Occurrence of Organochlorine Pesticides in Farmland Soils of Xi'an, China

In this study, 25 representative farmland soil samples from suburban areas in Xi&#39;an, the capital city of Shaanxi province, China, were collected and analyzed for 20 organochlorine pesticides (OCPs). The concentrations were in the ranges of 0.22-11.24 ng g(-1) for HCHs (sum of alpha, beta, gamma and delta-HCH, avg. 3.56 ng g(-1)), 0.76-56.30 ng g(-1) for DDTs (sum of p,p&#39;-DDT, p,p&#39;-DDD, p,p&#39;-DDE, avg. 12.80 ng g(-1)), 0.47-12.95 ng g(-1) for CHLs (sum of heptachlor, heptachlor epoxide isomer B, alpha-chlordane and gamma-chlordane, avg. 5.90 ng g(-1)), 0.64-31.51 ng g(-1) for other organochlorine pesticides (sum of aldrin, dieldrin, endrin, endosulfan I, endosulfan II, endosulfan sulfate, endrin aldehyde, endrin ketone and methoxychlor, avg. 11.89 ngg(-1)). HCHs, DDTs and CHLs were the most dominant compounds among the 20 organochlorine pesticides. Source identification analysis indicated that the residues of HCHs, DDTs and CHLs were mostly due to historical use of these chemicals or from other source regions. The quality of Xi&#39;an farmland soil was classified as low pollution by organochlorine pesticides according to the national environmental quality standards for soils of China (GB15618-1995).</p

Characterization and Risk Assessment of PolychlorinatedBiphenyls in City Park Soils of Xi’An, China

Polychlorinated biphenyl (PCB) concentrations in surface soil samples (0&ndash;10 cm) from 23 city parks (8 urban and 15 suburban) from Xi&rsquo;An, China were presented. The average concentration of R7 PCBs among all the sites was 1.68 ng g-1 dry weight. High detection frequency (100 %) of PCB 28 and PCB 52 suggested wide occurrence of PCB contaminations in Xi&rsquo;An. Among these PCBs, PCB 28, 52 and 153 were the most dominant compounds (14.9 %, 39.3 % and 9.5 % of the R7 PCBs on average, respectively). &lsquo;&lsquo;Urban fractionation effect&rsquo;&rsquo; was found in Xi&rsquo;An. In other words, PCB concentrations were higher in the urban city park soils than those in suburban park soils. The PCB contamination in Xi&rsquo;An city park soils were at a low level based on the Dutch guideline. However, dioxinlike PCB congeners were detected from 12 parks, which indicated further investigation was urgently required in future. Furthermore, total PCB concentrations were used to evaluate the cancer risk via ingestion, dermal and inhalation and the results showed that the total cancer risk was at the very low level in this area.</p

Vertical distributions of organochlorine pesticidesand polychlorinated biphenyls in an agricultural soil corefrom the Guanzhong Basin, China

The concentrations and distributions of hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs), and polychlorinated biphenyls (PCBs) in an agricultural soil core in the Guanzhong Basin, China were determined. Overall, p,p&rsquo;-DDT and p,p&rsquo;-DDE were dominant contaminants and accounted for approximately 48.4 and 23.3 % of the total detected DDTs. Low chlorinated PCBs (PCB 28 and PCB 52) were generally detected at higher concentrations and more frequently than high chlorinated PCBs. The peak values of &sum;DDT (12.92 ng/g), &sum;HCH (2.25 ng/g), and &sum;PCB (3.44 ng/g) occurred in the 10&ndash;15, 15&ndash;20, and 5&ndash; 10 cm sections, respectively. The negative correlation between the organochlorine pesticide (OCP) concentrations and the soil depths and the relatively high p,p&rsquo;- DDT/p,p&rsquo;-DDE ratios in the surface soils indicated that these chemicals were recently used illegally, despite their official ban in 1983. The increase in the ratio of &alpha;-/&gamma;-HCH with increasing soil depth indicated that the use of lindane decreased relative to the use of technical HCHs in recent years.</p

Isotopic and REE evidence for the paleoenvironmental evolution of the late Ediacaran Dengying Section, Ningqiang of Shaanxi Province, China

Weakly mineralized taxa are most likely the ancestors of higher organisms that existed during the Cambrian explosion, thereby representing an important yet least understood evolutionary link between simple and complex life. An investigation of the seawater temperature and the carbon cycle during the late Ediacaran, in the time span of the emergence of weakly mineralized taxa, contributes to the deeper understanding of the environmental conditions existing during the early stages of animal skeleton mineralization. Towards this end, we conducted the analyses on the carbon and oxygen isotope composition, petrography, major elements, and trace elements, involving the rare earth elements (REEs) variations in the carbonate rocks of Ningqiang County in Shaanxi Province of China. The samples from the Dengying Formation (Fm.) include the Gaojiashan and Beiwan Members, in ascending order. In addition, the Gaojiashan Member hosts one of the most diverse collections of biota with weakly mineralized skeletons discovered to date. Our data shows that a positive carbon excursion, high &delta;18O values, positive correlation between &delta;13C and &delta;18O values, high REE concentrations, a distinctive MREE-enriched pattern, high Fe concentrations and slightly negative Ce anomalies in the Gaojiashan Member. These evidences indicate a restricted warm sea environment with an influx of river water or groundwater. Conversely, the low carbon isotope values, high &delta;18O values and its heterogeneity, the absence of correlation between carbon and oxygen, combined with a seawater-like REE distribution pattern in the Beiwan Member suggested that a restrict, shallow, slightly cool and/or arid sea environment condition that was subject to periodic perturbations in the hydrologic balance. Therefore, we surmised that the environmental differences between the Gaojiashan and the Beiwan Members probably resulted in the preservation of a number of animal skeleton fossils in the middle section of the Dengying Fm.</p

Tracing the Source of Cooking Oils with an Integrated Approach of Using Stable Carbon Isotope and Fatty Acid Abundance

We report a new approach to identify swill-cooked oils that are recycled from tainted food and livestock waste from commercial vegetable and animal oils by means of carbon isotope values and relative abundance of fatty acids. We test this method using 40 cooking oil samples of different types with known sources. We found significant differences in both total organic carbon isotope as well as compound-specific isotope values and fatty acid C-14/C-18 ratios between commercial vegetable oils refined from C-3 plants (from -35.7 to -27.0 parts per thousand and from 0 to 0.15) and animal oils (from -28.3 to -14.3 parts per thousand and from 0.1 to 0.6). Tested swill-cooked oils, which were generally refined by mixing with animal waste illegally, fall into a narrow delta C-13/fatty acid ratio distribution: from -25.9 to -24.1 parts per thousand and from 0.1 to 0.2. Our data demonstrate that the index of a cross-plotting between fatty acid delta C-13 values and C-14/C-18 ratios can be used to distinguish clean commercial cooking oils from illegal swill-cooked oils.</p

Variation of the winter monsoon in South China Sea over the past 183 years: Evidence from oxygen isotopes in coral

Oxygen isotope (&delta;18O) data in winter months in living coral Porites lutea collected from the Xisha Islands, South China Sea is significantly correlated to the measured winter monsoon velocity (WMV) with a correlation coefficient of 0.63. Based on 40-year (1961&ndash;2000) instrumental data, a transfer function between the WMV and the winter &delta;18O is established: WMV = 2.819 &delta;18O + 19.615 (N = 40, p &lt; 0.0001). Based on the calculated WMV from &delta;18O over the past 183 years, the sequence of winter monsoon velocity (WMV) from year 1818 to 2000 in the South China Sea is re-constructed. The sequence can be divided into three stages: the first stage shows a decreasing trend of 0.009 m/s&middot;yr from 1818 to 1954, the second stage indicates an increasing trend of 0.011 m/s&middot;yr from 1955 to 1976, and the last stage shows a decreasing trend of 0.026 m/s&middot;yr from 1977 to 2000. The maximum reduction in winter monsoon velocity over the last 24 years (1977&ndash;2000) is approximately 20% of the average over the last 183 years (1918&ndash;2000). The variation of wind velocity shows two complete cycles over the past 183 years. In particular, the strongest and weakest winter monsoon velocities in the last two centuries occurred in the 1830s and 1940s, respectively. The variation in winter monsoon velocity in the 20th century is closely linked to the surface temperature of the South China Sea, as well as air temperature over continental China. In addition, the winter monsoon was weak during two warm periods, i.e. the 1940s and 1980s. Statistical analysis of the winter monsoon velocity anomaly as well as the El Ni&ntilde;o (warm event) and La Ni&ntilde;a (cold event) phenomena indicates that 70% of El Ni&ntilde;o events correspond to the weakness of the winter monsoon.</p

Carbon isotope fractionation during low temperature carbonization of foxtail and common millets

Stable carbon isotopes of organic matter and fossilized plant remains can be used to effectively reconstruct local palaeoclimate changes, especially from plants using a single photosynthetic mode. The charred grains of foxtail and common millet are chemically stable in the environment and have been preserved widely and continuously throughout the Holocene in North China. The charred remains of these species are ideal materials for reconstructing the palaeoclimate based on delta(13)C of foxtail and common millets heated to temperatures up to around 250 degrees C. This study reports delta(13)C values of modern millets carbonized at different temperatures. The results indicate that there are no significant changes in delta(13)C of intact and charred samples of foxtail millet (&lt;= 0.46 parts per thousand) and common millet (&lt;= 0.49 parts per thousand) for temperatures below 300 degrees C. The delta(13)C of charred foxtail millet formed at 250 degrees C were 0.2 parts per thousand higher in delta(13)C than the source samples. In contrast, the delta(13)C of charred common millet formed at 250 degrees C were 0.2 parts per thousand lighter in delta(13)C than the source samples. The delta(13)C values of grains were determined in part by the carbon content (i.e., starches, lignins and lipids) and the variable thermal tolerances of these compounds to heating. However, the observed (13)C carbonization associated with fractionation of only 0.2 parts per thousand in grains is much less than the natural variation typically found in wood. We therefore suggest that delta(13)C measured in carbonized grains can serve as an effective indicator for paleoenvironmental and archaeological reconstructions. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.</p

Soil carbon isotope ratios of the Zijing site, Qinling Mountains, China: Implications for defining the southern limit of millet agriculture

The inner Qinling Mountain basin is an ideal geographic area for examining the adaptation of the Yellow River Civilization into the transition zone of subtropical and warm temperate climates. Paleosol isotope and other geochemical and geophysical analyses were used to examine ancient farming and animal raising strategies, food structure, and past environment at the Zijing site on the inner Qinling Mountain basin. The organic carbon isotope suggests that the Neolithic and Bronze Age farmers in Zijing could cultivate up to 50% millet-like C-4 plants, developed from the Yellow River Civilization, and 50% C-3-like local plants during the interval from the Yangshao to the Xia-Shang cultures. The carbonate carbon isotope suggests that Zijing farmers could raise livestock on a relatively large scale during the Yangshao and Longshan periods. The carbon isotopic results are in agreement with other geochemical parameters, including soil organic and carbonate carbon contents, as well as the ratio of organic carbon and nitrogen. Magnetic susceptibility indicates a warmer and wetter climate condition from the Yangshao to the Xia-Shang cultures that facilitated agricultural development at this Neolithic site. The long cultural sequence sampled at this site shows that the millet-based agricultural system of the Yellow River Civilization at the Zijing site on the inner Qinling Mountain basin could have been practiced. In addition, the unusually negative delta C-13(sc) values likely also reflected a highly developed ancient agricultural civilization, which potentially has important implications for archaeology in China because of the southernmost record of millet agriculture in the Zijing site.</p

Organic stable carbon isotopic composition reveals late Quaternary vegetation changes in the dune fields of northern China

Vegetation changes during the late Quaternary in the dune fields of northern China are not well understood. We investigated organic carbon stable isotopic composition of surface soils, related mainly to the ratio of C-3 and C-4 plants, across a range of arid to subhumid climates in this region. Isotopic composition is weakly related to both temperature and moisture (multiple R-2=0.53), with the highest delta C-13 (greatest C4 abundance) in the warm, subhumid Horqin dune field. In late Quaternary, eolian stratigraphic sections of the Mu Us and Horqin dune fields, but not in the much colder Otindag dune field, delta C-13 is higher in organic carbon from paleosols than in eolian sands. This contrast, most evident for paleosols recording a major early to middle Holocene phase of dune stabilization, is interpreted as evidence for expansion of C4 plants due to increased effective moisture, high temperature because of high insolation, and decreased disturbance related to eolian erosion and deposition.</p

Cenozoic Environmental Changes in the Northern Qaidam Basin Inferred from n-alkane Records

Cenozoic climatic and environmental changes in the arid Asian interior, and their possible relations with global climatic changes and the Tibetan Plateau uplift, have been intensively investigated and debated over past decades. Here we present 40-Myr (million years)-long n-alkane records from a continuous Cenozoic sediment sequence in the Dahonggou Section, Qaidam Basin, northern Tibetan Plateau, to infer environmental changes in the northern basin. A set of n-alkane indexes, including ACL, CPI and Paq, vary substantially and consistently throughout the records, which are interpreted to reflect relative contributions from terrestrial vascular plants vs. aquatic macrophytes, and thus indicate depositional environments. ACL values vary between 21 and 30; CPI values range from 1.0 to 8.0; and Paq values change from &lt;0.1 to 0.8 over the past 40-Myr. We have roughly identified two periods, at 25.8-21.0 Ma (million years ago) and 13.0-17.5 Ma, with higher ACL and CPI and lower Paq values indicating predominant lacustrine environments. Lower ACL and CPI values, together with higher Paq values, occurred at &gt;25.8 Ma, 17.5-21.0 Ma, and &lt;13.0 Ma, corresponding to alluvial fan/river deltaic deposits and shallow lacustrine settings, consistent with the observed features in sedimentological facies. The inferred Cenozoic environmental changes in the northern Qaidam Basin appear to correspond to global climatic changes.</p