and PCBs. The pollution levels in the water of each sampling point in the study area were quite different; however, the seasonal distribution of OCPs and PCBs was relatively uniform. Source analyses revealed that HCHs' source was the input of lindane in the surrounding environment, DDTs recently originated from illegal use of industrial DDT, other OCPs originated from atmospheric deposition and agricultural input, and PCBs' sources included both historical remains and enterprise production processes. The results of Pearson correlation analyses revealed that some organo-halogen pollutants were homologous or had similar sources and decomposition mechanisms. According to health risk assessment model, drinking water in the study area would not cause obvious harm to human health, but children were more sensitive to pollutants than adults.

Characteristics and ecological risk assessment of polycyclic aromatic hydrocarbons in soil seepage water in karst terrains, southwest China.

Concentrations of polycyclic aromatic hydrocarbons (PAHs) in soils and soil seepage waters were analyzed along with dissolved organic carbon (DOC) to investigate the ecological risks and factors controlling the subsurface transport of PAHs in karst terrain in southwest China. The concentrations of dissolved PAHs in soil seepage water increased with depth and the mean concentrations at a depth of 80 cm were relatively high (exceeding 1147 ng/L). PAH composition in soil seepage water was dominated by low molecular weight (LMW) PAHs, whereas those associated with soil matrix were dominated by high molecular weight (HMW) PAHs. The results revealed that HMW PAHs in soil seepage water were closer to the equilibrium of dissolution than LMW and medium molecular weight (MMW) PAHs. However, due to the carrier functions of dissolved organic matter (DOM) for HMW PAHs, all PAHs can be continuously dissolved in the soil seepage water from soil matrix as the water moved vertical downward through the profiles. During this process, dynamic sorption and desorption processes were occurring between constituents in the soil seepage water and the soil matrix. This study demonstrates soil seepage water has posed a high risk to the groundwater, and effective protection is urgently needed.

Vertical migration from surface soils to groundwater and source appointment of polycyclic aromatic hydrocarbons in epikarst spring systems, southwest China.

Understanding the transfer process of polycyclic aromatic hydrocarbons (PAHs) in the karst terrain is of great importance to their ecological risk assessments, however, the impact of the vertical transfer of the soil PAHs on the underground water is largely unknown in the karst system. Here, the vertical distribution and the seasonal variation of 16 PAHs in the soils and the water of 4 epikarst spring catchments in Southwest China were investigated. The total concentration of the PAHs ranged within 61-3285 ng g-1 in the soils, and 341-4969 ng L-1 in the spring water. The vertical distribution of the PAHs in soils varied with ring numbers and altitude of the catchment. PAHs concentrations were linearly related with the total organic carbon (TOC) at different depths in the catchments 563-783 m above the sea level (A.S.L.). However, no correlation with TOC was observed in the catchment of a high altitude (2090 m A.S.L.), because the large water flux led to the fast migration of the 2-3 rings PAHs in soils. The PAHs in soils and springs were mainly derived from the combustion of grass/wood/coal, closely related with the primary fossil fuels used in this area. This study demonstrate that the groundwater was heavily polluted by PAHs in the karst terrains of Southwest China, due to the vertical transfer of PAHs from the surface soils, and effective protection was urgently needed.

Transport of polycyclic aromatic hydrocarbons in a highly vulnerable karst underground river system of southwest China.

The concentration and fluxes of polycyclic aromatic hydrocarbons (PAHs) were investigated in a karst underground river system in southwest China. Groundwater, particles, and sediments from underground river, topsoil, and surface water were monitored, allowing establishment of a conceptual model of PAH transport at the watershed scale. The results showed that PAHs could be transported from the surface to the subsurface through two migration pathways, which were slow-flowing water in the karst fissure and fast-flowing water in conduits. During rainfall events, increasing PAH levels (concentrations and fluxes) at the underground river exit indicated that hydrodynamic force could facilitate PAH transport. The PAHs in water were dominated by dissolved PAHs, accounting for 58.7% of total, especially in the freely dissolved phase, in which SPM-associated PAHs accounted for 41.3% of the total PAHs. Low molecular weight PAHs dominated transport and were mainly transported in dissolved form, whereas high molecular weight PAHs were dominated by SPM-associated transport during the rainfall events. A significantly positive correlation was observed between two-ring and three-ring freely dissolved PAHs and dissolved organic carbon (p < 0.01), respectively. Moreover, PAHs with four to five rings were relatively more abundant in the dissolved organic matter (DOM) associated phase than in the freely dissolved phase, suggesting a major role of DOM in their transport during rainfall events. The trend of PAH fluxes suggested that particle-facilitated transport was another dominant cause of PAH mobilization.

[Sources and Variation Characteristics of Dissolved Lipid Biomarkers in a Typical Karst Underground River].

Water samples in Qingmuguan underground river were collected to determine the concentration of dissolved lipids, and their sources, composition and migration characteristics in underground river were studied. The results were obtained as follows. (1) The average content of various dissolved lipids decreased with increasing distance of migration in Qingmuguan underground river, and the most distinctive was dissolved saturated straight chain fatty acids with its content decreasing by about 81.71%, from the initial 5,704 ng · L⁻¹ to 1,043 ng · L⁻¹. (2) N-alkane could indicate the sources of dissolved organic matter in underground river, but saturated straight chain fatty acid and fatty alcohol had the advantage in indicating algae, bacteria and other microorganisms. (3) With the increasing migration distance of Qingmuguan underground river, the input type of dissolved organic matter in underground river was different, which might be resulted from the heterogeneity of karst surface. (4) In ternary plot of alkane sources, aquatic plants constituted the major contribution of dissolved organic matter in Qingmuguan underground river, followed by higher plant, algae/ bacteria. Unlike higher plants and algae/bacteria, the contribution from aquatic plants decreased with increasing migration distance of underground river. (5) To a certain extent, TAR (alkane) values could reflect the rainfall, and the values of CPI, L/H in saturated straight chain fatty acids might indicate the degradation activities of bacteria.

[Distribution Characteristics and Source Identification of Organochlorine Pesticides in Surface Soil in Karst Underground River Basin].

Six typical surface soil samples were taken in Laolongdong underground river basin, and 20 OCPs were analyzed by gas chromatography equipped with micro-6³Ni electron capture detector. The purpose of this study was to investigate the distribution, composition and source of organochlorine pesticides ( OCPs) in the surface soil of Laolongdong underground river basin, and to further evaluate the pollution level. The results showed that 20 OCPs were inordinately detected in the soil samples and the detection rate of 16 OCPs (except for p,p'-DDE, cis-Chlordane, trans-Chlordane, dieldrin) was 100%. Moreover, the CHLs and DDTs were the main contaminants, and there were obvious differences in the concentrations of organochlorine pesticides between different sampling points. The concentration range of total OCPs was 5.57-2,618.57 ng · g⁻¹ with a mean of 467.28 ng · g⁻¹. Compared with other regions both at home and abroad, the concentrations of HCHs and DDTs in the surface soil samples of the studied area were arranged from high to middle levels. The total concentrations of OCPs, HCHs, DDTs and CHLs had a similar variation tendency in spatial distribution, upstream > midstream > downstream, and the concentrations of OCPs in upstream were obviously higher than those in midstream and downstream. Source analysis indicated that the HCHs mainly came from the use of lindane. DDTs in soil came from not only the early residues but also recently illegal use of industrial DDTs and the input of dicofol. In addition, chlordan was mainly from the early residues and atmospheric deposition. Compared with the Environmental Quality Standard for Soils of China and Netherlands, the level of OCPs in Xinli vilage soil was categorized as highly polluted, but the levels of OCPs in Longjing bay, Xia spit, and Zhao courtyard soils were classified as slightly polluted, while the Longjing adjacency and gaozhong temple soils belonged to unpolluted ones.

Simulation of the transfer and fate of γ-HCH in epikarst system.

The thin surface soil layer and karst features in karst terrains lead to poor filtration, poor pre-purification and rapid infiltration, so that karst groundwater systems are particularly vulnerable to contamination. Due to its extensive use in past, gamma-hexachlorocyclohexane (γ-HCH) is ubiquitous in various environmental compartments of China, even though it has been prohibited since 1984. However, very little is known about its movement and behavior in special karst system. In this study, a dynamic fugacity model was established for γ-HCH in epikarst system via dividing the karst soil into multiple layers coupled with the physical-chemical properties of γ-HCH. The simulated results in soil profile were in good agreement with the measured values of γ-HCH. The modeled results predict that only 18 g γ-HCH will be left in the studied area in 2020, which is only 0.4% of the largest reserves in 1983, and about 99.99% of γ-HCH will remains in soil. The concentrations of γ-HCH in air, plant and 0-20 cm layer soil in the studied area descended quickly after HCHs was prohibited in 1984, while its concentration in soil layer deeper than 20 cm (deeper soil) increased continuously till 1997. The dominant transfer process of γ-HCH between the adjacent compartments in the studied area was from 0-20 cm layer to the deeper soil. Sensitivity analysis results showed that emission rate, infiltration coefficient, total organic carbon of soil, degradation rate in soil, compartment area and volume were the top six influential parameters for predicting γ-HCH concentration.

[Distribution Characteristics and Source Identification of Polycyclic Aromatic Hydrocarbons, Fatty Acids in Water of Karst Underground River].

In order to explore the contents, composition, distribution characteristics, sources and pollution level of polycyclic aromatic hydrocarbons(PAHs) and fatty acids in water of Qingmuguan karst underground river in Chongqing, water samples were respectively collected from underground river in rainy season and dry season, 2013 and polycyclic aromatic hydrocarbons, fatty acids of the water samples were quantitatively analyzed by Gas Chromatography-Mass Spectrometer(GC-MS). The results showed that the contents of PAHs and fatty acids in water of Qingmuguan karst underground river ranged from 77.3 to 702ng·L-1 and 3302 to 45254 ng·L-1, respectively. In terms of composition, the PAHs profiles were dominated by (2-3) rings PAHs in water samples, which accounted for more than 90% of the total PAHs contents, while the carbon numbers of fatty acids ranged from C10 to C28, and fatty acids profiles were dominated by saturated straight chain fatty acids, followed by mono-unsaturated fatty acids. In terms of the distribution characteristics, the contents of PAHs had minor difference at each sample point in water of underground river in rainy season. At the entrance, exposed and exits, the contents of fatty acids reduced in turn, moreover the contents of fatty acids were close at the exposed and exits. dry season:at the entrance, exposed and exits, the contents of PAHs in water of underground river decreased firstly and then increased. The contents of fatty acids were close at each sample point in water of underground river. As a whole, the contents of PAHs and fatty acids in water of underground river in rainy season were significantly higher than those in dry season. Source analysis indicated that the PAHs in water of Qingmuguan underground river were mainly originated from the combustion of coal and biomass (wood, crop straw, etc) at the underground river catchment. The fatty acids were mainly originated from aquatic algae (diatoms and green alga, etc), and bacteria, with the contribution of aquatic algae dominated. The water of underground river was suffered the middle to mild pollution by PAHs, and compared with the dry season, the rainy season was more severely polluted.

[Fecal Contamination in Laolongdong Underground River as Measured by the Sterol Biomarkers].

To investigate whether the underground river was polluted or not, and trace the source of fecal sterols, the particulate water samples were collected from typical karst underground river named Laolongdong in Nan'an District, Chongqing Municipality in October, 2014, January, March and May, 2015. Ten prior steroids in the underground river were quantitatively analyzed by the gas chromatography-mass spectrometer (GC-MS). The results showed ten steroids including 9 sterols and 1 ketone were detected. During the sampling period, the mass concentrations of particulate steroids (ranging between 1573 and 5007 ng·L-1) in March and May were higher than those in October and January. The 3 principal steroids-cholesterol, ß-sitosterol and coprosterol-in the river accounted for 50.8%-80.4% of the total steroids. The ratios of (epicoprostanol+coprostanol) to (coprostanol+epicoprostanol+cholestanol) of three samples were greater than 0.7, which indicated the river was contaminated in sampling months. The ratio of epicoprostanol to coprostanol was less than 0.2 in October, which indicated the wastewater came from the upstream sewage treatment plant. The ratios of coprostanol to ΣSteroids and coprostanol to 24-ethylcoprostanol in January, March and May were respectively 0.109-0.254 and 6.3-10.3, which indicated that Laolongdong underground river was mainly polluted by human feces. The ratio of 24-ethylcoprostanol to 24-ethylcholestanol in March (0.86) was less than those in January (5.4) and May (2.3), which showed the river was polluted more severely in March than in January and May by poultry dung.

[Impacts of Land Use on the Source of Dissolved Fatty Acids in Epikarst Spring During Rainy Season].

Fatty acids were quantitatively analyzed by gas chromatography-mass spectrometer (GC-MS). Dissolved fatty acids were collected from Nanchuan epikarst spring. The results of BQ, LQ, HQ showed that the average contents of fatty acids were 14870, 12912 and 8801 ng·L-1 from May to July, respectively, and followed the order of SFA> MUFA> BrFA> PUFA. The monomers with highest content were C16:0 and C18:0. From May to July, the fatty acid content increased in BQ , LQ, HQ. The differences in vegetation coverage and bedrock bare rate, as well as the interaction of the dilution effect and soil transfer increase, led to the changes in content and the composition of the fatty acids. Based on the molecular characteristic indices of fatty acids, like H/L, CPIh, TARFA about BQ, LQ, HQ, and contents of fatty acids which were mainly originated from bacteria, phytoplankton or terrigenous higher plant, it was indicated that fatty acids were mainly originated from higher plant in LQ in May, from phytoplankton input in HQ in July, while from bacteria in the other months in LQ, HQ and from May to July in BQ.

[Distribution Characteristics and Source Identification of Organochlorine Pesticides in the Karst Groundwater System].

Chongqing Laolongdong and Qingmuguan karst underground rivers were selected as the research objects, and 21 kinds of OCPs in those two underground rivers were analyzed by gas chromatography (GC-µECD). The results showed that, o,p'-DDE,p,p'-DDE, o,p'-DDD were not detected in Nanshan and Qingmuguan underground rivers; o,p'-DDT and dieldrin were not detected in Qingmugang; but the detection rate of the rest of the OCPs in those two underground rivers was as high as 100%. HCHs and ALDs were the most dominant compounds in Laolongdong underground river, whereas HCHs and methoxychlor were the most dominant compounds in Qingmuguan. The concentration range of total OCPs in Qingmuguan was 145-278 ng·L-1 with a mean value of 213 ng·L-1. The concentration range of total OCPs in Laolongdong was 17.7-40.8 ng·L-1 with a mean value of 32.7 ng·L-1. The OCPs component showed an increasing trend from the entrance to the exit of those two underground rivers. By analyzing the source of OCPs pollution, DDTs in the two underground river basin came from the historical industrial DDTs input; chlordane mainly came from atmospheric deposition. HCHs was the main source of Lin Dan's input, Nanshan underground river was historical pollution, whereas there was a new HCHs input from Ganjiachao in Qingmuguan upstream. Compared with the water bodies at home and abroad, the concentrations of HCHs and DDTs in Nanshan underground river water were at low level, whereas those in Qingmuguan were at medium to high level. Comparing with the hygienic standard of foreign water, it could be observed that Nanshan underground river and Qingmuguan underground river were not able to meet the standard of drinking water safety standard. For the sake of protecting the ecological environment of the underground river, land application of organic chlorine pesticide should be banned in Qingmuguan.

[Impact of Urbanization on the Sources of Dissolved n-alkane in Underground River].

To investigate the influence of urbanization on the component features of dissolved n-alkanes (D-ALK) in the underground river in the dry season, water samples were collected respectively at the outlet of the two underground rivers. Components of D-ALK in these samples were quantitatively analyzed by gas chromatography-mass spectrometry (GC-MS). The results showed that the distribution of D-ALK carbon number at the two sites ranged from nC14 to nC35 in dry season. The total concentration of D-ALK (DT-ALK) in Jiangjia spring ranged from 102 to 356 ng·L-1, with an average of 230 ng·L-1. The low-number carbons were predominant in December 2014, January and April 2015. The ratios of LMH/HMH (nC21-/nC22+) ranged from 2.0 to 10. The carbon preference index (CPI) between nC14 and nC25 ranged from 0.19 to 0.57, with a maximum of C16 (Cmax16). However, in November 2014, February and March 2015, these samples had a bimodal distribution in n-alkane. All of the CPI14-25 and the ratios of LMH/HMH were less than 1. The CPI24-35 ranged from 1.2 to 23 with the Cmax 31 or Cmax33. During the three months, the values of Paq were 0.2, 0.7 and 0.1, respectively. The alkane indexes (AI) in November 2014 and March 2015 were 0.95 and 0.98, respectively. The values of DT-ALK in Laolongdong ranged from 110 to 697 ng·L-1 with an average of 310 ng·L-1. The carbon number distribution of each month had a low predominance, and the CPI14-25 was less than 1. In the dry season, under the influence of different human activities, the content and component of D-AKL in Laolongdong which originated mainly from microorganisms was more stable than that in Jiangjia spring, which was mainly derived from microorganisms and a mixture of microorganisms and plants.

[Comparison Study of the Alkanes in Different Aquifer Medium Under Qingmuguan Underground System].

Dissolved alkanes were collected from Dalv spring and Jiangjia spring from July to November, 2013, and were quantitatively analyzed by the gas chromatography-mass spectrometer (GC-MS). The results show that the total content of dissolved alkanes in Dalv spring is 175-3279 ng x L(-1), with a mean value of 1011 ng x L(-1). In Jiangjia spring, the total content of dissolved alkanes is 282-775 ng x L(-1), with a mean value of 527 ng x L(-1). Ratios of the content of alkanes with high carbon number( C25-C32) to the total alkanes vary from 27.89% to 52.92% in Dalv spring, and 23.66% to 49.73% in Jangjia spring. Combined with CPI and OEP the relative contribution to the dissolved alkanes of higher plants are increasing in Dalv spring, however, it is different in Jiangjia spring. In addition, the values of L/H couldn't reflect different organic contributions to the dissolved alkanes, and the values of TAR may relate with rainfall.

[Vertical Migration Characteristics of Organochlorine Pesticides in Overlying Soil in Karst Terranes and Its Impact on Groundwater].

Five soil profiles and four typical epikarst springs were selected in Nanchuan District, Chongqing Municipality as objects of the study on vertical migration of organochlorine pesticides (OCPs) in the soils and its impact on groundwater. OCPs in soil and epikarst spring water samples were quantitatively analyzed by gas chromatography. The results showed that HCHs and DDTs were detected in all the 5 soil profiles, varying in the range of 0.77-18.3 and 0.34-226 ng · g(-1), and averaging 5.16 and 16 ng · g(-1) in concentration, respectively. The highest concentrations of HCHs and DDTs were found in the subsoil (10-40 cm) in most sampling sites. The detection ratios of HCHs and DDTs in four springs were 100%. The concentrations of HCHs and DDTs fluctuated greatly in epikarst spring water during the one-year observation, and the concentration ranged from 2.09 to 60.1 and from N. D. to 79.8 ng · L(-1), with a mean value of 12 and 9.16 ng · L(-1), respectively. The concentrations of HCHs and DDTs in Hougou, Baishuwan and Lanhuagou spring in rainy season were all. higher than those in dry season in these three epikarst springs. There were no good corresponding relationship between HCHs and DDTs contents in spring water and those in corresponding spring catchment soil. TOC, soil water content, clay content and pH all inhibited the vertical migration of OCPs in Hougou spring catchment, which led to the lowest content of OCPs in spring water, although the OCPs content in Hougou spring catchment soils was the highest in the four spring catchments. However, the four factors didn't inhibit the vertical migration of OCPs in Shuifang spring catchment, which led to higher OCPs content in spring water, although the OCPs content in spring catchment soils was the lowest in the four spring catchments.