800-kyr land temperature variations modulated by vegetation changes on Chinese Loess Plateau.

The complicity of long-term land surface temperature (LST) changes has been under investigated and less understood, hindering our understanding of the history and mechanism of terrestrial climate change. Here, we report the longest (800 thousand years) LSTs based on distributions of soil fossil bacterial glycerol dialkyl glycerol tetraethers preserved in well-dated loess-paleosol sequences at the center of the Chinese Loess Plateau. We have found a previously-unrecognized increasing early and prolonged warming pattern toward the northwestern plateau at the onset of the past seven deglaciations, corresponding to the decrease in vegetation coverage, suggesting underlying surface vegetation or lack of has played an important role in regulating LSTs, superimposed on the fundamental global glacial-interglacial changes. Our results support that LSTs in semi-humid and semi-arid regions with little vegetation will be more sensitive to the anticipated global temperature rise, while improving vegetation coverage would reduce LSTs and thus ecological impacts.

Characterization and risk assessment of polychlorinated biphenyls in city park soils of Xi'an, China.

Polychlorinated biphenyl (PCB) concentrations in surface soil samples (0-10 cm) from 23 city parks (8 urban and 15 suburban) from Xi'an, China were presented. The average concentration of Σ7 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'an. Among these PCBs, PCB 28, 52 and 153 were the most dominant compounds (14.9 %, 39.3 % and 9.5 % of the Σ7 PCBs on average, respectively). "Urban fractionation effect" was found in Xi'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'an city park soils were at a low level based on the Dutch guideline. However, dioxin-like 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.

Vertical distributions of organochlorine pesticides and polychlorinated biphenyls in an agricultural soil core from 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'-DDT and p,p'-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 ∑DDT (12.92 ng/g), ∑HCH (2.25 ng/g), and ∑PCB (3.44 ng/g) occurred in the 10-15, 15-20, and 5-10 cm sections, respectively. The negative correlation between the organochlorine pesticide (OCP) concentrations and the soil depths and the relatively high p,p'-DDT/p,p'-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 α-/γ-HCH with increasing soil depth indicated that the use of lindane decreased relative to the use of technical HCHs in recent years.

Occurrence of organochlorine pesticides in surface soils from college school yards of Xi'an, China.

In this study, surface soil samples from 14 representative college school yards in Xi'an, the capital city of Shaanxi province, China, were collected and analyzed for 21 organochlorine pesticides (OCPs). The total concentrations were in the ranges of 0.2-67.0 ng/g. HCHs and DDTs were the most dominant compounds among the 21 OCPs, and their concentrations ranged from 0.1-8.5 to 0.1-56.3 ng/g, respectively. Source identification analysis indicated that the residues of HCHs and DDTs were mostly due to historical use of these chemicals or from other source regions. The quality of all the Xi'an college school yard soils except sample XAUAT was classified as low pollution by OCPs according to the National Environmental Quality Standards for Soils of China (GB15618-1995).