Polycyclic aromatic hydrocarbons (PAHs) and Pb isotopic ratios in a sediment core from Shilianghe Reservoir,eastern China: Implying pollution sources

The history records of polycyclic aromatic hydrocarbons (PAHs), lead and its stable isotope ratios were determined in a sediment core to receive anthropogenic impacts on the Shilianghe Reservoir in eastern China. The historical changes of PAHs concentrations, PAHs fluxes, Pb/Al and Pb isotope ratios showed a synchronous trend throughout the core, suggesting changes in energy usage and correlating closely with the experience of a rapid economic and industrial development of the catchment, Linyi City in eastern China. PAHs isomer ratios results reveal PAHs in sediments are dominantly anthropogenic pyrogenic source, dominated by the combustion of coal and biomass. Furthermore, the Pb isotopic composition also clearly indicates that coal combustion dust mainly contributed to the Pb burden in the reservoir sediments. Based on mix end member model of Pb isotope ratios, coal combustion dust dominated anthropogenic Pb sources over fifty years contributing from 31% to 62% of total Pb in sediment. And the contribution of leaded gasoline was low than average 25%. In addition, a stable increase of coal combustion source was found in sediment core, while the contribution of leaded gasoline had declined in recent decades, with the phase-out of leaded gasoline in China.     

Rapid Change of Lava Composition from 1998 to 2002 at Piton de la Fournaise (Reunion) Inferred from Pb Isotopes and Trace Elements: Evidence for Variable Crustal Contamination

After an unusually long quiet period of nearly 6 years, in 1998the Piton de la Fournaise volcano started a new cycle of intensevolcanic activity. We report geochemical data on the first nineevents (53 samples), from the long-lived initial eruption (sixand a half months) of 1998 to the high-flux picritic eruptionof January 2002. Pb isotopes and trace elements display systematic,coupled variations, which are mostly confined to the beginningand the end of the period. Two well-defined binary mixing trendsare shown by Pb–Pb and Pb–trace element relationships.These trends indicate a change of end-member components betweenMarch and June 2001 that coincides with the transition fromsteady-state basalts to picrites. A three-component mixing modelinvolving a homogeneous plume and two contaminants successfullyexplains the data. The Pb–Pb relationship requires thattwo mixing processes occur successively: plume-derived magmainteracts first with altered oceanic crust, and the resultinghybrid product then interacts at shallower level with the oldlavas constituting the base of the volcanic edifice. Assimilationof edifice material decreased continuously from 1998 to 2002,whereas assimilation of oceanic crust drastically increasedduring the late-stage picritic eruption. These results suggestthat picrites may have resided for an unusually long time atan oceanic crustal level before ascending rapidly through thevolcanic edifice with little interaction with channel walls. KEY WORDS: assimilation; lead isotopes; picrites; Piton de la Fournaise; trace elements